63314619 e-gprs-radio-networks-planning-theory-s13

(E)GPRS Radio Networks Planning Theory Version 3.0

2/166 CMO SBU MS Network & Service Optimization Capability Management

16/12/2008

Copyright 2007 Nokia Siemens Networks. All rights reserved.

DOCUMENT DESCRIPTION

Title and version (E)GPRS Radio Networks - Planning Theory v3.0 Reference Target Group Radio, Tranmission, E2E Technology and SW release

GERAN - S13

Related Service Items

Service Item number

Author Pal Szabadszallasi Date Approver Villa Salomaa

CHANGE RECORD

This section provides a history of changes made to this document

VERSION DATE EDITED BY SECTION/S COMMENTS 1.0 17.06.2005 Pal Szabadszallasi 2.0 18.12.2006 Pal Szabadszallasi 3.0 16.12.2008 Pal Szabadszallasi

Copyright © Nokia Siemens Networks. This material, including documentation and any related computer programs, is protected by copyright controlled by Nokia Siemens Networks. All rights are reserved. Copying, including reproducing, storing, adapting or translating, any or all of this material requires the prior written consent of Nokia Siemens Networks. This material also contains confidential information which may not be disclosed to others without the prior written consent of Nokia Siemens Networks.


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Table of contents

1. Introduction....................................................................................... 7

1.1 (E)GPRS Dimensioning, Planning and Optimization Structure........................................8 1.2 Data hardware and site solutions....................................................................................8 1.2.1 BSC and PCU variants ...................................................................................................8 1.2.1.1 PCU2 Plug-in Unit Variants and Hardware Architecture..................................................9 1.2.1.2 PCU2 Software Architecture.........................................................................................10 1.2.1.3 PCU1 and PCU2 Software Differences on Air Interface................................................11 1.2.2 BTS variants.................................................................................................................12 1.3 Data features................................................................................................................12 1.3.1 S10 / S10.5ED..............................................................................................................12 1.3.2 S11 / S11.5...................................................................................................................13 1.3.3 S12...............................................................................................................................13 1.4 S13...............................................................................................................................14

2. (E)GPRS Modulation ...................................................................... 15

2.1 GMSK and 8-PSK Modulation ......................................................................................15 2.2 Modulation Block Diagrams ..........................................................................................16 2.3 Back-off in EGPRS.......................................................................................................17 2.4 Burst Structure .............................................................................................................19

3. Coding Schemes ............................................................................ 21

3.1 Protocol Architecture ....................................................................................................21 3.1.1 Physical Layer ..............................................................................................................22 3.1.2 RLC/MAC Layer ...........................................................................................................22 3.1.2.1 Radio Link Control ........................................................................................................22 3.1.2.2 Medium Access Control................................................................................................22 3.1.2.3 RLC/MAC Header Formats...........................................................................................22 3.1.3 Logical Link Control ......................................................................................................27 3.1.4 SNDCP Layer ...............................................................................................................28 3.1.5 IP, TCP/UDP and Application Layer .............................................................................28 3.2 RLC/MAC Coding Schemes .........................................................................................30 3.2.1 GPRS Coding Schemes (CSs) .....................................................................................30 3.2.2 EGPRS Modulation and Coding Schemes (MCSs).......................................................33

4. (E)GPRS Procedures...................................................................... 36

4.1 TBF Establishment .......................................................................................................36 4.1.1 Channel Request and Packet Immediate Assignment ..................................................36 4.1.2 DL TBF Assignment .....................................................................................................37 4.1.3 UL TBF Assignment .....................................................................................................39 4.1.3.1 Channel Request - Packet Access Procedure (CCCH / PCCH)....................................39 4.1.3.2 EGPRS Packet Channel Request.................................................................................40 4.1.3.3 Dynamic and Extended Dynamic Allocation on UL with and without USF4...................41 4.1.3.4 UL TBF ASSIGNMENT, MS on CCCH, 2 phase access...............................................42 4.1.3.5 UL TBF ASSIGNMENT, MS on CCCH, 1 phase access...............................................43 4.1.3.6 EGPRS UL TBF ASSIGNMENT, MS on PCCCH with 2 phase access.........................45 4.1.3.7 EGPRS UL TBF ASSIGNMENT, MS on PCCCH with 1 phase access.........................45 4.1.3.8 Establishment of EGPRS UL TBF when DL TBF is ongoing.........................................46 4.2 (E)GPRS Data Transfer................................................................................................47 4.2.1 (E)GPRS Data Transfer DL ..........................................................................................47


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4.2.2 (E)GPRS Data Transfer UL ..........................................................................................47 4.3 Mobility with Cell-reselection ........................................................................................49 4.3.1 Intra PCU Cell-Reselection...........................................................................................49 4.3.2 Inter PCU Cell-reselection (Intra BSC)..........................................................................50 4.3.3 RA/LA Update (intra PAPU)..........................................................................................51 4.3.4 RA/LA Update (Inter PAPU or inter SGSN)...................................................................52 4.4 TBF Release ................................................................................................................53 4.4.1 Packet TBF Release Content .......................................................................................54 4.4.2 Abnormal Releases ......................................................................................................54 4.4.3 TBF Release in PCU2 ..................................................................................................55

5. (E)GPRS Accessibility .................................................................... 56

5.1 Air Interface Signaling Load..........................................................................................56 5.1.1 Common Control Channels ..........................................................................................57 5.1.1.1 Paging Channel ............................................................................................................57 5.1.1.2 Access Grand Channel.................................................................................................57 5.1.1.3 Random Access Channel .............................................................................................58 5.1.2 SDCCH ........................................................................................................................58 5.2 TRXSIG Load ...............................................................................................................59 5.2.1 TRXSIG Load Theory ...................................................................................................59 5.2.1.1 Abis Protocols ..............................................................................................................59 5.2.1.2 TRXSIG Load Components, Measurement and Analysis..............................................61 5.3 BCSU Load ..................................................................................................................64 5.3.1 BSC RAW Measurement Results .................................................................................64 5.3.2 Reporting Suit 184 Report ............................................................................................64 5.4 Signaling Load with DTM Usage...................................................................................65

6. Resource Allocation in BSS ............................................................ 66

6.1 Cell Reselection............................................................................................................67 6.1.1 C1 and C2 ....................................................................................................................67 6.1.2 C31/C32 .......................................................................................................................68 6.1.3 Network Controlled Cell Reselection.............................................................................71 6.1.3.1 NCCR Benefits .............................................................................................................72 6.1.3.2 NCCR Functionality ......................................................................................................72 6.1.3.3 Target cell selection......................................................................................................73 6.1.3.4 Signaling Flow ..............................................................................................................74 6.1.3.5 BLER Limits are Needed for the Quality Control Function in PCU2 ..............................75 6.2 BTS Selection...............................................................................................................76 6.2.1 Initial BTS Selection .....................................................................................................76 6.2.2 BTS Selection for Reallocating TBF..............................................................................79 6.2.2.1 Uplink Rx Lev Reallocation...........................................................................................81 6.2.2.2 Downlink Rx Lev Reallocation ......................................................................................82 6.2.2.3 Downlink RX Lev Received First Time Reallocation .....................................................82 6.2.2.4 BTS Selection in PCU2.................................................................................................82 6.2.2.5 Territory Upgrade Request in PCU2 .............................................................................83 6.3 Channel Scheduling .....................................................................................................84 6.3.1 Priority based Quality of Service...................................................................................84 6.3.2 Channel Allocation........................................................................................................85 6.3.3 TBF Scheduling ............................................................................................................86 6.3.4 QoS Information Delivery..............................................................................................87 6.3.5 Nokia HLR QoS Settings ..............................................................................................88 6.4 Flow Control on Gb.......................................................................................................91 6.5 Gb over IP ....................................................................................................................91


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7. (E)GPRS Timeslot Data Rate ......................................................... 93

7.1 GSM Network Performance..........................................................................................93 7.1.1 Impact of Coverage Level.............................................................................................93 7.1.1.1 Signal Strength Requirements ......................................................................................94 7.1.1.2 Receiving End ..............................................................................................................95 7.1.1.3 Measurement Results...................................................................................................96 7.1.2 Impact of Interference Level .........................................................................................98 7.1.2.1 Simulation Results........................................................................................................98 7.1.2.2 Spectrum Efficiency and Frequency Reuse ................................................................103 7.1.2.3 Measurement Results.................................................................................................104 7.1.3 Mixture of Signal Level and Interference.....................................................................104 7.2 TSL Utilization Improvement.......................................................................................106 7.2.1 Acknowledge Request Parameters.............................................................................106 7.2.1.1 GPRS DL/UL Penalty and Threshold..........................................................................106 7.2.1.2 (E)GPRS DL/UL Penalty and Threshold .....................................................................106 7.2.2 PRE_EMPTIVE_TRANSMISSIO ................................................................................107 7.3 TBF Release Delay Parameters (S10.5 ED)...............................................................107 7.3.1 DL_TBF_RELEASE_DELAY ......................................................................................107 7.3.2 DL_TBF_RELEASE_DELAY in PCU2 ........................................................................108 7.3.3 UL_TBF_RELEASE_DELAY ......................................................................................108 7.3.4 Release of downlink Temporary Block Flow ...............................................................109 7.3.5 Release of uplink Temporary Block Flow....................................................................109 7.4 TBF Release Delay Extended (S11 onwards).............................................................110 7.4.1 TBF is Continued based on EUTM .............................................................................110 7.4.2 TBF is Not Continued based on EUTM.......................................................................111 7.4.3 EUTM in PCU2...........................................................................................................112 7.5 BS_CV_MAX..............................................................................................................112 7.6 GPRS and EGPRS Link Adaptation............................................................................115 7.6.1 GPRS Link Adaptation (S11) ......................................................................................115 7.6.2 GPRS Link Adaptation with CS1-4 (PCU2).................................................................116 7.6.2.1 Link Adaptation Algorithm Used in Uplink Direction ....................................................118 7.6.3 EGPRS Link Adaptation with Incremental Redundancy..............................................121 7.6.3.1 Link Adaptation Introduction .......................................................................................121 7.6.3.2 MCS Selection............................................................................................................123 7.6.3.3 Bit Error Probability.....................................................................................................125 7.6.3.4 Link Adaptation Procedure .........................................................................................131 7.6.3.5 Incremental Redundancy in EGPRS...........................................................................138 7.6.3.6 MCS Selection Based on BLER Limits .......................................................................142 7.6.3.7 EGPRS LA in PCU2 ...................................................................................................143 7.7 Multiplexing ................................................................................................................144 7.7.1 Synchronization ..........................................................................................................144 7.7.2 Dynamic Allocation on UL...........................................................................................144 7.7.2.1 GPRS and EGPRS Dynamic Allocation......................................................................144 7.7.2.2 GPRS and EGPRS Dynamic Allocation without USF4...............................................145 7.7.2.3 GPRS and EGPRS Dynamic Allocation with USF4.....................................................145 7.7.2.4 GPRS and EGPRS Extended Dynamic Allocation with/without USF4.........................146

8. (E)GPRS Territory Settings........................................................... 147

8.1 Timeslot Allocation between Circuit Switched and (E)GPRS Services........................147 8.1.1 PSW Territory.............................................................................................................147 8.1.1.1 Dedicated (E)GPRS Capacity.....................................................................................147 8.1.1.2 Default GPRS Capacity ..............................................................................................148 8.1.1.3 Additional (E)GPRS Capacity .....................................................................................148


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8.1.2 CSW Territory.............................................................................................................148 8.1.2.1 Free Timeslots............................................................................................................149 8.1.3 Territory Upgrade/Downgrade – Dynamic Variation of Timeslots................................151 8.1.3.1 Downgrade .................................................................................................................151 8.1.3.2 Upgrade .....................................................................................................................152 8.1.3.3 Territory Upgrade and Downgrade S10 Changes .......................................................152 8.1.3.4 Multislot TSL Allocation for Using max Capability of Mobile........................................153 8.2 Multislot Usage...........................................................................................................153 8.2.1 Average Window Size ................................................................................................155 8.3 High Multislot Class (HMC).........................................................................................155

9. Mobility ......................................................................................... 157

9.1 Intra/Inter PCU Cell Re-selection................................................................................157 9.1.1 BSS and Data Outage ................................................................................................157 9.1.1.1 BSS Cell-reselection outage.......................................................................................158 9.1.1.2 Data outage................................................................................................................158 9.1.2 Benchmark Results ....................................................................................................160 9.2 LA /RA Cell-reselection...............................................................................................161 9.2.1 Data Outage ...............................................................................................................161 9.2.1.1 Location Area Update.................................................................................................161 9.2.1.2 Routing Area Update ..................................................................................................161 9.2.1.3 Data outage (LA/RA Update) ......................................................................................161 9.2.2 Benchmark Results ....................................................................................................163 9.3 Cell-reselect Hysteresis ..............................................................................................164 9.4 Network Assisted Cell Change ...................................................................................165


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1. Introduction The (E)GPRS Radio Networks – Planning Theory document was prepared to provide the basic theoretical knowledge for (E)GPRS Radio Network dimensioning, planning and optimization. The (E)GPRS Radio Networks planning document set structure listed below:

• (E)GPRS Radio Networks – Planning Theory

• (E)GPRS Radio Networks – Dimensioning and Planning Guidelines

• (E)GPRS Radio Networks – Optimization Guidelines

The Planning Theory gives the theoretical knowledge while “Dimensioning and Planning Guidelines” and “Optimization Guidelines” contain all the practical information for daily planning and optimization activities.

The materials listed above are based on S10.5 ED, S11, S11.5, S12 and S13 BSS software releases; moreover both PCU1 and PCU2 are taken into account.

The detailed Abis, EDAP, PCU and Gb planning theory are not included in this document. For more information pls. see the latest guidelines on the links below:

GSM Access:

https://sharenet-ims.inside.nokiasiemensnetworks.com/Open/358201395

MW Radio Transmission (and Mobile Backhaul)


GERAN Radio


The 3GPP specifications can be found at the following intranet location:

http://www.3gpp.org/specification-numbering


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1.1 (E)GPRS Dimensioning, Planning and Optimization Structure

The general way of (E)GPRS radio dimensioning, planning and optimization procedure is listed below:

(E)GPRS Dimensioning and Planning

• Operators’ business plan investigation

• Operators’ BSS network structure audit (with core network)

• Deployment plan preparation

• Capacity calculations based on deployment plan

• Parameter setting

(E)GPRS Optimization

• Configuration and feature audit

• BSS and E2E Performance measurements

• GSM network optimization

• (E)GPRS network optimization

All the points above are described in (E)GPRS Radio Networks - Dimensioning and Planning Guidelines and (E)GPRS Radio Networks - Optimization Guidelines.

(E)GPRS Radio Networks - Dimensioning and Planning Guidelines:


(E)GPRS Radio Networks - Optimization Guidelines:


1.2 Data hardware and site solutions The following sessions describe the PS related hardware elements in the BSS chain.

1.2.1 BSC and PCU variants Nokia Packet Control Unit (PCU) is a Plug-in unit in a Base Station Controller (BSC). PCU hardware is embedded in BSCs in every BCSU (BSC Signaling unit).

The Nokia PCU product family consists of following products:


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PCU variant BSC Type Release BSS11BSS11.5

ownwards

BTS 64 64

TRX 128 128Radio TSLs 256 128Abis 16 kbps channels 256 256Gb 64 kbps channels 31 31BTS 64 64

TRX 128 128Radio TSLs 256 128Abis 16 kbps channels 256 256Gb 64 kbps channels 31 31BTS 64 64TRX 128 128Radio TSLs 256 256Abis 16 kbps channels 256 256Gb 64 kbps channels 31 31BTS N/A 128TRX N/A 256Radio TSLs N/A 256Abis 16 kbps channels N/A 256Gb 64 kbps channels N/A 31BTS 2 x 64 2 x 64TRX 2 x 128 2 x 128Radio TSLs 2 x 256 2 x 256Abis 16 kbps channels 2 x 256 2 x 256Gb 64 kbps channels 2 x 31 2 x 31BTS N/A 2 x 128TRX N/A 2 x 256Radio TSLs N/A 2 x 256Abis 16 kbps channels N/A 2 x 256Gb 64 kbps channels N/A 2 x 31

PCU2-D BSC3i

PCU2-U

PCU-T BSCE, BSC2, BSCi, BSC2i

BSCE, BSC2, BSCi, BSC2i

PCU-B BSC3i

PCU BSCE, BSC2, BSCi, BSC2i

PCU-S BSCE, BSC2, BSCi, BSC2i

Table 1 PCU product family

The PCU-S is the first and PCU-T the second evolution of PCU variant having more memory and higher CPU clock rate.

1.2.1.1 PCU2 Plug-in Unit Variants and Hardware Architecture In the PCU2 solution, there are two PCU2 plug-in unit variants which implement the new hardware architecture. PCU2-D is used for BSC3i, which includes two logical PCU2 units, and PCU2-U is used for the older BSC versions. For more information on the PCU2 plug-in unit variants, see the PCU2 hardware plug-in unit descriptions in BSC/TCSM documentation.

PCU2 introduces more processing capacity for both PowerQuicc II (PQII) and digital signal processors (DSP) with external memory and hardware architecture enhancements to create a basis for new packet data related functionalities.

The functionalities include enhancements in following areas:

• Enhanced processing capabilities for PQII and DSPs with external memory and a higher DSP-level Abis channel connectivity to fully support the software architecture enhancements

• Actual traffic and O&M information separated on different paths between PQII and DSPs


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Figure 1 Main hardware blocks in the PCU1 and PCU2 variants

1.2.1.2 PCU2 Software Architecture The new software architecture, with its modular decomposition and restructured task management, uses the hardware architecture changes to provide a basis for the new packet data related functionalities.

With PCU2, the DSPs take care of more tasks than in PCU1. The tasks include radio link control (RLC), scheduling, quality control, as well as Abis L1 processing. With PCU1, the DSPs only take care of the Abis L1 processing.

Figure 2 Restructured task management in PCU2

The PCU2’s new software architecture introduces enhancements in the following areas:

• The RLC, Scheduler, and Quality control functionalities implemented on the DSPs improve the RTT and balances load between PQII and DSPs.


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• The asynchronous data transfer of LLC PDUs, which is used instead of the synchronous transfer of RLC/MAC blocks between PQII and DSP, reduces the load in the PQII – DSP interface and provides faster PQII – DSP transactions.

• Increased BTS and TRX resources: with PCU2, the BTS resources are increased from 64 to 128, and the TRX resources extended from 128 to 256, consequently providing more flexibility to the segment concept used with Multi-BCF Control and Common BCCH.

• The new GPRS link adaptation algorithm enables the support for the GPRS coding schemes 3 and 4 (CS3&CS4). It also gives the possibility to reach a higher throughput per subscriber when the GPRS coding schemes 3 and 4 are used.

• The use of uplink state flag (USF) granularity 4 improves the use of the radio interface resources in a situation where the GPRS and EGPRS mobiles are in the same radio time-slot (RTSL).

• Dynamic Abis improvements, which enable a more efficient use of EDAPs. The recommended number of EDAP’s in PCU1 is 1, 2, 4 or 8. Recommended number of EDAP’s is in PCU2 is 1-8.

• Improved end user service perception: The PCU2 software architecture implements RLC on DSPs and, depending on the radio conditions, gives benefit to application level delays i.e. active and idle RTTs. The active RTT measures delay from the data transfer point of view has an impact for example on the duration of file downloads experienced by the end users as well as on services with fast interaction requirements. The idle RTT measures delay from the access point of view, that is, the impact to TCP startup, improves on its part the end user experience for example in downloading web pages.

• BTS selection improvements in case of Common BCCH / Multi BCF cell

• Dynamic Abis improvements

PCU2 doesn’t provide support for following functionalities available with PCU1:

• PBCCH/PCCCH

• GPRS support for InSite BTS

1.2.1.3 PCU1 and PCU2 Software Differences on Air Interface Due to different feature set and software architecture between PCU generations, there are multiple differences concerning to Air interface. These differences have influences to radio resource allocation and scheduling, round-trip time, throughput and cell change times.

The most important differences are:

• New GPRS link adaptation algorithm in the PCU2 that can use CS-3 and CS-4, too

• Utilization of USF granularity 4 in the PCU2

• BTS selection differences


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• Inter DSP TBF reallocation and cell change in the PCU2

The detailed description of the most important differences can be found in the relevant chapters below in this document.

1.2.2 BTS variants

TALK InSite** PrimeSite MetroSite UltraSite FlexiEDGE

GSM Ok Ok Ok Ok Ok Ok

GPRS CS1 – 2 CS1 – 2 CS1 - 2 CS1 – 2* CS1-2* CS1-2*

EGPRS No No No MCS1-9 MCS1-9 MCS1-9

*CS1-4 with PCU2 **Insite is not supported by PCU2

1.3 Data features The next sessions describe the most important PS features on S release basis.

1.3.1 S10 / S10.5ED

The following features are implemented with S10/S10.5ED releases:

BSS 10091 Enhanced Data Rates for Global Evolution, EDGE

Detailed description of GPRS and EGPRS dimensioning and planning is available in (E)GPRS Radio Networks - Dimensioning and Planning Guidelines:

https://sharenet-ims.inside.nokiasiemensnetworks.com/Download/362642110

Detailed description of GPRS and EGPRS optimization is available in (E)GPRS Radio Networks - Optimization Guidelines


BSS 10045 Dynamic Abis Allocation


BSS 10074 Support of PCCCH/PBCCH

Support for PBCCH/PCCCH is no longer supported from S13 onwards.

BSS 10084 Priority Class Based Quality of Service

With Priority Based Scheduling, an operator can give users different priorities. Higher priority users will get better service than lower priority users. There will be no extra blocking to any user, only the experienced service quality changes.

The concept of ‘Priority Class’ is based on a combination of the GPRS Delay class and GPRS Precedence class values. Packets will be evenly scattered within the (E)GPRS


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territory between different time slots. After that packets with a higher priority are sent before packets that have a lower priority.

The description of priority based QoS is available in (E)GPRS Radio Networks - Optimization Guidelines


1.3.2 S11 / S11.5 The following features are implemented with S11/S11.5 releases:

BSS 11112 Network Controlled Cell Reselection (NCCR )

BSS 11506 Network Assisted Cell Change (NACC)

BSS 115171 Dynamic Abis Enhancements

BSS 11088 GPRS Coding Schemes CS3 and CS4

BSS 30065 GPRS Resume

BSS 11151 Extended Uplink TBF

BSS 11156 EGPRS: Channel Request on CCCH

The detailed description of below listed features are (E)GPRS Radio Networks - Dimensioning and Planning Guidelines: https://sharenet-ims.inside.nokiasiemensnetworks.com/Download/362642110

(E)GPRS Radio Networks - Optimization Guidelines:


1.3.3 S12

The following features are implemented with S12 release:

BSS 20088 Dual Transfer Mode (DTM)

Dual Transfer Mode (DTM) provides mobile users with simultaneous circuit-switched (CS) voice and packet-switched (PS) data services. This means that users can, for example, send and receive e-mail during an ongoing phone call.

The Planning Theory of DTM can be downloaded from the following link:


Information about DTM planning is available in DTM – Planning guidelines:



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BSS 20084 High Multislot Classes (HMC)

More information about HMC is available in the (E)GPRS Radio Networks - Optimization Guidelines:


BSS 20089 Extended Dynamic Allocation (EDA)

More information about EDA is available in Chapter 7.7.2.

1.4 S13 The following feature is implemented with S13 releases:

BSS20094 Extended Cell for GPRS/EDGE

More information is available in extended cell range and Long Reach timeslot planning guidelines:



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2. (E)GPRS Modulation (E)GPRS uses not only GMSK but 8PSK (8 Phase Shift Keying) modulation as well, producing a 3bit word for every change in carrier phase. This effectively triples the data rate offered by GPRS.

The differences between GMSK and 8-PSK, the block diagram of modulators, and the burst structure with back-off are described below in this chapter.

2.1 GMSK and 8-PSK Modulation GSM system is using GMSK (Gaussian Minimum Shift Keying), a constant-envelope modulation scheme. The advantage of the constant envelope modulation is that it allows the transmitter power amplifiers to be operated in a non-linear (saturated) mode, offering high power efficiency. The saturation means that even if the input signal level is increased, no increasement will be seen in the output power, as shown on upper part of Figure 3.

8-PSK, in the form used in EDGE, has a varying envelope, see the lower part of Figure 3. It means that the amplifier must be operated in the linear region in case of 8-PSK since distortion is to be avoided. (There is an additional 22.5 deg rotation to avoid zero crossing.)

GMSK

8PSK(0,0,1)

(1,0,1)

(0,0,0) (0,1,0)

(0,1,1)

(1,1,1)

(1,1,0)

(1,0,0)

Time

Envelope (amplitude)

Time


GMSK

8PSK(0,0,1)

(1,0,1)

(0,0,0) (0,1,0)

(0,1,1)

(1,1,1)

(1,1,0)

(1,0,0)

Time


Time


Time


TimeTime


Time


TimeTime


Figure 3 Modulation scheme for GMSK and 8-PSK


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2.2 Modulation Block Diagrams The Figure 4 and Figure 5 show that GMSK and 8-PSK modulation arrangements are completely different.

Figure 4 GSM - GMSK modulation

Figure 5 EDGE - 8-PSK modulation

differentialencoding

-1, +1

Gaussianprefiltering

for frequencypulses

frequencymodulator

local oscillator

rotation byk3pi/8

LinearizedGaussian

Filterfor Diracpulses

Gray mappingto 8PSK

constellation

3 bits persymbol

I & Q


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2.3 Back-off in EGPRS This varying envelope generates peak-mean power difference that is 2-6 dB for 8-PSK, thus the mean output power in amplifier must be at least this amount down on the saturated output power to achieve linearity.

Figure 6 Phase state vector diagram in 8-PSK

So the position of the information is there on the yellow dots of the dark blue circle above in Figure 6 (yellow dots: where the phase and amplitude of the signal is containing the information). The area between the dark blue circle and red circle is the room for overshooting.

This “overshoot” is required to ensure smooth and continuous transition between phase-states (as shown by the yellow trace above).

It means that the mean output power has to be app. 2-6 dB less (back-off) to avoid saturation in amplifier. This ‘back-off’ is shown in Figure 7.


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GMSK

8PSK

Time


Time


=> Peak to Average of ≅≅≅≅ 2-4 dB

Pin

Pout

Back Off= 2 dB

Compression point

Figure 7 Back-off in power amplifier

In practice, BTS equipment is less likely to be in saturation than MS equipment. Therefore the back-off for the two sets of equipment may be different, and in the link budget presented a 2dB back-off is assumed for BTS and the full 4dB for MS. The amount of MS back-off also depends on the used system frequency (different output power, different PA characteristics, etc. – 900 MHz: 6dB; 1800 MHz: 4dB).

The UltraSite 2 dB APD and mobiles’ 4-6 dB applies only when the transmitter is set to maximum output power.

If the entire TRX is set to second highest output power, there is no difference between the average power of 8-PSK and GMSK signals.


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2.4 Burst Structure 3GPP TS 05.05, Annex B identifies the following GMSK/8-PSK burst structures for transmitted power level versus time. The first figure below (Figure 8) shows the time mask for normal duration bursts at GMSK modulation. The second figure (Figure 9) shows the time mask for normal duration bursts at 8-PSK modulations. The blue “envelope” shows a conceptual example of the appearance of a normal burst.

dB

t

- 6

- 30

+ 4

8 µs 10 µs 10 µs 8 µs

(147 bits)

7056/13 (542.8) µs 10 µs

(*)

10 µs

- 1+ 1

(***)

(**)

dB

t

- 6

- 30

+ 4

8 µs 10 µs 10 µs 8 µs

(147 bits)

7056/13 (542.8) µs 10 µs

(*)

10 µs

- 1+ 1

(***)

(**)

Figure 8 GMSK Burst

10 8 10 10 8 10 t (µs)

dB

-30

(*)

-6

+2,4

+4

-20

-2

(***)

(**)

2 2 22

7056/13 (542,8)µs

(147 symbols)

0

10 8 10 10 8 10 t (µs)

dB

-30

(*)

-6

+2,4

+4

-20

-2

(***)

(**)

2 2 22

7056/13 (542,8)µs

(147 symbols)

0

Figure 9 8-PSK Burst

The following figure (Figure 10 ) shows an example of GSM/EDGE BCCH TRX with a 3TSL EDGE mobile active on the downlink 5 normal bursts in GMSK (Average Power Decrease (APD)=0 dB) and 3 normal bursts in 8-PSK (APD=2 dB).


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TSL1 TCH

GMSK

TSL2 TCH

GMSK

TSL3 TCH

GMSK

TSL4 TCH

GMSK

TSL5 PD T CH 8 - PSK / GMSK



TSL0 BCCH GMSK

P (dB)

t ( us )

Figure 10 5 normal bursts in GMSK (APD=0 dB) for voice and 3 normal bursts in 8-PSK (APD=2 dB) for data

Note that the average power decreased by 2 dB during the last three bursts due to APD of 2 dB.

This has the following key impacts on EDGE service:

1) “Slightly” lower throughput near cell edge or in poor C/I environment,

2) 2 dB lower signal level to neighboring cells or GSM phones evaluating neighbors.

If the operator decides to allow 8-PSK modulation on the BCCH carrier in certain cells, the cell selection, cell reselection and handover procedures involving these cells will be somewhat sub-optimal. This is due to the fact that the signal level measured by the MS at some instances in time will be affected by the possibly lower mean power level of the 8-PSK modulation and by the power fluctuation resulting from the 8-PSK modulation characteristics.

The extent of the performance degradation is dependent upon the measurement schedule in each particular MS as well as upon the used average power decrease (APD) and the current 8-PSK load. By limiting the maximum number of 8-PSK slots simultaneously allowed on the BCCH carrier, and/or carefully selecting the values of involved network parameters, the impact on the above-mentioned procedures may be minimized. Additionally, in areas with very low cell overlap, some coverage loss effects may have to be taken into account by the operator when selecting network parameters (the measurement of the cell for neighbor decision is based on the average value of TSLs’ signal level, so the reduced output power due to 8-PSK can modify this measurement results).

The power budget margins for handover are around 4/6 dB. This means the signal strength in the neighbor EGPRS cell has to be 4/6 dB larger than the serving cell in order to perform the handover. Moreover, the mobiles have a certain inaccuracy when performing neighbor measurements so the impact of average power differences in GMSK and 8PSK will be probably minor.

Note that the average power remains constant since both GMSK and 8-PSK are operating in the linear range of the PA.


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3. Coding Schemes The following subsections describe the protocol architecture used by (E)GPRS and the coding schemes for GPRS, GPRS with CS1-4 and EGPRS.

3.1 Protocol Architecture The following figure shows the different protocols between the different network elements of a (E)GPRS networks. As it can be seen from Figure 11, the BSS network related protocols are the physical (L1/RF) and RLC/MAC layers. The RLC/MAC, LLC and SNDCP layers are (E)GPRS specific layers, but the higher layers are application dependent.

LLC

SNDCP

LLC

SNDCP

L1/RF L1/RF

UmMS BTS

FR

NS

BSSGP

FR

NS

BSSGP

GbSGSN

GTP

UDP

IP

L1

L2

GTP

UDP

IP

L1

L2

GnGGSN

RLC/MAC RLC/MAC

DAbis DAbis

AbisBSC / PCU

IP

L1

L2

WWW/FTP

Server

Gi

TCP

HTTPor FTP

L1

L2

IP

TCP

HTTPor FTP

Figure 11 (E)GPRS Protocol Stack

The protocols are communicating via Service Access Points (SAP). The Figure 12 shows the data block segmentation from IP to GSM RF.

LLC

SNDCP

IP

RLC

MAC

GSM RF

N-PDU

SN-DATA PDUs

LLC Frames

RLC Blocks

RLC/MAC Blocks

TDMA Bursts

Figure 12 Data Blocks segmentation between protoco ls


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3.1.1 Physical Layer

The physical layer of the (E)GPRS networks is the standard GSM TDMA interface (with new modulation method for higher MCSs of EGPRS). Therefore the appropriate functionality of the GSM network is basic requirement to provide good (E)GPRS service.

The main tasks of the physical layer are listed below:

• Modulation/demodulation (GMSK and 8-PSK)

• TDMA frame formatting

• Bit inter-leaving

• Cell selection/reselection

• Tx power control

• Discontinuous reception (DRx)

The basic element of air interface in (E)GPRS planning is the timeslot. It lasts 0,577 milliseconds (=15/26) which corresponds to 156,25 bits. Four TDMA TSLs are needed to convey one RLC/MAC block as it can be seen in the Figure 12 above.

3.1.2 RLC/MAC Layer

This subsection briefly describes the Radio Resource layer (RLC/MAC) since this layer is responsible for most of the important BSS related functionalities.

3.1.2.1 Radio Link Control The main tasks of Radio Link Control (RLC) are:

• Reliable transmission of data across air interface

• Segmentation/de-segmentation of data from/to LLC layer

The RLC layer can be operated in both acknowledged and unacknowledged modes, and this is defined by the Quality of Service (QoS) profile within the PDP context (reliability class).

3.1.2.2 Medium Access Control The following list shows the main tasks of Medium Access Control (MAC):

• Control of MS access to common air-interface medium

• Flagging of PDTCH/PACCH occupancy

This layer controls MS access to the common air interface and provides queuing and scheduling of the associated signaling.

3.1.2.3 RLC/MAC Header Formats All the header formats are described below.


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The following figure shows the downlink GPRS RLC block with MAC header.

Figure 13 DL RLC/MAC format

Detailed field description: Uplink State Flag (USF) field is sent in all downlink RLC/MAC blocks and indicates the owner or use of the next uplink Radio block on the same timeslot. The USF field is three bits in length and eight different USF values can be assigned, except on PCCCH, where the value '111' (USF=FREE) indicates that the corresponding uplink Radio block contains PRACH.

Supplementary/polling (S/P) bit is used to indicate whether the RRBP field is valid or not.

bit 4 S/P 0 RRBP field is not valid 1 RRBP field is valid

Table 2 S/P bit

Relative Reserved Block Period (RRBP) field specifies a single uplink block in which mobile station shall transmit either a Packet Control Acknowledgement message or a PACCH block to the network. The mobile station shall only react on RLC/MAC block containing a valid RRBP field.


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Final Block Indicator (FBI) bit indicates that the downlink RLC data block is the last RLC data block of the DL TBF.

bit 1 Final block indicator 0 Current block is not last RLC data block in TBF 1 Current block is last RLC data block in TBF

Table 3 FBI bit

Power reduction (PR) fields indicate the power level reduction of the current RLC block. The coding of PR field depends on downlink power control mode – mode A and B defined in BTS_PWR_CTRL_MODE bit sent in assignment messages.

Payload Type field shall indicate the type of data contained in remainder of RLC/MAC block. The encoding of the payload type field is shown below. The payload Type field is present in both downlink and uplink MAC header.

bit 8 7

Payload Type

0 0 RLC/MAC block contains an RLC data block 0 1 RLC/MAC block contains an RLC/MAC control block

that does not include the optional octets of the RLC/MAC control header

10 In the downlink direction, the RLC/MAC block contains an RLC/MAC control block that includes the optional first octet of the RLC/MAC control header. In the uplink direction, this value is reserved.

1 1 Reserved. In this version of the protocol, the mobile station shall ignore all fields of the RLC/MAC block except for the USF field

Table 4 Payload Type field

Temporary Flow Identity (TFI) field in RLC data blocks identifies the Temporary Block Flow (TBF) to which the RLC data belongs. For the downlink and uplink TFI the field is 5 bits in length and are encoded as a binary number with range 0 to 31.

Block Sequence Number (BSN) field carries the sequence absolute Block Sequence Number (BSN’) modulo 128 of each RLC data block within the TBF. The BSN is 7 bits in length and is encoded as a binary number with range 0 to 127. The following figure shows the uplink RLC block with MAC header.


