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(E)GPRS Radio Networks Optimization GuidelinesVersion 2.0 DRAFT
(E)GPRS Radio Networks Optimization Guidelines v1.1.2 DRAFTOwner:(E)GPRS Program - Ville Salomaa
Scope:EDGE Radio Networks - Optimization
Originator:OS / OSP
Status:Version 2.0 DRAFT
Document ID:
Location:
Change History
IssueDateHandled byComments
1.024.11.2004Pal Szabadszallasi
2.0
Approved by
Ville Salomaa
41.Introduction
1.1BSS Optimization Approach51.2Parameters and Features Having Main Impact on Network Performance62.Configuration, Parameter and Feature Audit72.1BSS Configuration and Parameter Audit82.1.1Area and Network Element Audit82.1.2RF Deployment and PSW Parameter Audit92.1.3BSC and PCU and Flow Control Parameter Audit102.1.4HLR Setting Audit112.2BSS Feature Audit123.Performance Audit143.1OSS KPI Analysis143.1.1Network Doctor153.1.2NetAct Reporter153.2Field Tests153.3Real-Time Protocol Testing153.4Application Testers163.5Post-Processing Tools164.GSM Coverage and Quality Optimization174.1(E)GPRS Coverage Area Estimation and Maximization174.1.1Signal Level vs. TSL Data Rate174.1.2Interference vs. TSL Data Rate184.1.3Signal Level and Interference vs. TSL Data Rate194.2Site Arrangement204.3Frequency Plan204.4Optimal GSM Network for PSW Services205.(E)GPRS BSS Optimization215.1Signaling Capacity Improvement215.1.1Air Interface Signaling215.1.1.1PCH (NMO II)215.1.1.2PCH (NMO I)225.1.1.3AGCH235.1.1.4RACH255.1.1.5SDCCH255.1.1.6Parameters265.1.1.7Features275.1.2TRXSIG295.1.3PCU295.1.4BCSU305.1.5MM and SM Signaling305.2Resource Allocation Improvement315.2.1PSW Activation and Territory Settings315.2.1.1Parameters315.2.1.2Measurements KPIs325.2.2Cell (Re)-Selection345.2.2.1C1 and C2 and HYS345.2.2.2C31/32355.2.2.3Cell re-selection Measurements (NC_0)365.2.3NCCR375.2.3.1NCCR Criteria385.2.3.2NCCR Power Budget385.2.3.3NCCR Quality Control (PCU1)385.2.3.4NCCR Parameters with Power Budget and Quality Control425.2.3.5Cell re-selection Measurements (NC_2)435.2.4BTS Selection in Segment (MultiBCF and CBCCH without EQoS)445.2.4.1Parameters445.2.4.2Measurements445.2.5Scheduling (TSL Selection with Priority based QoS)455.2.5.1Parameters455.2.5.2Measurements465.2.6DAP Resource Allocation in PCU1475.2.7Cell, BTS and TSL Selection with EQoS485.3E2E Data Rate Maximization495.3.1Connectivity Capacity Optimization (BSS)495.3.1.1Connectivity Limits in PCU495.3.1.2Connectivity Limits in SGSN and PAPU (SG4)505.3.1.3Connectivity Capacity Optimization Maximized Capacity505.3.1.4Connectivity Capacity Optimization Maximized Data Rate515.3.1.5Connectivity Limit related Measurements - KPIs515.3.2RLC/MAC TSL Data Rate Maximization535.3.2.1TSL Utilization545.3.2.2TBF Release Delay, TBF Release Delay Ext and BS_CV_MAX565.3.2.3GPRS Link Adaptation595.3.2.4EGPRS Link Adaptation615.3.2.5Multiplexing635.3.2.6UL Power Control665.3.3Multislot Usage Maximization685.3.4End-to-End Data Rate Maximization715.3.4.1HLR Settings715.3.4.2Flow Control735.3.4.3TCP/IP745.3.4.4Applications755.3.4.5Measurements775.4Mobility Optimization785.4.1Cell-reselection without LA/RA Update (Intra/Inter PCU)795.4.2Cell-reselection with LA/RA Update845.4.2.1Cell-reselection with uncombined LA/RA Update845.4.2.2Cell-reselection with combined RAU (NMO1, Gs interface required)875.4.3Cell-reselections with Inter PAPU875.4.4Cell-reselections with Inter SGSN875.4.5Cell-reselect Hysteresis885.4.6PCU Balancing895.4.7LA/RA Design915.4.8NACC92
1. Introduction
The purpose of EDGE Radio Networks Optimization Guidelines is to describe the (E)GPRS BSS Network Optimization requirements and activities.
The form of this document is same as a closing report of Optimization Projects, so the same structure with the same topics can be used as reference for EGPRS optimization projects.
This document is part of EDGE Radio Networks planning document set, which is separated on the following way:
- EDGE Radio Networks Planning Theory
- EDGE Radio Networks Dimensioning and Planning Guidelines
- EDGE Radio Networks Optimization Guidelines
These documents are strongly linked to each other, thus the separated usage is not recommended.
(E)GPRS BSS optimization contains BSS network elements such as air interface, EDAP and PCU, therefore the RLC/MAC layer is investigated only in the (E)GPRS protocol stack. See RLC/MAC layer between mobile and BSC/PCU in Figure 1 below.
Figure 1 (E)GPRS protocol stack
This version of the Optimization Guidelines is based on S11.5 BSS software with PCU1.
The simulation and measurement results in the document were gathered from Nokia Test Network, operators test and live networks.
1.1 BSS Optimization Approach
The (E)GPRS BSS network optimization approach can be seen in Figure 2 below:
Figure 2 (E)GPRS Optimization steps
There is lot of references to 3GPP Specifications in the document. The specifications can be found at the following intranet location:
http://srss.research.nokia.com/orgs/3gpp/specs.htm1.2 Parameters and Features Having Main Impact on Network PerformanceGood to have this list. Still, I am missing a more consistent division into Quick and Dirty optimization activities and Really complete, going for 100% activities The following items have the main impact on (E)GPRS network performance: GSM signal level and interference
Resource Allocation
CS and PSW traffic volume and allocation (TRP, BFG)
GENA / EGENA settings
CDEF, CDED and CMAX settings
Connectivity Limits
PCU limits (CDEF and DAP)
RLC/MAC TSL and multislot data rate
TBF Release Delay, TBF Release Delay Ext and BS_CV_MAX
Link Adaptation (MCA) Multislot usage
E2E data rate Flow control parameters and utilization (link size) TCP/IP settings (TCP window, TCP buffer, MCU, MSS) Applications (terminal type, application type)
Mobility (cell outage)
Proper PCU and LA/RA design
NACC
2. Configuration, Parameter and Feature Audit
This chapter contains the description of the BSS configuration, parameter and feature audit.
The Figure 3 is an example to introduce the end-to-end network configuration.
Figure 3 End-to-end network configuration
2.1 BSS Configuration and Parameter Audit
The aim of this chapter is to summarize the initial configuration of the sites involved in optimization project. The OSS Radio Manager and MML commands are used to obtain the parameter information. More information related to parameters is available from [2]. The chapter is organized in the following sections:
Area and network element information
RF configuration and PSW parameters
BSC, PCU parameters HLR setting2.1.1 Area and Network Element Audit
The following information should be collected related to area:
Area size
# of sites
# of cells, segments
# of cells, segments / site
The above information gives picture about built in capacity situation.
Average distance among sites
Antenna types
Average antenna height
Frequency bands
Reuse factors
The information above shows the signal and interference situation in general.
The following information should be collected related to network element types and software:
BSC types
PCU types
BTS types
BSC SW
BTS SW
The BSC, PCU and BTS hardware and SW limits can be checked by the information above.
The following information should be collected related to the volume of network element and connectivity usage of network elements:
# of BSCs
# of PCU/BSC ratio
# of BCF/PCU ratio
# of Cells/PCU
# of Abis TSLs/PCU
# of DAP/PCU
Average DAP size/BCF
# of Gb TSLs (64 kbps)/PCU
The connectivity limits can be estimated based on the list above.
The following information should be collected related to terminals used in the network:
Ratio of AMR capable terminals
Ratio of R97, R98, R99, R4 capable terminals
Ratio of the different tsl capability terminals (like 1+2, 2+4, etc)
The capacity requirements and feature possibilities can be analyzed by the list above.