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Figure 14 UL RLC/MAC format

Detailed field description: Retry (R) bit shall indicate whether the MS transmitted CHANNEL REQUEST message or PACKET CHANNEL REQUEST message one time or more than one time during its most recent channel access. The mobile station shall send the same value for the R bit each uplink RLC/MAC block of the TBF.

bit 1 Retry (R) bit 0 MS sent channel request message once 1 MS sent channel request message twice or more

Table 5 Retry bit

The Stall indicator (SI) bit indicates whether the mobile's RLC transmit window can advance (i.e. is not stalled) or cannot advance (i.e., is stalled). The mobile station shall set the SI bit in all uplink RLC data blocks.

bit 2 Stall indicator 0 MS RLC transmit window is not stalled 1 MS RLC transmit window is stalled

Table 6 SI bit

The Countdown Value (CV) field is sent by the mobile station to allow the network to calculate the number of RLC data blocks remaining for the current uplink TBF. The CV field is 4 bits in length and is encoded as a binary number with range 0 to 15.

The TLLI Indicator (TI) bit indicates the presence of an optional TLLI field within the RLC data block.


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bit 1 TLLI indicator (TI) bit 0 TLLI field is not present 1 TLLI field is present

Table 7 TLLI indicator bit

For EDGE the DL RLC/MAC header will change depends on the MCS used. The MCS7, 8 and 9 have 5 octets header (header type 1) as shown on Table 8.

Bit

8 7 6 5 4 3 2 1 Octet TFI RRBP ES/P USF 1

BSN1 PR TFI 2 BSN1 3

BSN2 BSN1 4 CPS BSN2 5

Table 8 DL RLC/MAC header for EDGE MCS 7-9

Bit



CPS BSN1 4 Table 9 DL RLC/MAC header for EDGE MCS 5 and 6 (he ader type 2)

Bit



SPB CPS BSN1 4 Table 10 DL RLC/MAC header for EDGE MCS 1 to 4 (he ader type 3)

There are three header formats, because the header code rates are different for MCS1-4 and MCS5-9, and MCS5-6 have one RLC/MAC block while MCS7-9 have two RLC/MAC blocks (see Table 13).

The Downlink RLC/MAC control block together with its MAC header is formatted as shown in Table 11.

Bit 8 7 6 5 4 3 2 1

Payload Type RRBP S/P USF MAC header RBSN RTI FS AC Octet 1 (optional)

PR TFI D Octet 2 (optional) Octet M

Control Message Contents

.

.

. Octet 21 Octet 22

Table 11 Downlink RLC/MAC control block together w ith its MAC header


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The Uplink RLC/MAC control block together with its MAC header is formatted as shown in Table 12.

Bit 8 7 6 5 4 3 2 1

Payload Type spare R MAC header Octet 1 Octet 2 Octet 3

Control Message Contents

.

.

. Octet 21 Octet 22

Table 12 Uplink RLC/MAC control block together wit h its MAC header

The detailed description of the different header formats can be found in 3GPP 04.60.

3.1.3 Logical Link Control

Logical Link Control (LLC) layer provides a reliable ciphered link between the SGSN and the MS. This protocol is independent of the underlying radio interface protocols. LLC is considered to be a sub layer of layer 2 in the ISO 7-layer model. The purpose of LLC is to convey information between layer-3 entities in the MS and SGSN. Specifically, LLC shall support:

• multiple MSs at the Um interface; • multiple layer-3 entities within an MS.

LLC includes functions for:

• the provision of one or more logical link connections discriminated between by means of a DLCI;

• sequence control, to maintain the sequential order of frames across a logical link connection;

• detection of transmission, format and operational errors on a logical link connection;

• recovery from detected transmission, format, and operational errors; • notification of unrecoverable errors; • flow control • ciphering

LLC layer functions provide the means for information transfer via peer-to-peer logical link connections between an MS and SGSN pair. This layer can be operated in both acknowledged and unacknowledged modes, and this is defined by the Quality of Service (QoS) profile within the PDP context (reliability class).


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3.1.4 SNDCP Layer

Maps the network level Packet Data Units (N-PDU) on to the underlying Logical Link Control (LLC) layer. The basic functionality of SNDCP layer is listed below:

• Multiplexer/demultiplexer for different network layer entities onto LLC layer

• Compression of protocol control information (e.g. TCP/IP header)

• Compression of data content (if used)

• Segmentation/de-segmentation of data to/from LLC layer

In details the SNDCP shall perform the following functions:

• Mapping of SN-DATA primitives onto LL-DATA primitives. • Mapping of SN-UNITDATA primitives onto LL-UNITDATA primitives. • Multiplexing of N-PDUs from one or several network layer entities onto the

appropriate LLC connection. • Establishment, re-establishment and release of acknowledged peer-to-peer

LLC operation. • Supplementing the LLC layer in maintaining data integrity for acknowledged

peer-to-peer LLC operation by buffering and retransmission of N-PDUs. • Management of delivery sequence for each NSAPI, independently. • Compression of redundant protocol control information (e.g., TCP/IP header)

at the transmitting entity and decompression at the receiving entity. The compression method is specific to the particular network layer or transport layer protocols in use.

• Compression of redundant user data at the transmitting entity and decompression at the receiving entity. Data compression is performed independently for each SAPI, and may be performed independently for each PDP context. Compression parameters are negotiated between the MS and the SGSN.

• Segmentation and reassembly. The output of the compressor functions is segmented to the maximum length of LL-PDU. These procedures are independent of the particular network layer protocol in use.

• Negotiation of the XID parameters between peer SNDCP entities using XID exchange.

3.1.5 IP, TCP/UDP and Application Layer

The IP (Internet Protocol), TCP/UDP (Transmission Control Protocol/ User Datagram Protocol) and application layer’s functionality is described in EDGE_TCP_TWEAK_1_2 document in QP.

The Internet Protocol (IP) is a network-layer (Layer 3) protocol that contains addressing information and some control information that enables packets to be routed. IP is documented in RFC 791 and is the primary network-layer protocol in the Internet protocol suite. Along with the Transmission Control Protocol (TCP), IP represents the heart of the Internet protocols. IP has two primary responsibilities: providing connectionless, best-effort delivery of datagrams through an internetwork; and providing fragmentation and reassembly of datagrams to support data links with different maximum-transmission unit (MTU) sizes.


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Transmission Control Protocol (TCP) provides reliable transmission of data in an IP environment. TCP corresponds to the transport layer (Layer 4) of the OSI reference model. Among the services TCP provides are stream data transfer, reliability, efficient flow control, full-duplex operation, and multiplexing.

With stream data transfer, TCP delivers an unstructured stream of bytes identified by sequence numbers. This service benefits applications because they do not have to chop data into blocks before handing it off to TCP. Instead, TCP groups bytes into segments and passes them to IP for delivery.

TCP offers reliability by providing connection-oriented, end-to-end reliable packet delivery through an internetwork. It does this by sequencing bytes with a forwarding acknowledgment number that indicates to the destination the next byte the source expects to receive. Bytes not acknowledged within a specified time period are retransmitted. The reliability mechanism of TCP allows devices to deal with lost, delayed, duplicate, or misread packets. A time-out mechanism allows devices to detect lost packets and request retransmission.

TCP offers efficient flow control, which means that, when sending acknowledgments back to the source, the receiving TCP process indicates the highest sequence number it can receive without overflowing its internal buffers.

Full-duplex operation means that TCP processes can both send and receive at the same time.

User Datagram Protocol (UDP) is a connectionless transport-layer protocol (Layer 4) that belongs to the Internet protocol family. UDP is basically an interface between IP and upper-layer processes. UDP protocol ports distinguish multiple applications running on a single device from one another.

Unlike the TCP, UDP adds no reliability, flow-control, or error-recovery functions to IP. Because of UDP's simplicity, UDP headers contain fewer bytes and consume less network overhead than TCP.

UDP is useful in situations where the reliability mechanisms of TCP are not necessary, such as in cases where a higher-layer protocol might provide error and flow control.

UDP is the transport protocol for several well-known application-layer protocols, including Network File System (NFS), Simple Network Management Protocol (SNMP), Domain Name System (DNS), and Trivial File Transfer Protocol (TFTP).

The UDP packet format contains four fields; these include source and destination ports, length, and checksum fields.

Application-layer protocols are one piece of a network application. For example the Web's application layer protocol is HTTP, and defines format and sequence of messages, application layer protocols for Push to Talk over Cellular (PoC) are RTP and SIP.

Application-layer protocol defines:

• The types of messages exchanged, for example, request messages and response messages


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• The syntax of the various message types, such as the fields in the message and how the fields are delineated

• The semantics of the fields, that is, the meaning of the information in the fields • Rules for determining when and how a process sends messages and responds to

messages

3.2 RLC/MAC Coding Schemes While the symbol rate is the same for GMSK and 8-PSK modulation the bit rate is different since one GMSK symbol contains only 1 bit but one 8-PSK symbol contains 3 bits altogether.

So the differentiations of RLC/MAC data rate of the different coding schemes are based on convolutional coding and puncturing.

The CS1 and CS2 Coding Schemes (CS) are used for GPRS with PCU (PCU, PCU-S, PCU-T, PCU-B). If PCU2 (PCU2-U, PCU2-D) is implemented the CS3 and CS4 will be used as well.

Modulation and Coding Schemes (MCS) are used for EGPRS both in GMSK and 8-PSK modulations.

3.2.1 GPRS Coding Schemes (CSs)

For error protection each RLC data block is encoded using one of the available channel coding schemes. ETSI has specified four coding schemes of which Nokia supports coding scheme CS-1 and CS-2 only with PCU1, while PCU2 supports all the four CSs (see the figure below).

Coding Scheme

Payload (bits)per RLC block

Data Rate (kbit/s)

CS1 181 9.05

CS2 268 13.4

CS3 312 15.6

CS4 428 21.4

More Data =

Less Error Correction

S11.5 with PCU2D

ata

Err

orC

orre

ctio

n

PCU1

Coding Scheme

Payload (bits)per RLC block

Data Rate (kbit/s)

CS1 181 9.05

CS2 268 13.4

CS3 312 15.6

CS4 428 21.4

More Data =

Less Error Correction

S11.5 with PCU2D

ata

Err

orC

orre

ctio

n

Dat

a

Err

orC

orre

ctio

n

PCU1

Figure 15 Coding Schemes in GPRS

Each of the coding schemes has been developed based on a compromise between error protection and the amount of user data carried. Coding scheme CS-1 has the lowest user data rate, but the highest error protection. CS-4 has the highest data rate but no error protection on the user data.


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The following figure shows the segmentation of an RLC block with MAC header in case of different CSs to/from the GSM TDMA frames.

CS-1

CS-2

CS-3

57 57 57 57 57 57 57 57

456 bits

MAC

USF BCS +4

puncturing

rate a/b convolutional coding

CS-1 CS-2 CS-3

RLC/MAC Block Size: 181 268 312

Block Check Sequence: 40 16 16

Precoded USF: 3 6 6

1/2 ~2/3 ~3/4

length: 456 588 676

0 132 220

Data rate (kbit/s): 9.05 13.4 15 .6

interleaving

MAC

USF BCS

RLC/MAC Block Size: 428

BCS Size: 16

Precoded USF: 12

Data rate (kbit/s): 21.4

CS-4

20 ms

CS-1

CS-2

CS-3

57 57 57 57 57 57 57 57

456 bits

MAC

USF BCS +4

puncturing


CS-1 CS-2 CS-3



Precoded USF: 3 6 6

1/2 ~2/3 ~3/4

length: 456 588 676

0 132 220

Data rate (kbit/s): 9.05 13.4 15 .6

interleaving

CS-1

CS-2

CS-3

57 57 57 57 57 57 57 57

456 bits

57 57 57 57 57 57 57 5757 575757 5757 57 575757 5757 57 575757 5757 57 575757 5757

456 bits

MAC

USF BCS +4

puncturing


CS-1 CS-2 CS-3



Precoded USF: 3 6 6

1/2 ~2/3 ~3/4

length: 456 588 676

0 132 220

Data rate (kbit/s): 9.05 13.4 15 .6

interleaving

MAC

USF BCS


BCS Size: 16

Precoded USF: 12


CS-4

20 ms

MAC

USF BCS

MAC

USF BCS


BCS Size: 16

Precoded USF: 12


CS-4

20 ms20 ms

Figure 16 Coding Scheme segmentation in GPRS

The detailed segmentation procedure for CS1 and CS2 can be seen in the following figures.

USF Header & Data BCS

1/2 rate convolutional

coding + 4 tail bits

3 181 40 224 bits

6 456 bits

181bits/20ms = 9.05kbit/s



coding + 4 tail bits

3 181 40 224 bits

6 456 bits

181bits/20ms = 9.05kbit/s

Figure 17 RLC/MAC segmentation for CS1


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coding

6 268 16 294 bits

12 588 bits

Puncturing (132 bits)

456 bits12

268 bits/20ms = 13.4kbit/s



coding

6 268 16 294 bits

12 588 bits


456 bits12



When CS1-4 option is on, Dynamic Abis pool and (E)GPRS territories are created and when a TBF is allocated to a TRX which supports EDAP then all GPRS coding schemes (CS1 – CS4) are available for data transfer according to the parameters pcu_cs_hopping and pcu_cs_non_hop. If these parameters indicate Link Adaptation, the LA algorithm determines for each TBF separately which coding scheme (CS1 – CS4) is used.

The detailed segmentation procedure for CS3 and CS4 can be seen in the following figures.



coding

6 312 16 338 bits

12 676 bits


456 bits12




coding

6 312 16 338 bits

12 676 bits


456 bits12




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12 428 16

428bits/20ms = 21.4 kbit/s


12 428 16

428bits/20ms = 21.4 kbit/s


CS3 and CS4 is using modified LA algorithm (more details are available in Section 7.6.2.

Coding schemes CS3 and CS4 are supported only by PCU2. It is application software feature requiring a separate license.

To ensure successful BCSU switch-over it is not possible to enable CS3 & CS4 if there are PCU1 units on the same slot as PCU2 in any of the BCSUs.

3.2.2 EGPRS Modulation and Coding Schemes (MCSs)

The EGPRS standard defines nine coding schemes MCS1 to MCS9, providing different throughputs depending on the amount of redundancy implemented in each coding scheme.

In EGPRS MCSs the user data from higher layers and the RLC/MAC header are having different code rates. The header code rate is more robust for having the header even in very bad radio conditions. That is why there are “bad header, bad data” and “valid header, bad data” counters.

The different data rates per timeslot are presented below:

Scheme Code rate Header Code rate

Modulation RLC blocks per Radio

Block (20ms)

Raw Data within one

Radio Block

Family BCS Tail payload

HCS Data rate kb/s

MCS-9 1.0 0.36 2 2x592 A 59.2

MCS-8 0.92 0.36 2 2x544 A 54.4

MCS-7 0.76 0.36 2 2x448 B

2x12 2x6

44.8

MCS-6 0.49 1/3 1 592 544+48

A 29.6 27.2

MCS-5 0.37 1/3

8PSK

1 448 B 22.4

MCS-4 1.0 0.53 1 352 C 17.6

MCS-3 0.80 0.53 1 296 272+24

A 14.8 13.6

MCS-2 0.66 0.53 1 224 B 11.2

MCS-1 0.53 0.53

GMSK

1 176 C

12

6

8

8.8

NOTE: the italic captions indicate the padding.

Table 13 Coding scheme performance versus Eb/No.

The MCSs are divided into different families A, B and C. Each family has a different basic unit of payload: 37 (and 34), 28 and 22 octets respectively. Different code rates


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within a family are achieved by transmitting a different number of payload units within one Radio Block.

The family concept is used for retransmission only, so the retransmitted RLC/MAC block’s MCS can be the initial MCS or an MCS inside the family.

For families A and B, 1 or 2 or 4 payload units are transmitted, for family C, only 1 or 2 payload units are transmitted (see Figure 21 below).

37 octets 37 octets 37 octets37 octets

MCS-3

MCS-6

Family A

MCS-9


MCS-2

MCS-5

MCS-7

Family B

22 octets22 octets

MCS-1

MCS-4

Family C

34+3 octets34+3 octets

MCS-3

MCS-6Family Apadding

MCS-8



MCS-3

MCS-6

Family A

MCS-9


MCS-2

MCS-5

MCS-7

Family B

22 octets22 octets

MCS-1

MCS-4

Family C

34+3 octets34+3 octets

MCS-3

MCS-6Family Apadding

MCS-8


Figure 21 MCS Families

The following figure shows the RLC/MAC segmentation (convolutional coding and puncturing) to 4 normal GSM bursts.


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P2 P3P1 P2

puncturingpuncturing

1836 bits

USF RLC/MACHdr.

36 bits

Rate 1/3 convolutional coding

135 bits

612 bits

612 bits124 bits36 bitsSB = 8

1392 bits

45 bits

Data = 592 bitsBCS TB

612 bits

612 bits 612 bits

1836 bits

Rate 1/3 convolutional coding

EFBIData = 592 bitsBCS TBEFBI

612 bits 612 bits 612 bits

P3 P1

3 bits

HCS

puncturing

Figure 22 MCS9 Coding and puncturing


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4. (E)GPRS Procedures The knowledge of (E)GPRS procedures can help to analyze the signaling traffic. So before the analysis of signaling situation in Chapter 5 the procedure of

• TBF establishment

• Data transfer

• TBF release

should be studied in details.

After GPRS Attach and PDP Context Activation the next procedure is the TBF establishment with Packet Immediate Assignment (attach and PDP context activation also require TBF establishment, but that is not discussed here in this section).

4.1 TBF Establishment The TBF establishment is triggered by Channel Request (UL), Paging (DL) and Immediate Assignment (DL).

4.1.1 Channel Request and Packet Immediate Assignment

On receipt of a CHANNEL REQUEST message indicating a packet access, the network may allocate a temporary flow identity and assign a packet uplink resource comprising one PDCH for an uplink temporary block flow in GPRS TBF mode.

On receipt of an EGPRS PACKET CHANNEL REQUEST message, the network may allocate a temporary flow identity and assign a packet uplink resource comprising one PDCH for an uplink temporary block flow in EGPRS TBF mode or GPRS TBF mode. (3GPP 04.18-8.0)

Channel Request Message: If the establishment cause in the CHANNEL REQUEST message indicates a request for a single block packet access, the network shall grant only the single block period on the assigned packet uplink resource if the network allocates resource for the mobile station.

EGPRS Packet Channel Request Message: If the establishment cause in the EGPRS PACKET CHANNEL REQUEST (EPCR) message indicates a request for a two phase access, the network shall grant one or two radio blocks for the mobile station (within a Multi Block allocation) to send a PACKET RESOURCE REQUEST and possibly an ADDITIONAL MS RADIO ACCESS CAPABILITIES messages on the assigned packet uplink resource if the network allocates resource for the mobile station.

Immediate Assignment Message: The packet uplink resource is assigned to the mobile station in an IMMEDIATE ASSIGNMENT message sent in unacknowledged mode on the same CCCH timeslot on which the network has received the CHANNEL REQUEST or the EGPRS PACKET CHANNEL REQUEST message. There is no further restriction on what part of the downlink CCCH timeslot the IMMEDIATE ASSIGNMENT message can be sent. Timer T3141 is started on the network side.


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4.1.2 DL TBF Assignment

Reason for paging is DL user data or signaling while MS is on STANDBY state. The terminal has to be paged by the network in the STANDBY state since its position is known only on the Routing Area level.

5. Any LLC Frame

4. Any LLC Frame

3. GPRS Paging Request

2. Paging Request

1. PDP PDU

MS BSS SGSN

Figure 23 Paging flow chart

DL TBF Assignment, MS on CCCH

The DL TBF assignment is based on the following procedure (Figure 24).

TBF per priority90000(S10)

/c72084(S9)packet_immed_ass_msg

/c72085(S9)packet_immed_ass_ack_msg

MS BTS BSC SGSN

P-Immediate Assignment

Immediate Assignment (CCCH)P-Immediate Assignment Ack

Packet Polling Request

Packet Polling Request (PACCH)

Packet Control Ack Packet Control Ack (PACCH)

MS on ready state

Sent on the PDTCH to find out the MS Timing Advance. In Nokia implementation, always sent when DL TBF Assignment is from CCCH. Not sent when DL TBF is assigned on PACCH

Packet Power Control/Timing Advance

Alternatively, Packet DownlinkAssignmnet may be sent if more timeslots are required


DL TBF Establ.72005(S9)

DL RLC MAC/c72077(S9)

Max sim. DL TBF .72007(S9)


EGPRS DL TBF UNACK72091(S10)

EGPRS DL TBF72089(S10) PossiblyPossibly

Req 1 tsl DL72039(S9)

Alloc 1 tsl DL72049(S9)

Only 1 TCH is allocated first.

If requested and available



/c72085(S9)packet_immed_ass_ack_msg

MS BTS BSC SGSNMS BTS BSC SGSN

P-Immediate Assignment

Immediate Assignment (CCCH)P-Immediate Assignment Ack

Packet Polling Request

Packet Polling Request (PACCH)

Packet Control Ack Packet Control Ack (PACCH)

MS on ready state

Sent on the PDTCH to find out the MS Timing Advance. In Nokia implementation, always sent when DL TBF Assignment is from CCCH. Not sent when DL TBF is assigned on PACCH


Alternatively, Packet DownlinkAssignmnet may be sent if more timeslots are required







EGPRS DL TBF72089(S10) PossiblyPossibly

Req 1 tsl DL72039(S9)

Alloc 1 tsl DL72049(S9)

Only 1 TCH is allocated first.

If requested and available

Figure 24 DL TBF Assignment, MS on CCCH


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DL TBF Assignment when UL TBF is ongoing

If there is an UL TBF ongoing, the channel request and immediate assignment is not needed. The DL TBF is allocated by sending Packet Downlink Assignment on PACCH.

MS BTS BSC SGSN

Packet Downlink Assignment (PACCH)

DL TBF DUR. UL/c72075(S9)


DL RLC Data Block

LLC PDU


Req x tsl DL72039(S9)

Alloc x tsl DL72049(S9)


DL RLC ACK MSC1…9/c79000(S10)

orDL RLC UNACK MSC1…9/c79001(S10)



EGPRS DL TBF72089(S10)

New TBF is established in the same mode (GPRS, EGPRS) than the ongoing TBF.

If UL TBF is EGPRS



DL TBF DUR. UL/c72075(S9)


DL RLC Data Block

LLC PDU


Req x tsl DL72039(S9)

Alloc x tsl DL72049(S9)


DL RLC ACK MSC1…9/c79000(S10)

orDL RLC UNACK MSC1…9/c79001(S10)



EGPRS DL TBF72089(S10)


If UL TBF is EGPRS

Figure 25 DL TBF Assignment when UL TBF is ongoing


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4.1.3 UL TBF Assignment

Depending on the network configuration different establishments procedures are used during the data connection. One phase access may reduce the TBF establishment time when accessing the cell and allows the system to allocate more than 1 RTSL for the UL TBF.

When CCCH is in use, the Uplink Establishment offers:

• GPRS: one-phase access is possible, but only 1 TSL can be allocated to the TBF. Timeslot reconfiguration would be needed for multi slot allocation

• EGPRS: two-phase access is mandatory (in case of EPCR (S11, SX 4.0) implemented on CCCH the one phase access is possible as well)

When PCCCH is in use, the Uplink Establishment offers:

• GPRS: one-phase access is possible. Network can allocate more than one TSL to the UL TBF.

The gain is obtained from the transmission side due to timeslot allocation. In CCCH case only one TSL is assigned, while in PBCCH case there can be more then one. This explains the increasing importance of the gain as the ping packet size becomes bigger.

• EGPRS: one-phase access is possible only if “EGPRS Packet Channel Request” (EPCR) is supported by the network (see Chapter 4.1.3.2). (If EPCR is not supported, then EGPRS is forced to use two-phase access even if working in the PCCCH.)

4.1.3.1 Channel Request - Packet Access Procedure (CCCH / PCCH) The following tables show the packet access procedure on CCCH (3GPP 04.18) and PCCH (3GPP 04.60).

The table describes the differences of the Channel Request (S10.5ED)and EGPRS Packet Channel Request (S11) functionality. All the access modes are described in unacknowledged and acknowledged mode (8>= bit or 8< bit).


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Purpose of the packet access procedure

EGPRS PACKET CHANNEL REQUEST supported in the cell

EGPRS PACKET CHANNEL REQUEST not supported in the cell

User data transfer – requested RLC mode = unacknowledged

EGPRS PACKET CHANNEL REQUEST with access type = 'Two-phase access'

CHANNEL REQUEST with establishment cause = 'Single block packet access' for initiation of a two-phase access

User data transfer – requested RLC mode = acknowledged and number of RLC data blocks ? 8 (note 1)

EGPRS PACKET CHANNEL REQUEST with access type = 'Short Access' or 'One-phase access' or 'Two-phase access'


User data transfer – requested RLC mode = acknowledged and number of RLC data blocks > 8 (note 1)

EGPRS PACKET CHANNEL REQUEST with access type = 'One-phase access' or 'Two-phase access'


Upper layer signalling transfer (e.g. page response, cell update, MM signalling, etc)

EGPRS PACKET CHANNEL REQUEST with access type = 'signalling' or CHANNEL REQUEST with establishment cause 'one-phase access'

CHANNEL REQUEST with establishment cause = 'Single block packet access' for initiation of a two-phase access or CHANNEL REQUEST with establishment cause value 'one-phase access'

Sending of a measurement report or of a PACKET CELL CHANGE FAILURE

CHANNEL REQUEST with establishment cause = 'Single block packet access'

Sending of a PACKET PAUSE message

CHANNEL REQUEST with establishment cause = 'Single block packet access' (note 2)

NOTE 1: The number of blocks shall be calculated assuming channel coding scheme MCS-1. NOTE 2: Upon sending the first CHANNEL REQUESTmessage the mobile station shall start timer T3204. If timer

T3204 expires before an IMMEDIATE ASSIGNMENT message granting a single block period on an assigned packet uplink resource is received, the packet access procedure is aborted. If the mobile station receives an IMMEDIATE ASSIGNMENT message during the packet access procedure indicating a packet downlink assignment procedure, the mobile station shall ignore the message.

Table 14 Packet Access Procedure (CCCH)

Purpose of the packet access procedure

EGPRS PACKET CHANNEL REQUEST supported in the cell

EGPRS PACKET CHANNEL REQUEST not supported in the cell

User data transfer – requested RLC mode = unacknowledged

EGPRS PACKET CHANNEL REQUEST with access type = 'Two-phase access'

PACKET CHANNEL REQUEST with access type = 'Two-phase access' (NOTE 2)

User data transfer – requested RLC mode = acknowledged and number of RLC data blocks ? 8 (NOTE 1)

EGPRS PACKET CHANNEL REQUEST with access type = 'Short Access' or 'One-phase access' or 'Two-phase access'


User data transfer – requested RLC mode = acknowledged and number of RLC data blocks > 8 (NOTE1)

EGPRS PACKET CHANNEL REQUEST with access type = 'One-phase access' or 'Two-phase access'


Upper layer signalling transfer (e.g. page response, cell update, MM signalling, etc)

EGPRS PACKET CHANNEL REQUEST with access type = 'signalling' or PACKET CHANNEL REQUEST with corresponding access type (NOTE 2)

PACKET CHANNEL REQUEST with access type = 'Two-phase access' or PACKET CHANNEL REQUEST with corresponding access type (NOTE 2)

Sending of a measurement report or of a PACKET CELL CHANGE FAILURE

PACKET CHANNEL REQUEST with access type = 'Single block without TBF establishment' (NOTE 2)

Sending of a PACKET PAUSE message

PACKET CHANNEL REQUEST with access type = 'Single block without TBF establishment' (NOTE 2) (NOTE 3)

NOTE 1: The number of blocks shall be calculated assuming channel coding scheme MCS-1. NOTE 2: The format to be used for the PACKET CHANNEL REQUEST message is defined by the parameter

ACC_BURST_TYPE. NOTE 3: Upon the first attempt to send a PACKET CHANNEL REQUEST message the mobile station shall start

timer T3204. If the mobile station receives a PACKET DOWNLINK ASSIGNMENT message before expiry of timer T3204, the mobile station shall ignore the message.

Table 15 Packet Access Procedure (PCCCH)

4.1.3.2 EGPRS Packet Channel Request SI13 contains the EPCR information. PCU always includes Access Technology Request into EDGE UL assignment. Therefore MS sends Packet Resource Request


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(PRR) message in first allocated USF, and optionally the Additional Radio Access Capability (ARAC) message in second one.

GPRS & EGPRS short access is basically same scenario as GPRS one phase access; Access Technology Request is never included in UL assignment message.

MS requests one-phase access, PCU makes final decision whether used or not. (E.g. Common BCCH (multiband) and EGPRS territory in non-BCCH band => forced 2-phase access).

The following figure shows the flow chart of One phase access on EGPRS.

One Phase/Short Access

MS BSC / PCU

UL Data Block + TLLI

Immediate Assignment (UL assignment)

EGPRS Packet Channel Request - one phase access or short access

Packet UL ACK/NACK + TLLI

Packet Control ACK or

UL Data Block w/o TLLI

…

SI13 (EPCR Support)

Decision –one-phase vs.

two-phase

UL TBF ready

(Additional Radio Access capability)

(Packet Resource Request)

One Phase Access:If NW has requested RAC

info from MS in Immediate Assignment,

MS responds with Packet Resource

RequestOne Phase Access:

If not all RAC info fits in PRR, MS

sends this additional message

One Phase/Short Access

MS BSC / PCU

UL Data Block + TLLI

Immediate Assignment (UL assignment)

EGPRS Packet Channel Request - one phase access or short access

Packet UL ACK/NACK + TLLI

Packet Control ACK or

UL Data Block w/o TLLI

…

SI13 (EPCR Support)

Decision –one-phase vs.

two-phase

UL TBF ready

(Additional Radio Access capability)

(Packet Resource Request)

One Phase Access:If NW has requested RAC

info from MS in Immediate Assignment,

MS responds with Packet Resource

RequestOne Phase Access:

If not all RAC info fits in PRR, MS

sends this additional message

Figure 26 EGPRS one phase access on CCCH

4.1.3.3 Dynamic and Extended Dynamic Allocation on UL with and without USF4 The number of RLC/MAC blocks to transmit is controlled by the USF_GRANULARITY parameter characterizing the uplink TBF. USF Granularity 1 means that the mobile station shall transmit one RLC/MAC block. USF Granularity 4 means that the mobile station shall transmit four consecutive RLC/MAC blocks.

PCU2 uses USF Granularity 4 for GPRS MSs in EGPRS territory.

USF granularity 4 is useful when there is GPRS UL TBF multiplexed in the same timeslot with EGPRS DL TBF. In this case only every fourth DL data block need to be


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GSMK coded, and the other three blocks can be 8-PSK coded. PCU1 uses always USF granularity 1, meaning that EGPRS DL TBF does not utilize 8-PSK coding schemes while a GPRS UL TBF is transferring data on the same timeslot.

The detailed description of Dynamic Allocation with and without USF4 and Extebded Dynamic Allocation with/without USF4 can be found in Section 7.7.2.

4.1.3.4 UL TBF ASSIGNMENT, MS on CCCH, 2 phase access After Channel Request and Immediate Assignment the network sends PACKET_UL_ASSIGNMENT message including Single Block Allocation or MultiBlock Allocation, indicating 2-phase access.

MultiBlock Allocation may be used only if MS is EGPRS capable (e.g. network receives an EGPRS_PACKET_CHANNEL_REQ).

In PACKET_UL_ASSIGNMENT, network reserves limited resources on 1 PDCH for the MS, and MS may transmit PACKET_RESOURCE_REQUEST and optionally ADDITIONAL MS RADIO ACCESSS CAPABILITIES.

In PBCCH, 2-phase access can be initiated by:

• Network: When sending a PACKET_UL_ASSIGNMENT it includes Single or MultiBLock Allocation, which forces the MS to send a PACKET_RESOURCE_REQ (-> 2-phase access).

• MS: By requiring a 2-phase access in the PACKET_CHANNEL_REQ or EGPRS_PACKET_CHANNEL_REQ. If access is granted, the Network shall order the MS to send PACKET_RESOURCE_REQ in the PACKET_UL_ASSIGNMENT.

MS BTS BSC SGSN

Channel Request (RACH)

Immediate Assignment (CCCH)

P_Channel Required

P-Immediate Assignment Cmd

UL TBF ASSIGNMENT, MS ON CCCH. 2 phase access.

Packet Resource Request (PACCH)Packet Resource Request

Packet Uplink AssignmentPacket Uplink Assignment (PACCH)

RLC Data block

Packet Uplink Ack/Nack

RLC Data Block

Packet Uplink Ack/Nack (specs)

Single blockNOTE: BTS does not send Imm Ass Ackfor Single block Immediate Assignment

The Contention resolution was already done above. The PCU does not immediatelysend Packet UplinkAck/Nack (as it does in one phaseaccess for contentionresolution) but only after a certain amount of blocks orafter Final UL Data Block.

Including TLLI for contention resolution

Including TLLI for contention resolution UL TBF Establ.72000(S9)

UL RLC CS1/c72062(S9)

UL RLC CS2/c72064(S9)or


/c72082(S9)packet_ch_req

UL RLC MAC/c72076(S9)


Max.sim.UL TBF72002(S9)

Req X tsl UL72034(S9)

Alloc X tsl UL72044(S9)


Establ.cause '2-ph.access'

More than 1 TCH can be allocated.


UL TBF UNACK72010(S9)Possibly

Max.sim.UL TBF UNACK72012(S9) Possibly




P_Channel Required





RLC Data block


RLC Data Block


Single blockNOTE: BTS does not send Imm Ass Ackfor Single block Immediate Assignment

The Contention resolution was already done above. The PCU does not immediatelysend Packet UplinkAck/Nack (as it does in one phaseaccess for contentionresolution) but only after a certain amount of blocks orafter Final UL Data Block.


Including TLLI for contention resolution UL TBF Establ.72000(S9)

UL RLC CS1/c72062(S9)

UL RLC CS2/c72064(S9)or


/c72082(S9)packet_ch_req












Figure 27 UL TBF ASSIGNMENT, MS on CCCH, 2 phase ac cess


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4.1.3.5 UL TBF ASSIGNMENT, MS on CCCH, 1 phase access Contention Resolution

Before establishing an UL TBF, the network must assign a TFI to the TLLI, which identifies uniquely the MS (3GPP 04.60):

• Until contention resolution the TLLI must be included in every RLC block, and if MCS9-7 is used, in both RLC blocks

• TLLI shall be included in PACKET_RESOURCE_REQUEST and ADDITIONAL_MS_RADIO_ACCESS_CAPABILITIES

• It applies for retransmission of RLC blocks as well

• NW responds with TLLI in PACKET_UL_ACK/NACK

• For an EGPRS TBF the network may respond with PACKET_UL_ASSIGNMENT if resources allocated to the TBF need to be reallocated

• On network side, Contention Resolution is completed when the network receives RLC block with TLLI and TFI associated to the TBF

• On MS side, Contention Resolution is completed when MS receives PACKET_UL_ACK/NACK with TLLI and TFI. MS shall then stop T3166 and N3104

MS sends a PACKET_CONTROL_ACK containing the TA index if a valid RRBP is received.

CCCH p- imm.ass./c72084(S9)packet_immed_ass_msg

MS BTS BSC SGSN



P-Channel Required

P-Immediate Assignment Cmd(CCCH)

P-Immediate Assignment Ack

UL TBF ASSIGNMENT,MS ON CCCH.1 phase access.

Sent 6 TDMA frames before the Imm Ass goes to air. Includes the air-if TDMA frame number of the Imm Ass message

RACH p-ch.req./c72082(S9)packet_ch_req

CCCH p- imm.ass. ack/c72085(S9)packet_immed_ass_ack_msg

UL TBF Establ.72000(S9)


Req 1 tsl UL72034(S9)

Alloc 1 tsl UL72044(S9)


Only 1 TCH can be allocated.

CCCH p- imm.ass./c72084(S9)packet_immed_ass_msg




P-Channel Required

P-Immediate Assignment Cmd(CCCH)

P-Immediate Assignment Ack

UL TBF ASSIGNMENT,MS ON CCCH.1 phase access.

Sent 6 TDMA frames before the Imm Ass goes to air. Includes the air-if TDMA frame number of the Imm Ass message

RACH p-ch.req./c72082(S9)packet_ch_req

CCCH p- imm.ass. ack/c72085(S9)packet_immed_ass_ack_msg



Req 1 tsl UL72034(S9)

Alloc 1 tsl UL72044(S9)


Only 1 TCH can be allocated.

Figure 28 UL TBF ASSIGNMENT, MS on CCCH, 1 phase ac cess

The PACKET_UL_ASSIGNMENT construction contains the following information (3GPP 04.18-8.0):


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• Temporary flow identity, TFI;

• USF value, if the medium access method is dynamic allocation; or the fixed allocation bitmap, if the medium access method is fixed allocation;

• Channel coding scheme for RLC data blocks;

• Power control parameters;

• Polling bit;

• Optionally, the timing advance index (see 3GPP TS 05.10);

• Optionally, the TBF starting time (note: TBF starting time is mandatory if medium access method is fixed allocation).

In addition, the EGPRS packet uplink assignment construction also contains:

• EGPRS modulation and coding scheme;

• Information whether retransmitted uplink data blocks shall be resegmented or not;

• EGPRS window size to be used within the transmission;

• Optionally a request for the mobile station to send its radio access capability information.


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4.1.3.6 EGPRS UL TBF ASSIGNMENT, MS on PCCCH with 2 phase access


MS BTS BSC SGSN



RLC Data block


RLC Data Block


The Contention resolution was already done above. The PCU does not immediatelysend Packet Uplink

Ack/Nack (as it does in one phaseaccess for contention

resolution) but only after a certain amount of blocks orafter Final UL Data Block.




UL RLC ACK MSC1…9/c79002(S10)

or









EGPRS Packet Channel Request (PRACH) EGPRS Packet Channel RequestPRACH p-ch req./c91002 (S10)nbr_of_packet_channel_reqs

Packet UL Assignment (PCCCH)

Packet UL Assignment

/c91021(10)p_ul_ass_msgs_on_pccch

EGPRS UL TBF UNACK72090(S10)

EGPRS UL TBF72088(S10)

UL RLC UNACK MSC1…9/c79003(S10)




PossiblyEGPRS TBF if there are resouces

Possibly





RLC Data block


RLC Data Block


The Contention resolution was already done above. The PCU does not immediatelysend Packet Uplink

Ack/Nack (as it does in one phaseaccess for contention

resolution) but only after a certain amount of blocks orafter Final UL Data Block.





or









EGPRS Packet Channel Request (PRACH) EGPRS Packet Channel RequestPRACH p-ch req./c91002 (S10)nbr_of_packet_channel_reqs






UL RLC UNACK MSC1…9/c79003(S10)




PossiblyEGPRS TBF if there are resouces

Possibly

Figure 29 EGPRS UL TBF ASSIGNMENT, MS on PCCCH with 2 phase access

4.1.3.7 EGPRS UL TBF ASSIGNMENT, MS on PCCCH with 1 phase access

MS BTS BSC SGSN

EGPRS Packet Channel Request (PRACH)


EGPRS Packet Channel Request


UL TBF ASSIGNMENT,MS ON PCCCH.1 phase access.



More than 1 TCH can be requested

QoS information.

PRACH p-ch req./c91002 (S10)nbr_of_packet_channel_reqs


UL TBF establ.72000(S9)


Req x tsl UL72034..38(S9)

Alloc x tsl UL72044..48(S9)

EGPRS UL TBF72088(S10) Possibly

EGPRS TBF if there are resouces


EGPRS Packet Channel Request (PRACH)


EGPRS Packet Channel Request


UL TBF ASSIGNMENT,MS ON PCCCH.1 phase access.



More than 1 TCH can be requested

QoS information.

PRACH p-ch req./c91002 (S10)nbr_of_packet_channel_reqs


UL TBF establ.72000(S9)


Req x tsl UL72034..38(S9)

Alloc x tsl UL72044..48(S9)

EGPRS UL TBF72088(S10) Possibly

EGPRS TBF if there are resouces

Figure 30 EGPRS UL TBF ASSIGNMENT, MS on PCCCH with 1 phase access


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4.1.3.8 Establishment of EGPRS UL TBF when DL TBF is ongoing

MS BTS BSC SGSN

Packet Uplink Assignment (PACCH)

EGPRS Packet_DL_Ack/Nack(Channel Request Description)


UL RLC Data Block

The MS may request UL TBF by including a Channel Request Description IE in a Packet Downlink Ack/Nack message


orUL RLC UNACK MSC1…9/c79003(S10)




UL TBF DUR. DL/c72074(S9)








Possibly



Packet Uplink Assignment (PACCH)

EGPRS Packet_DL_Ack/Nack(Channel Request Description)


UL RLC Data Block

The MS may request UL TBF by including a Channel Request Description IE in a Packet Downlink Ack/Nack message


orUL RLC UNACK MSC1…9/c79003(S10)




UL TBF DUR. DL/c72074(S9)








Possibly


Figure 31 Establishment of EGPRS UL TBF when DL TBF is ongoing


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4.2 (E)GPRS Data Transfer After TBF establishment the data transfer signaling is conveyed on PACCH.

4.2.1 (E)GPRS Data Transfer DL MS BTS BSC SGSN

DL TBF ASSIGNMENT

DL Data Packets The SGSN encrypts each DL packet according to parametersnegortiated in PDP context activation

Downlink Data Packets

Downlink Data Packets (PDTCH)

Gtp_packets_sent_in_dl/c3001

Gtp_data_in_bytes_sent_in_dl /c3003

bytes_in_of_vjhc_in_sndcp /c3008

bytes_out_of_vjhc_in_sndcp /c3009Header compr

bytes_in_of_v42bis_in_sndcp /c3010

bytes_out_of_v42bis_in_sndcp /c3011Data compr

NSCV_passed_data_in_bytes /c3017

Packet Downlink Ack/Nack (PACCH)Packet Downlink Ack/Nack

If NACK received andack mode usedDownlink Data Packets


DL RLC retransm CS1/c72068(S9)

or DL RLC retransm CS2/c72069(S9)


After TBF released

Flowrate per priority/c90005/90006(S10) 1sec sampling

(retransm.not incl.)

DL TBF releasecounter group

DL RLC blockcounter

PCU controls how often the ack should come (polling in DL data block). It is about every 18 blocks but gets adapted to radio conditions.


DL TBF ASSIGNMENT

DL Data Packets The SGSN encrypts each DL packet according to parametersnegortiated in PDP context activation



Gtp_packets_sent_in_dl/c3001

Gtp_data_in_bytes_sent_in_dl /c3003


bytes_out_of_vjhc_in_sndcp /c3009Header compr


bytes_out_of_v42bis_in_sndcp /c3011Data compr

NSCV_passed_data_in_bytes /c3017


If NACK received andack mode usedDownlink Data Packets


DL RLC retransm CS1/c72068(S9)

or DL RLC retransm CS2/c72069(S9)


After TBF released

Flowrate per priority/c90005/90006(S10) 1sec sampling

(retransm.not incl.)


DL RLC blockcounter

PCU controls how often the ack should come (polling in DL data block). It is about every 18 blocks but gets adapted to radio conditions.

Figure 32 (E)GPRS Data Transfer DL

4.2.2 (E)GPRS Data Transfer UL


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MS BTS BSC SGSN

UL TBF ASSIGNMENT

Packet Uplink Ack/Nack (PACCH) Packet Uplink Ack/Nack (FAI=1 when last)

Packet control ack (PACCH)Packet control ack

"First data blocks" (PDTCH) "First data blocks" (PDTCH)

LLC frames The LLC frameis already ciphered

LLC ack (window 1-16)

Gtp_packets_sent_in_ul/c3000

Gtp_data_in_bytes_sent_in_ul /c3002


bytes_out_of_vjhc_in_sndcp /c3009Header compr.


bytes_out_of_v42bis_in_sndcp /c3011

Data compr.



There is a dummy DL MACblock before each UL data block


DL dummy control block

RLC blocks per priority90001(S10)

Also if priority changed

Flowrate per priority/c90005/90006(S10)

1sec sampling

UL TBF releasecounter group

UL RLC blockcounter

PCU controls after how many blocks the ack is sent. It is about every 20 blocks but can be adapted to radio conditions.


UL TBF ASSIGNMENT

Packet Uplink Ack/Nack (PACCH) Packet Uplink Ack/Nack (FAI=1 when last)


"First data blocks" (PDTCH) "First data blocks" (PDTCH)

LLC frames The LLC frameis already ciphered

LLC ack (window 1-16)

Gtp_packets_sent_in_ul/c3000

Gtp_data_in_bytes_sent_in_ul /c3002


bytes_out_of_vjhc_in_sndcp /c3009Header compr.


bytes_out_of_v42bis_in_sndcp /c3011

Data compr.



There is a dummy DL MACblock before each UL data block


DL dummy control block

RLC blocks per priority90001(S10)

Also if priority changed

Flowrate per priority/c90005/90006(S10)

1sec sampling


UL RLC blockcounter

PCU controls after how many blocks the ack is sent. It is about every 20 blocks but can be adapted to radio conditions.

Figure 33 (E)GPRS Data Transfer UL


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4.3 Mobility with Cell-reselection The following mobility related signaling flowcharts are show in this chapter:

• Intra PCU cell-reselection

• Inter PCU cell-reselection (intra BSC)

• RA/LA Update (intra PAPU)

• RA/LA Update (Inter PAPU or inter SGSN)

4.3.1 Intra PCU Cell-Reselection

08.18:

Queued BSSGP signalling, e.g. pages, shall not be affected by Flush. These will thus go wasted if Cell Change happens.

MS BTS1 BSC SGSN

DL TBF ASSIGNMENT, MS ON CCCH, via BTS 1

DL Data Packets

The SGSN encrypts each DL packet according to parametersnegortiated in PDP context activation

BTS2

DL Data PacketsDL Data Packets (PDTCH)

The MS notices a need for a cell change (measurement strategy in 05.08).The MS stops receiving the DL Data Packets and tunes to the new frequency. While doing the neighboring measurement, the MS also checks for a possible RAchange; if the cell change results in RA change, a RA update is performed instead of a cell update.

03.60:: "LLC frame of any type, including MS identity"03.60:: "LLC frame of any type", BSS adds CGI

PCU buffers LLC pdu's in RLC ACK-mode until all RLC blocks of the LLC pdu are acknowledged. (reliability class 1-3)

In RLC UNACK-mode PCU buffers until all RLC blocks of LLC pdu are sent.

DL TBF ASSIGNMENT, via BTS 2


Flush-LL PDU( Old BVCI+MS TLLI)

If new BVCI is given in Flush-LL, and thenew BVCI is served by the same NSE, the queued data packets are forwarded to the new BVCI. In the Intra-PCU case theNSE is the same, since In the Nokiaimplementation each PCU represents one and only one Network Service Entity (NSE).

In Flush-LL Ack the PCU tellswhether the queued data packetswere deleted or forwarded to new BVCI

The SGSN does not wait for Flush-LL ackbefore it forwardsnew DL Data Packets towards newBVCI

If MS is in UL data transfer it starts UL TBF in the new cell to transfer data. Cell Update is performed, too.

UL flush/c72058(S9)

DL flush/c72059(S9)

DL Data Packets

Flush-LL Ack

UL TBF ASSIGNMENT, MS ON CCCH, via BTS 2

08.18:

Queued BSSGP signalling, e.g. pages, shall not be affected by Flush. These will thus go wasted if Cell Change happens.

MS BTS1 BSC SGSN


DL Data Packets


BTS2


The MS notices a need for a cell change (measurement strategy in 05.08).The MS stops receiving the DL Data Packets and tunes to the new frequency. While doing the neighboring measurement, the MS also checks for a possible RAchange; if the cell change results in RA change, a RA update is performed instead of a cell update.

03.60:: "LLC frame of any type, including MS identity"03.60:: "LLC frame of any type", BSS adds CGI

PCU buffers LLC pdu's in RLC ACK-mode until all RLC blocks of the LLC pdu are acknowledged. (reliability class 1-3)

In RLC UNACK-mode PCU buffers until all RLC blocks of LLC pdu are sent.




If new BVCI is given in Flush-LL, and thenew BVCI is served by the same NSE, the queued data packets are forwarded to the new BVCI. In the Intra-PCU case theNSE is the same, since In the Nokiaimplementation each PCU represents one and only one Network Service Entity (NSE).


The SGSN does not wait for Flush-LL ackbefore it forwardsnew DL Data Packets towards newBVCI

If MS is in UL data transfer it starts UL TBF in the new cell to transfer data. Cell Update is performed, too.

UL flush/c72058(S9)

DL flush/c72059(S9)

DL Data Packets

Flush-LL Ack


Figure 34 Intra PCU Cell-reselection


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4.3.2 Inter PCU Cell-reselection (Intra BSC)

MS Cell1 BSC SGSN


DL Data Packets


Cell2


The MS notices a need for a cell change (measurement strategy in 05.08).The MS stops receiving the DL Data Packets and tunes to the new frequency. While doing the neighbouring measurement, the MS also checks for a possible RAchange; if the cell change results in RA change, a RA update is performed instead of a cell update.

03.60:: "LLC frame of any type, including MS identity"


03.60:: "LLC frame of any type", BSS adds CGI

PCU buffers until RLC/MAC ack (relaibility class 1-3)


DL Data Packets



In Nokia implementation, the inter-PCU cellchange is also a inter-NSE cell change, thusthe PCU destroys queued data packets aftera Flush that follows inter-PCU cell change.

Thus if PCU is sending DL data when MS makes an inter PCU cell change, data is probably lost and retransmissions rely on the LLC layer acknowlegements

Flush-LL Ack


UL flush/c72058(S9)

DL flush/c72059(S9)Related

to cell1

MS Cell1 BSC SGSN


DL Data Packets


Cell2


The MS notices a need for a cell change (measurement strategy in 05.08).The MS stops receiving the DL Data Packets and tunes to the new frequency. While doing the neighbouring measurement, the MS also checks for a possible RAchange; if the cell change results in RA change, a RA update is performed instead of a cell update.

03.60:: "LLC frame of any type, including MS identity"


03.60:: "LLC frame of any type", BSS adds CGI

PCU buffers until RLC/MAC ack (relaibility class 1-3)


DL Data Packets



In Nokia implementation, the inter-PCU cellchange is also a inter-NSE cell change, thusthe PCU destroys queued data packets aftera Flush that follows inter-PCU cell change.

Thus if PCU is sending DL data when MS makes an inter PCU cell change, data is probably lost and retransmissions rely on the LLC layer acknowlegements

Flush-LL Ack


UL flush/c72058(S9)

DL flush/c72059(S9)Related

to cell1

Figure 35 Inter PCU Cell-reselection (Intra BSC)


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4.3.3 RA/LA Update (intra PAPU)

1. Routeing Area Update Request

3. Routeing Area Update Accept

2. Security Functions

MS BSS SGSN

4. Routeing Area Update Complete

Figure 36 RA/LA Update (intra PAPU)

MS BTS BSC New SGSN

DL TBF ASSIGNMENT

Routeing Area Update Accept

Routing Area Update Accept (PDCCH)Routing Area Update Accept

Location update request (SDDCH)

Routing Area Update complete (PDCH)Routing Area Update complete

First System information message [ 1].

Location update request

Location Update AcceptLocation Update Accept



P_Channel Required


Caneel Release (SDCCH)

SECURITY FUNCTIONS AS SET BY THE OPERATOR

Routing Area Update RequestRouting Area Update Request (PDTCH) Routing Area Update Request

Location area Update [ 2].

Routing area Update [ 3].

Cel

l res

elec

tion

dat

a O

utag

e

First System information message(BCCH)

MS BTS BSC New SGSNMS BTS BSC New SGSN

DL TBF ASSIGNMENT










P_Channel Required







Cel

l res

elec

tion

dat

a O

utag

e


Figure 37 RA/LA Update (intra PAPU) in BSS network


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4.3.4 RA/LA Update (Inter PAPU or inter SGSN)

MS BSS new SGSN HLRGGSNold SGSN

2. SGSN Context Response

3. Security Functions

1. Routeing Area Update Request

2. SGSN Context Request

6. Update PDP Context Request

6. Update PDP Context Response

7. Update Location

10. Update Location Ack

11. Routeing Area Update Accept

8. Cancel Location

8. Cancel Location Ack

9. Insert Subscriber Data Ack

9. Insert Subscriber Data

12. Routeing Area Update Complete

5. Forward Packets

4. SGSN Context Acknowledge

Figure 38 RA/LA Update (Inter PAPU or inter SGSN)

In case of inter-PAPU RA replace SGSN with PAPU.

The flow chart for RA/LA Update from the radio part point of view is included below:


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MS BTS BSC New SGSN

Routeing Area Update Request (PDTCH) Routeing Area Update Request

Packet Uplink Ack/Nack (PACCH)




Including TLLI for contention resolutionIncluding TLLI for contention resolution

Routeing Area Update Request

DL TBF ASSIGNMENT


Routeing Area Update AcceptRouteing Area Update Accept









UL RLC blockcounter

DL RLC blockcounter

Start T3330, 15s (max.5 tries)


New SGSN sends context req to old SGSN. Old SGSN sends response and starts tunneling data to new SGSN . New SGSN sends ‘Update PDP context request’ to GGSN. New SGSN informs HLR about SGSN change by sending ‘Upate location’. HLR sends ‘Cancel location’ to old SGSN.

UL TBF ASSIGNMENT, MS ON CCCH 1-ph.access


Routeing Area Update Request (PDTCH) Routeing Area Update Request






Routeing Area Update Request

DL TBF ASSIGNMENT


Routeing Area Update AcceptRouteing Area Update Accept









UL RLC blockcounter

DL RLC blockcounter



New SGSN sends context req to old SGSN. Old SGSN sends response and starts tunneling data to new SGSN . New SGSN sends ‘Update PDP context request’ to GGSN. New SGSN informs HLR about SGSN change by sending ‘Upate location’. HLR sends ‘Cancel location’ to old SGSN.

UL TBF ASSIGNMENT, MS ON CCCH 1-ph.access

Figure 39 RA/LA Update (Inter PAPU or inter SGSN) in BSS network 1/2

MS BTS BSC New SGSN

UL TBF ASSIGNMENT

Routeing Area Update Complete (PDTCH) Routeing Area Update Complete






Routeing Area Update Complete

Succ_inter_sgsn_ra_updat/c1019DL RLC MAC

/c72077(S9)


UL RLC blockcounter


UL TBF ASSIGNMENT

Routeing Area Update Complete (PDTCH) Routeing Area Update Complete






Routeing Area Update Complete

Succ_inter_sgsn_ra_updat/c1019DL RLC MAC

/c72077(S9)


UL RLC blockcounter

Figure 40 RA/LA Update (Inter PAPU or inter SGSN) in BSS network 2/2

4.4 TBF Release PACKET TBF RELEASE message is sent on the PACCH by the network to the mobile station to initiate release of an uplink or downlink TBF.


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The delayed TBF functionality is described in section 7.3 and section 7.4.

4.4.1 Packet TBF Release Content

The PACKET TBF RELEASE information element contains the following information among others (3GPP 04.60):

Global TFI IE

This information element contains the TFI of the mobile station's which uplink and/or downlink TBF to be released.

Uplink_Release (1 bit field) Downlink_Release (1 bit field) These fields indicate which TBF shall be release, uplink or downlink. Both directions can be released at the same time.

0 TBF shall not be released 1 TBF shall be released

TBF_RELEASE_CAUSE (8 bit field) This field indicates the reason for the release of the TBF. This field is encoded according to the following table:

bit 4 3 2 1 0 0 0 0 Normal release 0 0 1 0 Abnormal release All other values are reserved, the same behavior in reception as if 'Abnormal release'.

The network may initiate immediate abnormal release of a downlink TBF by transmitting a PACKET TBF RELEASE message to the mobile station on the PACCH.

The mobile station shall immediately stop monitoring its assigned downlink PDCHs. If a valid RRBP field is received as part of the PACKET TBF RELEASE message, the mobile station shall transmit a PACKET CONTROL ACKNOWLEDGMENT message in the uplink radio block specified.

If there is no on-going uplink TBF, the mobile station in packet transfer mode shall enter packet idle mode.

4.4.2 Abnormal Releases

In Nokia implementation the following abnormal releases can be listed:

• TBF Releases due to CSW traffic will occur when during a data session the CS call or SMS is received.

• TBF Releases due to Flush will occur during a cell change.

• TBF Release due to no response from MS will occur when the mobile will loose the connection e.g. due to lack of coverage – TBF drop.

• The TBF release due to suspend.


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4.4.3 TBF Release in PCU2

Network may send PACKET TBF RELEASE message on the PACCH to the mobile station to initiate release of an uplink or downlink TBF. /44.060/

PCU1 never uses PACKET TBF RELEASE.

PCU2 uses PACKET TBF RELEASE message with following scenarios:

• Abnormal release because of N3101/N3103/N3105 counters reaching maximum value for the TBF.

• Abnormal release because of T3193 timer expiry.

• TBF release because of territory downgrade or cell delete or Abis sync loss.

• When Channel Request Description IE and FAI=1 is received in PACKET DOWNLINK ACK/NACK from the MS, PCU2 sends PACKET TIMESLOT RECONFIGURE and establish both the UL and DL TBFs. If the MS has started using new resources and there is no DL PDU at PCU, then PCU2 releases the DL TBF by sending PACKET TBF RELEASE.

• If Uplink/Downlink TBF establishment fails, then in some cases PCU2 sends Packet TBF release message to the MS to make sure that the MS move to CCCH.

• Reallocation Failure from non-hopping to hopping band. After initial allocation on non-hopping/BCCH band, if BTS reallocation to Hopping BTS fails then PACKET TBF RELEASE message is sent to mobile. See Note1.

Note 1. If EGPRS is configured to hopping non-BCCH BTS, EGPRS DL TBF may be initially established on non-EGPRS BCCH band, but the TBF is immediately reallocated to EGPRS band. If there is congestion in EGPRS territory, the PCU releases the EGPRS TBF and establish new GPRS TBF for the MS. Because the PCU2 can send PACKET TBF RELEASE message to the MS then PCU2 can initiate GPRS DL TBF to the MS immediately. In the same situation the PCU1 does wait 5 seconds until it can initiate GPRS DL TBF to the MS

PACKET PDCH RELEASE message is sent on PACCH by the network to notify all mobile stations listening to that PDCH that one or more PDCHs will be immediately released and become unavailable for packet data traffic. /44.060/

PCU2 sends PACKET PDCH RELEASE message on all timeslots of the territory. PCU1 does not send PACKET PDCH RELEASE message on the timeslots that were not allocated to any MS.


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5. (E)GPRS Accessibility The fast access to the network is very important in (E)GPRS functionality. If the TBF establishment is delayed due to congestion on signaling channels, the (E)GPRS performance will be degraded.

The aim of signaling load analysis and planning is to avoid service degradation on (E)GPRS due to overload situation on signaling channels.

The signaling traffic analysis is important from CSW point of view as well, because the (E)GPRS attach/detach, PDP Context Activation, TBF establishment and (E)GPRS mobility using the signaling channels and generate additional BSS signaling traffic on top of the CSW signaling load (except for PBCCH usage).

The signaling load analysis in BSS network is based on the following items:

• Air interface signaling

• TRXSIG on Abis interface

• BCSU in BSC

In the following subsections the above-mentioned items are described from analysis and planning point of view.

5.1 Air Interface Signaling Load The logical channels are split into traffic channels (TCH), Common Channels (CCH) and Dedicated Channels (DCH).

The CCH is further divided to Broadcast Channels (BCH) and Common Control Channels (CCCH).

The BCH is downlink channel and contains three logical channels: Frequency Correction Channel (FCCH), Synchronization Channel (SCH) and Broadcast Control Channel (BCCH).

The DCH contains the Stand Alone Dedicated Control Channel (SDCCH), Slow Associated Control Channel (SACCH) and Fast Associated Control Channel (FACCH).

The BCH channels do not need any planning consideration, but the CCCH channels and SDCCH can limit the (E)GPRS performance.

The implementation of PBCCH brings additional capacity and features, too. The following figures show the logical channels for GSM and channels with PBCCH.


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COMMONCHANNELSCOMMON

CHANNELS

BROADCASTCHANNELS

BROADCASTCHANNELS

COMMONCONTROL

CHANNELS

COMMONCONTROL

CHANNELS

DEDICATEDCONTROL

CHANNELS

DEDICATEDCONTROL

CHANNELS

TRAFFICCHANNELSTRAFFIC

CHANNELS

FCCHFCCH SCHSCH BCCHBCCH SDCCHSDCCH SACCHSACCH FACCHFACCH

PCHPCH RACHRACH AGCHAGCH TCH/FTCH/F TCH/HTCH/H TCH/EFRTCH/EFR

DEDICATEDCHANNELS

DEDICATEDCHANNELS

LOGICALCHANNELSLOGICAL

CHANNELS

Figure 41 Logical Channels

5.1.1 Common Control Channels The Common Control Channel contains the following channels:

• RACH, Random Access Channel;

• AGCH, Access Grant Channel;

• PCH, Paging channel;

• CBCH, Cell Broadcast Channel;

Common control channels are multiplexed in a 51 slots multiframe with the broadcast channel BCCH, different configurations are possible, they are explained below.

5.1.1.1 Paging Channel When the system initiates a communication towards a mobile station (for a call, an authentication, a short message service), the identity is broadcast in a group of cells (location area). The information is sending on the Paging Channel. It includes the subscriber's identity, either its TMSI or IMSI. The IMSI is anyway sent by the MSC to compute the paging group (see below).

PAGING REQUEST comes in 3 types:

Type 1 carries 2 identities (IMSI or TMSI)

Type 2 carries 3 identities (2 TMSI + 1 TMSI/IMSI)

Type 3 carries 4 identities (TMSI).

PCH is a downlink non-dedicated logical channel.

5.1.1.2 Access Grand Channel When the request has reached the system, a dedicated signaling resource has to be allocated to the original mobile to continue the process (identification, authentication,


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set-up, etc.). This allocation is done on a set of downlink slots, which constitute the AGCH. It is a downlink non-dedicated logical channel.

The allocation message contains information about the carrier to use: channel number, slot number, frequency hopping description if used and an estimated timing advance. The message is called IMMEDIATE ASSIGNMENT. If BSC is not able to allocate a resource, it will warn the mobile station and forbid it to retry within a time indication, this message is called IMMEDIATE ASSIGNMENT REJECT. If, for congestion reason, BTS is not able to send an IMMEDIATE ASSIGNMENT message on the air-interface, it will send a DELETE INDICATION to the BSC, indicating the overload.

Each AGCH can carry:

• 1 Immediate Assignment

• 2 Immediate Assignment Extended

• Up to 4 Immediate Assignments Reject

5.1.1.3 Random Access Channel When a mobile station has to execute any kind of operation with the system (location update, call establishment, emergency call, etc.), it has to establish a contact. A short request (coded on one burst, called Access Burst) is sent on a particular slot using a synchronized ALOHA (see GSM recommendation) access type; the set of these slots is called RACH.

RACH is an uplink non-dedicated logical channel, shared between mobile stations served by a specific cell.

5.1.2 SDCCH

The SDCCH is a dedicated signaling channel utilized on the air interface between mobile station and base station. The SDCCH channel is allocated between the MS and BTS following successful MS RACH and access grant by the BSC.

SDCCH usage is required for the 5 cases listed below:

• Call set-up (includes MOC, SMS, SS activation’s)

• Answer to paging

• Emergency call

• Call re-establishment

• Other reasons (which includes most commonly, location updates)

The random access by the mobile can be due to call set up, location update request or to answer a paging message from the Network. The RACH message is very data content limited with the initial RACH not controlled by the network. Accordingly, the access grant procedure is reasonably complex culminating in the initial channel assignment of a dedicated signaling channel.


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This dedicated signaling channel is then utilized by the network to control the subsequent network access by the mobile. Thus the SDCCH channel is key in achieving successful & efficient RA/LA update in (E)GPRS cell-reselection.

5.2 TRXSIG Load One TRX signaling channel (also called LAPD channel or D-channel) is defined for each TRX in Nokia BTS. The capacity of a LAPD channel is 16 kbps, 32 kbps or 64 kbps.

Many of the customer’s end-user service is generating new TRX load to existing network. Also the load profile has been changed due to the changes of the end user behavior compared to the days the network was dimensioned. The signaling load might also have been increased in a given signaling link due to a recent BSS feature activation in the BSS network.

To ensure that the A-bis signaling links are able to carry the increased signaling traffic it is recommended to offer the A-bis signaling optimization service, whenever either the radio network is optimized or an upper level end-user service is optimized. Non-optimized A-bis signaling could easily be the bottleneck in achieving the target performance level.

In addition to A-bis signaling link optimization service the physical layer transmission quality audits could be considered as an offered service module as the physical layer is the foundation for the whole A-bis respectively. [1]

The signaling is generated on TRXSIG and data TSLs as PACCH. In case of PBCCH the TRXSIG is not loaded by (E)GPRS signaling anymore.

5.2.1 TRXSIG Load Theory

The Abis protocols and TRXSIG load components are described below:

5.2.1.1 Abis Protocols The protocol layers of Abis can be seen in the Figure 42 below:


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Figure 42 Abis protocol layer

TRXSIG Load on DL

Overload could occur in downlink direction because of high amount of paging, immediate assignment, location update, etc. The buffer of the LAPD links handling the Abis signaling may overflow especially with the 16 kbit/s Abis links.

In heavy downlink situation normally paging and immediate assignment reject messages are being discarded on the LAPD signaling link to ensure the uninterrupted flow of call signaling traffic which always has the highest priority. If the situation gets worse and the congestion level of the transmit buffers still very high, all the signaling messages on the channels causing the congestion may be discarded.

In order to ensure paging does not overload the TRXSIG link in downlink, a precaution is needed, and traffic margin is given. In theory, the length of the paging message including Layer 2 header is about 21 octets (vary depends on TMSI or IMSI being used).

According to the system documentation of BSC nominal load and call mix, if the system is running on 50% of entire TRXSIG link capacity is consider running on the limit and it is referring to maximum system capacity.

About 60% of maximum system capacity is allocated for paging messages. Thus the average paging message for 16kbit/s link is calculated as 0.6 * 1000 octets / 21 octets = 29 pages per second, which roughly equals to 100 000 pages per hour.

As a result of the case studies conducted, the downlink messages putting the highest load on the Abis link in BCCH TRXSIG is paging message.


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TRXSIG Load on UL

Most of the messages received by the BCSU are radio measurements coming from the MS and access requests. These messages come from the LAPD link, and those are distributed to the RCSPRB (Radio Connection Supervision Program Block) in the BSC that processes them further. Before the distribution, the load state of the BCSU is checked. If the load exceeds a certain predefined limit, the messages are discarded.

If the load does not exceed the limit, messages are distributed and handled normally. The loss of the radio measurement result does not affect the service quality significantly; some reports are lost anyway due to the load on the LAPD link. The method of discarding messages is random as well, so the loss of messages for one particular connection stays within reasonable limits.

However, if the uplink traffic load is heavy enough and the LAPD buffer is full, the BTS starts to delete messages. When the LAPDm receives a message from the Radio Resources (RR management), buffer availability is checked and the message is deleted if there is no free space available. L3 messages (including RACH messages) are deleted if there are over 35 messages in the buffer, and measurement results are deleted if there are over six messages in the LAPD buffer.

In Nokia’s BSS implementation, a heavy traffic load usually first comes to attention via missing measurement results. If the traffic load gets heavier, other messages will also be deleted.

In order to reduce the uplink signaling traffic, measurement results can be averaged out from the BTS before sending to the network with the help of the BMA parameter. The value of the BMA can vary from 1 to 4.

5.2.1.2 TRXSIG Load Components, Measurement and Analysis The overload of TRXSIG can degrade the (E)GPRS performance, because e.g. the TBF establishment needs resources from TRXSIG. Therefore the first step in accessibility analysis and planning is the TRXSIG load analysis.

TRXSIG is a signaling link located on Abis interface. It conveys signaling messages (including SMS) between TRX and BSC using LAPD protocols.

When the signaling link gets congested, the buffer of conveyed messages becomes full on both side of the Abis interface then the signaling messages will be discarded. This can lead to failure of any function that is using the signaling connection.

From RF signaling planning point of view, the TRXSIG link is used to transmit those messages that are sent between MS and BSC on the following channels (depending on the channel configuration of the concrete TRX):

� BCCH

TRXSIG is used to download SYS INFO messages to BTS; BTS then sends them continuously on the BCCH.

� CCCH subchannels (RACH, AGCH, PCH and CBCH)

� SDCCH and its assigned SACCH

� FACCH and SACCH assigned to a TCH


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The TRXSIG conveys the e.g. Radio Link Layer management and TRX management messages as well, but these massages are not related to RF signaling.

In (E)GPRS the signaling information can be transmitted on TRXSIG channel but also on PACCH traffic channel (16 kbit/s PCU frames, a derivative of TRAU frames). So the signaling on PACCH is not transmitted over TRXSIG.

(E)GPRS mobile may or may not (this is controlled by the network) send any measurement report. These messages are sent using PCU frames, since the PCU controls the MS power. This MS power control information is signaled to the mobile via transparent RLC/MAC signaling messages, which are sent using PCU frames. Therefore, all of these messages (measurements and MS power control information) are not sent through the TRXSIG link.

The load measurement are generated in BSC and based on the following activities:

1. Data Collection

As the Abis signaling link service is flexible and can be anything between a 24h snap shot to continuous trend monitoring the actual tasks need to be planned carefully.

The LAPD-channel potential overload is taking place during the busy hour of the LAPD-channel. Different cells have the busy hour in different moment. In order to detect the potential overload situations it is essential to collect the data so that the busy hour of each LAPD-channel is covered. If the individual LAPD-channel busy hour is not known it is recommended to use at least two weeks continuous data collection period.

At least the following issues need to be planned and agreed before starting the data collection.

• The duration of the measurement period(s) • The start time of the measurement(s) • The BSCs included in each measurement • Agreement who (having necessary operating rights) is responsible for

the required file-transfer activities and running the Unix scripts. • Awareness of the other planned work for the same BSS areas

2. Data Processing

Data processing is done off-line and it is not causing load to the BSS network. The log files are transferred from the NMS to the Windows PC. First the files are prepared by the Excel macro tool and then they are further processed by the MS Access tool.

3. Data Analysis

The agreed service delivery may contain one or more of the following analysis.

• Unavailability analysis • Load Analysis • Quality Analysis • Delay Analysis


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• Configuration Analysis

The data collection period is also agreed and may be a series of consecutive 30 min periods (e.g. 48 periods each 30 min for 24h) or samples of limited consecutive period in given intervals (e.g. 15:00 to 23:00 every Friday). For comprehensive error analysis it is recommended to have consecutive data collection periods covering sufficient time period.

The detailed description of TRXSIG load measurement and analysis can be found in the link below:


LAPD KPIs

The evaluation of KPI can be implemented via MML using the command ZDMF, which gives the Total amount of Traffic Transmitted and Received in number of Octets in 30-minute windows.

To come in line with the KPI, the amount of data in each direction should not exceed 30% capacity of the existing link capacity otherwise an upgrade is necessary. For example TRANSMITTED TOTAL OCTET COUNT and RECEIVED TOTAL OCTET COUNT should not exceed 1080 000 octets for 30-minutes in case of a 16kbps TRX signaling link applied.

The OCTET COUNT figures in ZDMF report do not include the FCS- and Flag fields of the LAPD frame.

To compliment the KPI, MML’s command ZDMI is used to interrogate the working condition of the LAPD link. (The transmission quality of the abis links cannot be measured, except by sending people out to measure).

LAPD load and quality KPIs in S13

Abi_6a indicates the LAPD link (D-channel) load. It reports maximum of DL and UL load in a given D-channel.

Abi_4a gives DL D-channel load and abi_5a UL D-channel load.

Abi_1a to abi_3a are used to monitor LADP link and thus the whole Abis line connection quality._

These KPIs are available in LAPD Statistics for Abis Interface report.


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5.3 BCSU Load The BCSU handles the LAPD (TRXSIG and OMUSIG) and SS7.

The BSC elements’ load measurements register information on the peak and the average load rate of the computer units inside the BSC.