2.1.2 RF Deployment and PSW Parameter Audit
The following issues (planning approaches, parameter settings) can be investigated on air interface:
Cell, segment structure: MultiBCF and CBCCH usage
Deployment options
Idle mode related parameters like Cell-reselect hysteresis, Rx Lev Access Min, C1, C2 related parameters and C31/32 related parameters
RF related parameters:
GENA, EGENA
TRP, BFG
TRP, BFG (S11 onwards)
CMAX
CDEF
CDED
TERRIT_UPD_GTIME_GPRS
FREE TSL FOR CS DOWNGRADE
FREE TSL FOR CS UPGRADE
MAXIMUM NUMBER OF DL TBF
MAXIMUM NUMBER OF UL TBF
MultiBCF and CBCCH: NBL, DIRE, LSEG, GPU, GPL
2.1.3 BSC and PCU and Flow Control Parameter Audit
The following PCU, PAFILE and PRFILE parameters must be investigated:
GPRS Link Adaptation related parameters: DLA, ULA, CODH, COD, DLBH, ULBH, DLB, ULB
GPRS Link Adaptation related parameters (PCU2): CS34, DCSA, UCSA, DCSU, UCSU
EGPRS Link Adaptation related parameters: ELA, MCA, BLA, MBG, MBP
Priority based QoS: SSS parameters
UL Power Control: ALPHA, GAMMA, IFP, TFP
DL_TBF_RELEASE_DELAY UL_TBF_RELEASE_DELAY
UL_TBF_RELEASE_DELAY_EXT
UL_TBF_SCHED_RATE_EXT
BS_CV_MAX
GPRS_UPLINK_PENALTY
GPRS_UPLINK_THRESHOLD
GPRS_DOWNLINK_PENALTY
GPRS_DOWNLINK_THRESHOLD
EGPRS_UPLINK_PENALTY
EGPRS_UPLINK_THRESHOLD
EGPRS_DOWNLINK_PENALTY
EGPRS_DOWNLINK_THRESHOLD
FC_R_DIF_TRG_LIMIT FC_MS_R_DEF FC_MS_R_DEF_EGPRS FC_MS_R_MIN FC_MS_B_MAX_DEF FC_MS_B_MAX_DEF_EGPRS FC_R_TSL FC_R_TSL_EGPRS FC_B_MAX_TSL FC_B_MAX_TSL_EGPRS NCCR_STOP_DL_SCHEDULING NCCR_STOP_UL_SCHEDULING NCCR_NON_DRX_PERIOD NCCR_MEAS_REPORT_TYPEThe detailed description of the above parameters can be found in [2].2.1.4 HLR Setting Audit
The following QoS settings have impact on BSS performance, so it must be checked:
Reliability class = 3
Traffic Class (TC) = Interactive
RLC mode = Acknowledged
THP = 1
ARP = 1
SDU error ratio = 10^-4
Maximum Bitrate = 2048 kbps
Transfer delay = 1000ms
2.2 BSS Feature Audit
All the CSW and PSW BSS features that are impacting the PSW traffic are explained in this chapter.
Idle mode settings and Directed Retry
If there is real TCH congestion in the accessed cell, then a Directed Retry due to congestion with or without queuing will be made. If there are TCHs available in accessed cell, then BSC will act according to the direct access criteria usage/determination (C/I evaluation) and cell load. BB and RF Hopping
BB and RF hopping can be used to spread the interference among the cells evenly. So the areas with very bad C/I parameters will be improved, while the areas with very good C/I figures will be decreased a bit.
Different layers can have different hopping policy, therefore the appropriate layer selection is important to maximize the (E)GPRS data rate.
If EDGE and non-EDGE TRXs are mixed in same BTS, BB Hopping requires segment solution and own hopping groups. (EDGE cannot move to non-EDGE TRX). MultiBCF and Common BCCH
The most appropriate layer can be selected by MultiBCF and CBCCH features, so the separation of GPRS from EGPRS is working properly.
FR / HR / DR / AMR
Each radio time slot of the BTS TRX can be configured to be a FR, HR, or dual rate (DR) TCH. In the case of dual rate, the BSC dynamically allocates the idle radio time slot either for half rate or full rate coding on a call basis.The CSW calls will be allocated to FR firstly.
More timeslots are available for (E)GPRS traffic without more hardware (Increased average (E)GPRS total cell throughput for all users and improved probability for occasional high bit rate services for individual end users).
The drawback is a slight decrease in the speech quality using AMR half rate when compared to AMR full rate in very bad C/I environment. So smaller coverage is expected for AMR calls in low C/I networks.
The FRL, FRU, HRL and HRU parameters are based on available full rate TCH resource (not including signaling and GPRS territory - dedicated and default territory or DR RTSLs). The half rate is allocated before the CS traffic starts to use the GPRS territory (if FRL, FRU, HRL and HRU are set accordingly). In essence the GPRS territory is safeguarded to some degree. However in severe congestion, unoccupied dual rate timeslots can still be allocated to GPRS. HSCSD
CSW data has priority over PSW traffic without EQoS. Therefore the analysis of HSCSD traffic behavior is important.
Extended Cell
ETRX cannot carry (E)GPRS TCHs in extended cell, but NTRX is able to handle it. Extended Cell can be used only with the BTS software BTS 1063 Extended cell radius. Extended Cell feature in UltraSite is available from S11.5 only.
Intelligent Underlay Overlay
The IUO feature enables definition of super layer and regular layers by defining TRXs as such, i.e. trxFrequencyType=1 for a super TRX. IUO does not support (E)GPRS. Priority based QoS
The users can be prioritized, so the users with higher priority will have more allocations to Air interface. The Priority based QoS cannot be used for guarantied services, because it is prioritizing the available resources only.
However, Priority QoS is only way to differentiate BSS statistics based on services. So cell level statistics (from BSS) are available compared to network level based server statistics.
EQoS
Enhanced Quality of Service will be available with PCU2 and described in the next version of this document.
NMO1
NMO1 with Gs interface allows to have combined RAU, so the cell-reselection is faster (SDCCH is not required). Clarify that it is LU which does not take place, not RAU that does not need SDCCH NCCR
Network Controlled Cell Reselection helps to allocate terminals more effectively to those resources, where the data rate can be maximized.
CS1-4
CS1-4 will be available with PCU2 and described in the next version of this document.
NACC
Network Assisted Cell Change feature reduces the cell-outage time (it is used with R4 devices only).
The detailed description of these features above can be found in [14] and [15].3. Performance Audit
Performance measurements are needed to get clear picture about network functionality and find the possibilities for increasing the performance. The (E)GPRS performance measurements and its analysis are usually separated to
OSS KPI Analysis Drive Test Analysis Real-time measurement analysis Analyzers and post-processing3.1 OSS KPI AnalysisOSS counter and KPI analysis gives exact picture about network performance. The analysis of the networks based on KPIs can be based on the following benchmark KPI list:
1. Table Benchmark KPIsThe planning and optimization related KPIs can be found in the following file:
The detailed description of KPIs can be found in [7].3.1.1 Network Doctor
Detailed and latest information about Network Doctor can be found on the following link:
http://enact.ntc.nokia.com/webrarian/netdoc_OSS31pdfs.htmThe Network Doctor formulas can be found in the JUMP page below:
hBttp://wwwalltr.ntc.nokia.com/CSTRE/NOS/SE/jump.htmThe detailed descriptions of the KPIs used in (E)GPRS optimization can be found in [7].
3.1.2 NetAct Reporter
The following link gives information about NetAct Reporter:
http://www6.connecting.nokia.com/net/marksales.nsf/document/es386aba7e?opendocument&click3.2 Field Tests
The Nokia projects are mainly using Nemo Outdoor (former TOM) and TEMS Investigation. In some projects the SwissQual and Agilent are used as well. (Other field measurement tools are available from Anritsu, Cuoei, Condat, QualComm and Rohde&Schwarz.)
The detailed information about field measurement tools can be found in [17].3.3 Real-Time Protocol Testing
The following testers are recommended and described in the subsections below.
Traffica
3rd party tools
Agilent
NetHawk
RadCom
Tektronix
The detailed information about real-time protocol testing tools can be found in [17].3.4 Application Testers
The most common application testers are listed below:
Application Tester
Ethereal
Commview
IP Dump should also be mentioned here
The detailed information about application testers can be found in [17].3.5 Post-Processing Tools
The most common post-processing tools are listed below: Actix Analyzer NetCare NetTest
The detailed information about post-processing tools can be found in [17].4. GSM Coverage and Quality Optimization
Good summary of the requirements to the GSM network. I like this!!!The physical layer of (E)GPRS is the existing GSM network, therefore the analysis of GSM network performance is important step in (E)GPRS optimization. The aim here is to estimate and maximize the (E)GPRS service area for each coding schemes based on GSM functionality.
The following subchapters describe the function of signal level, interference and data rate from test lab and live test measurements.4.1 (E)GPRS Coverage Area Estimation and Maximization
The GSM coverage and interference analysis is needed to estimate the current GSM functionality to find the possible room for improving signal level and C/I, hence improving (E)GPRS data rate as well.
The following subchapters contain the impact of signal level and interference on data rate.
4.1.1 Signal Level vs. TSL Data Rate
The target of this chapter is to show the effect of signal level on data rate. The sensitivity threshold of the receivers determines the MCSs used during the connections.
The Figure 10 shows that if the signal level is less then around 90 dBm and there is not any interference, than the RLC/MAC throughput will be lower then 100 kbps (Nokia Test Network (NTN) result). The outdoor field strength in city environment is higher than 90 dBm, but the indoor performance can be lower many cases (moreover most of the PSW users are located inside the buildings).
Figure 10 DL RLC/MAC throughput vs. Rx Lev (NTN)
The Figure 10 above shows the data rate dependency clearly based on signal level. The interference can further reduce the throughput with the same signal level.
4.1.2 Interference vs. TSL Data Rate
The curve in the graph below shows the relation between C/I and RLC/MAC data rate based on NTN measurement results (Figure 11). The RxLev is 70 dBm, so the performance is limited by interference only (LA enabled).
Figure 11 DL RLC/MAC throughput vs. interference in NTN
As it can be seen in the graph above the interference starts to be limiting factor from 24 dB. Between 24 and 14 dB there is a significant degradation in data rate and from 14 dB till 9 dB the Link Adaptation is choosing robust enough MCSs (MCS3 and MCS2) to stabilize the throughput on 20 kbps/TSL.
The curve in the graph above is based on averaged values from Application Tester logs.
4.1.3 Signal Level and Interference vs. TSL Data Rate
In the above chapters the impact of signal level and interference were investigated separately. Here in this chapter the complex effect of GSM performance will be studied (mixture of RxLev and C/I).
Figure 12 DL RLC/MAC throughput vs. interference and signal level in NTN
In city environment the indoor signal level is usually around 70 and - 90 dBm, while the C/I is around 15-25 dB. Therefore in worst case with 90 dBm signal level and 15 dB C/I the practically available data rate on two TSLs is around 50 kbps only, just based on GSM functionality.
4.2 Site Arrangement
The TSL data rate can be improved if the signal level is raised. It can be achieved by tuning of the radio network elements, like antenna turning, uptilting, changing, usage of MHA, etc, etc.
This is a normal GSM optimization activity.
4.3 Frequency Plan
The TSL data rate can be improved if the C/I is increased. If the site arrangement is optimized and the cells have dominant coverage areas, the C/I can be improved with better frequency allocation as well.
This is a normal GSM optimization activity.
4.4 Optimal GSM Network for PSW Services
The optimal GSM network from PSW services point of view has:
As high signal level as possible
It means that even the indoor signal level should be high enough to have MCS9 for getting the highest data rate on RLC/MAC layer.
As low interference as possible
The aim of having high C/I is to avoid throughput reduction based on interference.
Enough capacity
Enough hardware capacity is needed to provide the required capacity for PSW services in time. Both CSW and PSW traffic management should be harmonized with the layer structure and long term plans.
As few cell-reselection as possible
The dominant cell coverage is important to avoid unnecessary cell-reselections in mobility. The prudent PCU allocation can help to reduce the inter PCU cell reselections.
Dominant cell structure can help to maximize the signal level and reduce the interference, too.
Features
All the features should be used which can improve the PSW service coverage, capacity and quality in general.
5. (E)GPRS BSS Optimization
The EGPRS BSS optimization based on the performance analysis of existing GSM and (E)GPRS network functionality and contains the following activities:
Signaling capacity Resource allocation improvement
E2E Data rate maximization
Connectivity capacity
RLC/MAC data rate and Multislot usage E2E data rate
Mobility improvement
5.1 Signaling Capacity Improvement
The congestion and long delay on signaling can reduce the TBF establishment time. Therefore the signaling channels must be analyzed and optimized, if the TBF establishment is suffering from signaling channel bottlenecks.
The following interfaces and network elements must be analyzed and optimized for avoiding bottlenecks in signaling:
Air interface
TRXSIG
PCU
BCSU
MM and SM signaling
5.1.1 Air Interface Signaling
The air interface signaling optimization for avoiding signaling capacity bottlenecks is based on the PCH, AGCH, RACH and SDCCH analysis and modification.5.1.1.1 PCH (NMO II)On PCH the following counters and KPIs can be investigated:
5.1.1.1.1 Traffic Volume
paging_msg_sent (c3000) (CS pagings from Aif)
cs_paging_msg_sent (c3058) (CS pagings from Gb) This one should actually be zero if NMO II is used ps_paging_msg_sent (c3057) (PS pagings from Gb)
PCH load on CCCH = AVE_PCH_LOAD (c3008) / RES_ACC_DENOM2 (c3009) Not in the list of KPIs that we agreed on. max_paging_gb_buf (c3050)
5.1.1.1.2 Rejection delete_paging_command (c3038) (includes both PS and CS paging)
5.1.1.1.3 Paging success ratio on PS and CS together
delete_paging_command / (paging_msg_sent+ cs_paging_msg_sent+ ps_paging_msg_sent) Not in the list of KPIs that we agreed on.5.1.1.1.4 Paging success ratio on PS (2G SGSN)
sum(UNSUCC_PAGINGS(05002))
mob_sgsn141a = ----------------------------------------------------------------------* 100
sum(LLGMM_PAGING_ATTEMPTS (005003))
5.1.1.1.5 Solution for reducing PCH rejection and loadThe following activities can be done for better PCH functionality: Usage of combined structure I guess you mean non-combined CCCH/SDCCH, right? Modifying MFR and PER parameters Modifying in what way? PBCCH implementation (in case of high (E)GPRS signaling traffic)
5.1.1.2 PCH (NMO I)
On PCH with NMO I the following counters and KPIs can be investigated:
5.1.1.2.1 Traffic Volume
cs_paging_msg_sent (c3058) (CS pagings from Gb)
ps_paging_msg_sent (c3057) (PS pagings from Gb) 5.1.1.2.2 Congestion (CS + PS)
max_paging_gb_buf (003050)
5.1.1.2.3 Paging of MSs in Packet Transfer Mode
PAC_PAG_REQ_FOR_CS_PAG (c72083) /(cs_paging_msg_sent) (c3000) Pgn_14 is the id.5.1.1.2.4 Gs interface overload (2G SGSN)
sum(DL_MESSAGES_DISCARDED_IN_GS(11000))
Sgsn_961a = ----------------------------------------------------------------------- * 100
sum(CS_PAGING_MSGS + DL_TOM_MSGS)
5.1.1.3 AGCHAGCH is used for Immediate Assignment messages. The following items can be investigated:5.1.1.3.1 Traffic Volume (with Rejection)
imm_assgn_sent (c3001) - Imm Assign)
imm_assgn_rej (c3002) - Imm Assign Rejected
packet_immed_ass_msg (c72084) - P-Imm Assign
packet_immed_ass_rej_msg (c72087) - P-Imm Assign
5.1.1.3.2 Congestion
packet_immed_ass_nack_msg blck_21b =-------------------------------------------------------------------------
packet_immed_ass_nack_msg + packet_immed_ass_ack_msg
5.1.1.3.3 Solution for reducing AGCH rejection and loadThe following activities can be done for better AGCH functionality: Usage of combined structure, modifying AG and CALC parameters. Non-combined, right? Modifying in what way? Immediate Assignment messages are shared between PCH and AGCH
PBCCH implementation (in case of high (E)GPRS signaling traffic)
Note that for GPRS & EGPRS, most of the Immediate Assignment messages are actually sent on the PCH and not on the AGCH.
In case of PCH and/or AGCH congestion LA/RA border and size planning, MSC paging parameters, CCCH configuration, CS paging load can be investigated to reduce CCCH load.
This section has a lot of parameters and KPIs, still the actual workflow is not so clear to me. Which KPIs to start looking at in practice? How to proceed with the identification of the problem?
5.1.1.4 RACH
The counters and KPIs below can be investigated related to RACH functionality:5.1.1.4.1 Traffic Volume
PACKET_CH_REQ (c072082) (PSW)
CH_REQ_MSG_REC (c003004) (CSW) Not in the list of agreed KPIs5.1.1.4.2 Load
100 * avg(ave_rach_busy(C3014)/res_acc_denom3(c3015))
avg(ave_rach_slot(c3006)/res_acc_denom1(c3007)) This is rach_45.1.1.4.3 Load and quality (repetitions of PS channel requests)
UL_TBF_WITH_RETRY_BIT_SET (c072020) / PACKET_CH_REQ (c072082) This is rach_95.1.1.4.4 Solution for reducing RACH rejection and loadThe following activities can be done for better RACH functionality: Usage of combined structure, modifying RET parameter
PBCCH implementation (in case of high (E)GPRS signaling traffic)
5.1.1.5 SDCCH
The counters and KPIs below can be analyzed related to SDCCH functionality:5.1.1.5.1 Traffic Volume
SDCCH seizure attempts (c1000)
Average available SDCCH (ava_45a) Not in agreed list5.1.1.5.2 Congestion
Blocking on SDCCH, before FCS (blck_5)
5.1.1.5.3 Solution for reducing SDCCH loadThe following activities can be done for better SDCCH functionality: Increase of Periodic location update timer / Periodic RA update timer (PRAU) Increase of MS Reachable timer (MSRT) More SDCCH allocation and Dynamic SDCCH feature usage
Combined RAU (NMO-I with Gs for (E)GPRS) (Resume feature decreases the amount of RAUs) But this does not matter for SDCCH, does it? LA/RA re-planning5.1.1.6 Parameters
The descriptions of the parameters are used for RF signaling optimization is listed below: Number of Multiframes (MFR)
With this parameter you define the number of multiframes between two transmissions of the same paging message to the MSs of the same paging group. (def 4)
Number of Blocks for Access Grant Msg (AG)
With this parameter you define the number of blocks reserved for access grant messages from the CCCH during the 51 TDMA frame (a multiframe). (def 1)
Max Number of Retransmission (RET)
With this parameter you define the maximum number of retransmissions on the RACH (random access channel) that the MS can perform. (def 4)
Calculation of Minimum Number of Slots (CALC)
With this parameter you calculate the minimum number of slots between two successive Packet Channel Request messages. (def 30)
Preferred BCCH TRX (PREF)
With this parameter you mark one or more TRXs as preferred TRXs where the BCCH is reconfigured, if possible. Timer for Periodic MS Location Updating (PER)
With this parameter you define the interval between periodic MS location updates. The value 0 means that the periodic location update is not used.Parameters for RF Signaling with PBCCH (not supported with PCU2 rel-1): PBCCH Usage
PBCCH Blocks (PBB)
With this parameter you define the amount of blocks allocated to the PBCCH in the multiframe. With this parameter you define the amount of blocks allocated to the PBCCH in the multiframe. (def 3)
PAGCH Blocks (PAB)
With this parameter you indicate the number of blocks on each PDCH carrying the PCCCH per multiframe where neither packet paging nor PBCCH should appear. This number corresponds therefore to the number of blocks reserved for PAGCH, PNCH, PDTCH and PACCH. (def 4)
PRACH Blocks (PRB)
With this parameter you indicate the number of blocks reserved in a fixed way to the PRACH channel on any PDCH carrying the PCCCH. (def 6)
GPRS Number of Slots Spread Transmission (GSLO)
With this parameter you define the number of slots used to spread transmission on the PRACH (Packet random access Channel). (def 10)
GPRS Max Number of Retransmission (GRET)
With this parameter you indicate the maximum number of retransmissions allowed on the PRACH for each Radio Priority level 1 to 4. Radio Priority level 1 represents the highest priority. One parameter contains four values. (def 4 4 4 4)5.1.1.7 FeaturesThe subsections below show the features, which can help to avoid signaling issues.5.1.1.7.1 Implementation of PBCCH
In case of PBCCH implementation the (E)GPRS signaling is conveyed on PBCCH TSL, so the signaling channels used for CSW signaling will not be used anymore (and TRXSIG is used for CSW signaling only).