5.3.1 BSC RAW Measurement Results

An example of load results can be seen below (Table 16):

Table 16 BSC Unit Load Measurement Results from raw BSC measurement file converted with PCBSCS105 program

5.3.2 Reporting Suit 184 Report


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The RS 184 report contains the BSC Unit load per hour for each BSC. For processor units the average load of 70% is critical and the average of 60% should not be exceeded. For MB the average load should not exceed 50%. An example can be seen in Table 17.

Unit name and index Average load

(%)Min peak load

(%)Max peak load

(%)Peak hour

(YYYYMMDDHH)BCSU-0 0 1 1 2004120200BCSU-1 6.7 15 15 2004120215BCSU-2 7.01 17 17 2004120219BCSU-3 7.15 17 17 2004120218BCSU-4 7.15 17 17 2004120215BCSU-5 6.02 15 15 2004120219BCSU-6 5.26 14 14 2004120219BCSU-7 7.52 18 18 2004120215BCSU-8 8.07 20 20 2004120219MB-0 2.28 19 19 2004120214MCMU-0 8.95 79 79 2004120214MCMU-1 5.71 27 27 2004120214OMU-0 1.18 32 32 2004120215

Table 17 SD 184 report example

5.4 Signaling Load with DTM Usage The signaling load generated by the DTM co-ordination is dependent on the penetration of DTM mobiles.

• When the large majority of the mobiles are DTM capable, then the DTM co-ordination will generate a considerable signaling load at the PCUSIG interface

• In the overload situation the BSC is perhaps not able to handle all the DTM co-ordination messages generated and the message might be discarded. The following can happen

• The PCU may not receive an indication that a DTM MS has entered dedicated mode.

• If the PCU receives a data PDU for the MS in this case, the DL TBF establishment fails and the MS is considered as unreachable.

• The PCU may not receive an indication that a DTM MS has left dedicated mode. The PCU is not able to remove the MS from the IMSI record resulting in a ‘hanging’ record that consumes memory of the PCU.


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6. Resource Allocation in BSS In the previous chapter the accessibility has been investigated from signaling capacity and signaling limitation point of view in the whole BSS chain.

If the required signaling capacity is provided, the next step will be to find the most appropriate source for maximizing the user data rate (based on maximized RLC/MAC data rate).

The network resources are usually limited (capacity, coverage and interference limited); therefore the proper allocation of users among the resources is very important.

The (E)GPRS traffic is allocated among:

• Cells (Segments)

In some of the cases the resource allocations are based on simple and independent measurements (C1, C2) while others are using many planning parameters like C31/C32.

From S11.5 Network Controlled Cell Reselection (NCCR) can be used as well based on planning parameters.

• BTSs inside segments

The resource allocation inside segment is based on some parameters like GENA, EGENA and PCU allocation algorithm as well.

• TSLs inside BTS

The resource allocation among TSLs is based mainly on PCU algorithm (load calculations), as well as in case of QoS or EQoS scheduling.

In BSS network further bottlenecks can limit the access to the resources, like EDAP and PCU limitations.

So the resource allocation is based on the following items below:

• Cell-Reselection

• BTS selection and TSL allocation

• Scheduling

The terminal is firstly allocated to a cell, secondly to a BTS inside segment (if MultiBCF / CBCCH is used) and at the end the allocation is finally based on scheduling.


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6.1 Cell Reselection First step in resource allocation procedure is the cell selection (and reselection in mobility). The cell selection and reselection is based on C1, C2, C31/C32, NCCR and NACC.

ETSI define three network control order parameters, which determine the measurement reporting and network control on the MS.

• NC0: MS controlled cell reselection, no measurement reporting;

• NC1: MS controlled cell reselection, MS sends measurement reports;

• NC2: Network controlled cell reselection, MS sends measurement.

6.1.1 C1 and C2

The Nokia BSS supports network control order NC0, and therefore there are no network controlled handovers in GPRS, the cell is selected autonomously by the mobile using the existing path loss criteria C1 and cell reselection parameter C2.

The network broadcasts on the BCCH the Modified system info 3 and System info 13 parameters related to mobility management, which the (E)GPRS mobiles utilize to ensure that they are camped on the cell offering best service in each area (the PBCCH functionality will be described later on in this document). The process for this purpose is called Cell Selection and is based on C1 and C2 comparison.

The MS calculates the value of C1 and C2 for the serving cell and will re-calculate C1 and C2 values for the neighbouring cells every 5 seconds. The MS will then check whether:

• The path loss criterion (C1) for current serving cell falls below zero for a period of 5 seconds. This indicates that the path loss to the cell has become too high.

• The calculated value of C2 for a non-serving suitable cell exceeds the value of C2 for the serving cell for a period of 5 seconds.

If, however, in the case of the new cell being in a different location area or, for a GPRS MS, in a different routing area or always for a GPRS MS in ready state, the C2 value for the new cell shall exceed the C2 value of the serving cell by at least CELL_RESELECT_HYSTERESIS dB.

The idea is that the MS compares field strength levels of different cells defined in the idle mode BA list and selects the most appropriate using the C1 criteria:

C1 =(a-Max(B,0))

A= received level Average – p1

B= p2-maximum RF Power of the Mobile Station

p1= Rxlevel access min (gprsRxLevAccessMin)

p2= MS TXPower MAX CCH (gprsMsTxpwrMaxCCH)

All values are expressed in dBm. POWER_OFFSET is not used.


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The C2 parameter can be utilized together with the C1 parameter to provide the operator with greater traffic management capability. The C2 parameter was introduced in GSM phase two and designed for use in layered-architecture networks (micro/macro cell/Dual Band).

The C2 feature brings associated parameters that are related to microcellular planning.

• penaltyTime (20 ... 640 s) describes the time delay before the final

comparison is made between two cells.

• temporaryOffset (0 ... 70 dB) describes how much field strength could have been dropped during this penalty time,

• cellReselectOffset (0 ... 126 dB) describes an offset to cell reselection. C2 cell reselection is calculated by equation

C2 = C1 + cellReselectOffset - temporaryOffset x H(penaltyTime-T) when penaltyTime < 640

or

C2 = C1 - cellReselectOffset when penaltyTime=640

6.1.2 C31/C32

The C31/C32 parameters will give the possibility to optimize the cell reselection for (E)GPRS without affecting the circuit switched cell reselection behavior. This will allow more flexible use of cell resources, allowing, for example, some cells to be packet free if this is the intention.

The C31/32 functionality will only be applicable if the PBCCH is allocated, otherwise the circuit switch signaling channels will be used and consequently C1 and C2.

In a multi-vendor environment one requirement is that all the vendors should support broadcasting of the C31/C32 parameters.

C31 parameter

Signal strength threshold criterion (C31) for hierarchical cell structures (HCS) is used to decide whether the cell is qualified for prioritized hierarchical cell selection.

C31(s) = RLA(s) - hcsThreshold (s) (serving cell)

C31(n) = RLA(n) – hcsThreshold (n) - TO(n) * L(n) (neighbor cell)

Where

HCS_THR = signal threshold for applying HCS reselection

TO(n) = gprsTemporaryOffset (n) * H(gprsPenaltyTime (n) – T(n))

L(n) = 0, if hcsPriorityClass (n) = PRIORITY_CLASS(s)


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1, if hcsPriorityClass (n) ‡ hcsPriorityClass (s)

H(x) = 0, if x < 0

1, if x >= 0

gprsTemporaryOffset applies a negative offset to C31/C32 for the duration of gprsPenaltyTime after the timer T has started for that cell.

T is a timer implemented for each cell in the list of strongest carriers. T shall be started from zero at the time the cell is placed by the MS on the list of strongest carriers, except when the previous serving cell is placed on the list of strongest carriers at cell reselection. In this case, T shall be set to the value of PENALTY_TIME (i.e. expired).

C32 parameter

The cell ranking criterion (C32) is used to select cells among those with the same priority

C32(s) = C1(s) (serving cell)

C32(n) = C1(n) + gprsReselectOffset (n) – TO(n) * (1 – L(n)) (neighbour cell)

Where

gprsReselectOffset applies an offset and hysteresis value to each cell.

TO and L as in C31.

gprsReselectOffset applies an offset and hysteresis value to each cell.

The MS must select the cell having the highest C32 value among those that have the highest priority class among those that fulfill the criterion C31 >= 0. The priority classes may correspond to different HCS layers. If no cells fulfill the C31>=0 criterion, the MS must select the cell having the highest C32 value.

If PBCCH is not allocated to the cell, criterions C1 and C2 are used as they are used in current CSW services.


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Q3 parameter name

Range MML default

gprsRxLevAccessMin -110…-47 dBm

-105

gprsMsTxpwrMaxCCH 5 .. 43 dBm with 2 dBm step for GSM 850 and 900 0 .. 36 dBm with 2 dBm step for GSM 1800 0 .. 32 dBm with 2 dBm step and 33 dBm for GSM 1900

33 dBm for GSM 850 and 900. 30 dBm for GSM 1800 and 1900.

hcsThreshold -110, -108, …,, -48 dB with 2 dB step

N (not used)

gprsTemporaryOffset 0 .. 70 dB with a step size of 10 dB

0

gprsPenaltyTime 10 .. 320 (s) with a step size of 10 s

10

hcsPriorityClass 0 to 7 7

gprsReselectOffset -52, -48,..., -12, -10,..., 12, 16, ...,48 (dB)

0

gprsCellReselHysteresis 0, 2, 4, 6, 8, 10, 12, 14 dB

4

c31Hysteresis Y/N N

c32Qual Y/N N

raReselectHysteresis 0, 2, 4, 6, 8, 10, 12, 14 dB

4

Table 18 GPRS parameters


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MS cell reselection algorithm

MS makes cell reselection if path loss criterion (C1) for the serving cell falls below zero.

MS can make cell reselection also when it founds a non-serving suitable cell better than the serving cell. The best cell is the cell with the highest value of C32 among the cells with the highest PRIORITY_CLASS and fulfill the criterion C31 >= 0 or all cells if there no cell fulfilling the C31 >= 0 criterion.

If c32Qual parameter is set, positive gprsReselectOffset values shall only be applied to the neighbour cell with the highest RLA_P value of those cells for which C32 is compared above.

When the MS is in ready state , time defined by gprsCellReselHysteresis value is subtracted from C32 value for neighbour cells. If parameter c31Hysteresis is set the GPRS_CELL_RESELECT_HYSTERESIS is subtracted also from C31 neighbour cells. When the new cell is from different routing area raReselectHysteresis parameter value is subtracted from C32 for neighbour cells. In case of a cell reselection occurred within the previous 15 seconds, 5 dBs are subtracted from C32 for neighbour cells.

Abnormal Cell reselection

Whenever the MS receives PACKET UL ACK/NACK (Packet Ack/Nack is PAN) that allows the advancement of data transmit, the mobile station shall increment N3102 by the broadcast value PAN_INC, however N3102 shall never exceed the value PAN_MAX. Each time T3182 expires the mobile station shall decrement N3102 by the broadcast value PAN_DEC. When N3102 <= 0 is reached, the mobile station shall perform an abnormal release with cell reselection.

BSC parameters:

• An other reason for abnormal cell reselection is MS not being able to read PSI1 in 60 sec. (both in packet idle or in packet transfer mode)

• Abnormal cell reselection will happen if randomAccessRetry = 1

• Going back to the original cell is prohibited by parameter tResel sec if another suitable cell is available.

More information about cell reselection parameters and its optimization can be found in (E)GPRS Radio Networks – Optimization Guidelines.

6.1.3 Network Controlled Cell Reselection

Target cell to which the cell reselection is done, can be selected by the MS itself or by the network.

In earlier releases Nokia implemented only MS controlled cell reselection without measurement reports, which is basically commanded by Network Control Order 0 (NC0). In NC0, cell reselection is controlled by MS alone in both MM Ready and MM Standby states whether MS is in Packet Idle Mode or Packet Transfer Mode. When there is NCCR in the network cell reselection for MSs in MM Ready state are controlled by the network. When MSs go back to MM Stand By state, cell reselection


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is done by MS as in NC0. NCCR support is indicated by setting the Network Control Order to NC2.

PBCCH is not needed for NCCR.

NCCR can be enabled for Release97 mobiles onward.

Handover procedure, where cell resources are reserved in the target cell before ordering MS cell change is not provided for packet switched services in 3GPP release 4.

6.1.3.1 NCCR Benefits

Benefits that S11.5 Network Controlled Cell Reselection introduces:

o Efficient allocation of EGPRS resources. Some operators introduce EGPRS TRXs gradually in GSM networks. Some cells have EGPRS TRXs and some will not. EGPRS resources will be scarce and will need to be allocated efficiently. PCU will push EGPRS capable MSs to EGPRS cells and GPRS capable MSs to non-EGPRS capable cells by power budget NCCR criterion. Cell attractiveness can be defined neighbour cell specifically also taking into account each neighbour cell’s capacities (e.g. CS-3/CS-4 or EQoS support).

o Quality criterion allows NCCR when the serving cell quality drops even if the signal level is good.

o Quality Control may trigger NCCR. It means that EQoS can trigger NCCR to make cell selection.

o Service based NCCR is possible (SGSN UTRAN CCO BSSGP procedure)

o Possibility to select WCDMA network as soon as it is available or when GSM coverage ends, depending on operator choice.

NCCR is an optional feature. Operator can set the feature on/off on BSC level, and decide whether NCCR to WCDMA FDD cells is allowed.

NCCR is a standard feature for MS and SGSN. However, there may be MSs, which do not support NCCR and the PCU has to be prepared for that. PCU will monitor only MSs, which send neighbour cell measurement reports. Further there is a possibility to switch the NCCR off on 3GPP release basis (Release 97, 99, 04).

6.1.3.2 NCCR Functionality The operator has to set cell adjacencies, NCCR algorithm parameters, Network Control Order (NCO) mode and MS reporting period parameters.

Cell adjacencies and NCO mode are broadcast to MS. Depending on the operator parameter the MS may be commanded to send neighbour cell measurements by broadcasting the command to all MSs or by commanding individual MSs during TBF.

Once commanded to report neighbour cell measurements MS will send neighbour cell measurements to PCU in a frequency defined by the reporting period parameters. MS sends neighbour cell measurements in MM ready state, i.e. RR packet transfer and packet idle modes.

PCU sets MS NCCR context for each MS, which has been commanded, to NCO when first TBF is set for such MS or when first measurement report from such MS is received. PCU performs averaging for the measurements and applies NCCR algorithm to averaged measurements. The NCCR algorithm is based on operator set threshold values, so when certain threshold triggers NCCR is started.


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S11.5 includes following NCCR criteria:

• Power budget NCCR

(NCCR EGPRS PBGT margin, NCCR GPRS PBGT margin, NCCR streaming TBF offset, NCCR other PCU cell offset)

• Quality Controlled NCCR

• Coverage reason ISNCCR

The later BSS releases will introduce the following NCCR types:

• EQoS Quality Control

When serving cell cannot provide the guaranteed throughput or the transmission quality is below operator set threshold, NCCR may be tried to offer better service.

The Quality Control (QC) NCCR triggering is described in EQoS planning materials. The radio link quality based NCCR is required even irrespective of S11.5 EQoS feature implementation. Target cell selection is performed when the QC NCCR trigger comes and always when new PACKET (ENHANCED) MEASUREMENT REPORT message is received until:

• MS NCCR context is deleted

• TBF is released, or

• QC cancels the NCCR trigger.

• Service based ISNCCR

6.1.3.3 Target cell selection The target cell evaluation is based on an RXLEV threshold algorithm, depicted in Figure 43. In this figure it is shown the algorithm that the BSC would apply for an EGPRS MS. For GPRS MSs the algorithm is the same except for the Rx level margin comparison, which is:

AV_RXLEV_NCELL(N) > AV_RXLEV_SERV + CellReselMarginQualforGPRSMS(n)

for GPRS MS.

Due to separate thresholds for EGPRS capable and non-capable MSs, this criterion cannot be used before the MS EGPRS capability is known.


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Measurement report processing

Is reported BLER over

BLER_THRESHOLD?

Search for the neighbouring cell with

highest AV_RXLEV_NCELL(n)

NO

YES

NO

YES

AV_RXLEV_NCELL(n) >

AV_RXLEV_SERV +

CellReselMarginQualforEGPRSMS(n)

NOYESTrigger NCCR to cell (n)

NCCR successful

NO

YES

AV_RXLEV_NCELL(n) >

RxLevMinCell(n) + Max(0, Pa)

Erase the cell where the failure

occurred from target candidate cell

list until timer

T_NCELL_PENALTY expires

Figure 43 Target cell selection

6.1.3.4 Signaling Flow The signaling flow of NCCR can be seen below:


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Uplink Packet Data transfer

PACCH

Packet (Enhanced) Measurement Report

MS Serving cell

PACCHPacket Cell Change Order

Measurement and NCCR information regarding target cell

T3174 startsTarget cell

PBCCH

Current TBF on serving cell is aborted!

PBCCH

PBCCH of target cell is received

Waits until PSI1 ocurrence in B0

PBCCHPSI messages

• data transmission is resumed in target cell after all the relevant PSI messages have been received

•The service outage is 2-5 sec

Packet Channel Request

Packet Uplink Assignment

PRACH

PAGCH

T3174 stops


PACCH

Packet (Enhanced) Measurement Report

MS Serving cell

PACCHPacket Cell Change Order


T3174 startsTarget cell

PBCCH


PBCCH

PBCCH of target cell is received

Waits until PSI1 ocurrence in B0

PBCCHPSI messages

• data transmission is resumed in target cell after all the relevant PSI messages have been received

•The service outage is 2-5 sec



PRACH

PAGCH

T3174 stops

Figure 44 NCCR signaling flow

6.1.3.5 BLER Limits are Needed for the Quality Control Function in PCU2 The maximum block error rate (BLER) limit is set with different parameters in PCU1 and PCU2.

For PCU1:

• MAXIMUM BLER IN ACKNOWLEDGED MODE (BLA)

• MAXIMUM BLER IN UNACKNOWLEDGED MODE (BLU)

For PCU2:

• PFC ACK BLER LIMIT FOR TRANSFER DELAY 1 (ABL1)

• PFC UNACK BLER LIMIT FOR SDU ERROR RATIO 1 (UBL1)

The EQoS specific packet flow context (PFC) feature is not applicable with BSC SW release S11.5 and PCU2 Only the ABL1 and UBL1 parameters are used, although all ABL1-5 and UBL 1-6 parameters are visible. All BLER limit parameters are visible regardless of the EQoS feature’s state.

In Quality Control function the above corresponding parameters are used similarly in both PCU1 and PCU2.The BLER parameter values are not directly comparable though, so they are not converted in the upgrade.


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6.2 BTS Selection The Common BCCH/Multi BCF features are bringing the new Segment (SEG) concept into planning. The affect on GPRS is that there may be more than one BTS under one segment, which supports GPRS. Therefore at the TBF establishment and also later for reallocations of the TBF (if necessary) a BTS selection procedure will be utilized.

For example there is one Talk family BTS, which supports GPRS, and EGPRS capable BTS, which can also support GPRS, under the same segment. Also the operating frequency of the BTSs under one segment can be different for example the BTS which carries BCCH/PBCCH operates in 900 MHz and the other BTS(s) operates in 1800 MHz.

The main principle of BTS selection is primarily to allocate GPRS TBF to a GPRS BTS and EGPRS TBF to an EGPRS BTS.

Multi BCF feature can be used in single band environment and this feature will allow also having only one BCCH in the segment. For dual band solution common BCCH has to be applied. Common BCCH is an optional feature while multi BCF is standard.

6.2.1 Initial BTS Selection

Initial BTS from SEG is selected in CHM (Channel Management) when new TBF is created.

The main steps of initial BTS selection is listed below:

• BTSs supporting the frequency bands, which are indicated in Radio Access Capability (RAC) of the (E) GPRS MS, are selected.

RAC may not be known at the time of TBF initiation (RAC information is delivered to the SGSN during the GPRS attach). Therefore for a DL TBF the SGSN most probably has the RAC of the (E)GPRS MS. It is more likely that for the UL TBF, the RAC is not known at the establishment. (For more on RAC refer to 3GPP 04.60). If the RAC is not known then BTSs supporting the same frequency band as BCCH BTS are selected. Therefore there must be GPRS territory in the BCCH band.

• The signal level must be good enough on the selected BTS:

- If RX_level (C-value) is known then the BTS selected for allocation has to satisfy the following: RX_Lev - BTS's non_bcch_layer_offset > BTS's GPRS_non_BCCH_layer_rxlev_upper_limit.

- If RX_level is not known then Direct access BTS is selected. Direct_GPRS_access_threshold parameter is used to compare BTS objects relative preference: when the value of Direct_GPRS_access_threshold parameter is higher than the value of the parameter non BCCH layer offset then the BTS is valid for allocation.

At the TBF establishment phase there may not be any Rx-lev measurement results yet because of that RX-Lev criteria cannot be used. TBF is initially


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allocated to a BTS where DirectGPRSAccessBTS is set on (in practice it means that DirectGPRSaccessBTS > nonBCCHlayerOffset)* .

• An EGPRS capable BTS will be selected for a GPRS TBF only if:

- The segment doesn’t have GPRS capable BTS, or

- TBF/TSL > MaxTBFinTSL in every TSL in every GPRS capable BTS (i.e. the GPRS territory is totally full) AND average TBF/TSL < MaxTBFinTSL in every EGPRS capable BTS.

• If there are several possible BTSs then the BTS in segment with minimum downlink TBF/TSL QoS load is selected.

• If there is no possible BTS then BTS is not selected and TBF is not created.

*DirectGPRSaccessBTS concept has basically been developed for selecting the appropriate BTS at the initial BTS selection. It is possible to indicate the preferred BTSs for allocation if the Rx_lev is not known at the TBF establishment. Preferred GPRS BTS has nonBCCHlayerOffset parameter set so that it is smaller than DirectGPRSaccessBTS. This parameter (nonBCCHlayerOffset) indicates coverage area of a BTS in the segment compared to the BCCH BTS. The smaller the value is, the closer the coverage of the BTS is to the BCCH BTS. DirectGPRSaccessBTS indicates the risk that can be allowed when allocating a non BCCH BTS in case of no Rx_Lev measurement.

So if the DirectGPRSaccessBTS = 2 in this segment this means that BTSs with 2 dB less coverage than the BCCH BTS to be allocated as an initial BTS for a TBF. And if compare the nonBCCHlayerOffset with this parameter it is checked whether the BTS fulfils this requirement. Then list the BTSs that are appropriate for initial BTS selection, of course BCCH BTS is also included. Operator may want to direct all the GPRS traffic to the non BCCH BTS(s). In order to do that the GPRSenabledTRX parameter on all the TRXs in the BCCH BTS must be set to OFF. However it is possible that the RAC of the MS is unknown during initial TBF selection. In that case the non-BCCH BTS must be from the same band as BCCH band.

Rx-Lev Measurements are used as BTS selection criteria, when available;

The DL Rx_Lev measurements (C_value) are sent to the PCU in the DL ACK/NACK messages. The receiving frequency of these measurements depends on the polling frequency of the TBF. Actually the Rx-lev reported is averaged by the MS during the polling period.

The UL Rx- Lev measurement is included to each PCU frame by the BTS. The receiving frequency of these measurements depends on how often the uplink TBF gets a transmission turn. These measurements are averaged in PCU and the average is used by the allocation algorithm.

For more information on measurements done by MS please check 3GPP 05.08.

The following figure shows the block diagram of initial BTS selection.


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START

MS RAC ? MS is EGPRS capable

Is there any EGPRS BTS in the BTS_LIST_2 ?

Is there any GPRS BTS in the BTS_LIST_2 ?

Remove EGPRS BTSs from BTS_LIST_2

Yes

Remove GPRS BTSs from BTS_LIST_2

Yes No

TBF type ? concurrent

UL and DL

READY

Select the BTS that is already serving the MS

MS is only GPRS capable

Select BTSs whose frequency band is included in the MS RAC band information and save them in BTS_LIST_1 Note1 , Note2, Note3, Note4

BTS_LIST_2 empty ?

Yes

No

No

Select from BTS_LIST_1 the BTSs whose non_bcch_layer_offset is less than direct_gprs_access_ threshold and save them in BTS_LIST_2

Select the BTS who has the lowest QoS load among the BTSs in the BTS_LIST_2

READY

RX-level ?

RX-level is known

RX-level is not known

Select from BTS_LIST_1 the BTSs for whom (RX-level - non_bcch_layer_offset) is bigger than GPRS_non_BCCH_ layer_rxlev_upper_limit and save them in BTS_LIST_2

Select from BTS_LIST_1 the BTS whose non_bcch_layer_offset is lowest

READY

Figure 45 Initial BTS selection

Note1 : If MS RAC band is not known then BCCH band BTSs are selected

Note2 : BTSs that don’t have PSW territory or channels for PSW are not selected.

Note3 : UL: BTSs whose average TBF/TSL is not less than MaximumNumberOfULTBF are not selected Note4 : DL: BTSs whose average TBF/TSL is not less than MaximumNumberOfDLTBF are not selected


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6.2.2 BTS Selection for Reallocating TBF

TBF reallocation processing can take place if better quality data transfer is expected (related to Rx_level) or BTS packet traffic load is unevenly spread in a segment or between supported frequency bands in a segment.

Procedures used to check TBF reallocation activation need in Channel Management (CHM) are in order below. Reallocation request to MAC shall be activated in any of the procedures at once (1-4).

1. BTS Load reallocation

2. Uplink Rx level reallocation

3. Downlink Rx level reallocation

4. Downlink RX level received first time reallocation

Periodical checks are done every time TBF_LOAD_GUARD_THRSHLD amount of block periods are used by the TBF after the last reallocation.

Periodic reallocation check in PCU2 is tied to the amount of transmitted data, not to time as in PCU1.

PCU2 does periodic reallocation check for all non-streaming TBFs to check and reallocate if there are better resources that could be allocated to an MS. Reallocation check is triggered on transmission of TBF_LOAD_GUARD_THRSHLD RLC data blocks to the MS.

PCU1 triggers periodic reallocation check after TBF_LOAD_GUARD_THRSHLD RLC block periods. With TBF_LOAD_GUARD_THRSHLD parameter’s default value, PCU1 does periodic reallocation check for an MS once in second.

For example, if there are heavy traffic and an MS get transmission turns not so often, time between periodic reallocation checks for the MS in PCU2 is longer. A certain amount of data blocks are transmitted before PCU2 triggers periodic reallocation check.

If the result of checking is that reallocation is needed then the CHM requests for a reallocation from MAC. It can happen that there are several simultaneous reasons for reallocation. The CHM should take care that when it has requested a reallocation for a TBF, it will not anymore request reallocations for the same TBF.

Selection algorithm for BTS reallocation is quite similar to the case of BTS initial selection but more information is available: Rx-level measurement data is normally available as well as MS RAC information. The same algorithm is used for both uplink and downlink reallocation.

The mode of the TBF is not changed during reallocation. It means that EGPRS TBF cannot be reallocated to GPRS BTS.

GPRS TBF is reallocated primarily to GPRS BTS. If there is not suitable GPRS BTS then EGPRS BTS can be used. When better acceptable BTS is not found, the TBF is not reallocated.


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Concurrent TBF means that the MS has uplink TBF and downlink TBF. Both TBFs are of same mode, either EGPRS or GPRS.

The following figure shows the block diagram of TBF reallocation process:

Reason for reallocation?

other

Select from BTS_LIST_1 the BTSs for whom (RX-level - non_bcch_layer_offset) is bigger than GPRS_non_BCCH_ layer_rxlev_upper_limit and save them in BTS_LIST_2

RX-level ?

RX-level is known

RX-level is not known

Select from BTS_LIST_1 the BTSs whose non_bcch_layer_offset is less than or equal to the value of current BTS and save them in BTS_LIST_2

UL signal level is too low

Select from BTS_LIST_1 the BTSs whose non_bcch_layer_offset is lower than the value of current BTS and save them in BTS_LIST_2

START

Select BTSs whose frequency band is included in the MS RAC band information and save them in BTS_LIST_1 Note1 , Note2, Note3 for UL and concurrent TBF, Note4 for DL and concurrent TBF

Note1 : If MS RAC band is not known then BCCH band BTSs are selected Note2 : BTSs that don’t have PSW territory or channels for PSW are not selected. Note3 : BTSs whose average TBF/TSL is not less than MaximumNumberOfULTBF are not selected (special case: current BTS) Note4 : BTSs whose average TBF/TSL is not less than MaximumNumberOfDLTBF are not selected (special case: current BTS)

BTS_LIST_2 empty ?

Yes

No

Select the BTS that is already serving the TBF

READY

Select the BTS who has the lowest QoS load among the BTSs in the BTS_LIST_2

READY

TBF mode ? EGPRS TBF

Is there any GPRS BTS in the BTS_LIST_2?

No

Yes

GPRS TBF

Remove EGPRS BTSs from BTS_LIST_2

Remove GPRS BTSs from BTS_LIST_2

Is there any EGPRS BTS in the BTS_LIST_2 ?

Yes

No

(UL or concurrent TBF)

Figure 46 TBF reallocation process

BTS Load Reallocation

The load checking is based on QoS load. The BTS, TSL and TBF QoS load is described below:

• BTS_QoS_load: Average QoS load in the BTS.


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PSfor allocated timeslotssBTS' ofnumber

timeslotall sBTS' of adTSL_QoS_lo ∑

• TSL_QoS_load: Sum of TBF_QoS_load of TSL’s all TBF

• TBF_QoS_load: Calculated value for load that TBF creates on a TSL. The calculated value is weighted with QoS class of the TBF.

There are three load checks:

1. BTS QoS load is too high when compared to other BTS

The target is to balance BTS_QoS_load between BTSs.

For GPRS TBF: if there is a GPRS BTS with 30% lower QoS load and with suitable MS RAC band and with proper signal levels then CHM requests for a reallocation from MAC (or a concurrent reallocation if a concurrent TBF exist).

For EGPRS TBF: if there is an EGPRS BTS with 30% lower QoS load and with suitable MS RAC band and with proper signal levels then CHM requests for a reallocation from MAC (or a concurrent reallocation if a concurrent RAT exist).

2. GPRS TBF in EGPRS territory

This check is done for GPRS TBF in EGPRS BTS. The target is to reallocate a GPRS TBF away from EGPRS territory.

If there is GPRS BTS with proper UL/DL signal levels and the average TBF/TSL of the GPRS BTS is less than maximum_number_of_UL_TBF / maximum_number_of_DL_TBF then CHM requests for a reallocation from MAC (or a concurrent reallocation if a concurrent TBF exist).

3. BTS timeslot load too high when compared to BTS load

The target is to balance TSL_QoS_load inside the BTS.

If BTS_QoS_load / (average QoS load of timeslots where the TBF is allocated) is less than 0.7, then the CHM requests reallocation from the MAC.

6.2.2.1 Uplink Rx Lev Reallocation The TBF uplink Rx-lev Reallocation check is triggered always when uplink block with signal level value is received. This is done for uplink TBFs and concurrent TBFs. If the average uplink value gets too low:

Uplink_Lev < BTS's GPRS_non_BCCH_layer_rxlev_lower_limit

and the segment has ms_supported bands (as indicated in RAC) with lower non_bcch_layer_offset values than the BTS of the current allocation, then CHM requests for a reallocation from MAC (or a concurrent reallocation if a concurrent TBF exist).

Target is to reallocate TBF to BTS with lower non_bcch_layer_offset value.


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6.2.2.2 Downlink Rx Lev Reallocation The TBF Rx-lev Reallocation check is triggered always when Rx_lev value is received. This is done for downlink TBFs and concurrent TBFs. If RX_Lev(BCCH) is too low:

RX_Lev(BCCH) - BTS's non_bcch_layer_offset < BTS's GPRS_non_BCCH_layer_rxlev_lower_limit

and the segment has ms_supported bands with lower non_bcch_layer_offset values than the BTS of the current allocation, then CHM requests for a reallocation from MAC (or a concurrent reallocation if a concurrent TBF exist).

The target is to find BTS with:

RX_Lev(BCCH) - BTS's non_bcch_layer_offset > BTS's GPRS_non_BCCH_layer_rxlev_upper_limit

The next figure can help to understand the functionality of Rx Lev dependent TBF reallocation.

BTS 1

BTS 2

-48

Time

Segment 1NBL (Offset). Can be used for between Bands

GRPSNonBCCHlayerRxlevUpperLimit = -48

GRPSNonBCCHlayerRxlevLowerLimit = -70



BTS 1

BTS 2

-48

Time

Segment 1NBL (Offset). Can be used for between Bands





Figure 47 Level based TBF reallocation

6.2.2.3 Downlink RX Lev Received First Time Reallocation When RX_Lev of a TBF had not been defined (its value is 0xFF) and a value is received for the first time, CHM checks if the TBF should be reallocated to BTS of another band.

If received RX_Lev allows reallocation into a different ms_supported band and that BTS has 30% lower load than the BTS currently used by the mobile.

CHM requests reallocation from MAC. The purpose of this is to minimize the loss due to not being able to allocate directly into e.g. 1800 band by doing a reallocation as soon as possible.

6.2.2.4 BTS Selection in PCU2 In PCU1, BTS selection is made in a way that GPRS MSs are primarily allocated to GPRS BTS and EGPRS MSs to EGPRS BTSs.


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PCU2 has solution which selects the BTS that provides best calculated capacity for the MS. The calculation is done by using throughput-factor parameters, the amount of channels and the usage of the channels. There can be situation, where the selected BTS is GPRS BTS (although the MS is EDGE capable). In that case TBF will be GPRS TBF to the end of the TBF. So the TBF cannot be changed to EGPRS TBF before the TBF has ended.

PCU1 solution is done to avoid multiplexing, but in PCU2 multiplexing is not considered as such problem since USF Granularity 4.

6.2.2.5 Territory Upgrade Request in PCU2 Moreover, if there are both GPRS and EGPRS TBFs multiplexed in same TSL in a territory, PCU1 triggers territory upgrade request when 1TBF/TSL is exceeded.

PCU2 uses normal 1.5 TBF/TSL triggering. PCU2 has not lower territory upgrade trigger for multiplexing situation, because multiplexing is not considered as such problem in PCU2 since USF Granularity 4.


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6.3 Channel Scheduling In the GPRS Rel1 the scheduling was done by giving equal amount of air time for each TBF sharing the same TSL. This way the TBFs on the same TSL would share the capacity of the channel equally. In the scheduling in GPRS Rel2 priority is taken into account. Thus, higher priority TBFs will have a bigger share of the shared TSLs compared to lower priority TBFs.

6.3.1 Priority based Quality of Service

With the GPRS Rel1 all the users have the same priority. This means that they experience the same level of service. They use the same resources equally. This is the result of the scheduling algorithm in the PCU. The PCU scheduling algorithm, Priority Based Scheduling, is used with S10.5. Priority Based Scheduling is introduced as a first step towards QoS defined by 3GPP. With the Priority Based Scheduling in BSC the operator can assign different priorities to he users. The PCU scheduling algorithm will make use of the priority information in the scheduling process. The service experienced (QoE) by high priority users and low priority users are different from each other.

QoS is actually associated with the PDP context. Every subscriber has a QoS profile in the operator’s HLR. The subscriber promised or perceived quality is a combination of the different attributes defined by the 3GPP. Below is the table showing the QoS attributes in GPRS Release 97/98 and the correspondence to GPRS Release 99. In this document we use the R99 attributes.

Figure 48 QoS mapping

An operator may support some combinations of those factors. During the PDP context activation the Network and the MS negotiate the QoS. The MS may request certain values for each attribute. Network checks the resource situation and the subscriber QoS profile in the HLR. Eventually the Network sends the QoS to be used to the MS. Later on if the SGSN decides to change the QoS of an MS, a PDP Context


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Modification message is sent to the MS, informing the new QoS. If the MS does not accept the new QoS it can deactivate the PDP context.

The RLC/MAC layer supports four Radio Priority levels and an additional level for signaling messages. Upon uplink access the MS can indicate one of the four priority levels, and whether the cause for the uplink access is user data or signaling message transmission. Depending on the QoS agreed with the SGSN the MS will request certain Radio Priority in accessing the network. Also the radio priority level to be used for user data transmission shall be determined by the SGSN based on the negotiated QoS profile and shall be delivered to the MS during the PDP Context Activation and PDP Context Modification procedures.