PBCCH feature will not be available from PCU2 implementation.
5.1.1.7.2 NMO1 with Gs Interface
In case of combined LAU/RAU the RA Update is generated without LA Update. The time used for combined RAU is much less compared to uncombined LAU/RAU.
5.1.1.7.3 EPCR (S11, UltraSite, MS R99) with one phase access
EPCR is always on when BSS 11 is used and supported by MS Rel99 onwards. Ultrasite supports EPCR (CX4.0-x) and EDGE support required as well.
If EDGE one phase access is used on CCCH, only one TS is allocated , so reallocation need is checked when establishment is completed.
Nokia solution has PACKET RESOURCE REQUEST (PRR) implemented with one phase access. How does this affect to signaling load? More or less?5.1.1.7.4 Resume
GPRS suspension procedure enables the network to suspend GPRS services packet flow in the downlink direction. When the terminal leaves the suspended mode (and CSW dedicated mode), the BSS shall signal to the SGSN that an MS's GPRS service shall be resumed.
Less signaling is generated, so more user data can be sent. The counters related to Resume feature are listed below: 057049 GPRS_SUSPEND - Number of MS initiated GPRS suspension requests.
057050 GPRS_SUSPEND_FAILURE - Number of unsuccessful GPRS suspension procedures.
057051 GPRS_RESUME GPRS - Number of BSC initiated GPRS resume requests.
057052 GPRS_RESUME_FAILURE - Number of unsuccessful GPRS resume procedures.To check how much the Resume function has reduced the signaling, SGSN counters can be checked before and after S11.5 is loaded (check the amount of intra-PAPU routing area updates).Mention that Resume comes with S11.5, otherwise it is not clear why S11.5 load can change the signalling
More information about KPIs can be found in [7].5.1.2 TRXSIG
The LAPD links are used for CSW and PSW signaling as well, so the congestion on TRXSIG can increase the connection time and reduce the reliability (the TRXSIG has important role in connection establishment).
(E)GPRS differs from GSM in that signaling information data packets can be transmitted on TRXSIG channel but also on PDTCH/PACCH traffic channel (16 kbit/s PCU frames, a derivative of TRAU frames). So the signaling on PDTCH/PACCH is not transmitted over TRXSIG.
More information is available in [3]. The Abis LAPD link can be configured to 16Kbps, 32Kbps or 64Kbps. A bottleneck can be arise, as in some cases BTS processors can handle more messages than the Abis link can transfer.
In case of PBCCH implementation the (E)GPRS signaling is conveyed over PBCCH TSL, so the TRXSIG is used for CSW signaling only. PBCCH feature will be not available from S11.5 - PCU2 implementation.
The TRXSIG load measurement description can be found in the link below:
http://qp1.connecting.nokia.com/QuickPlace/npcommunity/PageLibraryC2256BDE0034D11A.nsf/h_7EC47F5CADD0CE50C2256BEA0033B1FE/F3EE98BB6051EB49C2256F8F0027E581/?OpenDocument A short description of what is behind this link, would be nice (ie that MML scripts are used and that no OSS counters are available)5.1.3 PCU
The PCU can be analyzed from processing and connectivity capacity point of view.
The processing capacity limits have alarms:
Notification 0125 (90% load, PCU starts to reduce cell reselection calculations)
Alarm 3164 (95% load, PCU starts to discard blocks)
While the connectivity capacity limits can be observed by KPIs (S11.5 onwards): UL MCS selection limited by PCU dap_10
DL MCS selection limited by PCU dap_9Both processing and connectivity related issues can be solved by better allocation of BCFs among PCUs. More information is available in Section 5.3.1. 5.1.4 BCSU
The BCSU handles the LAPD (TRXSIG and OMUSIG) and SS7. From BSC load audit point of view the TRXSIG should be mainly taken into account.
The ND 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 2.
Table 2 Network Doctor 184 report example5.1.5 MM and SM Signaling
How to use this info in practice? By giving low priority to signaling-only areas?
Mobility Management (MM) and State Management (SM) signaling are used for attach, PDP context activation, RAU update, etc.
The capacity situation on RF signaling has impact on the success rate of MM and SM.
For BSS, there are KPIs which tell how many of all the established TBFs are used for MM and SM signaling:
Ratio of DL signaling TBFs tbf_62
Ratio of UL signaling TBFs tbf_61In addition, the amount of different procedures can be checked from the relevant tables in the SGSN: p_sgsn_mobility_management (Nokia SGSN)
p_sgsn_session_management (Nokia SGSN)5.2 Resource Allocation Improvement
The aim of resource allocation improvement is to ensure not only the fast access to the network but also the access to the right cells and TSLs, which provide the fastest data rate.
Usually the following items should be checked in BSS resource allocation improvement:
PSW activation and territory settings
Cell selection
BTS selection
TSL selection
5.2.1 PSW Activation and Territory Settings
The aim of PSW activation and territory setting is to provide enough capacity to PSW traffic and provide the appropriate balance between CSW and PSW traffic.
The TRX, cell (segment) are used for signaling, CSW traffic, Free TSLs and PSW traffic. I dont understand this sentence, especially not the beginning
13. Figure TSL OccupationI dont understand figure 13. How can a timeslot be half free?5.2.1.1 Parameters
The PSW activation and territory can be optimized by the following parameters:PSW Activation
GPRS Enabled (GENA)
EGPRS Enabled (EGENA)
GPRS Enabled TRX (GTRX)
Adjacent GPRS Enabled (AGENA)
GPRS Cell Barred (GBAR)
Not Allowed Access Classes (ACC)
GPRS Not Allowed Access Classes (GACC) with PBCCH Also the 3 bullet points above require PBCCH!Territory Settings
Default GPRS Capacity (CDEF)
Dedicated GPRS Capacity (CDED)
MAX GPRS Capacity (CMAX)
Channel Allocation Parameters Prefer BCCH frequency GPRS (BFG)
TRX priority in TCH allocation (TRP)5.2.1.2 Measurements KPIsThe following counters and KPIs can be used to analyze the territory related situation on cell and BTS level.5.2.1.2.1 Actual Territory
ava_44
Peak PS territory (c2063)
Recommendation: Ava_44 and c2063 can be compared with the CDEF settings. If too big difference, then CDEF should perhaps be changed, or more capacity should be added to the cell.5.2.1.2.2 Multislot Blocking
DL multislot blocking soft (blck_33)
UL / DL multislot allocation blocking hard (tbf_15, tbf_16)
Recommendation: Too much multislot blocking shows that the territory is perhaps not enough.
5.2.1.2.3 TSL Sharing
UL / DL timeslot sharing TBFs pr time slot (tbf_37c, tbf_38c)
Recommendation: Too much sharing shows that the territory is perhaps not enough.
5.2.1.2.4 Impact of PSW territory upgrades/downgrades on CSW
ho_61Recommendation: Too much CSW HOs (because of PSW territory upgrades/downgrades) shows that the territory is perhaps not enough, which generates instability to CSW, too. Or maybe BFG and TRP should be looked at.5.2.2 Cell (Re)-Selection
The terminals must be allocated to that cell, where the maximized TSL data rate and territory are available.
If low data rate and/or limited territory generate low user throughput, the optimized cell selection can be a solution among many others.
In cell selection the C1, C2, C31/C32 and NCCR parameters are taken into account.
5.2.2.1 C1 and C2 and HYS
In C1 the following parameters must be observed:
The too low RXP will generate high retransmission, but probably less unexpected TBF release.
TXP1 is used for 800/900 MHz, while TXP2 is used for 1800/1900 MHz.
C2 parameters are used to push slow moving users to the cells with less cell size but probably better signal level, C/l and capacity, so the user data rate can be increased (because of higher TSL RLC/MAC data rate and bigger territory) on micro and pico cells.
The following parameters are used in C2 implementation:
14. Figure C2 parameters usage in multilayer network environment5.2.2.2 C31/32
C31/32 parameters are used with PBCCH with PCU1 (PBCCH feature will not be available from PCU2 implementation, PBCCH with PCU1 is E6 candidate for S13). So the neighbor cells and the target cells can be separated from CSW allocation, therefore the PSW traffic can be pushed to those cells, where the expected data rate and territory are enough.
The following C31/32 parameters are used:
The Figure 14 shows the throughput map of a simulation with C1. The EGPRS terminal penetration is 25 % and the of the BTSs are EGPRS capable only.
Figure 15 Throughput map with C1
The Figure 15 results are based on the same inputs but with C31/C32 usage. The location probability is much higher for EGPRS, but the number of EGPRS capable BTSs is the same.
Figure 16 Throughput map with C31/C32
The excel table below helps to plan the C31/C32 parameters:
Unfortunately the planning and maintenance of C31/C32 parameters on network level are very time consuming and need lot of resources.
More information and link to excel-table is available in [13].
5.2.2.3 Cell re-selection Measurements (NC_0)
The following KPIs tell how often a TBF is interrupted due to a cell re-selection.
This is calculated on the source cell, there is no information of where the target is, so it is not possible to distinguish between e.g. C2 and C31/C32 effects.
tbf_35a use tbf_63 instead tbf_36a use tbf_64 insteadThe duration and thereby the impact on the applications are not known.
The following parameter shows the number of NACC usage to assist MS in network control mode 0.
c95017 (NACC_WITH_NC0)
Drive tests are needed to measure cell re-selection behavior properly.5.2.3 NCCRNCCR (Network Controlled Cell Reselection) enables the network to control the resource allocation when the MS performs the cell reselection.
NCCR is an optional feature in Nokia BSC. Operator can enable/disable the feature on BSC level.
Benefits with NCCR are the efficient allocation of resources: EDGE MS can be held on EDGE TRX longer => better throughput for EDGE MS.
GPRS MS can be prevented to access an EDGE TRX => better throughput for EDGE MS. But NCCR also brings benefits even if there is EDGE in all cells (ie prevent ping pong etc.The better control over mobile stations is possible and more counter statistics helps in detailed analysis.
Network Control Mode (NCM) defines how cell re-selection is performed:
Network Control Mode = 0 (NC0): the MS will perform an autonomous cell reselection.Network Control Mode = 1 (NC1): it is not supported.Network Control Mode = 2 (NC2): the MS sends neighbour cell measurements to the network and the network commands the MS to perform cell re-selection (NCM is modified with MML command ZEEM).
17. Figure Flow chart NC0 and NC2
5.2.3.1 NCCR Criteria interesting stuff, but most of it belongs in the theory documentThe following points summaries the NCCR criteria: Power budget push EGPRS capable MSs to EGPRS cells and non-EGPRS capable MSs to non-EGPRS capable cells. As you also mention below, this feature can also be useful in e.g. non-EDGE networks! Quality Control (without EQoS) triggers NCCR when the serving cell transmission quality drops even if the serving cell signal level is good. Quality Control (with EQoS) PFC downgrade and deletion actions are used, too. Coverage based ISNCCR selects 3G network as soon as it is available or when GSM coverage ends, depending on operator choice.
Service based ISNCCR selects 3G network according to SGSN Service UTRAN CCO BSSGP procedure if the serving cell signal level is good. Feature candidate for S14.
5.2.3.2 NCCR Power BudgetWith NCCR Power Budget parameters it is possible to:
push EGPRS capable MSs to EGPRS cells
push non-EGPRS capable MSs to non-EGPRS capable cells
delay MSs entrance into a cell
avoid moving MSs unnecessary entrance into cells they only briefly pass
NCCR EGPRS PBGT margin (EPM) and NCCR GPRS PBGT margin (GPM) can be used to effectively allocate EDGE and GPRS capable MSs on different cells.
GPRS temporary offset (GTEO) and GPRS Penalty Time (GPET) can be used to avoid unnecessary cell reselection from moving MS to cells they briefly pass. E.g. Pico cells.
Priority Class (PRC) and HCS signal level threshold (HCS) should be used carefully! Preferably not used at all! Wrongly used they can increase ping-ponging and decrease network performance.5.2.3.3 NCCR Quality Control (PCU1)The purpose of Quality Control (QC) in BSS11.5 is to monitor and detect degradation periods in service quality, and to perform corrective actions to remove the service degradation. The possible actions in BSS11.5 include TBF reallocation and network controlled cell reselection.NCCR is triggered only if the NCCR feature is active. NCCR activity is controlled by a BSC level parameter NCCR control mode.The Quality Control shall maintain statistics about BLER for each TBF as well as bitrate per radio block for each TBF in RLC ACK mode. QC uses this information for monitoring radio link performance and delay.The monitored samples are filtered. The filtering is based on appropriate threshold values:
For BLER sample filtering, the threshold value is operator parameter maximum BLER in acknowledged mode (BLA) or maximum BLER in unacknowledged mode (BLU), depending on the RLC mode of the TBF.
For bitrate per radio block sample filtering, the threshold value is one of the four operator parameters QC GPRS DL/UL RLC Ack Throughput Threshold or QC EGPRS DL/UL RLC Ack Throughput Threshold, depending on the type and mode of the TBF, multiplied with e.g. 1.2 in order to have a safety margin of some degree during the first calculation cycles.5.2.3.3.1 Block Error Rate (BLER)
RLC shall report to QC the BLER statistics - number of correctly transmitted RLC data blocks and number of RLC data blocks actually needed to transmit the correct blocks - for all TBFs, independently for UL and DL, and RLC ACK and UNACK mode. Based on BLER information provided by RLC, QC shall calculate and maintain the actual BLER values for each RAT, independently for UL and DL, and RLC ACK and UNACK mode.The BLER definition in GPRS is straightforward, as the RLC block reception is an independent event. Thus, the BLER in GPRS is the probability of any RLC block received incorrectly. On the contrary in EGPRS with Incremental Redundancy, the reception of a retransmitted RLC block is not an independent event, but depends on the previous receptions of the same block. Thus, the BLER definition in EGPRS must be more general. However, the following formula is justified in both cases:
where is the number of RLC data blocks received correctly in the reporting period, and is the number of transmissions needed for correct receptions (initial transmission + retransmissions). This definition is valid for both GPRS and EGPRS.
5.2.3.3.2 BLER Degradation Duration Counter
QC shall maintain the BLER degradation duration counter for each TBF according to the following rules:
The BLER degradation duration counter shall be incremented by 10, if ;
the counter shall not be modified, if ;
The counter shall be cleared (set to zero), if.
The QC thread shall monitor the BLER degradation duration counter, and if the counter is larger than predefined triggering levels (BLA, BLU parameters), the corresponding corrective action is tried.5.2.3.3.3 Bitrate (BER)QC shall monitor bitrate per radio block for each RAT in RLC ACK mode, for UL and DL separately. The statistic is gathered by RLC, and reported to QC. RLC shall calculate and report values in the following way:
In downlink, RLC shall maintain counters for transmitted bits (only the payload bits in each RLC data block are taken into account) and transmitted radio blocks. The counter for transmitted bits shall contain only new RLC data block transmissions; for the retransmissions, the number of bits transmitted is zero. Pending ACK retransmissions as well as the RLC data blocks containing only an LLC dummy block, but no real data, shall be ignored in this calculation.
In uplink, RLC shall maintain counters for received RLC data block payload bits and received radio blocks. When a radio block is received, the counter of received radio block is increased by one. If the RLC data block(s) is/are received correctly, RLC shall update the counter of the received RLC data block payload bits accordingly. If RLC data block(s) is/are received incorrectly, the number of received payload bits is zero. Radio blocks containing only pending ACK retransmission(s) shall be ignored in this calculation.
QC shall calculate the bitrate per radio block value once in its execution cycle (200 ms) and check it against the corresponding threshold value. Since the unit of the threshold values is kbit/s, QC shall convert RLC reported bitrate per radio block by dividing the values with 20 ms (1 block period corresponds 20 ms). Thus the value range of QC calculated bitrate per radio block is from 0 kbit/s to 59,2 kbit/s.
The threshold values are operator parameters and there is a separate value for UL and DL, as well as for GPRS and EGPRS, respectively (look at operator parameters QC GPRS DL/UL RLC Ack Throughput Threshold (QGDRT, QGURT) and QC EGPRS DL/UL RLC Ack Throughput Threshold (QEDRT, QEURT)).Note. Bitrate per radio block monitoring algorithm does not measure the actual throughput. The algorithm does not take into account the time between samples received from RLC, and thus cannot calculate the real throughput: the output of the algorithm merely describes the quality of the measured TBF in terms of bits it can theoretically transfer per second.
5.2.3.3.4 Bitrate per Radio Block Degradation Duration Counter
The bitrate per radio block degradation duration counter shall be maintained for each RAT according to the following rules:
The bitrate per radio block degradation duration counter shall be incremented by 10, when the bitrate per radio block is below the threshold value.
The counter shall be cleared (set to zero), when the bitrate per radio block is above or equal to the threshold value.
The QC thread shall monitor the bitrate per radio block degradation duration counter. If the counter is larger than predefined triggering levels (QGDRT, QGURT and QEDRT, QEURT parameters), the corresponding corrective action is tried.