In the UL the MS uses the Radio Priority information in accessing the network. This is a part of the 3GPP QoS description as mentioned above. The 4 Radio Priority will be mapped to 4 UL scheduling priorities in PCU: Gold, Silver, Bronze and Best Effort. The MS will indicate the network, which Radio Priority it requires and the PCU will take it into account while scheduling on UL TSLs for that UL TBF.

In the DL the allocation/retention priority in the PDP context profile is used. They will be mapped to 3 scheduling priorities: Gold, Silver and Best Effort. The PCU will take this information into account while scheduling the DL data. The allocation/retention priority values high, normal, low priorities are mapped to Gold, Silver, Best Effort Priority classes respectively.

In both UL and DL higher priority users will be given better service because the PCU will schedule their transmission more often thus they will be given chance to use the radio interface more often than lower priority subscribers. Lower priority subscribers will not experience more blocking than before, meaning that no GPRS call will be rejected due to QoS, but they will experience worse service. Therefore new priority based scheduling does not affect the number of subscribers served as compared to the Nokia GPRS Rel1.

6.3.2 Channel Allocation

QoS is also taken into account during the channel allocation. Previously in S9, the channel allocation used plainly chose the best combination of TSL for the data capacity. The new algorithm tries to find channel combination, which will also provide the best QoS for the TBF. The algorithm, tries to distribute the high priority TBFs evenly equal to the available channels. The reason is that high priority users will be scheduled more often because they are given higher promise to use the radio resources. If they are collected onto the same TSLs they limit each other.

Here comes a new concept called the QoS capacity of the channel. The QoS capacity will be used instead of the actual capacity in the allocation decisions. QoS capacity will be calculated, taking all the available channels into account. The QoS capacity of all the possible combinations, which can be given to the TBF, will be calculated. Finally, configuration with the highest QoS capacity will be chosen.

The QoS capacity of a number (A) of channels is estimated as the sum of the QoS capacity estimates of all the single channels:

c(A)=∑ c(ch),, ch=1…A

The estimation of the QoS capacity of a channel is affected by the below factors:


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The Scheduling Step Sizes (SSS) of the TBFs, which are on that channel. (More on the SSS later)

Preference of channels (dedicated channels are preferred to default channels, default channels are preferred to additional channels)

6.3.3 TBF Scheduling

The scheduling is channels independent. All the TBFs which are assigned to that TSL wait in a queue for that TLS. The current implementation of the scheduling algorithm gives every TBF a so-called latest service time, before which a TBF must be served meaning that it should get a turn to use the TSL. After each time a TBF uses the channel it is given a new latest service time. This time is acquired by adding the predefined Scheduling Step Size (SSS) to the current time. The current time is a TSL specific virtual time .The connection with the smallest latest service time uses the radio resource at a time. Periodically the scheduling algorithm checks the queue to find whose turn it is to use the TSL. In S9 the step sizes are the same value for every TBF. This results in every user having the same priority because there is no way to differentiate any TBF from the others. Every TBF equally uses the TSL.

The new algorithm in S10.5 makes use of the priorities. Different scheduling priorities (QoS classes) have different SSS values. That way different TBFs have different latest service times. A high priority TBF will be using a smaller SSS so it will have earlier latest service time, every time after its service. It will wait less for its turn next. This way it will take more turns than a low priority TBF on that TSL.

SSS are operator definable. There are 4 SSS for UL and 3 SSS for DL.

For determining their turn in scheduling each TBF has the following parameters:

• SSS, by which the current time is increased each time the TBF is served.

• A TSL specific latest service time.

Also there is a virtual time in the TSL, which is showing the current time as in the S9 algorithm.

Scheduling is done as follows:

• TBFs are in a queue in the TSL

• In each TSL the first TBF with the smallest latest service time is selected. After is it served the latest service time is increased with the SSS

• Virtual time is set equal to the smallest 'latest service time' that is found next and scheduling continues.

• When a new TBF is added for scheduling, its latest service time is the virtual time of the TSL.

• QoS does not affect the scheduling of the control messages; they are handled as they are handled in the S9 (there is not prioritization among user data and signaling).

The following figure tries to visualize the functionality of Priority based QoS feature with latest service time and SSS parameters.


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1 © NOKIA FILENAMs.PPT/ DATE / NN

7

Queue

1 2 3 4 5 6 7 7 8 9 10 11 12

1 2 3 4 5 6 6 7 8 9 10 11

6 6 6 6 6 6 7 12 12 12 12 12

TBF1 with SSS=6

TBF2 with SSS=1

(virtual time)

52 TDMA frames = 240 ms= 12 blocks

i t it

The scheduling is done based on latest service time, one TBF at a time is served by the RTSL

...Latest service time

Latest Service Time = Current Time + Scheduling Step Size

Figure 49 Priority based scheduling based on SSS p arameters

6.3.4 QoS Information Delivery

In the UL the Radio Priority Information is used to indicate the scheduling (user) priority. MS may start the UL TBF in different ways:

• If the access is one phase access on RACH, CHANNEL REQUEST is used. In the CHANNEL REQUEST message there is no space for Radio Priority Information thus QoS information is not available. MS cannot declare the priority of the TBF. Therefore the priority of the TBF in this case is fixed, it is always "best effort". Whenever there is one phase access on RACH what will happen in the BSC is that the UL priority for that TBF will be set as best effort in the RLC/MAC layer. The scheduling will use the set SSS for that particular priority class for the scheduling of that TBF. The priority information will be passed to the SGSN too.

• If the access is single block access (two phase access) on RACH , more details about the access can be given to the network with the PACKET RESOURCE REQUEST on PACCH later. The PACKET RESOURCE REQUEST has the two bits for Radio Priority information, which is mapped into the scheduling priority. What will happen in the BSC is that the UL priority for that TBF will be set in the RLC/MAC layer as indicated by the Radio Priority. RLC/MAC layer informs the scheduling of the priority of the UL TBF, so that it is taken into account during the scheduling. The scheduling will use the set SSS for that particular priority class for the scheduling of that TBF. The priority information will also be forwarded to the SGSN.

• If the access is on PRACH, in case of One Phase Access and Short Access Request, PACKET CHANNEL REQUEST is used. PACKET CHANNEL REQUEST has two bits for Radio Priority information. In case of Two Phase Access the following PACKET RESOURCE REQUEST on PACCH again has


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the Radio Priority information available. What will happen in the BSC is that the UL priority for that TBF will be set in the RLC/MAC layer as indicated by the Radio Priority. RLC/MAC layers inform the scheduler of the priority of the UL TBF, so that it is taken into account during the scheduling. The scheduling will use the set SSS for that particular priority class for the scheduling of that TBF. The priority information will also be forwarded to the SGSN.

If the MS wants to change the priority of an existing TBF, PACKET RESOURCE REQUEST message is used. The RLC/MAC informs the new priority to the scheduler. And the scheduler starts to use the new priority.

On downlink direction every DL DataUnit from SGSN to BSC includes the QoS .The priority is delivered in the Allocation/Retention priority field in QoS Profile. The Allocation/Retention priority values (high, normal, low) are mapped to three scheduling priorities (Gold, Silver, Best effort). Thus, PCU stores the Allocation/Retention priority of each LLC PDU. Priorities (QoS) are then forwarded to the scheduler. The scheduler will schedule the blocks from this TBF according to the priority values. The set SSS for that particular priority class will be used.

Also in the DL the PCU may receive LLC PDUs with different priority class than the one, which is currently used. The scheduler has to adjust its scheduling for that TBF.

QoS change in UL or DL affects the scheduling. Naturally it also affects the channel allocation of new TBFs. QoS change doesn’t trigger any reallocations evaluation. However, TSL load may cause reallocations when periodic reallocation occurs.

6.3.5 Nokia HLR QoS Settings

The Basic feature Quality of Services (QoS) allows different priority levels based on the APNs configurations per user in HLR. The Interactive and Background traffic class must be used when considering BSS10.5/SG3/PCU1. Streaming traffic class (with admission control and guaranteed bit rates) will be available with PCU2 Release2 and EQoS combination.

Different application servers are connected to the dedicated APNs. In HLR there is defined the QoS profile per APN and subscriber.

The QoS attributes are part of PDP context between the terminal and GGSN. Based on the attribute values the data can be marked and directed into different queues in the network elements and thus the packets are treated differently depending on their QoS attributes.


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Figure 50 QoS Priority Queues

Nokia HLR Parameters and Configuration:

Each user has several APNs configured in the HLR user profile. For each APN per user, there are two main parameters related to QoS: ARP and THP.

• ARP (Allocation/Retention Priority). With this parameter, the priority of each APN is defined:

- ARP=1 means High Priority;

- ARP=2 means Normal Priority;

-ARP=3 means Low Priority.

The ARP information will be used by the BSS (PCU) to identify the traffic from priority APNs and the SSS parameters can be applied. Please refer to the item “TBF Scheduling” for details.

• THP (Traffic Handling Priority).

For each APN configured for a user, there is also the indication of a mapped QoS Profile. This QoS Profile contains the requirements for each traffic class (Delivery Order, Delivery of erroneous SDUs, Residual BER, SDU error rate etc). Another information contained in the QoS Profile is Traffic Handling Priority. To allow the usage of the QoS Feature, the THP information must have the same value of ARP. The THP information will be used by the SGSN and GGSN to route the traffic to one of the three priority queues. Please refer to the previous figure.


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Follow examples of a Nokia user profile (left) configured in HLR and a QoS profile (right):

GPRS SUBSCRIBER DATA HANDLING COMMAND <MN_>

GPRS DATA PARAMETERS

IMSI ........................ XXXXXX103140304

SGSN ADDRESS ................ XXXXXX95035

MT-SMS VIA SGSN ............. N

CELL UPDATE INFORMATION ..... N

NETWORK ACCESS .............. BOTH

CHARGING CHARACTERISTIC .....

GPRS ROAMING PROFILE ........ N

PDP CONTEXT ID .............. 1

PDP TYPE .................... IPv4

PDP ADDRESS .................

VPLMN ALLOWED ............... Y

ALLOCATION CLASS ............ 2

QUALITY OF SERVICES PROFILE . 1

APN ......................... INTERNET.OPERATOR.COM

PDP CHARGING CHARACTERISTIC . NORM

PDP CONTEXT ID .............. 10

PDP TYPE .................... IPv4

PDP ADDRESS .................

VPLMN ALLOWED ............... N

ALLOCATION CLASS ............ 1

QUALITY OF SERVICES PROFILE . 6

APN ......................... POC.OPERATOR.COM

PDP CHARGING CHARACTERISTIC . NORM

PROFILE HANDLING COMMAND <MY_>

QOS PROFILE INFORMATION:

INDEX..QOS PROFILE INDEX.................... 6

NAME...QOS PROFILE NAME.....................POCxxx

CLASS..TRAFFIC CLASS........................ I

ORDER..DELIVERY ORDER....................... N

DELERR.DELIVERY OF ERRONEOUS SDU............ ND

SDUMAX.MAXIMUM SDU SIZE..................... 1500

DWNMAX.MAXIMUM BIT RATE FOR DOWNLINK.........16

UPMAX..MAXIMUM BIT RATE FOR UPLINK.......... 16

BER....RESIDUAL BER......................... 7

SDUERR.SDU ERROR RATIO...................... 7

DELAY..TRANSFER DELAY....................... 50

UPBR...GUARANTEED BIT RATE FOR UPLINK....... 16

DWNBR..GUARANTEED BIT RATE FOR DOWNLINK..... 16

PRIOR..TRAFFIC HANDLING PRIORITY............ 1

Figure 51 Nokia QoS HLR Settings Example

The most important HLR parameters are listed below:

Delivery order - indicates whether the UMTS bearer shall provide in-sequence SDU delivery or not.

Residual BER - indicates the undetected BER in the delivered SDU.

SDU error rate – indicates the fraction of SDUs lost or detected as erroneous

Delivery of erroneous SDUs – whether or not error detection is needed and if the error messages should be forwarded or not.


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6.4 Flow Control on Gb BSS performs flow control for the data between SGSN and BSC. The control is for each BVC (cell) separately and for each MS in each cell. The flow control mechanism manages the transfer of BSSGP UNITDATA PDUs sent by SGSN on the Gb interface to the BSC (PCU). The purpose is to prevent the buffers in the PCU from overflowing. BSS will indicate the maximum allowed throughput for a BVC(cell) and maximum allowed throughput for a TLLI (MS) to the SGSN. SGSN adjusts the transmission towards the PCU accordingly. When the BSS realizes these limits were exceeded, it sends Flow Control messages to the SGSN. This information contains the new flow control parameters for the cell or the MS, whichever had exceeded the limit. SGSN takes these parameters and stores them. It adjusts the flow according to the new parameters for that particular cell or MS.

In S10.5 the cell flow control is implemented. The MS specific control is taking care of the cell specific control also.

There is flow control only in the DL.

SGSN

BSS 1

Bearer Channel_1

Bearer Channel_2

DLCI_16

DLCI_17

DLCI_16

DLCI_17

DLCI_18

Bearer Channel_3

DLCI_16

Bearer Channel_5

Bearer Channel_6

DLCI_16

DLCI_17PAPU 3

PAPU 2

PAPU 1 PCU 1

PCU 2

PCU 3

LA

RA 1

BTS_6

BTS_3

RA 2

BTS_8

BTS_22Bearer Channel_4

DLCI_16

DLCI_17

BSS 2

PCU 3 LARA

BTS_22

NSEI_7

NS-VCI_6

NS-VCI_9

NSEI_3NS-VCI_4

NS-VCI_1

NS-VCI_11

NSEI_2NS-VCI_5

NS-VCI_8

NS-VCI_3

NSEI_1NS-VCI_7

NS-VCI_2

NSEI_7NS-VCI_6

NS-VCI_9

NSEI_3NS-VCI_4

NS-VCI_1

NS-VCI_11

NSEI_2NS-VCI_5

NS-VCI_8

NS-VCI_3

BSSGPNSFR

SignalData

Data & Signal

NSEI_1

BVCI_22

BVCI_0

BVCI_22

BVCI_0

BVCI_8

BVCI_8

BVCI_6

BVCI_0

BVCI_0

BVCI_22

BVCI_6

BVCI_0

BVCI_0

BVCI_3

BVCI_22

BVCI_0

NS-VCI_7

NS-VCI_2BVCI_3

BVCI_0

SGSN

BSS 1

Bearer Channel_1

Bearer Channel_2

DLCI_16

DLCI_17

DLCI_16

DLCI_17

DLCI_18

Bearer Channel_3

DLCI_16

Bearer Channel_5

Bearer Channel_6

DLCI_16

DLCI_17PAPU 3

PAPU 2

PAPU 1 PCU 1

PCU 2

PCU 3

LA

RA 1

BTS_6

BTS_3

RA 2

BTS_8

BTS_22Bearer Channel_4

DLCI_16

DLCI_17

BSS 2

PCU 3 LARA

BTS_22

NSEI_7

NS-VCI_6

NS-VCI_9

NSEI_3NS-VCI_4

NS-VCI_1

NS-VCI_11

NSEI_2NS-VCI_5

NS-VCI_8

NS-VCI_3

NSEI_1NS-VCI_7

NS-VCI_2

NSEI_7NS-VCI_6

NS-VCI_9

NSEI_3NS-VCI_4

NS-VCI_1

NS-VCI_11

NSEI_2NS-VCI_5

NS-VCI_8

NS-VCI_3

BSSGPNSFR

SignalData

Data & Signal

NSEI_1

BVCI_22

BVCI_0

BVCI_22

BVCI_0

BVCI_8

BVCI_8

BVCI_6

BVCI_0

BVCI_0

BVCI_22

BVCI_6

BVCI_0

BVCI_0

BVCI_3

BVCI_22

BVCI_0

NS-VCI_7

NS-VCI_2BVCI_3

BVCI_0

Figure 52 Gb Interface logical structure

More information about Gb planning is available in Gb Detailed Planning Guide document in IMS.

6.5 Gb over IP The increased demand for packet switched traffic transmission cost efficiency can be met by deploying IP in the transmission network.

IP offers an alternative way to configure the subnetwork of the Gb interface:


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• the subnetwork is IP-based and the physical layer is Ethernet

The introduction of IP makes it possible to build an efficient transport network for the IP based multimedia services of the future. Both the IPv6 and IPv4 protocol versions are supported.

IP transport can be used in parallel with FR under the same BSC and BCSU

• Within one BCSU, separate PCUs can use different transmission media

In the BSC, the capacity of the Gb interface remains the same, regardless of whether IP or FR is used as the transport technology.


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7. (E)GPRS Timeslot Data Rate RLC/MAC timeslot data rate and the number of allocated TSLs to one user give the exact picture about (E)GPRS functionality in BSS network.

Therefore the BSS network capacity is planned by RLC/MAC data rate and territory settings (see Chapter 8), moreover the network can be optimized by the same items, as well.

The (E)GPRS TSL data rate is depending on the following items:

• GSM network performance

• TSL Utilization

• TBF Release Delay

• BS_CV_MAX

• Link Adaptation Functionality

• Power Control (UL)

• Multiplexing

All the items above are further described in the subsections below.

7.1 GSM Network Performance The (E)GPRS TSL data rate is characterized by signal level and C/I ratio of the GSM network. The impact of both of these items is described in the following subsections below:

7.1.1 Impact of Coverage Level

The radio wave propagation formulas are the basis of coverage prediction. The design provides the basis for Uplink and Downlink Budget calculations. However, unlike CS network planning, packet services can tolerate delay and throughput variations and maximize the capacity thanks to advanced features like LA and IR.

The link budget calculation in excel format can be downloaded from the following link:


The physical layer of EGPRS is the existing GSM network. Therefore the EGPRS coverage area is depending on GSM service area. However the different coding schemes have different coverage area, as it can be seen in Figure 53.


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EGPRS Coverage Relative to MCS-5 (noise limited)

0

0.5

1

1.5

2

2.5

MCS1

MCS2

MCS3

MCS4

MCS5

MCS6

MCS7

MCS8

MCS9

Re

lativ

e ra

nge

Figure 53 EGPRS Relative coverage to MCS5

The MCS-5 coverage is approx 50% of MCS-1, while MCS-8 coverage is approx 40% of MCS-5.

The normal GSM voice coverage value is somewhere between MCS1 and MCS2.

7.1.1.1 Signal Strength Requirements Signal-to-noise levels in digitally modulated systems are commonly expressed in terms of Eb/No, Es/No or C/N.

• Eb/No is the available bit energy (received power * bit duration) divided by the noise spectral density (-174dBm/Hz).

• Es/No is the equivalent for the symbol case (1 bit = 1 symbol in GMSK, 3bits = 1 symbol in 8-PSK).

• C/N is received power divided by the total noise in the relevant RF bandwidth.

• C/N and Eb/No are linked by the spectral efficiency of the modulation scheme. For schemes with 1bit/s/Hz, Eb/No is equal to C/N. In GSM the spectral efficiency is 271kbit/s/200kHz =1.35 bit/s/Hz for GMSK modulation, assuming the receiver noise bandwidth is matched to the channel bandwidth. This represents on offset of 1.3dB in log terms, with C/N being Eb/No + 1.3dB.

For 8-PSK, Es/No = 3*Eb/No which is 10*log(3) = 4.77 in log terms. The above can be summarized in the Table 19.


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GSM Modulation

Es/No C/N

GMSK Es/No=Eb/No C/N = Eb/No +1.3dB

8-PSK Es/No = Eb/No + 4.77dB

C/N = Es/No + 1.3dB = Eb/No + 6.07dB

Table 19 Signal-to-noise measurement equivalence

The required Es/No is based on the required Eb/No (bit energy divided by noise spectral density) from simulation results. Typically link budgets may consider a certain modulation and coding scheme at a certain block error rate, however it is also possible to calculate for a given data rate. This latter case will become more widely used as functionality such as link adaptation and incremental redundancy will tend to mask, to some extent, the actual underlying channel performance.

7.1.1.2 Receiving End The receiving end contains the following items:

Sensitivity

Base station sensitivity should be checked from appropriate marketing personnel before each dimensioning (or other) exercise. UltraSite sensitivity is found to be a bit better than the previous generation's BTSs (Talk family).

Additional fast fading margin

For packet transmission, as no handover scheme is implemented, the link is based on retransmission and cell reselection. A 2 dB fast fading margin is assumed in the voice traffic case.

Cable loss + connector and Rx antenna gain

The system sensitivity is depending on cable and connector loss, antenna gain, MHA gain if applicable, additional noise, etc.

At the BS, a 16.5 dB antenna gain is assumed. However, depending on configurations lower antenna gains are found (14 dB in the GSM 900 bands). Moreover, antenna gains may vary across a network.

At the MS, the PDA type of configuration is assumed to have a 3dB advantage compared to MS near the head. Note that isotropic antenna will help in the Rx diversity schemes as the number of scatterers is increased (increased diversity and less subject to higher signal variation as well).

Body loss

As the next generation of data terminals is assumed to be hand-held in a PDA fashion, no body loss is taken into account for (E)GPRS scenarios. This compares with an assumed loss of 3dB for a handset held near the head.

MHA Gain

If the cable loss is that high that the signal level reaches or cross the noise floor at the input, the SNR will not be enough to guarantee the quality of the reception. However,


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the SNR without MHA will always be better if the noise floor is down enough. The difference between the SNR with MHA and without corresponds to the noise figure of the amplifier.

The usage of MHA is directly depending of the sensitivity and the noise floor at the input of the receiver and the loss the cable or the feeder is causing.

Diversity Gain

The diversity gain is depending on the separation of receiver antennas. In case of horizontal separation 4 meters separation generate around 3 dB diversity gain. Transmitting End

Tx RF output peak power

• The BS Tx powers are listed below:

GSM 900 Talk family: 43dBm

GSM 1800 Talk Family: 41.5 dBm

Ultrasite: 44.5 dBm

UltraSite EDGE BTS Mini: 47 dBm

FlexiEDGE: 47 dBm

• The MS Tx powers are listed below:

GSM 850/900: 33 dBm (2W)

GSM 1800/1900: 30 dBm (1W)

Back-off for 8-PSK

Pls. Refer to chapter 2.3.

Isolator+combiner+filter

Particular attention should be given to the configurations (combiner by-passed, 2:1 WBC, 4:1 WBC, RTC) as it impacts on the actual radiated power at the antenna.

Cable loss + connector and Tx antenna gain

It is same as in case of Receiving End.

UltraSite coverage for downlink MCS-5 very similar to Talk speech (within 0.5dB), while UltraSite coverage for uplink MCS-5 4dB worse than Talk speech.

7.1.1.3 Measurement Results The following figure shows the impact of signal level on RLC/MAC data rate (without interference):


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RLC/MAC Data Rate (2 TSLs)

0

20

40

60

80

100

120

-74 -76 -78 -80 -82 -84 -86 -88 -90 -92 -94 -96 -98 -100 -102 -104

RxLev (dBm)

kbps

RLC/MAC Data Rate (2M Download on 2 TSLs)

Figure 54 Signal level vs. RLC/MAC data rate


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7.1.2 Impact of Interference Level

The C/I target values will determine the (E)GPRS coverage and it is likely that frequency planning will need reconsidering in order to meet the required values.

At high load levels, C/I can be degraded, however it is worth notice that if the existing GPRS traffic tends to convert to EGPRS, the higher data rates will lead to reduced TCH occupancy, and, in turn, an increase in C/I.

7.1.2.1 Simulation Results The following figures show results of link-level simulations from RAS/Oulu. They do give a good estimation of the data rates achievable with EDGE and the effect of channel environment and frequency hopping.

Figure 55 8-PSK TU3 non-hopping, impairments inclu ded

8-PSK modulation is sensitive to distortion in the RF hardware. So ther is tx/rx impairment because of phase noise and non-linearity. (Phase noise: in an oscillator, rapid, short-term, random fluctuations in the phase of a wave, caused by time-domain instabilities.)

C/

kbit/s


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Figure 56 8-PSK TU3 ideal frequency hopping, impai rments NOT included

Observing the maximum available data rates it can be seen that MCS-9 with incremental redundancy offers the highest throughputs at all but the lowest C/Is. A consequence of this is that there is no hopping gain (in fact there is a small hopping ‘loss’ of up to 1.5dB). This is because MCS-9 has no Forward Error Correction (FEC) on the user data and, on average; frequency hopping can actually increase BLER due to the action of randomizing the error distribution. The same applies to MCS-7 and MCS-8, although for these the loss is closer to zero.

MCS-9 is also the MCS with the highest susceptibility to errors due to impairments, as there is no FEC to correct any errors that may occur. As a consequence of this, it may be more appropriate in some C/I intervals to select MCS-7 or MCS-8 which, although having slightly worse C/I in the ‘ideal’ case might perform better in the situation with impairments.

Simulations have been performed that indicate typical data throughputs that might be achievable in practical networks.


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Figure 57 Data rates – re-use 1/3 load =50%

The following simulation results show for static trials the throughput in a 3 sector site with 50% load and reuse 1/3. It is of interest to compare it with EDGE simulation where a 3/9 reuse pattern is implemented.

New C/I target values resulting coverage will be highly dependent on frequency reuse factors. On the other hand, higher reuse factors decrease the spectrum efficiency. Smaller reuse factor will limit those higher data rates on smaller coverage near the Base Station (BS) and will reduce to best effort during peak hours.


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Figure 58 Data rates – re-use 3/9 load =50%

Expected real scenarios should demonstrate average data rates of nearly 3 times GPRS data rates (roughly the increase due to higher modulation scheme).

Throughput [kbps/slot] vs reuse factor and range

0

10

20

30

40

50

60

MCS8-IRreuse 1/3

MCS8-FECreuse 1/3

MCS8-IRreuse 3/9

MCS8-FECreuse 3/9

coding schemes combination

thro

ughp

ut Whole cell

range< 2km

range< 1km

Figure 59 Data performance v re-use and range

In case of FEC the IR is not used, while in case of IR bars the incremental redundancy is under operation.


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The following figures show the throughput from static simulations for MCS1 and MCS5. The closer to the BS, the highest is the probability to achieve the maximum data rates. The system simulated is close to a 7/21 re-use.

Figure 60 MCS-1 performance


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Figure 61 MCS-5 performance

Control channel performance is also of primary concern as it conditions the traffic channels data rates. The following Figure shows the probability of error free reception of control blocks, e.g., access grants. From the results, for RLC block to work properly at BLER of 5%, indicates that reuse factors of at least 3/9 are needed. Depending on the real layout of Base stations, higher frequency reuse might be required.

Control channel performance

0

0.2

0.4

0.6

0.8

1

1.2

Whole cell range< 2km range< 1km

Range

BLE

R <

5% 4/12

3/9

1/3

Figure 62 Control Channel performance vs. Range

In dense network environment the 1/3 reuse’s performance can be the same compared to 3/9 and 4/12. If the cell range is bigger than 2 km, the 1/3 reuse has the worse performance compared to 3/9 and 4/12.

7.1.2.2 Spectrum Efficiency and Frequency Reuse As it can be seen from the Figure 63 the 2/6 reuse brings the most effective spectral usage.

The figure below shows the impact of reuse on spectral efficiency.


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Spectrum efficiency values with QoS criteria (IR + LA)

140

145

150

155

160

165

170

175

180

Spec

trum

eff

icie

ncy

[kbi

t/s/

km2 /M

Hz]

Reuse 1/3 174

Reuse 2/6 177.5

Reuse 3/9 175.4

Reuse 4/12 146.3

Figure 63 Reuse vs. spectral efficiency

7.1.2.3 Measurement Results The Figure 64 below shows the impact of interference on RLC/MAC data rate (the signal level is high enough to measure the impact of C/I only).

C/I dependency (FTP Download on 2 TSLs)

0

20

40

60

80

100

120

36 34 32 30 28 26 24 22 20 18 16 15 14 13 12 11 10 9

C/I

kbps

RLC/MAC Data Rate (2M Download 2TSLs)

Figure 64 C/I vs. RLC/MAC data rate

7.1.3 Mixture of Signal Level and Interference The following figure shows the impact of signal level and interference:


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RLC/MAC Data Rate (FTP Download on 2 TSLs)

0

20

40

60

80

100

120

-65 -70 -75 -80 -85 -90 -95 -100 -105

Signal level (dBm)

kbps

No Interference

C/I 25 dB

C/I 20 dB

C/I 15 dB

Figure 65 Impact of signal level and interference o n RLC/MAC data rate


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7.2 TSL Utilization Improvement The timeslot should be fully utilized. So the higher ratio of RLC/MAC data blocks compared to signaling on PACCH will lead to better user perception.

The TSL utilization can be optimized by

• Acknowledge Request

• Pre-emptive Transmission

7.2.1 Acknowledge Request Parameters These parameters below are used by the RLC acknowledgement algorithm to determine how frequently the PCU polls the mobile station having a DL / UL TBF in EGPRS mode. The PCU has a counter, which is incremented by one whenever an RLC data block is transmitted for the first time or retransmitted pre-emptively. The counter is incremented by (1 + (E)GPRS_DOWNLINK_PENALTY ((E)GPRS_UPLINK_PENALTY)) whenever a negatively acknowledged RLC data block is retransmitted. The mobile station is polled when the counter exceeds the threshold value of (E)GPRS_DOWNLINK_THRESHOLD ((E)GPRS_UPLINK_PENALTY).

7.2.1.1 GPRS DL/UL Penalty and Threshold • GPRS Uplink Penalty is used in RLC to trigger an uplink acknowledge

message to the MS.

• GPRS Uplink Threshold is used in RLC to trigger an uplink acknowledge message to the MS.

• GPRS Downlink Penalty is used in RLC to trigger a downlink acknowledge poll to the MS.

• GPRS Downlink Threshold is used in RLC to trigger a downlink acknowledge poll to the MS.

7.2.1.2 (E)GPRS DL/UL Penalty and Threshold • EGPRS Uplink Penalty is used in RLC to trigger an uplink acknowledge

message to the MS.

• EGPRS Uplink Threshold is used in RLC to trigger an uplink acknowledge message to the MS.

• EGPRS Downlink Penalty is used in RLC to trigger a downlink acknowledge poll to the MS.

• EGPRS Downlink Threshold is used in RLC to trigger a downlink acknowledge poll to the MS.


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7.2.2 PRE_EMPTIVE_TRANSMISSIO

If the pre-emptive transmission bit is set to '1' in the PACKET UPLINK ACK/NACK message and there are no further RLC data blocks available for transmission, the sending side shall transmit the oldest RLC data block which is in PENDING_ACK state.

The RLC selects RLC data blocks as specified in [04.60, 9.1.3.2 Acknowledge State Array V(B) for EGPRS TBF Mode].

The following principle is used. See details from [04.60].

1) The oldest NACKED state block is selected (In BSN order)

2) If no NACKED state block exists then a new block is generated

3) If no NACKED state block exists and transmit window is stalled or there is not new data then the oldest PENDING_ACK state block is selected

PRE_EMPTIVE_TRANSMISSION (1 bit field) bit informs the mobile station if it may or may not transmit the oldest RLC data block whose corresponding element in V(B) has the value PENDING_ACK when the protocol is stalled or has no more RLC data blocks to transmit.

0 The mobile station shall not use pre-emptive transmission.

1 The mobile station shall use pre-emptive transmission.

7.3 TBF Release Delay Parameters (S10.5 ED) The TBF Release Delay parameters are used to avoid the unnecessary TBF establishments and hereby provide faster data rate.

There are two modifiable parameters related to Delayed TBF feature among PRFILE parameters:

• DL_TBF_RELEASE_DELAY

• UL_TBF_RELEASE_DELAY

7.3.1 DL_TBF_RELEASE_DELAY

This parameter is used to adjust the delay in downlink TBF release (0,1-5sec, def 1s). An appropriate delay time increases the system performance, since the possibly following uplink TBF can be established faster or i f the new data arrive to the PCU the transmission can be immediately resumed . When using delayed TBF frequent releases and re-establishments of downlink TBF can be avoided.

When the MS wants to send data or upper layer signaling messages to the network, it requests the establishment of an uplink TBF from the BSC. There are the following main alternatives for the TBF establishment:

• on PACCH; used when a concurrent DL TBF exists


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The UL TBF establishment is faster if there is a concurrent DL TBF, therefore the longer delay in DL TBF Release can help to have faster signaling and finally faster data rate.

• on CCCH; used when there is no PCCCH in the cell and no concurrent DL TBF

• on PCCCH; used when a PCCCH exists in the cell and there is no concurrent DL TBF

During the delayed period the TBF is kept alive based on sending DL RLC/MAC blocks (generated by dummy LLC frames) in DL TBF (Polling the mobile, at least one time every 360 ms).

In the delayed period, a DL dummy block with S/P = 1 is sent in order to poll the MS. There can be lot of “TBF lost due to no response from MS”, because it seems that some mobiles are not supporting the transmission of dummy blocks in the delayed period very well, in the sense that some MSs do not respond to the dummy block with S/P set to 1. Probably, this situation is even more critical when the C/I conditions are bad and the MS has some problems in decoding USF.

7.3.2 DL_TBF_RELEASE_DELAY in PCU2

Delayed downlink TBF polling rate is different for PCU1 and PCU2.

In PCU2, POLLING_INTERVAL_BG defines the time in block periods how often the MS is polled during delayed downlink TBF release.

In PCU1 the time is not adjustable by any parameter.

PCU1 PCU2 How often the MS is polled during delayed downlink TBF release.

Defined by RLC RTT. New poll is sent as soon as the MS has responded to previous poll. Typical value is 220 ms (every 11 block periods).

Defined by PRFILE parameter: POLLING_INTERVAL_BG.

Default value is 80 ms (every 4 block periods).

Note: The first poll period may be longer (240 -280 ms) but after that the period is defined by POLLING_INTERVAL_BG.

7.3.3 UL_TBF_RELEASE_DELAY

This parameter is used to adjust the delay in uplink TBF release (0,1-3sec, def 0,5s). An appropriate delay time increases the system performance, since the possibly following downlink TBF can be established faster. If more data will arrive from the upper layer during the delayed period they can not be sent within existing TBF.

This parameter is Nokia specific and is not linked to the Extended UL TBF Rel 4 feature.


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The DL TBF establishment obviously takes time and done in one of the following ways:

• on PACCH; used when 1.) concurrent UL TBF exists or 2.) when the timer T3192 is running in the MS

1.) The effect of UL TBF release delay is taken into account when there is no concurrent DL TBF for the same MS. The purpose of the delay is to speed up the possibly following DL TBF establishment. No USF turns are scheduled during this delay. The establishment is done with a PACKET_DOWNLINK_ASSIGNMENT or PACKET_TIMESLOT_RECONFIGURE message.

2.) When the DL TBF is released, the MS starts the timer T3192 and continues monitoring the PACCH of the released TBF until T3192 expires. During the timer T3192 the PCU makes the establishment of a new DL TBF by sending a PACKET_DOWNLINK_ASSIGNMENT on the PACCH of the 'old' DL TBF.

• on CCCH; used when there is no PCCCH in the cell, no concurrent UL TBF, and T3192 is not running

• on PCCCH; used when a PCCCH exists in the cell, and there is no concurrent UL TBF and T3192 is not running

The faster DL TBF establishment can be achieved by using PACCH.

But during the release phase, the TBF is kept alive based on sending PACKET UL ACK/NACK in UL TBF.

According to test measurement results, HTTP likes it but PoC does not like TBF Release Delay.

7.3.4 Release of downlink Temporary Block Flow

The network initiates the release of a downlink TBF by sending an RLC data block with the Final Block Indicator (FBI) set to the value '1' and with a valid RRBP field. The RLC data block sent must have the highest BSN' (Block Sequence Number) of the downlink TBF. The network shall start timer T3191. While timer T3191 is running the network may retransmit the RLC data block with the FBI bit set to the value '1'. For each retransmission the timer T3191 is restarted.

7.3.5 Release of uplink Temporary Block Flow

The mobile station initiates release of the uplink TBF by beginning the countdown process. When the mobile station has sent the RLC data block with CV = 0 and there are no elements in the V(B) array set to the value Nacked, it shall start timer T3182. The mobile station shall continue to send RLC data blocks on each assigned uplink data block, according to the algorithm defined in sub-clause 3GPP 04.60 9.1.3.