5.2.3.3.5 Corrective Actions
When any of the degradation duration counters monitored by QC gets larger than a predefined action trigger threshold, QC shall try to corresponding corrective action in background thread, running with low priority. Each action shall be triggered only once for a TBF in QC (once for a call (UL+DL TBFs of the same phone) during one degradation period. If the degradation period ends and a new starts, new actions can be tried). For example, if reallocation is already done, next action to be performed is NCCR, triggered when a degradation duration counter exceeds the NCCR trigger threshold. The flags of already performed actions shall be cleared when the degradation ends, i.e. when all the degradation duration counters are cleared.
The action trigger thresholds are expressed in block periods and the values can be set by operator, see operator parameters QC Action Trigger Threshold:
QC reallocation action trigger threshold (QCATR)
QC NCCR action trigger threshold (QCATN)
QC QoS renegotiation action trigger threshold (QCATQ) (not implemented in S11.5) QC drop action trigger threshold (QCATD) (not implemented in S11.5)
It is possible to change the order of different actions by modifying the action trigger threshold values (If the value is set to 0, then no action of that kind is tried).5.2.3.4 NCCR Parameters with Power Budget and Quality Control
Which ones should be used in practice?
The following parameters are used to set the NCCR: NCCR Control Mode (NCM)
WCDMA FDD NCCR Enabled (WFNE)
NCCR Idle Mode Reporting Period (NIRP)
NCCR Transfer Mode Reporting Period (NTRP)
NCCR RxLev Transfer Mode Window Size (NRTW)
NCCR Rxlev Idle Mode Window Size (NRIW)
NCCR number of zero results (NNZR)
NCCR Return to Old Cell Time (NOCT)
NCCR Neighbor Cell Penalty (NNCP)
NCCR Target Cell Penalty Time (NTPT)
NCCR EGPRS PBGT margin (EPM)
NCCR GPRS PBGT margin (GPM)
NCCR streaming TBF offset (NSTO) (available only if EQoS exists)
NCCR other PCU cell offset (NOPO)
NCCR GPRS quality margin (GQM)
NCCR EGPRS quality margin (EQM)
ISNCCR FDD quality threshold (FQT)
Quality Control Maximum BLER in acknowledged mode (BLA) Maximum BLER in unacknowledged mode (BLU) QC GPRS DLRLC Ack Throughput Threshold (QGDRT) QC GPRS DL RLC Ack Throughput Threshold (QGURT) QC EGPRS DL RLC Ack Throughput Threshold (QEDRT) QC EGPRS UL RLC Ack Throughput Threshold (QEURT) NCCR_NON_DRX_PERIOD
NCCR_STOP_UL_SCHEDULING
NCCR_STOP_DL_SCHEDULING
NCCR_MEAS_REPORT_TYPE
BSSGP_T5
BSSGP_RAC_UPDATE_RETRIES5.2.3.5 Cell re-selection Measurements (NC_2)
The following KPIs show the NCCR functionality. Nccr_12: Number of network controlled cell reselections compared to data amount
Nccr_13: Successful NCCR ratio
Nccr_14: Average duration of successful NCCRs
The following parameter shows the number of NACC usage to assist MS in network control mode 2.
c95018 (NACC_WITH_NC2)5.2.4 BTS Selection in Segment (MultiBCF and CBCCH without EQoS)The right BTS (with the maximized TSL data rate and territory) must be selected if MultiBCF or CBCCH are used. So the GPRS capable mobiles can be allocated to BTS with GPRS, while the EGPRS capable terminals are allocated to the EGPRS capable BTS inside the segment.
If EDGE and non-EDGE TRXs are mixed in same BTS, BB Hopping requires segment solution and own hopping groups. (EDGE cannot move to non-EDGE TRX).5.2.4.1 ParametersThe following parameters have impact on allocation algorithm:
NonBCCHLayerOffset (NBL Offset)
Direct GPRS Access Threshold (DIRE)
BTS Load in SEG (LSEG)
TBF Load Guard Threshold
GPRS non BCCH Layer Rxlev Upper Limit (GPU)
GPRS non BCCH Layer Rxlev Lower Limit (GPL)
5.2.4.2 Measurements
Most of the GPRS/EDGE KPIs are on BTS level. E.g. the payload and Erlang formulas can be used to see how the different BTSs inside the segment are used:
Downlink GPRS RLC payload trf_213c
Downlink GPRS Erlangs trf_208b
Uplink GPRS RLC payload trf_212c
Uplink GPRS Erlangs trf_205b
Downlink EGPRS RLC payload trf_215a
Downlink EGPRS Erlangs trf_162f
Uplink EGPRS RLC payload trf_214a
Uplink EGPRS Erlangs trf_161h
PS Erlangs trf_237b
From S11.5 onwards, it can be checked if EDGE TBFs ends in GPRS territory (OSS4):
DL EDGE TBFs in non-EDGE territorytbf_60UL
EDGE TBFs in non-EDGE territorytbf_59
And if EDGE territory is wasted on GPRS TBFs:
tbf_57 = UL_GPRS_TBF_IN_EGPRS_TERR / (UPLINK_TBF - EGPRS_TBFS_UL)
tbf_58 = DL_GPRS_TBF_IN_EGPRS_TERR / (DOWNLINK_TBF - EGPRS_TBFS_DL)The NBL offset parameter has probably the biggest impact on the BTS selection, if the capacity is not limited. As it can be seen from the NBL measurement below, the average NBL offset value for the whole network is not a good solution.
Figure 18 NBL measurement results (example)
5.2.5 Scheduling (TSL Selection with Priority based QoS)The calculation of the load of TSLs is done by the PCU and based on the Priority based QoS parameters and different penalties given to the TSLs (PACCH, timeslot type and GPRS/EGPRS multiplexing).
5.2.5.1 Parameters
The following parameters are used to set the TSL usage:
DHP (DL high priority SSS) DNP (DL normal priority SSS)
DLP (DL low priority SSS) UP1 (UL priority 1 SSS) UP2 (UL priority 2 SSS) UP3 (UL priority 3 SSS)
UP4 (UL priority 4 SSS)
Sequence can be set by TBF Load Guard Threshold parameter.
5.2.5.2 Measurements
The following KPIs can be used to analyze the scheduling: trf_211b gives approximated payload pr QoS class
trf_125 gives user-experienced throughput, or at least something that comes close. This is pr QoS class but only in the DL direction
llc_4, llc_5 & llc_6 gives volume-weighted throughput pr QoS class
Note that in practice, there are some restrictions to the use of the QoS based KPIs
For trf_125, the value is very much dependent on the used application. Applications which does not transfer so much data (like WAP browsing) will have small throughput regardless of the network quality, while heavy applications such as mp3 downloading will have throughput correlated with network quality. Next slide illustrates this.
In order for trf_125 to be useful to monitor network quality, it is therefore needed to ensure that only heavy applications are using a particular QoS class
If above condition is met, it means that the payload estimation (trf_211b) becomes much less accurate.Until now, no practical experiences with llc_4, llc_5 & llc_6, but it is expected that they will not put so strong requirements to the distribution of applications into QoS classes.
There are throughput per used TSL formulas in ND 226, but the usage of those formulas is not recommended. Put explicit reference to the old formulas (trf_72, trf_73, trf_89, trf_90)5.2.6 DAP Resource Allocation in PCU1
No EDAP resource sharing algorithm is needed in that case where the number of slave channels required by the PS calls is lower than the EDAP capacity. This means that all the requests are served.EDAP resource sharing algorithm is needed in thas case where the number of slave channels required by the PS calls is higher (13 channels) than the EDAP capacity (12 channels). This means that the last requested call, with MCS-7 requires 3 slave channels (grey in Figure 14), which could not be served by the existent EDAP: they cannot be allocated in the configured EDAP.
An MCS adjustment (a downgrade in DL and a transmission turn skipped in UL) is needed and the biggest MCS available with the restricted slave amount will be granted for the RLC by the Dynamic Abis Manager.
19. Figure EDAP resource sharing Example
EDAP congestion situation in DL data transfer is handled differently in PCU1 than in PCU2. PCU1 reduces MCS for all MSs whereas PCU2 is recycling the EDAP resources between MSs.
If PCU1 can not allocate requested EDAP resources for all scheduled TBFs in DL direction, then requested EDAP resources are decreased evenly for all scheduled TBFs until requested EDAP resources match with available EDAP resources. In case of lack of EDAP resources some of the TBFs are totally left outside of the slave channel allocation. However, the 16 kbit/s EGPRS master channel can and shall be used for those TBFs this guarantees CS-1 and MCS-1 usage.
For example, if there is one EDAP sized one TSL and two MSs are trying to transfer data with MCS-9, then MCS is reduced to MCS-6 for both MSs.
More information is available in [10].The purpose of this chapter is a bit unclear to me. At least it should be more emphasized that EDAP congestion will lead to lower values of the RLC throughput formulas!5.2.7 Cell, BTS and TSL Selection with EQoSMore information is available in EQoS (E)GPRS Radio Networks EQoS Planning Theory document. Mention also that this is no more part of S11.55.3 E2E Data Rate MaximizationThe goal of E2E PSW data rate maximization is to increase the TSL data rate and territory used by the mobiles on BSS, and minimizes the negative affect of BSS parameters on higher layer performance (LLC, TCP/IP and application).