If the network has received all RLC data blocks when it detects the end of the TBF (when CV=0), it shall send the PACKET UPLINK ACK/NACK message with the Final Ack Indicator bit set to '1', include a valid RRBP field in the RLC/MAC control block header and clear counter N3103.


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7.4 TBF Release Delay Extended (S11 onwards) EUTM is Rel4 feature and both MS and NW-support are required (the network uses MS RAC to distinguish EUTM support).

MS Radio Access Capability (RAC) received from SGSN or MS with Packet Resource Request (PRR) message (one or two-phase access).

Extended UL TBF delay is used always when supported (with and without concurrent DL TBF)

EUTM might need MML-activation and BCSU restart (ZWOA:2,899,A;)

7.4.1 TBF is Continued based on EUTM

The following figure shows the flow chart when the TBF is continued based on EUTM.

UL T

BF e

xte

nded sta

te

MS BSC / PCU

Data block with CV = 0

EUTM delay timer starts

Schedule USF turn for MS

Data block with new BSN and CV


UL dummy control block

EUTM delay timer stopped, TBF continues

PACKET UL ACK/NACK (FAI=0, Polling=NO)

Data block

UL TBF Schedule Rate Ext

UL T

BF e

xte

nded sta

te

MS BSC / PCU




Data block with new BSN and CV



EUTM delay timer stopped, TBF continues


Data block


Figure 66 TBF is Continued based on EUTM

Countdown procedure is ongoing. EUTM supporting mobile is allowed to recalculate Countdown value (CV) during procedure, if it gets more data to send. PCU notices this by monitoring Block Sequence Number (BSN) and CV sent by MS.

After receiving CV=0 block PCU starts UL extended state. It sends Packet Uplink Ack/Nack message to MS with no Final Ack Indicator (FAI) on, but acknowledging all received blocks.


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During UL extended state PCU schedules USFs for MS according adjustable scheduling rate parameter. If MS has no new data to send it sends UL dummy control blocks on its sending turn.

When UL extended state ends, according adjustable release delay parameter, PCU sends Packet Uplink Ack/Nack message to MS with FAI on.

7.4.2 TBF is Not Continued based on EUTM

The following figure shows the flow chart when the TBF is not continued based on EUTM.

MS BSC / PCU







EUTM delay timer expiresPACKET UL ACK/NACK (FAI=1, Polling=YES)


PACKET CONTROL ACKUL TBF terminated


UL T

BF e

xte

nded sta

te




MS BSC / PCU







EUTM delay timer expiresPACKET UL ACK/NACK (FAI=1, Polling=YES)


PACKET CONTROL ACKUL TBF terminated


UL T

BF e

xte

nded sta

te




Figure 67 TBF is not continued based on EUTM

Countdown procedure is ongoing. EUTM supporting mobile is allowed to recalculate CV during procedure, if it gets more data to send. PCU notices this by monitoring Block Sequence Number (BSN) and Countdown value (CV) sent by MS.

After receiving CV=0 block PCU starts UL extended state. It sends Packet Uplink Ack/Nack message to MS with no Final Ack Indicator (FAI) on, but acknowledging all received blocks.

During UL extended state PCU schedules USFs for MS according adjustable scheduling rate parameter. If MS has no new data to send it sends UL dummy control blocks on its sending turn.


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When UL extended state ends, according adjustable release delay parameter, PCU sends Packet Uplink Ack/Nack message to MS with Final Ack Indicator (FAI) on.

7.4.3 EUTM in PCU2

Extended Uplink TBF Scheduling rate parameters and usage of those parameters are different for PCU1 and PCU2.

In PCU1, UL_TBF_SCHED_RATE_EXT defines the next block period when a TBF in extended mode is given a transmission turn. However, a TBF in extended mode cannot have better residual capacity than it would in normal mode.

In PCU2, POLLING_INTERVAL_BG defines the time in block periods that TBF in extended state cannot have transmission time. After POLLING_INTERVAL is elapsed, TBF is returned to scheduling and is gets a transmission turn when scheduler decides so.

PCU1 PCU2 How often a USF is scheduled for the MS during the inactivity period in Extended UL TBF Mode.

Defined by PRFILE parameter: UL_TBF_SCHED_RATE_EXT


Defined by PRFILE parameter: POLLING_INTERVAL_BG.


7.5 BS_CV_MAX The most important functionalities of BS_CV_MAX parameter from network planning point of view:

1) If the number of RLC block periods between the end of the RLC block period used for the last transmission of the corresponding RLC data block and the beginning of the block period containing the PACKET UPLINK ACK/NACK message is less than (max(BS_CV_MAX,1) – 1) (i.e., the RLC data block was recently retransmitted and thus can not be validly negatively acknowledged in this particular PACKET UPLINK ACK/NACK message), then the MS is not expecting to receive a nack for the transmitted block.

The mobile assumes that it takes at least BS_CV_MAX block period to:

-Transmit the block to the network and

-Transmit an acknowledgement message to the mobile.

2) T3200

The mobile station shall start an instance of timer T3200 following the receipt of an RLC/MAC control block whose RTI (Radio Transaction Identifier) value does not


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correspond to the RTI value of a partially received RLC/MAC control message or if the RLC/MAC control blocks were received on different PDCHs. In non-DRX mode the duration of timer T3200 shall be four BS_CV_MAX block periods. In DRX mode the duration of timer T3200 shall be four times the DRX period (see 3GPP TS 03.64).

• On receipt of an RLC/MAC control block containing a segment of an RLC/MAC control message such that the mobile station now has the complete RLC/MAC control message, the mobile station shall stop the corresponding instance of timer T3200.

• If the mobile station discards a partially received RLC/MAC control message while the corresponding instance of timer T3200 is running, the mobile station shall stop the corresponding instance of timer T3200.

• On expiry of an instance of timer T3200, the mobile station shall discard and ignore all segments of the corresponding partially received RLC/MAC control message.

• Upon successful change of PDCH allocation, the mobile station shall discard all partially received RLC/MAC control messages and stop the corresponding instances of timer T3200.

• The mobile station shall discard any control message segment that contains an unknown TFI.

3) N3104

When the mobile station sends the first RLC/MAC block the counter N3104 shall be initialized to 1. For each new RLC/MAC block the mobile station sends it shall increment N3104 by 1 until the first correct PACKET UPLINK ACK/NACK message is received. Then N3104 shall not be further incremented. If the N3104 counter is equal to N3104_MAX and no correct PACKET UPLINK ACK/NACK message has been received, the contention resolution fails and the mobile station behaves as specified in 04.60 sub-clause 7.1.2.3.

N3104_MAX shall have the value:

N3104_MAX = 3 * (BS_CV_MAX + 3) * number of uplink timeslots assigned.

4) Countdown procedure

When the mobile station nears the end of the close-ended TBF, it shall begin the count down procedure so that it sends the last RLC data block when CV = 0 (see 04.60 sub-clause 9.3.1). The mobile station and network shall then follow the appropriate procedure for release of TBF defined in 04.60 sub-clause 9.3.2.3 or sub-clause 9.3.3.3. Upon receipt of a PACKET TBF RELEASE message during a closed-end TBF, the mobile station shall follow the procedure in 04.60 sub-clause 8.1.1.4. If the number of RLC data blocks granted is not sufficient to empty the mobile station's send buffer, the mobile station shall attempt to establish a new uplink TBF for the transmission of the outstanding LLC frames following the end of the close-ended TBF.


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After a modification to this parameter it takes about 5 minutes for processes to get the new values. After 5 minutes disable and then re-enable GPRS in those cells where GPRS is active for the change to take effect.

Recommended values: 9

Planning: If the BS_CV_MAX parameter has too high value (e.g. 15), then the mobile may ignore some nacks that would require retransmissions. So in some cases a block has to be nacked twice before the mobile is willing to make the retransmission. This may reduce the performance slightly.

Basically the BS_CV_MAX parameter should define the RLC round-trip delay in block periods.

If the BS_CV_MAX parameter is lower than the actual round-trip delay or if the mobile is not able to do accurate time stamping for the UL RLC blocks, then the mobile may transmit needless retransmissions after processing a Packet UL ACK/NACK message.

On the other hand, if the BS_CV_MAX parameter is too large or if the mobile is not able to do accurate time stamping for the UL RLC blocks, then the mobile may ignore some negative acknowledgements that were received in the Packet UL ACK/NACK message. This may distort the ARQ procedure slightly.

The Figure 68 below shows the impact of BS_CV_MAX parameter (NTN results: RxLev –70 dBm, C/I 15 dB, 2 TSLs).

61.5

23.0

62.7

22.7

62.6

23.7

66.2

24.7

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

kbps

6 9 11 13

BS_CV_MAX

BS_CV_MAX

RLC/MAC Data Rate (2M Download x2) RLC/MAC Data Rate (500K Upload x2)

Figure 68 Impact of BS_CV_MAX on data rate

There is slightly improvement both on DL and UL when the BS_CV_MAX value is increased.


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7.6 GPRS and EGPRS Link Adaptation The RLC/MAC TSL data rate is depending on the 3GPP specifications (modulation, MCSs, etc.) and also Nokia implementation.

The Link Adaptation (LA) and Incremental Redundancy (IR) are specified by 3GPP but the implementation is Nokia dependant as well.

The following subsections describe the LA for GPRS and EGPRS.

7.6.1 GPRS Link Adaptation (S11)

Currently the coding schemes CS-1 and CS-2 are supported. The BSC level parameters coding scheme no hop (COD) and coding scheme hop (CODH) define whether the fixed CS value (CS-1/CS-2) is used or if the coding scheme is changed dynamically according to the Link Adaptation algorithm. In unacknowledged RLC mode CS-1 is always used regardless of the parameter values. When the Link Adaptation algorithm is deployed, then the initial value for the CS at the beginning of a TBF is CS-2.

For synchronization purposes, the network sends at least one radio block using CS-1 in the downlink direction every 360 milliseconds on every timeslot that has either uplink or downlink TBFs.

The Link Adaptation (LA) algorithm is used to select the optimum channel coding scheme (CS-1 or CS-2) for a particular RLC connection and it is based on detecting the occurred RLC block errors.

Essential for the LA algorithm is the crosspoint, where the two coding schemes give the same bit rate. In terms of block error rate (BLER) the following equation holds at the crosspoint: 8.0 kbps * (1 - BLER_CP_CS1) = 12 kbps * (1 - BLER_ CP_CS2) where:

• 8.0 kbps is the theoretical maximum bit rate for CS-1

• 12.0 kbps is the theoretical maximum bit rate for CS-2

• BLER_CP_CS1 is the block error rate at the crosspoint when CS-1 is used

• BLER_CP_CS2 is the block error rate at the crosspoint when CS-2 is used

If CS-1 is used and if BLER is less than BLER_CP_CS1, then it would be advantageous to change to CS-2. If CS-2 is used and if BLER is larger than BLER_CP_CS2, then it would be advantageous to change to CS-1. Since CS-1 is more robust than CS-2, BLER_CP_CS2 is larger than BLER_CP_CS1.

The crosspoint can be determined separately for UL and DL directions as well as for frequency hopping (FH) and non-FH cases. For this purpose the following BSC-level parameters are used by the LA algorithm:

• UL BLER crosspoint for CS selection hop (ULBH)

• DL BLER crosspoint for CS selection hop (DLBH)

• UL BLER crosspoint for CS selection no hop (ULB)


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• DL BLER crosspoint for CS selection no hop (DLB)

The given parameters correspond to the BLER_CP_CS1 (see equation above).

During transmission, two counters are updated: N_Number gives the total number of RLC data blocks and K_Number gives the number of corrupted RLC data blocks that have been transmitted after the last link adaptation decision.

More information is available in NED.

7.6.2 GPRS Link Adaptation with CS1-4 (PCU2)

In PCU2 the coding schemes CS-1 - CS-4 are supported. The BTS level parameters DL coding scheme in acknowledged mode (DCSA), ULcoding scheme in acknowledged mode (UCSA), DL coding scheme in unacknowledged mode (DCSU) and UL coding scheme in unacknowledged mode (UCSU) define whether the fixed CS value (CS-1 - CS-4) is used or if the coding scheme is changed dynamically according to the Link Adaptation algorithm.

The BTS level parameter adaptive LA algorithm (ALA) defines whether the Link Adaptation algorithm is adaptive or not. The new Link Adaptation algorithm can be used both in RLC acknowledged and in unacknowledged modes both in uplink and downlink direction.

When the Link Adaptation algorithm is deployed, the initial values for the CS at the beginning of a TBF can also be defined with the parameters DL coding scheme in acknowledged mode (DCSA), UL coding scheme in acknowledged mode (UCSA), DL coding scheme in unacknowledged mode (DCSU) and UL coding scheme in unacknowledged mode (UCSU).

The new Link Adaptation algorithm replaces the current LA algorithm in GPRS and covers the coding schemes:

• CS-1 and CS-2 if the CS-3 and CS-4 support is not enabled in the territory

• CS-1, CS-2, CS-3 and CS-4, if the CS3 and CS-4 support is enabled in the territory

The Link Adaptation algorithm is applied to measure the signal quality for each TBF in terms of RXQUAL, which refers to received signal quality. RXQUAL describes the channel quality with the accuracy of eight levels. It is expressed with three bits. RXQUAL is measured for each received RLC radio block being thus a more accurate estimate than the BLER, which has two levels: 0 and 1.

The PCU determines internally the average BLER separately for each coding scheme and the reported RXQUAL value. This is done separately for each segment by collecting continuously statistics from all the connections in the corresponding territory. The PCU can estimate the BLER if CS-1, CS-2, CS-3 or CS-4 coding schemes were deployed for this particular TBF. Moreover, based on BLER estimates the PCU can determine which coding scheme will give the best performance.

Link Adaptation Algorithm Used in Downlink Direction

When a new territory is created for (E)GPRS, two 2-dimensional tables are created (ACKS and NACKS) for the territory (another set of ACKS and NACKS tables are


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needed for UL direction). In these tables, the first index refers to the coding scheme and the second index refers to the RXQUAL value.

In territory creation the ACKS and NACKS tables are initialized with values obtained from the simulations. This is because the operation of the LA algorithm is initially based on the simulation results, whereas in case of traditional LA algorithms predefined threshold values are used.

Separate initialization is needed for hopping and non-hopping BTSs.

During the DL data transfer the mobile station measures the signal quality (RXQUAL) from the RLC radio blocks that are successfully decoded and addressed to the mobile station. The RXQUAL is averaged over the received RLC blocks and the averaged RXQUAL estimate is sent to the network in the Packet DL Ack/Nack messages. There can be eight different values for the RXQUAL. When RLC receives a valid Packet DL Ack/Nack message for the DL TBF that operates in an RLC acknowledged mode, the received bitmap is analyzed and the corresponding RLC blocks are marked as ACKED, if a positive acknowledgement is received, or as NACKED, if a negative acknowledgement is received. In this procedure, the RLC updates the ACKS and NACKS tables as follows:

• Whenever an RLC block is positively acknowledged, ACKS [CS][RXQ] = ACKS [CS][RXQ] + 1, where CS indicates the coding scheme with which this RLC block was transmitted and RXQ refers to the RXQUAL value received in this particular Packet DL Ack/Nack message.

• Whenever an RLC block is negatively acknowledged, NACKS [CS] [RXQ] = NACKS [CS][RXQ] + 1, where CS indicates the coding scheme with which this RLC block was originally transmitted and RXQ refers to the RXQUAL value received in this particular Packet DL Ack/Nack message.

If the value of the parameter adaptive LA algorithm (ALA) is N (disabled), the RLC does not update ACKS and NACKS tables but only the initial values of those tables will be used when the LA algorithm selects the optimal CS.

To avoid the BLER estimation disturbance caused by the pending ack transmissions, the PCU updates ACKS and NACKS tables based only on those RLC blocks that have never been transmitted as pending_ack blocks.

With this mechanism the LA algorithm can collect statistics about the actual block error rate. Based on this statistics it is possible to select a coding scheme that gives, on the average, the highest throughput with respect to the specific channel quality estimate.

Note that ACKS and NACKS tables contain ever-increasing figures. In the long run the figures would overflow resulting in erroneous behavior. To solve this, both figures are divided by 2, when the sum (ACKS [CS][RXQ] + NACKS [CS] [RXQ]) for CS and RXQ exceeds the threshold value, for instance:

• ACKS [CS][RXQ] = ACKS [CS][RXQ] / 2

• NACKS [CS][RXQ] = NACKS [CS][RXQ] / 2

Downlink Direction in RLC Acknowledged Mode


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After the bitmap is processed by RLC, the LA algorithm selects the optimal coding scheme for this particular link as follows:

1. The throughput of the link is estimated for each coding scheme separately as follows: throughput [CS] = K * ACKS [CS][RXQ] / (ACKS [CS][RXQ] + NACKS [CS][RXQ]) * RATE[CS], where: CS = CS-1, CS-2, CS-3, CS- 4, if CS-3 and CS-4 support is enabled in the territory, otherwise CS = CS- 1, CS-2.

• K is a correction factor that takes into account the throughput reduction due to the RLC protocol stalling

• RXQ is the RXQUAL value that was received in the newly-processed Packet DL Ack/Nack message

• RATE[4] -table contains the theoretical maximum throughput values for the available channel coding schemes

2. The coding scheme is selected based on the highest throughput with the condition of BLER (CS) < QC_ACK_BLER_LIMIT_T, where BLER (CS) = NACKS [CS] [RXQ] / (ACKS[CS] [RXQ] + NACKS [CS] [RXQ]). If no CS fulfills this condition, the coding scheme CS-1 is selected.

The correction factor K depends on the BLER and on the number of RLC radio blocks scheduled to the TBF within the RLC acknowledgement delay. Its value has been determined by simulations.

If the MS does not answer to polling, the coding number will be decreased step-by- step.

Downlink direction in RLC unacknowledged mode

In unacknowledged mode RLC does not have to update the ACKS and NACKS tables but it can use the same ACKS and NACKS tables updated by the TBFs in acknowledged mode.

The coding schemes that are in an unacknowledged mode are selected by choosing the highest CS for which BLER (CS) < QC_UNACK_BLER_LIMIT_T, where BLER (CS) = NACKS [CS] [RXQ] / (ACKS[CS] [RXQ] + NACKS [CS] [RXQ]) and RXQ is the RXQUAL estimate that is received in the Packet DL Ack/Nack message. If these conditions are not fulfilled the coding scheme CS-1 is selected.

7.6.2.1 Link Adaptation Algorithm Used in Uplink Direction In UL direction the channel quality estimate can be either RXQUAL or GMSK_BEP depending on the Abis interface. The PCU data frame used in the non-EDGE Abis interface reports the channel quality in terms of RXQUAL, which is expressed with three bits. In this case the only possible coding schemes are CS-1 and CS-2. Whereas the PCU master data frame used in the EDGE Abis interface reports the channel quality in terms of GMSK_BEP, which is expressed with four bits. The possible coding schemes are CS-1, CS-2, CS-3 and CS-4.

When a new territory is created for (E)GPRS, two 2-dimensional tables ACKS and NACKS are created for the territory (another set of ACKS and NACKS tables is needed for DL direction). In these tables, the first index refers to the coding scheme and the second index refers to the RXQUAL or GMSK BEP value. In territory creation


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the ACKS and NACKS tables are initialized to the values obtained from the simulations. There can be a separate initialization for hopping and non-hopping BTSs.

In case of RXQUAL, the RLC averages the RXQUAL estimates sent by the BTS for the correctly received RLC radio blocks. This is done for each uplink TBF.

In case of GMSK_BEP, the RLC averages the GMSK_BEP estimates sent by the BTS for both correctly and erroneously received RLC radio blocks. This is done for each UL TBF. The GMSK_BEP estimate should also be made from the bad frames because the GMSK_BEP estimate for successfully received CS-4 blocks alone approaches zero in all radio conditions (there is no error correction in CS- 4).

During the UL data transfer the RLC can estimate the number of successfully and unsuccessfully received RLC radio blocks for BLER estimation purposes as follows (this needs to be done only in RLC acknowledged mode):

Whenever RLC receives a new RLC block successfully, ACKS [CS][RXQ] = ACKS [CS][RXQ] + 1, where CS indicates the coding scheme with which this RLC block was transmitted and RXQ refers to the RXQUAL value is the current RXQUAL or GMSK BEP estimate for this UL TBF. Whenever RLC receives a RLC block unsuccessfully, NACKS [CS][RXQ] = NACKS [CS][RXQ] + 1, where CS indicates the coding scheme with which this RLC block was transmitted and RXQ refers to the RXQUAL value is the current RXQUAL or GMSK BEP estimate for this UL TBF.

When RLC constructs a Packet UL Ack/Nack message for an UL TBF that operates in RLC acknowledged mode, the RLC updates the ACKS and NACKS tables as follows:

• ACKS [CS][RXQ] = ACKS [CS][RXQ] + N_acks[CS], where CS runs through the available coding schemes and RXQ is the current RXQUAL or GMSK BEP estimate for this UL TBF (RXQUAL is derived from the averaged BER estimate and GMSK BEP is derived from the averaged BEP estimate)

• NACKS [CS][RXQ] = NACKS [CS][RXQ] + N_nacks[CS], where CS runs through the available coding schemes and RXQ is the current RXQUAL or GMSK BEP estimate for this UL TBF (RXQUAL is derived from the averaged BER estimate and GMSK BEP is derived from the averaged BEP estimate).

• After the ACKS and NACKS tables have been updated the counters N_acks[CS] and N_nacks[CS] are reset to zero.

As in the DL case the figures in the ACKS and NACKS tables are restricted so that when the sum (ACKS [CS][RXQ] + NACKS [CS][RXQ]) for certain CS and RXQ exceeds a certain threshold value, both figures are divided by 2, for instance:

• ACKS [CS][RXQ] = ACKS [CS][RXQ] / 2

• NACKS [CS][RXQ] = NACKS [CS][RXQ] / 2.

After the bitmap for the Packet UL Ack/Nack message is constructed by the RLC, the LA algorithm selects the commanded coding scheme for the UL TBF as follows:

Uplink direction in RLC acknowledged mode

1. The throughput of the link is estimated for each coding scheme separately as follows: throughput [CS] = K * ACKS [CS][RXQ] / (ACKS [CS][RXQ] + NACKS [CS][RXQ]) * RATE [CS], where: CS = CS-1, CS-2, CS-3, CS- 4, if CS-3 and


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CS-4 support is enabled in the territory, otherwise CS = CS- 1, CS-2. K is a correction factor that takes into account the throughput reduction due to the RLC protocol stalling, RXQ is the current RXQUAL or GMSK BEP estimate for this UL TBF and RATE [4] -table contains the theoretical maximum throughput values for the available channel coding schemes.

2. The coding scheme is selected based on the highest throughput with the condition of BLER (CS) <QC_ACK_BLER_LIMIT_T, where BLER (CS) = NACKS [CS] [RXQ] / (ACKS [CS] [RXQ] + NACKS [CS] [RXQ]). If no CS fulfills this condition, the coding scheme CS-1 is selected. The same correction factor table K can be used as in the DL case.

Uplink direction in RLC unacknowledged mode

In unacknowledged mode the RLC message does not have to update the ACKS and NACKS tables but it can use the same ACKS and NACKS tables that are updated by the TBFs in acknowledged mode. The coding schemes are selected in unacknowledged mode as follows:

The coding schemes that are in an unacknowledged mode are selected by choosing the highest CS for which BLER (CS) < QC_UNACK_BLER_LIMIT_T, where BLER (CS) = NACKS [CS] [RXQ] / (ACKS [CS] [RXQ] + NACKS [CS] [RXQ]) and RXQ is the current RXQUAL or GMSK BEP estimate for this UL TBF. If these conditions are not fulfilled for any CS the coding scheme CS-1 is selected. When an (E)GPRS territory is removed, the corresponding ACKS and NACKS tables can be removed as well.

The LA algorithm in PCU1 operates only in the RLC acknowledged mode. In the RLC unacknowledged mode, PCU1 uses always CS1. The LA algorithm in PCU2 operates in both in the RLC acknowledged and RLC unacknowledged modes.

The LA algorithm in PCU2 can be operated in two different modes:

• In adaptive mode (ADAPTIVE LA ALGORITHM = TRUE), the look-up tables that are used for RXQUAL -> BLER mapping are updated automatically based on the statistics gathered from the TBF connections.

• In non-adaptive mode (ADAPTIVE LA ALGORITHM = FALSE), the look-up tables have constant values that have been determined by means of simulations.

The LA algorithm in PCU1 uses the following parameters:

• DL ADAPTATION PROBABILITY THRESHOLD (DLA) • DL BLER CROSSPOINT FOR CS SELECTION HOP (DLBH) • DL BLER CROSSPOINT FOR CS SELECTION NO HOP (DLB) • UL ADAPTATION PROBABILITY THRESHOLD (ULA) • UL BLER CROSSPOINT FOR CS SELECTION HOP (ULBH) • UL BLER CROSSPOINT FOR CS SELECTION NO HOP (ULB)

The LA algorithm in PCU2 uses the following parameters:

• DL CODING SCHEME IN ACKNOWLEDGED MODE (DCSA) • DL CODING SCHEME IN ACKNOWLEDGED MODE (DCSA)


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• UL CODING SCHEME IN ACKNOWLEDGED MODE (UCSA) • DL CODING SCHEME IN UNACKNOWLEDGED MODE (DCSU) • UL CODING SCHEME IN UNACKNOWLEDGED MODE (UCSU) • ADAPTIVE LA ALGORITHM (ALA)

7.6.3 EGPRS Link Adaptation with Incremental Redundancy

Link Adaptation (LA) means that in order to adjust to channel conditions, a particular modulation and coding scheme combination is selected.

The increased data rate in GMSK and 8PSK modulations implies an increased sensitivity to noise in coverage-limited areas and to interference in interference limited cells.

The task of the LA algorithm is to select the optimal MCS for each radio conditions to maximize RLC/MAC data rate, so the LA algorithm is used to adapt to situations where signal strength and/or C/I level is low and changing within time.

Link Adaptation Algorithm with Incremental Redundancy

Normally, LA adapts to path loss and shadowing but not fast fading, while Incremental Redundancy (IR) is better suited to compensate fast fading.

The retransmission process is using IR, so the LA must take into account if IR combining is performed at the receiver and the effect of finite IR memory, too. It means that the MCS selection is not the same in case of initial transmission and retransmission.

7.6.3.1 Link Adaptation Introduction RLC control blocks are transmitted with GPRS CS-1 coding, so the LA is not used in case of control blocks.

LA is done independently for each UL TBF and DL TBF on RLC level, but the LA algorithm is the same for uplink and downlink direction.

LA algorithm works differently for acknowledged mode and unacknowledged mode. The details are described below:

• Downlink

o Ack: Downlink EGPRS packet transfer is controlled by RLC by using acknowledges and retransmission. Downlink acknowledges are polled from MS by RLC to keep up the status of the transmitted RLC data blocks (acked/nacked) and to monitor the quality of the radio link.

o Unack: The transfer of RLC data blocks in the RLC unacknowledged mode does not include any retransmissions, except during the release of a downlink TBF where the last transmitted downlink RLC data block may be retransmitted (max four times).

The MS sends Packet Ack/Nack messages in order to convey the necessary other control signaling (e.g. monitoring of channel quality for downlink transfer).

• Uplink


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o Ack: The RLC requests packet re-sending in uplink transfer from MS for the packets not received correctly. The RLC sends uplink acknowledgements within PACKET UPLINK ACK/NACK messages to MS. The PCU sends Packet Ack/Nack messages also in order to update the necessary other control signaling (e.g. timing advance correction for uplink transfers).

The PRE_EMPTIVE_TRANSMISSIO PRFILE parameter defines if the MS is allowed to send unacknowledged ‘PENDING_ACK’ RLC data blocks. To allow MS to send unacknowledged ‘PENDING_ACK’ RLC data blocks the PRE_EMPTIVE_TRANSMISSION shall be allowed, i.e. Value “0” shall be used in the Packet Uplink Ack/Nack field.

o Unack: The transfer of RLC data blocks in the RLC unacknowledged mode does not include any retransmissions, except during the release of an uplink TBF where the last transmitted uplink RLC data block may be retransmitted.

The PCU sends Packet Ack/Nack messages in order to update the necessary other control signaling (e.g. timing advance correction for uplink transfers).

The following figure shows the block diagram of MCS selection procedure:

Uplink averaging

PCU receives EGPRS Packet Downlink Ack/Nack message. The BEPs from the message are delivered to adaptation algorithm.

PCU receives Uplink radio block

UPLINK DOWNLINK

Link Adaptation algorithm

Downlink case outputs: - MCS for initial transmission - MCS for retransmission

PCU decides to send Packet Uplink Ack/Nack message. The BEPs from averaging are delivered to adaptation algorithm.

Uplink case output: - MCS that is sent to MS in Packet

Uplink Ack/Nack message

Averaged BEPs

Figure 69 Link Adaptation in PCU


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7.6.3.2 MCS Selection The MCS selection process is described below on block diagram level.

In DL case the MCS selection is based on EGPRS Channel Quality Report received in EGPRS PACKET DOWNLINK ACK/NACK message sent from the MS to network using PACCH to indicate the status of the downlink RLC data blocks received.

In DL the MCS selection is based on using the BEP measurement data from MS (which is available there in EGPRS PACKET DOWNLINK ACK/NACK message) and it is done by RLC.

RLC uses the Channel Management (CHM) and Dynamic Abis Management (DAM) in the decision as well.

RLC / Downlink TBF

LA

MCSs

MCS selection

Selected MCS for downlink radio block

CHM

DAM

read

write

Init MCS

Figure 70 MCS selection on DL

Downlink MCS selection is done every time when the RLC sends a RLC data block to the MS.

The CHM has allocated the TSLs of one TRX to DL TBFs

START

MCS limiting by CHM

Dynamic Abis allocation by DAM

Data block and MCS selection by RLC

READY

Data block and MCS prediction by RLC

Figure 71 MCS selection for TSLs of one TRX on DL


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In UL case the MCS selection is based on the respective BEP values, which are received within the UL PCU frames.

CHM

DAM

RLC / Uplink TBF

LA

MCS

Commanded MCS selection

read

write

Commanded MCS for uplink is sent to MS

Init MCS

MS

MCS selection

Figure 72 MCS selection on UL

So the MCS selection is based on RLC estimation but for the final decision the Channel Management and Dynamic Abis Management have to give the permission as well.

Channel Management: Generally the CHM accepts the MCS/CS from the RLC, but during scheduling the CHM checks if lower coding scheme must be used than the RLC has selected. Reasons for lower coding scheme:

• GPRS TBF and EGPRS TBF multiplexing

• MS synchronization

Dynamic Abis Management: The DAM allocates Abis slave channels for the TRX’s TSLs based on the MCS that the RLC/CHM has selected. If there are not enough slave channels available, as it is required by RLC and CHM, the DAM allocates fewer slaves and informs the RLC about next lower MCS that fits on the allocated Abis capacity.

Generally the MCS decided for initial transmission by LA algorithm is used.

Exceptions:

• If MCS would be MCS-9 or MCS-8 but the RLC could generate only one data block (Note1) then the RLC selects MCS-6

• If MCS would be MCS-7 but the RLC could generate only one data block (Note1) then the RLC selects MCS-5

• The CHM or the DAM has required lower MCS. If the RLC asked 8PSK MCS but the returned MCS is MCS-4 then the RLC decreases it to MCS-3


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• Operator defined initial MCS is used at the beginning of TBF

• Operator defined initial MCS is used after TBF reallocation to other BTS in the SEG

Note1: The RLC can generate only one data block if there is no RLC data block to be used as the second block. This can happen if the next RLC data block to be transmitted has a status of NACKED or PENDING and cannot be retransmitted with the MCS selected for the first block.

7.6.3.3 Bit Error Probability The LA algorithm is mainly based on Bit Error Probability (BEP), because the RLC selects MCS according to the BEP values. In GSM specification, there is a full support for BEP based LA algorithm.

The BEP is measured at the receiver (both for UL and DL) before the decoding. The receiver has to convert each symbol into bit(s) and during this process it estimates the bit error probability, which is the BEP.

The BEP is a decision, which includes information about the reliability of the decision (i.e. how sure the receiver is that the received bit is decided correctly) - BEP can be calculated from that certainty information.

BEP is invariant of the used coding scheme, but it depends on the modulation though. Both in ack and unack mode the BEP is used to estimate the BLER for each MCS, but BEP does not take BLER into account (ACK/NACK information).

The rules of BEP measurements and calculations are described in the following three points:

• Decoding L1 data and converting in RLC

o The BEP values are based on the received signal quality and BTS reports the measurement data to the PCU in the Abis L1 frame (MEAN_BEP, VAR_BEP). The measurement element is one burst.

o Before the reported values can be used for averaging the RLC converts MEAN_BEP to MEAN_BEP_gmsk, MEAN_BEP_8psk, VAR_BEP to CV_BEP for the RLC/MAC block. The measurement element is one RLC block (four radio bursts). The tables below show the conversions:

VAR_BEP received from BTS

CV_BEP

0 0.25

1 0.75

2 1.25

3 1.75

Table 20 An incoming VAR_BEP value is converted into CV_BEP


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MEAN_BEP received from BTS

MEAN_BEP_gmsk (if GMSK MCS used)

MEAN_BEP_8psk (if 8-PSK MCS used)

0 0.0002 0.00025

1 0.0005 0.00075

2 0.0008 0.0015

3 0.0015 0.0035

4 0.0025 0.0075

5 0.0035 0.0155

6 0.0050 0.0325

7 0.0080 0.0565

8 0.0130 0.076

9 0.0205 0.0915

10 0.0325 0.11

11 0.0515 0.13

12 0.0815 0.155

13 0.1300 0.19

14 0.2050 0.23

15 0.2900 0.275

Table 21 An incoming MEAN_BEP value is converted for GMSK or 8-PSK depending on MCS used

• Averaging of the decoded L1 data

o The PCU averages the quality parameters of the block individually for each MS per TSL and per modulation type (Mean_BEP_TNn, CV_BEP_TNn) (05.08, 10.2.3). The information element is the RLC/MAC blocks between two Ac/Nack messages.

The PCU averages the quality parameters of the block individually per TBF and per modulation type as follows [05.08]:

R is calculated for every block period. BEP values are calculated for block periods carrying block for the TBF.

For block periods carrying block for the TBF the R and BEP values of modulation of received packet are calculated as follows:


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eRe)(1R 1nn +⋅−= −

nblock,n

1nn

n MEAN_BEPR

eNMEAN_BEP_T)

R

e(1NMEAN_BEP_T ⋅+⋅−= −

nblock,n

1nn

n CV_BEPR

eCV_BEP_TN)

R

e(1CV_BEP_TN ⋅+⋅−= −

and for the other modulation the R value is calculated as follows:

1nn Re)(1R −⋅−=

Where: n is the iteration index, incremented per each uplink radio block for TBF.

Value from DX 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 BEP_PERIOD Reserved 25 20 15 12 10 7 5 4 3 2 1

e - 0.08 0.1 0.15 0.2 0.25 0.3 0.4 0.5 0.65 0.8 1

When an R-value reduces under a limit, BEP values are not used in Link Adaptation algorithm for that modulation (instead conversion table is used, see table 8). Limit is based on BEP_PERIOD as follows:

Value from DX 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 BEP_PERIOD Reserved 25 20 15 12 10 7 5 4 3 2 1

- 4.343885e-1

3.486784e-1

1.968744e-1

1.073742e-1

5.631351e-2

2.824752e-2

6.046618e-3

9.765625e-04

2.75855e-5

1.024e-7

0

Table values are calculated from equation: nn e)(1R −=

Where: n is set to 101

• BEP value is calculating from the averaged data

o If GMSK MCS was used then new GMSK_MEAN_BEP and GMSK_CV_BEP are defined from the averaged values using the table in [05.08, 8.2.5]. These values are used in the BEP matrix tables (see chapter 0).

1 Note! Currently n value means number of block periods carrying data blocks after which BEP values are ignored in LA calculation.