Therefore the (E)GPRS E2E data rate optimization is separated to the following items:
Connectivity Capacity Optimization (BSS) RLC/MAC TSL data rate improvement and multislot usage maximization (BSS)
E2E data rate optimization (applications)5.3.1 Connectivity Capacity Optimization (BSS)The aim of connectivity capacity optimization is to reallocate the sites (BCFs) among PCUs (BSCs) for avoiding connectivity limits and maximizing QoS.
The view here is on the E2E chain (MS-SGSN), so all the network elements and interfaces are optimized for enough connectivity capacity.The number of required PCUs is CDEF (well, it is the actual territory size that matters, not the CDEF setting itself) and DAP size dependent from physical layer point of view, while the amount of Gb links used by PCUs is PAPU limiting factor (or the limited number of PAPUs can limit the number of PCUs, because of Gb link limits in PAPU).
5.3.1.1 Connectivity Limits in PCUThe following table shows the limiting factors in case of different PCU types.
3. Table Limiting factors of PCUs
5.3.1.2 Connectivity Limits in SGSN and PAPU (SG4)
The following limits must be taken into account in connectivity capacity optimization:
1024 PCU can be connected to SGSN (with 16 PAPU)
64 PCU can be connected to PAPU
3072 Gb link can be connected to SGSN (with 16 PAPU)
192 Gb link can be connected to PAPU
120 E1 can be connected to SGSN (with 16 PAPU)5.3.1.3 Connectivity Capacity Optimization Maximized CapacityThe connectivity optimization for maximum capacity is based on the proper set of CDEF and DAP size.
To provide enough capacity for territory upgrade the 75 % utilization But I think that this 75% is not valid if the operator decides to set CDEF=1% in all cells in order to save PCU capacity? Then the margin needs to be higher in the connectivity limits is recommended by Nokia, therefore the following limits must be taken into account in optimization:
Table 4 PCU Connectivity capacity limits You are mixing two things here. The BTS margin is a kind of roll-out margin, where you dont want to dp PCU replanning just because you add a few sites. The abis margin is a dynamic margin caused by traffic fluctuations. I dont see any particular reason why you use the same margin in both cases. As mentioned above, the abis margin should also depend on the operators CDEF strategy The CDEF is allocated to the cells (BTSs in segment), so the too big CDEF territory will need more PCUs.
The Dynamic Abis Pool (DAP) is allocated to the sites (BCFs). Higher DAP size provides more MCS9 capable TSLs on air interfaces, but on the other side, higher DAP size needs more capacity on E1s and more PCUs as well. So the proper value of CDEF on cell (BTS) level and DAP on BCF level can help to be below the 192 radio TSL limit (with 75 % utilization) to avoid connectivity bottlenecks even in case of territory upgrades.
It is important to know that the PCU and PCU-S have 128 radio TSL limit with S11.5, which can be a real bottleneck in GPRS only networks. 5.3.1.4 Connectivity Capacity Optimization Maximized Data RateThe maximized data rate needs proper utilization of PCUs, so the following considerations must be taken into account:
The proper DSP allocation in PCU requires additional considerations, because the maximized data rate (200 kbps) can be achieved for 4 TSL (E)GPRS users in case of multiplexing with GPRS, if the number of connected radio TSLs to one PCU is not more than 64. This limit will not be valid with S11.5 PCU2.
In mixed GPRS/EGPRS networks the DAP usually eats the Abis channels (256 TSLs as limit for one PCU), so the average number of radio TSLs is usually less than 64 TSLs in dense network environment.
The number of EDAP pools depends on EDAP size, territory size and number of cells per EDAP, however the theoretical maximum is 16 for connectivity.More information related to EDAP pool analysis can be found in [11].In the live networks the balance between investment and QoS is the most important question, so the aim is to find the compromised solution between data rate and connectivity.
The detailed description of impact of PCU connectivity limits can be found in [11].5.3.1.5 Connectivity Limit related Measurements - KPIsThe TSL data rate cannot be maximized, because of connectivity limits on EDAP and PCU: DL MCS selection limited by EDAP dap_7a Why not move this to section 5.2.6? UL MCS selection limited by EDAP dap_8c Why not move this to section 5.2.6? DL_TBFS_WITHOUT_EDAP_RES (c076007)
DL_TBFS_WITH_INADEQ_EDAP_RES (c076008)
The EDAP related counter functionality can lead to excessive pegging of c076007 and c076008 even in situation where EDAP size is adequate. Estimated increase with EDAP blocking counters (in case there is adequate EDAP size) is around 2% of all allocations. This additional blocking is real blocking caused by S11.5 DAP slave channel reservation and will be corrected in near future. It will be corrected in CD4.1.
DL MCS selection limited by PCU dap_9 I would just keep dap_9 and dap_10 in this section UL MCS selection limited by PCU dap_10
DL inadequate EDAP channel time (dap_4)
EDAP congestion ratio (dap_5)
Peak DL EDAP usage (c76004) Territory upgrade rejection due to lack of PCU capacity (blck_32)
5.3.2 RLC/MAC TSL Data Rate MaximizationThe following features, parameters and events are studied below for maximizing TSL data rate:
TSL Utilization
TBF Release Delay, TBF Release Delay Extended and BS_CV_MAX
Link Adaptation and Incremental Redundancy
Multiplexing
UL Power Control
Multislot Usage
The detailed information related to the above parameters and functionality can be found in [14] and [15].The maximization is achieved by (E)GPRS related parameters modification only, because the GSM networks performance is already improved based on Chapter 4 items.
The TSL date rate can be maximized if:
There is not any connectivity limitation;
All the interfaces and network elements are having enough capacity.
There is not any functionality limitation;
E.g. the flow control parameters are set properly or the DSP allocation of PCU is working properly
The PSW calls are allocated to the most appropriate layer;
The signal level, C/I and capacity are providing good environment for maximized data rate.
The TBFs are established as fast as possible;
The proper parameter setting is needed to achieve fast TBF establishment
The retransmission ratio is optimized;
The higher retransmission with MCS9 can generate higher RLC/MAC data rate compared to lower retransmission with MSC6. So the higher retransmission does not mean higher throughput for sure. So the target here is to find the balance between MCSs (CSs) and retransmission.
5.3.2.1 TSL Utilization
The TSL utilization can be increased by the setting or usage of the following items: Acknowledgement Request Pre-emptive transmission This is not described here. Either add some explanation on what to do with this, or delete it. One Phase Access with EPCR5.3.2.1.1 Acknowledge Request
The Acknowledge Request parameters are used by the RLC acknowledgement algorithm to determine how frequently the PCU polls the mobile station having a DL 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.In case of EGPRS Downlink traffic the counter is incremented by (1 + EGPRS_DOWNLINK_PENALTY) whenever a negatively acknowledged RLC data block is retransmitted. The mobile station is polled when the counter exceeds the threshold value of EGPRS_DOWNLINK_THRESHOLD. All the Acknowledge Request parameters are listed below:
GPRS Uplink Penalty (Recommendation: 1) GPRS Uplink Threshold (Recommendation: 19) GPRS Downlink Penalty (Recommendation: 1) GPRS Downlink Threshold (Recommendation: 19) EGPRS Uplink Penalty (Recommendation: 1) EGPRS Uplink Threshold (Recommendation: 19) EGPRS Downlink Penalty (Recommendation: 1) EGPRS Downlink Threshold (Recommendation: 19)5.3.2.1.2 UL TBF Assignment with One / Two Phase Access and EPCR
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: one-phase access is possible only if EGPRS Packet Channel Request (EPCR) is supported by the network.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 EPCR is supported by the network. If EPCR is not supported, then EGPRS is forced to use two-phase access even if working in the PCCCH. The benefit of one-phase access compared to two-phase access: One phase access Packet Resource Request (PRR) will be sent faster than in two phase access
One phase next USF is used for PRR message
Typical delay between Immediate Assignment and PRR few milliseconds only
Two phase MS will send PRR and ARAC messages within given single/mutiblock allocation
Typical delay between Immediate Assignment and PRR few hundred milliseconds 5.3.2.1.3 EPCR
EPCR is always on when BSS 11 is used and supported by MS Rel99 onwards. Ultrasite supports EPCR (CX4.0-x) and EDGE support required as well.
One TS is allocated when EDGE one phase access is used on CCCH, so reallocation need is checked when establishment is completed.
Nokia solution has PACKET RESOURCE REQUEST (PRR) implemented with one phase access.
5.3.2.1.4 TSL Utilization related Measurements
The following Signaling / Payload ratio shows the utilization of the BTS from user data point of view:This KPI is not verified, and it seems that the principle is not working in practice, so I suggest to delete this
RLC_MAC_CNTRL_BLOCKS_DL
------------------------------------------------------------------------------------------
(RLC_MAC_CNTRL_BLOCKS_DL +
RLC_DATA_BLOCKS_DL_CS1+RLC_DATA_BLOCKS_DL_CS2 +
sum over MCS1 to 6 (xx) +
sum over MCS7 to 9 (xx)/2 +
sum over MCS11 to 12 (xx)
Where xx = DL_RLC_BLOCKS_IN_ACK_MODE + DL_RLC_BLOCKS_IN_UNACK_MODE 5.3.2.2 TBF Release Delay, TBF Release Delay Ext and BS_CV_MAXThe TBF Release Delay, TBF Release Delay Extended and BS_CV_MAX parameters are used to achieve faster data rate.