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Log10(MEAN_BEP_TN) GMSK_MEAN_BEP

-0.6 < log 0

-0.7 < log <= -0.6 1

-0.8 < log <= -0.7 2

-0.9 < log <= -0.8 3

-1.0 < log <= -0.9 4

-1.1 < log <= -1.0 5

-1.2 < log <= -1.1 6

-1.3 < log <= -1.2 7

-1.4 < log <= -1.3 8

-1.5 < log <= -1.4 9

-1.6 < log <= -1.5 10

-1.7 < log <= -1.6 11

-1.8 < log <= -1.7 12

-1.9 < log <= -1.8 13

-2.0 < log <= -1.9 14

-2.1 < log <= -2.0 15

-2.2 < log <= -2.1 16

-2.3 < log <= -2.2 17

-2.4 < log <= -2.3 18

-2.5 < log <= -2.4 19

-2.6 < log <= -2.5 20

-2.7 < log <= -2.6 21

-2.8 < log <= -2.7 22

-2.9 < log <= -2.8 23

-2.0 < log <= -2.9 24

-3.1 < log <= -3.0 25


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-3.2 < log <= -3.1 26

-3.3 < log <= -3.2 27

-3.4 < log <= -3.3 28

-3.5 < log <= -3.4 29

-3.6 < log <= -3.5 30

log <= -3.6 31

Table 22 GMSK_MEAN_BEP [05.08]

o If 8-PSK MCS was used then new 8PSK _MEAN_BEP and 8PSK _CV_BEP are defined from the averaged values using the table in [05.08, 8.2.5]

Log10(MEAN_BEP_TN) 8-PSK _MEAN_BEP

-0.6 < log 0

-0.64 < log <= -0.60 1

-0.68 < log <= -0.64 2

-0.72 < log <= -0.68 3

-0.76 < log <= -0.72 4

-0.80 < log <= -0.76 5

-0.84 < log <= -0.80 6

-0.88 < log <= -0.84 7

-0.92 < log <= -0.88 8

-0.96 < log <= -0.92 9

-1.00 < log <= -0.96 10

-1.04 < log <= -1.00 11

-1.08 < log <= -1.04 12

-1.12 < log <= -1.08 13

-1.16 < log <= -1.12 14

-1.20 < log <= -1.16 15

-1.36 < log <= -1.20 16


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-1.52 < log <= -1.36 17

-1.68 < log <= -1.52 18

-1.84 < log <= -1.68 19

-2.00 < log <= -1.84 20

-2.16 < log <= -2.00 21

-2.32 < log <= -2.16 22

-2.48 < log <= -2.32 23

-2.64 < log <= -2.48 24

-2.80 < log <= -2.64 25

-2.96 < log <= -2.80 26

-3.12 < log <= -2.96 27

-3.28 < log <= -3.12 28

-3.44 < log <= -3.28 29

-3.6 < log <= -3.44 30

log <= -3.6 31

Table 23 8-PSK_MEANBEP [05.08]

CV_BEP_TN 8-PSK/GMSK CV_BEP

1.75 < cv <= 2.00 0

1.50 < cv <= 1.75 1

1.25 < cv <= 1.50 2

1.00 < cv <= 1.25 3

0.75 < cv <= 1.00 4

0.50 < cv <= 0.75 5

0.25 < cv <= 0.50 6

0.00 < cv <= 0.25 7

Table 24 CV_BEP [05.08]


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Usage of BEP on DL

BEP measurements are initiated to MS in downlink using IMMEDIATE ASSIGNMENT, PACKET_TIMESLOT_RECONFIGURE or PACKET DOWNLINK ASSIGNMENT messages when TBF is created.

Operator setting for Initial MCS is used until first BEPs measured by MS are received in EGPRS Packet Downlink Ack/Nack message.

Input parameters for downlink link adaptation algorithm are the BEP values in the EGPRS Packet Downlink Ack/Nack message (GMSK_MEAN_BEP, 8-PSK_MEAN_BEP, GMSK_CV_BEP, 8-PSK_CV_BEP).

Downlink Link Adaptation algorithm produces two MCS values, a MCS for initial transmission and a MCS for retransmission.

If no BEPs have arrived during the entire TBF, the MCS from parameter initial MCS is used.

Usage of BEP on UL

When uplink TBF is created PACKET UPLINK ASSIGNMENT or PACKET_TIMESLOT_RECONFIGURE is used to set TBF properties.

• EGPRS Channel Coding Command, operator setting for initial MCS is used

• RESEGMENT, always 0 = Retransmitted RLC data blocks shall not be re-segmented (IR)

Operator setting for Initial MCS is used until the first Packet Uplink Ack/Nack is sent after the first uplink measurement has become available.

Input parameters for uplink link adaptation algorithm are the BEP values from averaging as follows: GMSK_MEAN_BEP, 8-PSK_MEAN_BEP, GMSK_CV_BEP, 8-PSK_CV_BEP.

The RLC activates Link adaptation for uplink TBF when the RLC decides to send ack to the MS (no polling on UL).

Uplink Link Adaptation algorithm produces one MCS value that is sent to MS in the Packet Uplink Ack/Nack message.

7.6.3.4 Link Adaptation Procedure If the operator has disabled EGPRS link adaptation then the LA algorithm does not change the output MCS values. LA is controlled with EGPRS Link adaptation enabled parameter that has three values:

0 = EGPRS link adaptation is disabled

1 = EGPRS link adaptation is enabled for RLC acknowledged mode

2 = EGPRS link adaptation is enabled for both RLC acknowledged and RLC unacknowledged modes


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If the operator setting for Initial MCS is bigger than max_MCS then Initial MCS is replaced with max_MCS (parameter in DX 200, BSC non directly modifiable).

In the Figure 73 below the LA algorithm flowchart in PCU is shown.

The BEPs from the EGPRS Packet Downlink Ack/Nack message are delivered to adaptation algorithm.

UPLINK DOWNLINK

Adaptation algorithm

RLC mode?

Define MCS candidate A basing on BLER limits *)

Define MCS candidate B using optimal MCS method *)

Define MCS basing on BLER limits *)

unack ack

Select the smaller of the candidates A and B

Downlink case outputs: - MCS for initial transmission - MCS for retransmission

Uplink case output: - MCS for initial transmission

*) when defining uplink MCS the output of these phases is a GMSK MCS if the MS is not 8-PSK capable in uplink

Handle missing modulation data

Add user defined mean_bep_offsets

Downlink only: Define retransmission MCS

Downlink only: If MS IR memory full then restrict MCSs

READY

START

The BEPs from Uplink averaging are delivered to adaptation algorithm.

For CX3.2 only: Change MCS8/9 to MCS7

Figure 73 Flowchart of link adaptation algorithm


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MCS Selection with BEP Matrix Tables

MCS selection can be divided in four classes:

1. Initial MCS to be used when entering the packet transfer mode

2. Modulation selection

3. MCS selection for initial transmissions of each RLC block in ACK mode

4. MCS to be used for retransmissions

Remember that, the algorithm is activated on downlink whenever a measurement report from MS is received. The algorithm is activated on uplink whenever the channel coding command is to be transmitted from network to the MS.

The LA procedure is based on static MCS selection tables in the PCU.

1. Initial MCS to be used when entering the packet transfer mode.

The initial MCS selection is set by means of the following BTS level parameters:

InitMcsAckMode set by default to the highest value (=9 which correspond to MCS9)

InitMcsUnackMode set by default to value 6 (MCS=6)

In reliability class 3 (RLC/MAC acknowledged mode and LLC not acknowledged) we can set the initial MCS via initMcsAckMode to be used on first transmission before the MS start measuring the air interface and reporting to the network via ACK/NACK messages. Once the information is exchanged to the network then LA algorithm will select the proper MCS using so called look-up tables whose values is hard-coded and whose entries consist of mean BEP levels and CV BEP level.

2. Modulation selection

Even before the real coding scheme selection, the modulation needs to be selected.

Modulation selection is based on 8-PSK MEAN_BEP, 8-PSK CV_BEP and GMSK_MEAN BEP according to the table below (Table 25 ).

If MS does not support 8-PSK in the uplink, GMSK shall be chosen in the uplink algorithm.


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8PSK CV_BEP-class8PSKMEAN_BEP-class

0 1 2 3 4 5 6 7

0 4 4 4 4 4 4 41 6 6 6 6 6 5 52 9 9 9 9 9 7 63 – – – 21 12 11 84 – – – – 20 13 125 – – – – 24 21 21

6 – 31 – – – – – – –

Table 25 Modulation selection table (BEP limits for modulation selection)

The items in the table above are the 8PSK MEAN_BEP and CV_BEP values. The table is used as follows: the algorithm locates an entry in the table based on measured 8PSK MEAN_BEP and CV_BEP values. This entry is compared to the measured GMSK MEAN_BEP value. If the measured value is larger modulation GMSK is chosen, otherwise 8PSK is chosen.

If BEP for only one modulation is reported, the other one missing, the Table 26 shall be used to convert the MEAN_BEP value to the other modulation. The same CV_BEP value can be used for both modulations.

If both reports are missing, the previous ones shall be used. If no reports have arrived during the entire TBF, the MCS from parameter initial MCS shall be used.


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Reported GMSK

MEAN_BEP

Estimation for 8-PSK

MEAN_BEP

Reported 8-PSK

MEAN_BEP

Estimation for GMSK

MEAN_BEP 0 – 7 0 0 3

8 – 9 1 1 8

10 – 11 2 2 10

12 – 13 3 3 12

14 – 15 4 4 14

16 – 18 5 5 17

19 – 20 6 6 19

21 – 23 7 7 22

24 – 25 8 8 24

26 – 28 9 9 27

29 – 30 10 10 29

31 20 11-31 31

Table 26 Conversion from GMSK to 8-PSK and vice ver sa

With parameter meanBepOffsetGMSK and meanBepOffset8PSK an offset is introduced that will affect one of the two entries (mean bit error probability level range) of the look-up table in such a way to modify the commanded MCS to be used. In this way the modification of the offset could lead to a MCS higher or lower than the one which should have been commanded according to the C/I status of the air interface.

Final values is the following:

GMSK_MEAN_BEP = GMSK_MEAN_BEP + MEAN_BEP_OFFSET_GMSK;

8-PSK_MEAN_BEP = 8-PSK_MEAN_BEP + MEAN_BEP_OFFSET_8-PSK;

3. MCS selection for transmissions of each RLC block in ACK mode

Following is the optimal MCS selection.

For EGPRS, the MS shall calculate the following values for each radio block (4 bursts meaning Burst Period) addressed to it:

MEAN_BEPblock = mean(BEP) Mean Bit Error Probability (BEP) of a radio block

CV_BEPblock = std(BEP)/mean(BEP) Coefficient of variation of the Bit Error Probability of a radio block (a normalized standard deviation)


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Here, mean(BEP) and std(BEP) are the mean and the standard deviation respectively of the measured BEP values of the four bursts in the radio block, calculated in a linear scale. The appropriate table below is consulted for MCS selection for GMSK and 8-PSK (Table 27 and Table 28).

GMSK_CV_BEP GMSK_MEAN_BEP

0 1 2 3 4 5 6 7

0 – 3 1 1 1 1 1 1 1 1

4 2 2 1 1 1 1 1 1

5 2 2 2 1 1 1 1 1

6 2 2 2 2 2 2 1 1

7 – 9 2 2 2 2 2 2 2 2

10 – 19 3 3 3 3 3 3 3 3

20 – 31 4 4 4 4 4 4 4 4

Table 27 MCS selection for GMSK

8-PSK_CV_BEP

8-PSK_MEAN_BEP

0 1 2 3 4 5 6 7

0 – 3 5 5 5 5 5 5 5 5

4 6 5 5 5 5 5 5 5

5 6 6 5 5 5 5 5 5

6 6 6 6 5 5 5 5 5

7 6 6 6 5 5 5 5 5

8 6 6 6 6 5 5 5 5

9 6 6 6 6 6 5 5 5

10 – 16 6 6 6 6 6 6 6 6

17 – 21 7 7 7 7 7 7 7 7

22 – 25 8 8 8 8 8 8 8 8

26 – 31 9 9 9 9 9 9 9 9


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Table 28 MCS selection for 8-BSK

MCS limiting for CX3.2 BTS software

The CX3.2 software does not support MCS-8 and MCS-9.

The DX 200 SW informs the PCU about maximum MCS that the RLC is allowed to use in a cell. In the case of UltraSite CX3.2 the system sets maximum MCS to MCS-7, otherwise to MCS-9. The BSC internal parameter max_MCS is used for this purpose. The system checks the UltraSite SW level from the BTS SW package, and makes the decision based on that.

If the LA has given bigger MCS than the max_MCS (set in DX200 not operator definable) then the RLC replaces the MCS with max_MCS. The RLC does it for both initial transmission MCS and retransmission MCS.

If the operator setting for Initial MCS is bigger than max_MCS then Initial MCS is replaced with max_MCS.

Max_MCS parameter is not used from CX3.3.

4. MCS selection downlink for retransmissions in ACK mode

If modulation selection has selected to GMSK, GMSK will also be used for retransmissions of 8-PSK blocks by splitting the block (TBC)

For 8-PSK modulation, the table below shows the maximum MCS used for retransmissions.

CV_BEP-classMEAN_BEP-class

0 1 2 3 4 5 6 7

0 – 3 6 6 6 6 6 6 6 64 7 7 7 7 7 7 7 7

5 – 31 9 9 9 9 9 9 9 9

Table 29 Adaptation and retransmission with re-segm ent bit to 0

MCS reducing for downlink transmission if MS out of memory (IR), ack mode

The MCS selected in retransmission (as well as in transmission) can also be affected by the memory size of the MS and the fact that such size can be running out not allowing the highest MCS.

There is a PRFILE parameter that controls this function. The MEMORY_OUT_FLAG_SUM PRFILE parameter is used to activate the MS Out of Memory exception procedure in RLC to reduce the number of MCSs used. Allowed values for MEMORY_OUT_FLAG_SUM are 0 - 7. Value 0 deactivates algorithm use.

During IR operation in downlink packet transfer, MS may report MS Out of Memory condition in EGPRS PACKET DOWNLINK ACK/NACK Message. If there has been such report in MEMORY_OUT_FLAG_SUM or more consecutive EGPRS PACKET DOWNLINK ACK/NACK Message the RLC reduces the MCSs given by link adaptation. The RLC reduces MCSs using the tables below. The reduction is done until MS reports it has enough memory.


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MCS from LA algorithm Reduced MCS

1 1

2 1

3 2

4 3

5 5

6 5

7 6

8 7

9 7

Table 30 MCS for initial downlink transmission (MS Out of Memory)

MCS from LA algorithm Reduced MCS

6 6

7 6

9 7 Table 31 MCS for downlink retransmission (MS Out o f Memory)

Nokia implementation will select MCS3 as preferential GMSK coding scheme to be selected when downgraded from 8-PSK to GMSK.

7.6.3.5 Incremental Redundancy in EGPRS Incremental Redundancy (IR) matches the code rate to the channel conditions. The IR algorithm use a low rate convolutional code and puncture the code to get higher rate transmissions. If the first transmission of the radio block is unsuccessful, re-transmission is done with another puncturing storing the bits previously sent with a different puncturing to be used later for soft combination in order to recover the data block.

In the IR mode (available when the selected reliability class in SGSN allows RLC acknowledged mode), redundancy is increased gradually (Type II Hybrid ARQ). If the first transmission of radio block fails, it is retransmitted with a different puncturing scheme (P1, P2, P3 depending on the starting MCS) and soft combined with the old data. See Figure 74 below.


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Data Block

P1 P2 P3

P1 P2 P3

P1

P2

P3

Protection Level 1

1st transmission 2nd retransmissionupon receptionfailure

Stored

Stored

No datarecovered

No datarecovered

Combination : Protection Level x 2

Combination : Protection Level x 3

Stored

Transmitter

ReceiverP1

P1 P2

One MCS

1st retransmissionupon receptionfailure

Figure 74 Incremental redundancy processes

It should be noted that IR combining functionality is mandatory in EDGE MSs (as specified by ETSI, being the MS the receiving side). IR is not mandatory on the BSS side, but Nokia provides such functionality also from the BTS side.

Note then that for DL data retransmission the RLC selects MCS using the same or another in the MCS family in such a way that Incremental Redundancy is possible in the MS.

In UL data transfer the MS is either allowed or forbidden to use resegmentation for retransmissions, that is to say depending if the BSS side is set to store and combine the data or not. The RLC sets resegmentation always to non-active in the MS, supporting Incremental Redundancy in the BTS. Actually the RLC sets resegmentation according to EGPRS_RE_SEGMENTATION PRFILE parameter but the parameter value is always non-active by default.

This process is quite different to GPRS operation. For GPRS, if it is not be possible to correct for all introduces errors, then the block is discarded. In RLC acknowledged mode a retransmission will be requested. Should the retransmission fail, and then the received block will again be discarded. There is therefore no attempt to store those portions of the block that have been received correctly.

IR can offer significant gains in system throughput, but there are implications for the memory storage requirements in the MS/BTS, since storage of several versions of a number of RLC blocks may be required.

The IR performance (based on Nokia simulations) is shown in Figure 75. Note that the throughput is affected differently depending on the coding scheme - IR could nearly double the throughput for the higher coding schemes (MCS7-9) (especially true


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at lower Es/No value corresponding to lower C/I) as retransmission helps to correct errors in the block, as opposed to situations where redundancy is of no help.

Gain of IR vs C/I (TU3 iFH)

00.5

11.5

22.5

33.5

0 5 10 15 20 25 30

C/I [dB]

Gai

n [d

B]

Figure 75 Incremental Redundancy gain

The implication of this is that the 8-PSK schemes actually become the optimal schemes to use over practically the entire range of C/I where IR is implemented, provided that MS memory capabilities are sufficient to allow the highest MCS. (See on this regard more about MEMORY_OUT_FLAG_SUM PRFILE parameter and its relation with IR in Chapter 0).

Note that the gain introduced by IR is less at higher C/I values, in a normal network the average C/I corresponds range between 10 and 15 dB where the IR gain is around 2.5.

Overall, the IR process can be thought of as a means of increasing the redundancy contained within the data transmission where required. The below figure illustrates this.

original data

1/3 coded data

1st xmission

2nd xmission

3rd xmission

1st decoding attempt

2nd decoding attempt

3rd decoding attempt

r = 1/3

r = 1/2

r = 1/1

r = 1/1

r = 1/1

r = 1/1

IR: Increasing redundancy

Figure 76 IR Procedures


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The example in the figure assumes MCS-4 or MCS-9 where an initial code rate of 1/1 is used. Upon reception of the second transmission the code rate is now, in effect, ½. After the third transmission the code rate is 1/3. Because the retransmissions only occur where needed, IR is designed to optimize the code rate to the channel conditions.

The standards allow for a change in MCS between transmissions of the same source data, and this is based on the concept of MCS families. An MCS family is basically a set of possibilities of coding a block of source data into one or more RLC blocks for transmission over the air interface. Therefore a block that is initially sent in MCS-6 may be retransmitted with MCS-9. This leads to hybrid MCSs, such as MCS–6-9 or MCS-5-7. Typically the first transmission will be with the lowest MCS and then retransmissions will use the higher MCS.

IR is independent of LA, and to be specific IR won’t take into consideration the condition of the network as it happens with LA. In IR there is no measurements and averaging, the only thinks that is checked is the re-segmentation bit based on which, if LA is selected, different rules are followed in retransmission.

The re-segment field is used to select acknowledge mode to ARQI or ARQII (incremental redundancy) for UL TBF direction. NOTE that in DL the ARQII is mandatory (for MS). ETSI 04.60.

The re-segment field is determined by the network and indicated by the re-segment bit in messages PACKET UPLINK ACK/NACK, PACKET UPLINK ASSIGNMENT or PACKET TIMESLOT RECONFIGURE

Setting the retransmission to re-segment active "1" requires MS to use an MCS within the initial MCS family and the payload may be split (and in such a way IR not possible).

Setting the retransmission to re-segment non-active "0" requires the MS to use MCS within initial family without payload split (IR possible).

The uplink ARQ II mode (incremental redundancy) decoding is done in the BTS and RLC (BSC) receives full-encoded RLC data blocks together with information of MCS used in uplink for RLC header decoding purposes.

The downlink retransmissions are done by the BTS and RLC informs the BTS only the data block and MCS class and puncturing scheme PS to be used (IR combining is done in the MS). Figure 77 show how the MCSs are selected for retransmission depending on the re-segmentation bit (valid for the UL TBF only).


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Scheme used for

initial transmi

ssion

Scheme to use for retransmissions after switching t o a different MCS

MCS-9 Comm anded

MCS-8 Comm anded

MCS-7 Comm anded

MCS- 6-9

Comm anded

MCS-6 Comm anded

MCS- 5-7

Comm anded

MCS-5 Comm anded

MCS-4 Comm anded

MCS-3 Comm anded

MCS-2 Comm anded

MCS-1 Comm anded

MCS-9 MCS-9 MCS-6 MCS-6 MCS-6 MCS-6 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-8 MCS-8 MCS-8 MCS-6

(pad) MCS-6 (pad) MCS-6



(pad) MCS-3 pad) MCS-3

(pad) MCS-7 MCS-7 MCS-7 MCS-7 MCS-5 MCS-5 MCS-5 MCS-5 MCS-2 MCS-2 MCS-2 MCS-2 MCS-6 MCS-9 MCS-6 MCS-6 MCS-9 MCS-6 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-5 MCS-7 MCS-7 MCS-7 MCS-5 MCS-5 MCS-7 MCS-5 MCS-2 MCS-2 MCS-2 MCS-2 MCS-4 MCS-4 MCS-4 MCS-4 MCS-4 MCS-4 MCS-4 MCS-4 MCS-4 MCS-1 MCS-1 MCS-1 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1

Scheme used for

Initial transmi

ssion

Scheme to use for retransmissions after switching t o a different MCS

MCS-9 Comm anded

MCS-8 Comm anded

MCS-7 Comm anded

MCS- 6-9

Comm anded

MCS-6 Comm anded

MCS- 5-7

Comm anded

MCS-5 Comm anded

MCS-4 Comm anded

MCS-3 Comm anded

MCS-2 Comm anded

MCS-1 Comm anded

MCS-9 MCS-9 MCS-6 MCS-6 MCS-6 MCS-6 MCS-6 MCS-6 MCS-6 MCS-6 MCS-6 MCS-6 MCS-8 MCS-8 MCS-8 MCS-6

(pad) MCS-6 (pad)

MCS-6 (pad)

MCS-6 (pad)

MCS-6 (pad)

MCS-6 (pad)

MCS-6 (pad)

MCS-6 (pad)

MCS-6 (pad)

MCS-7 MCS-7 MCS-7 MCS-7 MCS-5 MCS-5 MCS-5 MCS-5 MCS-5 MCS-5 MCS-5 MCS-5 MCS-6 MCS-9 MCS-6 MCS-6 MCS-9 MCS-6 MCS-6 MCS-6 MCS-6 MCS-6 MCS-6 MCS-6 MCS-5 MCS-7 MCS-7 MCS-7 MCS-5 MCS-5 MCS-7 MCS-5 MCS-5 MCS-5 MCS-5 MCS-5 MCS-4 MCS-4 MCS-4 MCS-4 MCS-4 MCS-4 MCS-4 MCS-4 MCS-4 MCS-4 MCS-4 MCS-4 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-3 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-2 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1 MCS-1

Re - segment bit to "1" - > re - segmentation active

Re - segment bit to "0" - > re - segmentation non active

ETSI 04.60, Tables 2 and 3

ARQ Type I (No Increm. Redundancy)

ARQ Type II (Incremental Redundancy)

Figure 77 Tables for IR and adaptation behavior wit h the families

A re-segment bit is included within each PACKET UPLINK ACK/NACK, PACKET UPLINK ASSIGNMENT and PACKET TIMESLOT RECONFIGURE messages.

These messages are sent in the DL. For initial transmissions of new RLC blocks the channel coding commanded is applied. The resegment bit is used to set the ARQ mode to type I or type II (incremental redundancy) for uplink TBFs (allowing soft combining on BTS side). For retransmissions, setting the resegment bit to ‘1’ (type I ARQ) requires the mobile station to use an MCS within the same family as the initial transmission and the payload may be split (refer to table 1). For retransmissions, setting the resegment bit to ‘0’ (type II ARQ) requires the mobile station shall use an MCS within the same family as the initial transmission without splitting the payload even if the network has commanded it to use MCS-1, MCS-2 or MCS-3 for subsequent RLC blocks.

NOTE: This bit is particularly useful for networks with uplink IR capability (IR possible in BTS side) since it allows combining on retransmissions.

It should be noted that in EGPRS it is possible to retransmit a given RLC block in a different MCS (but within the same MCS family). This is not the case for GPRS where it is necessary to retransmit in the original CS in which the RLC block was sent.

7.6.3.6 MCS Selection Based on BLER Limits At the end of decision of the MCS also the BLER limits are checked by RLC within PCU (ack/unack mode).

There is a table per MCS that maps the pair (MEAN_BEP, CV_BEP) to BLER. The BLER values for each MCS are searched and compared to the operator parameters


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"MaxBlerAckmode" or "MaxBlerunackmode” on whether the mode is ACKed or UNACKed. The highest MCS that satisfies the BLER limit is chosen.

The GMSK _MEAN_BEP and GMSK _CV_BEP are used with GMSK BLER tables and 8-PSK _MEAN_BEP and 8-PSK _CV_BEP are used with 8-PSK BLER tables.

For UNACKed mode, this is the selected MCS used for all transmissions.

For ACKed mode, the minimum of this value and the value from optimal MCS selection is the selected MCS for initial transmissions of each new RLC block.

7.6.3.7 EGPRS LA in PCU2 The EGPRS LA algorithm is same in both PCUs. However, PCU2 provides about 20 ms shorter RLC RTT time, that mean LA in PCU2 gets response from MS faster than in PCU1. So, when compared to PCU1, the LA in PCU2 may react faster to radio condition changes.

PCU2 chooses initial MCS differently for sequential same direction TBF in certain situation. PCU1 uses always initial MCS value read from user parameter for new established TBF. PCU2 instead uses last used MCS of previous TBF as initial MCS for new TBF in situation when opposite direction of TBF has been active from last TBF release to new TBF establishment (so the MS context has stayed stored in PCU2 memory), and if no BTS re-selection was done for opposite direction of TBF.


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7.7 Multiplexing The TSL data rate can be decreased by multiplexing as well.

The multiplexing has the following effects:

• Synchronization (every 18th Radio Block)

• GPRS USF on DL EGPRS TBF

• TSL sharing – more than one TBF on a TSL

7.7.1 Synchronization

3GPP requires that for synchronization purpose, the network shall ensure that each MS with an active TBF in uplink or downlink receives at least one block transmitted with a coding scheme and a modulation that can be decoded by that MS every 360 millisecond interval (78 TDMA frames) to be used for DL power control. This function is implemented in the CHM. Timeslot scheduling algorithm in the CHM ensures that there is on each timeslot on downlink at least one Radio Block at least every 360 ms using MCS-1 (EGPRS TBF) or CS-1 (GPRS TBF) coding scheme.

S11.5 onwards:

For synchronization purposes, the network sends at least one radio block every 360 milliseconds using a MCS or CS low enough that all mobiles can be expected to be able to decode the block. If there are only EGPRS TBFs in the timeslot, the synchronization block is sent using CS-1 or a low enough MCS. If there are GPRS TBFs as well, the synchronization block is sent using CS-coding.

7.7.2 Dynamic Allocation on UL

In (E)GPRS the scheduling of UL and DL resources are independent. In the UL there can be three different allocation modes (MAC modes): fixed allocation, dynamic allocation and extended dynamic allocation.

The current Nokia implementation uses dynamic allocation to allocate resources to uplink TBFs. This means that in order for the MS to use a particular timeslot for uplink, it needs to listen to the downlink part of that timeslot to decode the USF (which tells which MS is allowed to use the uplink part of the timeslot).

So using 3 timeslots for uplink would mean that the MS should listen to the same 3 timeslots for downlink. This then means that a class 12 MS (max 5 UL/DL timeslots) cannot use more than 2 timeslots for uplink, as long as dynamic allocation is used by the network.

7.7.2.1 GPRS and EGPRS Dynamic Allocation In Nokia system GPRS and EGPRS TBFs can be multiplexed dynamically on the same timeslot (fixed allocation is not implemented).

When USF is addressed to GPRS TBF the downlink RLC radio block carrying the USF must use GMSK coding scheme, that is MCS-1 to MCS-4 if the DL RLC radio block is addressed to EGPRS TBF or CS-1 to CS-2, if the DL RLC radio block is addressed to GPRS TBF (without PCU2).


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If there are uplink GPRS TBF and downlink EGPRS TBF multiplexed on the same timeslot then the CHM restricts the EGPRS TBF to use MCS1-4 (MCS3 in Nokia implementation).

NOTE: The stealing bits in the EGPRS GMSK blocks to indicate CS-4. The coding and interleaving of the USF is done as defined for CS-4. That leads to:

1. A standard GPRS mobile station is able to detect the USF in EGPRS GMSK blocks. The risk that the rest of the block will be misinterpreted as valid information is low.

2. An EGPRS mobile station cannot differentiate CS-4 blocks and EGPRS GMSK blocks by decoding the stealing bits. However, an EGPRS mobile station in EGPRS TBF mode needs only to decode GMSK blocks assuming either of MCS-1 to MCS-4, in order to determine if they were aimed for it.

If fixed allocation is used, uplink blocks of the PDCH are reserved for only one mobile station at a time. Using fixed allocation, there is no particular restriction for the multiplexing of GPRS and EGPRS mobile stations on the same PDCH.

7.7.2.2 GPRS and EGPRS Dynamic Allocation without USF4

DL TSLs (originally 4 DL 8-PSK TSLs (TSL 4-7), but now TSL 7 is GMSK modulated, because of USF is pointed to GPRS MS (request for UL transmission on TSL 7))

0 1 2 3 4 5 6 7 Round 1 USF* Round 2 USF Round 3 USF ... USF ... USF ... …

*USF with GMSK modulation for all the USF cases in these tables

DL TSLs (originally 4 DL 8-PSK TSLs (TSL 4-7), but now TSL6 and 7 are GMSK modulates, because of USFs is pointed to GPRS MS (request for UL transmission on TSL 6 and 7))

0 1 2 3 4 5 6 7 Round 1 USF USF Round 2 USF USF Round 3 USF USF ... USF USF ... USF USF ... … …

7.7.2.3 GPRS and EGPRS Dynamic Allocation with USF4 The Dynamic Allocation on UL with USF4 is described below:


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On DL 4 TSLs are used by 8-PSK modulation (TSL 4-7), but now TSL 7 is GMSK modulated, because of USF is pointed to GPRS MS (request for UL transmission on TSL 7))

0 1 2 3 4 5 6 7 Round 1 USF Round 2 Round 3 ... ... USF ... …

On DL 4 TSLs are used by 8-PSK modulation (TSL 4-7), but now TSL 7 is GMSK modulated, because of USF is pointed to GPRS MS (request for UL transmission on TSL 6 and 7))

0 1 2 3 4 5 6 7 Round 1 USF USF Round 2 Round 3 ... ... USF USF ... … …

7.7.2.4 GPRS and EGPRS Extended Dynamic Allocation with/without USF4 Extended Dynamic Allocation functionality on UL is shown below:

On DL 4 TSLs are used by 8-PSK modulation (TSL 4-7), but now TSL 7 is GMSK modulated, because of USF is pointed to GPRS MS (request for UL transmission on TSL 7))

0 1 2 3 4 5 6 7 Round 1 USF Round 2 USF Round 3 USF ... USF ... USF ... …

On DL 4 TSLs are used by 8-PSK modulation (TSL 4-7), but now TSL 7 is GMSK modulated, because of USF is pointed to GPRS MS (request for UL transmission on TSL 4, 5, 6 and 7 ), but EDA is used)

0 1 2 3 4 5 6 7 Round 1 USF Round 2 USF Round 3 USF ... USF ... USF ... …

*If max 2 TSLs are needed on UL for GMSK MS, Dynamic Allocation (DA) will be used with USF4.


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8. (E)GPRS Territory Settings The following subchapters describe the territory definitions and allocations between CSW and PSW services.

Additionally to the territory settings the rate reduction due to territory occupancy is described as well.

8.1 Timeslot Allocation between Circuit Switched and (E)GPRS Services

The primary technique for dividing resources between circuit-switched (CSW) and packet ((E)GPRS) traffic in Nokia GSM is known as the Territory Method. In this, timeslots within a cell are dynamically divided into CSW and (E)GPRS territories. This means that a certain number of consecutive traffic timeslots are reserved for CSW GSM calls with the remainder being available for (E)GPRS traffic. Dynamic variation of the territory boundary (and hence number of timeslots in each territory) is controlled by territory parameters. This enables the system to adapt to different load levels, and traffic proportions, thus offering optimized performance under a variety of load conditions.

Figure 78 illustrates how traffic resource within a cell (2 TRX in this case) can be divided into CSW and (E)GPRS territories.

TRX 1

TRX 2

CCCH TS TS TS TS TS TS TS

TS TS TS TS TS TS TSTS

CircuitSwitchedTerritory

PacketSwitchedTerritory

Territory border movesDynamically based on Circuit

Switched traffic load

Default(E)GPRSCapacity

Dedicated(E)GPRSCapacity

TS TS

Additional(E)GPRSCapacity

TS TS

Figure 78 Illustration of cell territories.

8.1.1 PSW Territory

The PSW territory divided to dedicated, default and additional territories.

8.1.1.1 Dedicated (E)GPRS Capacity It is possible to assign dedicated (E)GPRS capacity, where a number of timeslots are allocated on a permanent basis to (E)GPRS. These timeslots are always configured for (E)GPRS and cannot be used by circuit-switched traffic. This ensures that (E)GPRS capacity is always available in a cell. The drawback with this approach is that, for a given cell configuration, blocking levels for CSW traffic will increase since the number of available channels will be reduced. This change in blocking decreases


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with increasing cell capacity (TRX count), and can be readily calculated using the Erlang-B formula.

The decision on whether to assign dedicated (E)GPRS territory is a trade-off between providing a minimum level of (E)GPRS service and increasing the blocking for CSW services. This decision needs to take into account operator priorities, network performance and predicted (E)GPRS usage levels.

The dedicated capacity can be set anywhere between zero and the full cell capacity.

If there are lot of dedicated territory, default territory in the PCU, the DSP allocation may not be efficiency, ending on performance decrease.

8.1.1.2 Default GPRS Capacity Another type of (E)GPRS capacity that can be defined is default (E)GPRS capacity. The default (E)GPRS territory is an area that will always be included in the instantaneous (E)GPRS territory provided that the current CSW traffic levels permit. With the exception of the dedicated (E)GPRS area, CSW services always take priority over (E)GPRS services and so, if circuit switched traffic levels dictate, circuit switched traffic will occupy as much (E)GPRS default territory as is needed. If, having previously occupied some of the (E)GPRS default territory, the CSW level decreases, these timeslots will automatically be re-allocated back to (E)GPRS irrespective of the actual (E)GPRS load.

Where circuit-switched traffic levels are falling, but outside the (E)GPRS default territory, allocation to (E)GPRS will only occur if the (E)GPRS load reaches a pre-defined condition (see later).

The setting of the default (E)GPRS territory level is a trade-off between improving the level of service (data rate, delay) for (E)GPRS users and high use of resources. Setting a higher level of default (E)GPRS territory will tend to increase the level of service experienced by the (E)GPRS users. However, a higher level for the number of default (E)GPRS territory timeslots may affect the overall (E)GPRS system capacity if a large number of (E)GPRS timeslots are taking up PCU connections without actually carrying (E)GPRS traffic. Another issue with setting a high level for default (E)GPRS territory is that it will tend to increase the number of intra-cell handovers for CSW users with the aim of keeping the (E)GPRS default territory free for (E)GPRS. Initially, it is recommended that the default territory is set to a level just below the anticipated mean load level. This will probably be with a minimum of three TCHs, however, to accommodate, where possible, 3-timeslot-capable mobiles at maximum available data rate without having to negotiate resource allocation with the CSRRM.

8.1.1.3 Additional (E)GPRS Capacity Where additional (E)GPRS capacity is assigned in response to load demand beyond that given by the default capacity, this capacity is termed additional (E)GPRS capacity. The upgrade/downgrade sections describe when this capacity will be used.

8.1.2 CSW Territory

In addition to the circuit-switched traffic load, the system attempts to keep one or more timeslots free in the CSW territory. The reason for this follows from the fact that if the CSW territory becomes fully occupied and further CSW connections need to be accommodated, then one or more timeslots from the (E)GPRS territory would be re-


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allocated for CSW use. This re-allocation introduces a delay due to associated signaling requirements.

8.1.2.1 Free Timeslots In order to avoid passing this delay onto the CSW user, the system attempts to keep a number of timeslots free (spare CSW timeslot) for such CSW allocations. The number of timeslots kept free is dependent on cell size and whether a downgrade or an upgrade has last occurred. Table 32 shows the values implemented initially (S9).

The values used for ‘after downgrade’ in table 1 are based on a 95% probability that a further downgrade would not be required while there is already a downgrade in process.

The values used for ‘after upgrade’ have been chosen with the aim of providing a 95% probability that there will be no need for a subsequent (E)GPRS downgrade within 4 seconds of an upgrade having occurred.

No. of TRXs Free TSLs (after downgrade)

Free TSLs (after upgrade)

Mean free TSL in CSW

1 1 1 1

2 1 2 1.5

3 1 2 1.5

4 2 3 2.5

5 2 4 3

6 2 4 3

Table 32 Free timeslots retained in CSW territory (valid for GPRS rel.1)

The effect of the free timeslots is a decrease in overall cell capacity. It should be noted, however, that the free slots will be occupied when required by the circuit switched traffic load.

Therefore, when considering overall cell (or TRX) capacity, this overhead must be taken into account.

With S10.5 ED the number of free TSLs after a downgrade or an upgrade become operator modifiable parameters following the rules as explained below.

The margin of idle TCH/Fs that is required as a condition for starting a GPRS territory upgrade is defined by the BSC parameter free TSL for CS upgrade freeTSLsCsUpgrade. In fact, the parameter defines how many traffic channel radio time slots have to be left free after the GPRS territory upgrade. When defining the margin, a two-dimensional table is used. In the two-dimensional table the columns are for different amounts of available resources (TRXs) in the BTS. The rows indicate a selected time period (seconds) during which probability for an expected downgrade is no more than 5%. The operator can modify the period with the BSC parameter freeTSLsCsUpgrade. Default value for the period length is 4 seconds.


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TRXs 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Time0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 1 1 2 2 2 2 2 2 3 3 3 3 3 3 2 1 1 2 2 2 3 3 3 3 4 4 4 4 5 5 5 3 1 1 2 3 3 3 4 4 4 5 5 6 6 6 6 6 4 1 2 2 3 4 4 4 5 5 6 6 6 7 7 7 7 5 1 2 3 3 4 5 5 5 6 6 7 7 7 8 8 8 6 1 2 3 4 4 5 5 6 6 7 7 8 8 8 9 9 7 1 2 3 4 5 5 6 7 7 7 8 8 9 9 9 9 8 1 3 4 4 5 6 6 7 7 7 8 9 9 9 9 9 9 1 3 4 5 5 6 7 7 8 8 9 9 9 9 9 9 10 2 3 4 5 6 7 7 8 8 8 9 9 9 9 9 9

The operator defines the margin of idle TCHs that the BSC tries to maintain free in a BTS for the incoming circuit switched resource requests using parameter free TSL for CS downgrade freeTSLsCsDowngrade. If the number of idle TCH resources in the circuit switched territory of the BTS decreases below the defined margin, a GPRS territory downgrade is started if possible. The definition of the margin involves a two-dimensional table. One index of the table is the number of TRXs in the BTS. Another index of the table is the needed amount of idle TCHs. Actual table items are percentage values indicating probability for TCH availability during a one-second downgrade operation with the selected resource criterion. Default probability 95% can be changed through the free TSL for CS downgrade parameter freeTSLsCsDowngrade.

TRXs 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 TCH0 94 84 76 69 63 58 54 50 48 45 43 41 40 38 37 35 1 99 98 96 93 91 87 85 82 79 77 74 72 70 68 66 64 2 100 99 99 99 98 97 96 94 93 92 90 89 87 86 84 83 3 100 99 99 99 98 98 97 97 96 95 94 94 93 4 100 99 99 99 99 99 98 98 98 97 5 100 100 99 99 99 99 6 100 100 100 7 100 100 8 100% 100% 100% 100% 9 100 100

That means that if we have 4TRXs/cell and at a certain moment we have a decreased number of TSLs for example the number of idle TSLs falls to 2 the associated probability of being free is 93%, less than the threshold (95%), that means that a GPRS downgrade will be started in such a way that the idle TSLs will be 3 where the probability for them of being free will be higher than said threshold.

The values above are Nokia simulated values.

There’s another parameter to include when talking about territory and that’s is maxGPRScapacity. With this parameter we limit the number of PSW channel per BTS which could be a problem especially when introducing the segment concept due to the possibility to have a GPRS capable BTS and a EGPRS capable BTS with their separated territory parameters defined and that would lead to a capacity problem due to PCU limitation.


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The following figure shows the number of free TSLs in case of different parameter sets.

TSL number after CS downgrade

TRX number 1 2 3 4 5

70 0 0 0 1 1

95 1 1 1 2 2

99 1 1 2 2 3

TSL number after CS upgradeTRX number 1 2 3 4 5

1 0 1 1 1 2

4 1 2 2 3 4

7 1 2 3 4 5

10 2 3 4 5 6

free TSL for CS downgrade (%) (CSD)

free TSL for CS upgrade (sec) (CSU)

Figure 79 # of free TSLs with different setup

8.1.3 Territory Upgrade/Downgrade – Dynamic Variation of Timeslots

In order to facilitate dynamic variations in the CSW/(E)GPRS territories in response to changing load conditions, mechanisms have been introduced to enable upgrades/downgrades of the (E)GPRS territory to occur.

The upgrade/downgrade procedures utilize three parameters - X1, X2 and X3. These parameters are not user-configurable but are set at pre-defined values that have been identified through detailed simulations aimed at establishing the optimum values for mixed circuit-switched and (E)GPRS operation. For (E)GPRS deployment, the values for these parameters are set to 1.5, 1.0 and 0.5, respectively (hard coded values in PCU). It should be noted that some refinements might be made to functionality prior to the deployment of EGPRS services to optimize performance. The function of the above parameters is described in the following sections.

8.1.3.1 Downgrade A (E)GPRS downgrade is requested/initiated if;

• A PSW territory timeslot is blocked or it loses synchronization. o RRM attempts to upgrade and rearrange a PSW territory to the

default configuration when timeslots in the original default territory become blocked.

o If the timeslot that is carrying the synchronization master channel is blocked, RRM removes all PSW territory timeslots of the TRX.

• A TRX containing PSW territory timeslots is blocked. • More CSW resources are required and the PSW territory contains

additional or default timeslots. • CHM requests a PSW territory downgrade.

For RRM to initiate a PSW territory downgrade it is also required that the previous PSW territory operation in the BTS has been completed.

In radio cells with both GPRS and EGPRS BTSs, CHM provides RRM with information on whether an upcoming downgrade should preferably be carried out on a GPRS PSW territory or on an EGPRS PSW territory. CHM bases this preference on the BTS channel loads in the radio cell; downgrade in the territory with less channel load is preferred. This territory balance information is sent to RRM if the following conditions are met:


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• The ratio of aggregate GPRS and EGPRS BTS channel loads the lower

aggregate load divided by the higher in the radio cell is less than TERRIT_BALANCE_THRSHLD.

• The preferred territory is not the same as that indicated in the previous

territory balance information message.

• At least TERRIT_UPD_GTIME_GPRS has elapsed since the previous territory balance information message was sent.

RRM takes the territory balance information into account when it removes PSW timeslots to accommodate new CSW connections.

8.1.3.2 Upgrade A (E)GPRS upgrade is requested/initiated if;

• A blocked or out-of-synch timeslot inside a default PSW territory becomes serviceable again.

• CSW traffic situation and the operator parameter CMAX allow a PSW territory extension, and either:

o CHM requests a PSW territory upgrade. o PSW territory has less timeslots than defined for the default

territory.

For RRM to initiate a PSW territory upgrade it is also required that the previous territory operation in the BTS has been completed and idle GPRS capable resources are available in the BTS.

RRM allows PSW territory upgrades if the existing CSW connections will not be unfavorably affected and a predefined amount of idle timeslots will remain in the CSW territory as an instant reserve for new CSW connections. This margin of idle timeslots is defined by operator parameters CSU (free TSL for CS upgrade) and CSD (free TSL for CS downgrade). If the requirements for a PSW territory upgrade are met but a CSW connection occupies a timeslot, which is to be allocated to PSW, RRM initiates an intra-cell handover to find a new channel allocation for the CSW connection.

Operator parameter GTUGT (GPRS territory update guard time) defines an interval between successive territory upgrades. The purpose of this interval is to prevent constant update request from channel management functions: while the timer is running, CHM does not send an upgrade request immediately after detecting an upgrade need but waits until the next expiry of the timer and sends a request only if a territory update is still needed at that time. Also RRM observes this guard time when it initiates BTS territory configuration updates.

8.1.3.3 Territory Upgrade and Downgrade S10 Changes In S10 the segment concept has been added. Segment ID has been added to upgrade and downgrade messages. In CHM segment concept will be implemented either by adding segment ID into BTS structure or a separate segment structure is to be used.

In S10, the amount of channels in a territory is limited by maxGPRScapacity given in the upgrade message. In CHM this is taken into account as follows:


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• If the territory contains the maximum amount of channels, PCU will not request for more channels.

• When PCU requests for more channels, it will limit the number of requested channels so that gprs_maximum_capa will not be exceeded.

If an upgrade would result in more channels than maxGPRScapacity, then PCU will reject the upgrade.

In territory upgrade in S9 implementation a response to DX 200 is sent only when the upgrade was successful. In S10 in case of a failure, psw_territory_downgrade_nack_s / psw_territory_downgrade_nack_s is sent.

In S10 a new field is added to:

psw_territory_downgrade_ack_s / psw_territory_upgrade_ack_s messages:

• Egprs / Gprs territory suggestion for next downgrade

When the CHM receives upgrade/downgrade request from the RRM the CHM counts TBF amount in GPRS territories in the segment and TBF amount in EGPRS territories in the segment. Then the CHM sends in ack message to RMM the territory type with smaller TBF amount.

8.1.3.4 Multislot TSL Allocation for Using max Capability of Mobile PCU1 does not take TSL amount into account in TSl allocation, if there are less channels available than preferred allocation requires. PCU2 does it.

For example, for multislot class 6 MSs, if 3+1 allocation is the preferred allocation and there is only 2 TSLs available for allocation, in such situation PCU1 allocates 2+1 allocation but PCU2 allocates 2+2 allocation to MS. Same analogy can be found from multislot class 10 MSs. If 4+1 is the wanted allocation and only 3 TSLs are available, then PCU1 allocates 3+1 but PCU2 3+2.

8.2 Multislot Usage An MS may be allocated several PDTCH/Us or PDTCH/Ds for one mobile originated or one mobile terminated communication respectively. In this context allocation refers to the list of PDCH that may dynamically carry the PDTCHs for that specific MS. The PACCH may be mapped onto any of the allocated PDCHs. If there are m timeslots allocated for reception and n timeslots allocated for transmission, there shall be Min(m,n) reception and transmission timeslots with the same timeslot number.

For multislot class Type 1 MS (Type 1 MS are not required to transmit and receive at the same time), the following table lists the number of slots that are possible to allocate (provided that it is supported by the MS according to its multislot class) for different medium access modes (see 3GPP TS 05.02). It also indicates if Tra or Tta (see 3GPP TS 05.02 Annex B) shall be applied for measurements.


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Medium access mode No of Slots Tra shall apply

Tta shall apply

Note

Downlink, any mode 1-6 Yes - 7-8 No - 1,2 Uplink, Fixed 1-4 Yes - 5-6 - Yes 3 7-8 - No 1,2,3 Uplink, Dynamic 1-2 Yes - Uplink, Ext. Dynamic 1-3 Yes - Down + up, Fixed d+u = 2-5 Yes - d+u = 6 No No 1,2 Down + up, Dynamic d+u = 2-5 Yes - Down + up, Ext. Dynamic d+u = 2-4 Yes - d+u = 5, d > 1 Yes - Note 1 Normal measurements are not possible (see 3GPP TS 05.08). Note 2 Normal BSIC decoding is not possible (see 3GPP TS 05.08). Note 3 Normal PACCH reception not possible (see 3GPP TS 04.60)

Table 33 Possible allocations in multislot usage

When an MS supports the use of multiple timeslots it shall belong to a multislot class as defined below:

Multislot class

Maximum number of slots Minimum number of slots Typ e

Rx Tx Sum T ta Ttb Tra Trb 1 1 1 2 3 2 4 2 1 2 2 1 3 3 2 3 1 1 3 2 2 3 3 2 3 1 1 4 3 1 4 3 1 3 1 1 5 2 2 4 3 1 3 1 1 6 3 2 4 3 1 3 1 1 7 3 3 4 3 1 3 1 1 8 4 1 5 3 1 2 1 1 9 3 2 5 3 1 2 1 1 10 4 2 5 3 1 2 1 1 11 4 3 5 3 1 2 1 1 12 4 4 5 2 1 2 1 1 13 3 3 NA NA a) 3 a) 2 14 4 4 NA NA a) 3 a) 2 15 5 5 NA NA a) 3 a) 2 16 6 6 NA NA a) 2 a) 2 17 7 7 NA NA a) 1 0 2 18 8 8 NA NA 0 0 0 2 19 6 2 NA 3 b) 2 c) 1 20 6 3 NA 3 b) 2 c) 1 21 6 4 NA 3 b) 2 c) 1 22 6 4 NA 2 b) 2 c) 1 23 6 6 NA 2 b) 2 c) 1 24 8 2 NA 3 b) 2 c) 1 25 8 3 NA 3 b) 2 c) 1 26 8 4 NA 3 b) 2 c) 1 27 8 4 NA 2 b) 2 c) 1 28 8 6 NA 2 b) 2 c) 1 29 8 8 NA 2 b) 2 c) 1

Details can be found in 3GPP TS 05.02 Annex B.

In Nokia S11 and S11.5 max 4 tsl downlink, max 2 tsl uplink are supported.


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8.2.1 Average Window Size

For EGPRS the window size (WS) shall be set by the network according to the number of timeslots allocated in the direction of the TBF (uplink or downlink). The allowed window sizes are shown in Table 34. Preferably, the selected window size should be the maximum.

Timeslots allocated (Multislot capability) Window size

Coding 1 2 3 4 5 6 7 8

64 00000 96 00001 128 00010 160 00011 192 00100 Max 224 00101 256 00110 Max 288 00111 320 01000 352 01001 384 01010 Max 416 01011 448 01100 480 01101 512 01110 Max 544 01111 576 10000 608 10001 640 10010 Max 672 10011 704 10100 736 10101 768 10110 Max 800 10111 832 11000 864 11001 896 11010 Max 928 11011 960 11100 992 11101

1024 11110 Max Reserved 11111 x x x x x x x X

Table 34 Max Window Size vs. multislot usage

The window size may be set independently on uplink and downlink. MS shall support the maximum window size corresponding to its multislot capability. The selected WS shall be indicated within PACKET UL/DL ASSIGNMENT and PACKET TIMESLOT RECONFIGURE using the coding defined in the Table 34.

Once a window size is selected for a given MS, it may be changed to a larger size but not to a smaller size, in order to prevent dropping data blocks from the window.

If the MS multislot class is not indicated during the packet data connection establishment (short access, access request for signaling message transfer), then a default window size (corresponding to the minimum window size for 1 timeslot) shall be selected.

8.3 High Multislot Class (HMC) High Multislot Classes increases GPRS/EDGE peak downlink throughput to 296 kbit/s.

3GPP release 4 or earlier MSs are limited to combined downlink and uplink timeslot sum of 5.

3GPP release 5 (TS 45.002) introduces new MS multislot classes which allow sum of downlink and uplink timeslots of 6


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• New maximum allocation configurations

• Downlink + uplink: 5+1 and 4+2

• With Extended Dynamic Allocation Application Software

• Downlink + uplink: 3+3 and 2+4


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9. Mobility The aim of mobility optimization is to reduce the cell-outage time during cell-reselection. The cell-outage time depends on the type of cell-reselection. It can be:

o intra-PCU / inter-PCU

o RAU cell-reselection

o Inter PAPU and Inter SGSN

This chapter below contains the description of cell-reselection types, Cell-reselect Hysteresis and Network Assisted Cell Change (NACC) as well.

9.1 Intra/Inter PCU Cell Re-selection The intra and inter PCU cell-reselection events and measurements are described below.

9.1.1 BSS and Data Outage

The cell-reselection events without LA/RA Update are listed below:

1. Mobile station (MS) is camped on Cell A and it notices a better Cell B

2. MS abnormally stops all the temporary block flow sessions (TBFs) from Cell A. (The network has no idea what is happening.)

3. MS camps on the new Cell B and reads system information (SI) messages

4. When MS has successfully read the SI messages, it asks for a channel and resources by sending CHANNEL REQUEST message for cell update and packet resource request message (Note: 2phase access for EDGE phone on CCCH)

5. PCU responds with an immediate assignment message and packet uplink assignment message respectively.

6. SGSN recognizes TLLI (in the packet resource request message) and understands that a cell reselection occurred and it sends Flush LLC packet data unit to the PCU. Note: The MS data stored in Cell A buffer is kept in the PCU buffer if Cell A and Cell B belong to the same PCU otherwise it is deleted and has to be retransmitted.

7. PCU sends an acknowledgement (FLUSH-LLC-ACK) to the SGSN.

8. SGSN sends an LLC PDU to the PCU.

9. PCU sends downlink assignment message for DL TBF establishment on PACCH.

10. Data transfer resumes

In the analysis we separated the BSS cell-reselection outage from data outage.


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9.1.1.1 BSS Cell-reselection outage It is the time it takes a mobile phone to synchronize to the target cell and establish an UL TBF in that target cell during cell reselection.

o In the measurements the first time stamp is taken for the first system information message after the last RCL/MAC block

o The last time is the time stamp from the packet uplink assignment

9.1.1.2 Data outage The cell reselection outage is the period after the last RLC/MAC block transmission in the old cell and the first payload DL RLC block transmission at the target cell.

o First time stamp is taken from the first system information message after the last RCL/MAC block transmitted.

o The last time is the time stamp from the packet downlink assignment.

The following figures show the cell-reselection process on signaling in case of FTP download.

MS BTS BSC SGSN



P_Channel Required


UL TBF ASSIGNMENT, MS ON CCCH. 2 phase access [ 2].

Packet Resource Request (PACCH) Packet Resource Request




LLC PDUDL TBF Establishment when UL TBF is ongoing [ 3]


Packet Downlink Assignment




RLC Data blocks (PDTCH)RLC Data blocks

Cel

l Res

elec

tion

BS

S O

utag

e

Packet downlink dummy control blocksPacket downlink dummy control blocks

Cel

l res

elec

tion

dat

a O

utag

e





P_Channel Required



Packet Resource Request (PACCH) Packet Resource Request




LLC PDUDL TBF Establishment when UL TBF is ongoing [ 3]


Packet Downlink Assignment




RLC Data blocks (PDTCH)RLC Data blocks

Cel

l Res

elec

tion

BS

S O

utag

e

Packet downlink dummy control blocksPacket downlink dummy control blocks

Cel

l res

elec

tion

dat

a O

utag

e


Figure 80 Cell-selection procedures for download


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Event name Time Channel MessageRLC/MAC Uplink 20:42.0 PACCH "EGPRS_PACKET_DOWNLINK_ACK/NACK"Layer 3 Downlink 20:42.0 BCCH "SYSTEM_INFORMATION_TYPE_1"Layer 3 Downlink 20:42.0 BCCH "SYSTEM_INFORMATION_TYPE_2"Layer 3 Downlink 20:42.0 BCCH "SYSTEM_INFORMATION_TYPE_3"Layer 3 Downlink 20:42.0 BCCH "SYSTEM_INFORMATION_TYPE_4"… … … …Layer 3 Downlink 20:42.6 BCCH "SYSTEM_INFORMATION_TYPE_4"Cell Reselection 20:42.8 from CI 5032 to CI 5033Layer 3 Downlink 20:42.8 BCCH "SYSTEM_INFORMATION_TYPE_2"… … … …

Layer 3 Downlink 20:43.1 BCCH "SYSTEM_INFORMATION_TYPE_13"Layer 3 Uplink 20:43.1 RACH "CHANNEL_REQUEST"Layer 3 Downlink 20:43.2 CCCH "IMMEDIATE_ASSIGNMENT"Layer 3 Downlink 20:43.2 CCCH "PAGING_REQUEST_TYPE_1"Layer 3 Downlink 20:43.2 CCCH "PAGING_REQUEST_TYPE_1"Layer 3 Downlink 20:43.3 CCCH "PAGING_REQUEST_TYPE_1"Layer 3 Downlink 20:43.3 BCCH "SYSTEM_INFORMATION_TYPE_2"… … … …

Layer 3 Downlink 20:43.8 BCCH "SYSTEM_INFORMATION_TYPE_13"RLC/MAC Uplink 20:43.8 PACCH "PACKET_RESOURCE_REQUEST"RLC/MAC Downlink 20:44.0 PACCH "PACKET_UPLINK_ASSIGNMENT"RLC/MAC Downlink 20:44.0 PACCH "PACKET_DOWNLINK_DUMMY_CONTROL_BLOCK"RLC/MAC Downlink 20:44.0 PACCH "PACKET_DOWNLINK_DUMMY_CONTROL_BLOCK"… … … …

RLC/MAC Downlink 20:44.2 PACCH "PACKET_DOWNLINK_DUMMY_CONTROL_BLOCK"RLC/MAC Downlink 20:44.2 PACCH "PACKET_DOWNLINK_ASSIGNMENT"RLC/MAC Uplink 20:44.3 PACCH "EGPRS_PACKET_DOWNLINK_ACK/NACK"

Table 35 Layer3 and RLC/MAC messages from Nemo TOM for download

The following figures show the cell-reselection process on signaling in case of FTP upload.

MS BTS BSC SGSN



P_Channel Required





RLC Data block (PDCH)


RLC Data Block


NOTE: BTS does not send Imm Ass Ackfor Single block Immediate Assignment





Uplink Data Packets

BS

S/D

ata

Cel

l Res

elec

tion

Out

age





P_Channel Required





RLC Data block (PDCH)


RLC Data Block


NOTE: BTS does not send Imm Ass Ackfor Single block Immediate Assignment





Uplink Data Packets

BS

S/D

ata

Cel

l Res

elec

tion

Out

age



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Figure 81 Cell-selection procedures for upload

Event name Time Channel MessageRLC/MAC Uplink 20:42.0 PACCH "EGPRS_PACKET_DOWNLINK_ACK/NACK"Layer 3 Downlink 20:42.0 BCCH "SYSTEM_INFORMATION_TYPE_1"Layer 3 Downlink 20:42.0 BCCH "SYSTEM_INFORMATION_TYPE_2"Layer 3 Downlink 20:42.0 BCCH "SYSTEM_INFORMATION_TYPE_3"Layer 3 Downlink 20:42.0 BCCH "SYSTEM_INFORMATION_TYPE_4"… … … …

Layer 3 Downlink 20:42.6 BCCH "SYSTEM_INFORMATION_TYPE_4"Cell Reselection 20:42.8 from CI 5032 to CI 5033Layer 3 Downlink 20:42.8 BCCH "SYSTEM_INFORMATION_TYPE_2"… … … …

Layer 3 Downlink 20:43.1 BCCH "SYSTEM_INFORMATION_TYPE_13"Layer 3 Uplink 20:43.1 RACH "CHANNEL_REQUEST"Layer 3 Downlink 20:43.2 CCCH "IMMEDIATE_ASSIGNMENT"Layer 3 Downlink 20:43.2 CCCH "PAGING_REQUEST_TYPE_1"Layer 3 Downlink 20:43.2 CCCH "PAGING_REQUEST_TYPE_1"Layer 3 Downlink 20:43.3 CCCH "PAGING_REQUEST_TYPE_1"Layer 3 Downlink 20:43.3 BCCH "SYSTEM_INFORMATION_TYPE_2"… … … …

Layer 3 Downlink 20:43.8 BCCH "SYSTEM_INFORMATION_TYPE_13"RLC/MAC Uplink 20:43.8 PACCH "PACKET_RESOURCE_REQUEST"RLC/MAC Downlink 20:44.0 PACCH "PACKET_UPLINK_ASSIGNMENT"RLC/MAC Downlink 20:44.0 PACCH "PACKET_DOWNLINK_DUMMY_CONTROL_BLOCK"

Table 36 Layer3 and RLC/MAC messages from Nemo TOM for upload

9.1.2 Benchmark Results The following table shows the BSS outage and Data Outage in case of intra and inter PCU cell-reselection.

Diff. Between BSS andtill Packet Uplink Assign. (ms) till Packet Downlink Assign. (ms) full cell-outage (ms)

2.07 2.341 0.273.07 3.349 0.282.09 2.354 0.262.10 2.358 0.262.09 2.375 0.282.11 2.393 0.282.10 2.658 0.562.09 2.355 0.262.11 2.395 0.282.10 2.38 0.286.00 6.254 0.262.12 2.379 0.26

2.094 2.629 0.542.09 2.631 0.542.14 2.7 0.562.07 4.011 1.942.10 2.379 0.282.10 2.385 0.28

average 2.37 2.80 0.43

From EGPRS PACKET DOWNLINK ACK/NACK

Table 37 Cell-reselection measurement results from Nemo TOM


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The results show that the BSS cell outage is almost same both in intra and inter PCU cells, but the data outage on downlink, where the Packet Downlink Assignment is needed based on LLC PDU from the SGSN, is half a ms longer.

9.2 LA /RA Cell-reselection The RA cell-reselection events and measurements are described below.

9.2.1 Data Outage

The cell-reselection events without RA Update are listed below:

1. MS is camped on Cell A and it notices a better Cell B

2. MS abnormally stops all the temporary block flow sessions (TBFs) from Cell A.

3. MS camps on the new Cell B and reads system information (SI) messages

4. When it has successfully read the SI messages, MS sends CHANNEL REQUEST message for location area update.

5. An SDCCH channel is created for this purpose.

6. MS then sends location area update

7. Security functions set by the operator take place.

8. When authentication is complete the SDCCH channel is released

9. Routing area update request is sent to the network

10. A channel and resources are requested for routing area update (Note: 2phase access for EDGE phone on CCCH)

11. When granted network sends routing area update accept to MS

12. And the MS acknowledges receipt of this message by sending routing area update complete

In the analysis we separated the Location Area Update, Routing Area Update and LA/RA Update BSS cell-reselection from each other.

9.2.1.1 Location Area Update The LAU time is the period between Channel_Request and Channel_Release for LAU.

o First time stamp is taken from the Channel_Request for LAU

o The last time is the time stamp from Channel_Release after Location_Updating_Accept message.

9.2.1.2 Routing Area Update o First time stamp is taken from the Routing_Area_Request

o The last time is the time stamp from Routing_Area_Update_Complete

9.2.1.3 Data outage (LA/RA Update)


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o First time stamp is taken from the first system information message after the last RCL/MAC block transmitted.

o The last time is the time stamp from Routing_Area_Update_Complete

The following figures show the cell-reselection process with RAU on signaling.

MS BTS BSC New SGSN

DL TBF ASSIGNMENT










P_Channel Required







Cel

l res

elec

tion

dat

a O

utag

e



DL TBF ASSIGNMENT










P_Channel Required







Cel

l res

elec

tion

dat

a O

utag

e


Figure 82 LA / RA Cell-selection procedures


16/12/2008


Event name Time Channel Message

… … … …

Layer 3 Downlink 8:44:05.801 BCCH "SYSTEM_INFORMATION_TYPE_1"… … … …Layer 3 Downlink 8:44:10.797 BCCH "SYSTEM_INFORMATION_TYPE_13"Cell Reselection 8:44:10.906 from 5691 to 5753Layer 3 Downlink 8:44:11.018 BCCH "SYSTEM_INFORMATION_TYPE_2"… … … …

Layer 3 Uplink 8:44:11.997 RACH "CHANNEL_REQUEST"Layer 3 Downlink 8:44:12.101 CCCH "IMMEDIATE_ASSIGNMENT"Layer 3 Uplink 8:44:12.313 SDCCH "LOCATION_UPDATING_REQUEST"Layer 3 Downlink 8:44:12.353 SACCH "SYSTEM_INFORMATION_TYPE_6"Layer 3 Uplink 8:44:12.388 SACCH "MEASUREMENT_REPORT"Layer 3 Uplink 8:44:12.548 SDCCH "CLASSMARK_CHANGE"Layer 3 Downlink 8:44:12.764 SDCCH "CIPHERING_MODE_COMMAND"Layer 3 Uplink 8:44:12.784 SDCCH "GPRS_SUSPENSION_REQUEST"Layer 3 Uplink 8:44:13.020 SDCCH "CIPHERING_MODE_COMPLETE"Layer 3 Downlink 8:44:13.224 SDCCH "IDENTITY_REQUEST"Layer 3 Uplink 8:44:13.350 SACCH "MEASUREMENT_REPORT"Layer 3 Uplink 8:44:13.490 SDCCH "IDENTITY_RESPONSE"Layer 3 Downlink 8:44:13.697 SDCCH "LOCATION_UPDATING_ACCEPT"Layer 3 Uplink 8:44:13.799 SACCH "MEASUREMENT_REPORT"Layer 3 Downlink 8:44:14.168 SDCCH "MM_INFORMATION"Layer 3 Uplink 8:44:14.284 SACCH "MEASUREMENT_REPORT"Layer 3 Downlink 8:44:14.399 SDCCH "CHANNEL_RELEASE"… … … …

Layer 3 Uplink 8:44:16.258 PDTCH "ROUTING_AREA_UPDATE_REQUEST"… … … …

Layer 3 Uplink 8:44:16.752 RACH "CHANNEL_REQUEST"Layer 3 Downlink 8:44:16.829 CCCH "IMMEDIATE_ASSIGNMENT"… … … …

Layer 3 Uplink 8:44:16.258 PDTCH "ROUTING_AREA_UPDATE_REQUEST"RLC/MAC Uplink 8:44:17.401 PACCH "PACKET_RESOURCE_REQUEST"RLC/MAC Downlink 8:44:17.607 PACCH "PACKET_UPLINK_ASSIGNMENT"… … … …

RLC/MAC Downlink 8:44:17.886 PACCH "PACKET_DOWNLINK_ASSIGNMENT"… … … …

Layer 3 Downlink 8:44:18.950 PDTCH "ROUTING_AREA_UPDATE_ACCEPT"Layer 3 Uplink 8:44:18.964 PDTCH "ROUTING_AREA_UPDATE_COMPLETE"RLC/MAC Uplink 8:44:19.119 PACCH "EGPRS_PACKET_DOWNLINK_ACK/NACK"

… … … …

Table 38 Layer3 and RLC/MAC messages from Nemo TOM

9.2.2 Benchmark Results

The next table shows the RAU cell-reselection results.


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Time to LAC [sec.] Time for RAC [sec.] Full LAU/RAU [sec.]4.056 3.37 10.2272.808 3.15 8.7853.886 2.99 9.613.813 2.96 9.5733.814 3.53 10.1462.888 2.925 8.6022.922 2.949 8.6173.042 2.953 8.6182.868 2.637 8.3263.048 2.955 8.8323.82 2.10 8.635

2.865 3.32 8.82.811 2.95 8.6181.045 3.301 11.0882.918 2.953 8.616

average 3.11 3.00 9.14

Table 39 LA / RA Cell-reselection measurement resul ts from Nemo TOM

9.3 Cell-reselect Hysteresis Path loss criteria and timings for cell reselection:

The MS is required to perform the following measurements (see 3GPP TS 03.22) to ensure that the path loss criterion to the serving cell is acceptable.

At least every 5 s the MS shall calculate the value of C1 and C2 for the serving cell and re-calculate C1 and C2 values for non-serving cells (if necessary). The MS shall then check whether:

i) The path loss criterion (C1) for current serving cell falls below zero for a period of 5 seconds. This indicates that the path loss to the cell has become too high.

ii) The calculated value of C2 for a non-serving suitable cell exceeds the value of C2 for the serving cell for a period of 5 seconds, except;

a) in the case of the new cell being in a different location area or, for a GPRS MS, in a different routing area or always for a GPRS MS in ready state in which case the C2 value for the new cell shall exceed the C2 value of the serving cell by at least CELL_RESELECT_HYSTERESIS dB as defined by the BCCH data from the current serving cell, for a period of 5 seconds; or

b) in case of a cell reselection occurring within the previous 15 seconds in which case the C2 value for the new cell shall exceed the C2 value of the serving cell by at least 5 dB for a period of 5 seconds.

This indicates that it is a better cell.

Cell reselection for any other reason (see 3GPP TS 03.22) shall take place immediately, but the cell that the MS was camped on shall not be returned to within 5 seconds if another suitable cell can be found. If valid RLA_C values are not available, the MS shall wait until these values are available and then perform the cell reselection if it is still required. The MS may accelerate the measurement procedure within the requirements in sub clause 6.6.1 to minimize the cell reselection delay.


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If no suitable cell is found within 10 seconds, the cell selection algorithm of 3GPP TS 03.22 shall be performed. Since information concerning a number of channels is already known to the MS, it may assign high priority to measurements on the strongest carriers from which it has not previously made attempts to obtain BCCH information, and omit repeated measurements on the known ones.

A GPRS MS in Ready state applies the READY_STATE CELL RESELECTION HYSTERESIS together with the path loss criterion when reselecting the cell within the registration area. The GPRS MS in Ready state shall inform the network about cell reselection within the registration area by the cell update procedure.

So if the terminal is not in ready state, then the cell reselect hysteresis is used only between RAUs. It can modify the results of this test.

9.4 Network Assisted Cell Change 3GPP specified Network Assisted Cell Change (NACC) procedure is enhancement to NCCR (NACC can work also without NCCR). NACC specifies procedures for network to send target cell system information prior to actual cell change. This reduces the data transmission break time during the cell change procedure.

NACC feature aims on reduce of service outage time for all QoS classes when a GPRS MS in packet transfer mode moves between GSM cells. NACC aims at reducing this packet data transfer outage time from seconds down to 300 msec – 1 sec, depending on the other features used.

Assistance is given by sending the specific set of neighbour cell (target cell) system information to certain MS during the cell change procedure while it’s still locating the serving cell.

When NCCR has triggered and NACC has been applied, PCU commands MS to target cell. The procedures in the MS and in the target PCU continue as if the cell reselection would have been triggered the MS.

The following figure shows the signaling flow of NACC:


16/12/2008



Network does not order the cell change until:

• PSI information regarding target cell is provided in serving cell

•PSI STATUS is supported in the target cell

•The service outage is only 300 - 700 ms


PACCH

Packet Enhanced Measurement Report

MS Serving cell

PACCH

Packet Cell Change Order

T3174 starts

Target cell



PRACH

PAGCH

Packet Neighbour Cell Data 1

Packet Neighbour Cell Data n


PACCH

PACCH

T3174 stops

PACKET SI STATUS


Network does not order the cell change until:

• PSI information regarding target cell is provided in serving cell

•PSI STATUS is supported in the target cell

•The service outage is only 300 - 700 ms


PACCH


MS Serving cell

PACCH


T3174 starts

Target cell



PRACH

PAGCH




PACCH

PACCH

T3174 stops


PACCH


MS Serving cell

PACCH


T3174 starts

Target cell



PRACH

PAGCH




PACCH

PACCH

T3174 stops

PACKET SI STATUS

Figure 83 NACC signaling flow

The PCU that commanded the cell reselection determines the success of the cell reselection from the MS and SGSN behavior. Existing abnormal release procedure with NCCR specific counters is used to stop TBF scheduling. Reserved resources are released when flush is received from SGSN or packet cell change timer expires.

If the MS fails to connect to the commanded cell it will send failure message and the operation will continue in the old cell.

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