5.3.2.2.1 DL_TBF_RELEASE_DELAY (0,1-5sec, def 1s) This parameter is used to adjust the delay in downlink TBF release. An appropriate delay time increases the system performance, since the possibly following uplink TBF can be established faster, and frequent releases and re-establishments of downlink TBF can be avoided.
When the MS wants to send data or upper layer signalling 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
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
The faster UL TBF establishment can be achieved by using PACCH.
But during the release phase, the TBF is kept alive based on sending DL dummy blocks in DL TBF (Polling the mobile, at least one time every 360 ms).
5.3.2.2.2 UL_TBF_RELEASE_DELAY (0,1-3sec, def 0,5s)
This parameter is used to adjust the delay in uplink TBF release. An appropriate delay time increases the system performance, since the possibly following downlink TBF can be established faster.
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. I would like another wording that likes5.3.2.2.3 Extended UL TBF Mode (EUTM)
EUTM is Rel4 feature - MS support and NW-support required. If EUTM is activated the UL TBF Release parameter is ignored.
When PCU does not know MS EUTM support (GPRS one-phase access on CCCH, short access on CCCH)
the PCU schedules USF to MS when EUTM capability is not known
based on MS behavior PCU concludes EUTM supportotherwise UL TBF release done immediately (concurrent DL TBF) or delayed UL TBF release is used.
5.3.2.2.4 BS_CV_MAX
The most important functionalities of BS_CV_MAX parameter from network planning point of view is described in [14].
Recommended value: 9
Basically the BS_CV_MAX parameter should define the RLC round-trip delay in block periods.
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.
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.
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.
It is recommended to tune the BS_CV_MAX parameter so that the minimum value is searched with which the mobile does not send needless RLC retransmissions right after the processing of a Packet UL ACK/NACK message.
After modification of 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.5.3.2.2.5 Measurements
EUTM usage
UL_DATA_CONT_AFTER_COUNTDOWN (c072115)
EXTENDED_UL_TBFS (c072116)
BS_CV_MAX
IGNOR_RLC_DATA_BL_UL_DUE_BSN is changed when BS_CV_MAX is changed.
The MS accepts a retransmission request for a block in Packet UL ACK/NACK even if it has (re)-transmitted the block so recently that the PCU has not had the chance to receive the block before sending the P UL ACK/NACK.
The new QoS formulas (llc_4, llc_5, llc_6) should be able to tell if the throughput gets worse, although it is not so easy to say directly that this is caused by BS_CV_Max changes.The benefit of EUTM and BS_CV_MAX can be measured by RTT tests.
5.3.2.2.6 Parameters
The following setup is recommended:
5. Table Parameter set
5.3.2.3 GPRS Link Adaptation
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.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
20. Figure CS1 and CS2 cross point5.3.2.3.1 Measurements
The following KPIs can be used to measure LA functionality: Downlink GPRS RLC throughput trf_235b
Uplink GPRS RLC throughput trf_233c
Downlink GPRS CS1 ratio rlc_55b
Downlink GPRS CS2 ratio rlc_33
Downlink GPRS CS1 retransmission ratio rlc_12a
Downlink GPRS CS2 retransmission ratio rlc_13
Uplink GPRS CS1 ratio rlc_54b
Uplink GPRS CS2 ratio rlc_32
Uplink GPRS CS1 retransmission ratio rlc_10e
Uplink GPRS CS2 retransmission ratio rlc_11f5.3.2.3.2 Parameters
The following parameters can be used to modify LA functionality.
GPRS Coding Scheme Hopping
GPRS Coding Scheme No Hopping
DL BLER Crosspoint for CS Selection Hopping (DLBH)
UL BLER Crosspoint for CS Selection Hopping (ULBH)
DL BLER Crosspoint for CS Selection Non Hopping (DLB)
UL BLER Crosspoint for CS Selection Non Hopping (ULB)5.3.2.4 EGPRS Link Adaptation
The goal for Link Adaptation (LA) algorithm is to adapt to situations where signal strength compared to interference level is changing within time. Therefore the task of the LA algorithm is to select the optimal MCS for each radio condition to maximize channel throughput and optimize retransmission.LA adapts to path loss and shadowing but not fast fading, while Incremental Redundancy (IR) is better suited for compensating fast fading.
5.3.2.4.1 Measurements
The following KPIs are used to analyze EGPRS LA: Downlink EGPRS RLC throughput trf_236a
Remember that also EDAP congestion can give low throughput. Downlink EGPRS coding scheme selection rlc_57
Downlink EGPRS retransmission ratio rlc_21
Uplink EGPRS RLC throughput trf_234
Uplink EGPRS coding scheme selection rlc_56
Uplink EGPRS retransmission ratio rlc_20b
Uplink EGPRS BLER rlc_605.3.2.4.2 Parameters
The following parameters are used to optimize EGPRS LA:
EGPRS Link Adaptation Enabled (ELA)
Initial MCS for Acknowledged Mode (MCA)
Initial MCS for Unacknowledged Mode (MCU)
Maximum BLER in Acknowledged Mode (BLA)
Maximum BLER in Unacknowledged Mode (BLU)
Mean BEP Offset GMSK (MBG)
Mean BEP Offset 8PSK (MBP)
5.3.2.4.3 Effect of Link Adaptation
There are few parameters that can modify the LA functionality and finally the data rate. The MCA parameter has impact mainly on the small file size transfer. As it can be seen on the Figure 18 below, the higher MCA settings allow higher data rate mainly in good radio condition (the file size is 55KB). If the interference is high (yellow curve below), the effect of MCA setting will be negligible even in case of small file size transfer, too.
Figure 21 MCA settings
The BLA parameter can improve the data rate in case of bad radio environment. If the setting of BLA is e.g. 30 % and the C/I is high, than the MCS degradation will take place quickly, so the retransmission ratio will be lower and the effective RLC/MAC data rate will be probably a bit higher.
The Mean BEP Offset GMSK and the Mean BEP Offset 8PSK parameter recommendation is the default value (0), because the LA functionality is optimized by PL based on simulations.
5.3.2.5 Multiplexing
Multiplexing can reduce the TSL data rate. The affect of multiplexing on TSL data rate is listed below (from S10.5):
Synchronization GPRS USF on DL EGPRS TBF
TSL sharing - GPRS/EGPRS TBFs multiplexing on a TSL
5.3.2.5.1 Synchronization
The synchronization is BSS SW release dependent:
In S11 basic release:
In case of GPRS territory only (if EGENA=N): the synchronization in every 17th block is not needed anymore.
In case of (E)GPRS territory (if EGENA=Y): "For synchronization purposes, the network sends at least one radio block using CS-1 or MCS-1 in the downlink direction every 360 milliseconds on every timeslot that has either uplink or downlink TBFs. If there are only EGPRS TBFs on the timeslot, the synchronization block is sent using MCS-1. If there are also GPRS TBFs on the timeslot, the synchronization block is sent using CS-1"
In S11 CD1.2 onwards:
In case of GPRS territory only (if EGENA=N): the synchronization in every 17th block is not needed anymore.
In case of (E)GPRS territory (if EGENA=Y): 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"
If any MS has not been decoding anything for a 17 block period, the PCU put the limit of the MCS (Modulation and Coding Scheme)/CS (Coding Scheme) for GPRS in the next downlink block so low that the MS can be expected to decode it. The block may be addressed to other MSs too but the MCS/CS is limited according to the rules below.
An EGPRS MS is expected to decode blocks that are using lower or equal MCS/CS than link adaptation has selected for the MSs downlink TBF. If any EGPRS MS only has uplink TBF, (M)CS-1 or (M)CS-2 in the downlink is considered robust enough to be correctly decoded.
An GPRS MS is expected to decode blocks that are using CS-1 or CS-2.
If any GPRS MS has not been decoding anything for a 17 block period, the PCU sends an CS-1 or CS-2 coded block. If possible, the turn is given to a GPRS downlink TBF. If only EGPRS TBF exist on the downlink connection, the PCU sends a CS-1 (dummy) control block.
So in S11 CD 1.2 onwards the CS1/MCS1 usage is reduced significantly compared to S11 basic release backwards.
5.3.2.5.2 GPRS and EGPRS Multiplexing
GPRS and EGPRS TBFs can be multiplexed dynamically on the same timeslot.
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 [04.60] 5.2.4a.If the RLC has selected 8-PSK MCS then the MCS will be GMSK MCS as follows:
Initial transmission of a RLC block: The downlink transmission of EGPRS DL TBF is forced to GMSK only on the timeslots used by the GPRS UL TBF and only for the block periods when GPRS USF is actually transmitted. Retransmission of a RLC block: If the RLC is retransmitting a downlink data block using 8-PSK MCS, USF will not be given to GPRS TBF at this time.
5.3.2.5.3 Timeslot sharing
If the timeslot is shared among TBFs, then the TSL data rate will be reduced. The rate reduction is the effect of territory occupation and needs further investigation to know the exact impact of it (if the TSL data rate is 50 kbps and this TSL is shared by two users, then the user RLC/MAC data rate will be less than 25 kbps, because of increased territory occupation).
5.3.2.5.4 Measurements
Amount of TBFs / TSL
Uplink TBFs pr timeslot tbf_37c
Downlink TBFs pr timeslot tbf_38cGPRS TBF multiplexed with EGPRS TBF
8PSK coding scheme downgrade due to GPRS multiplexing rlc_615.3.2.5.5 Parameters
The following parameters have direct impact on multiplexing:
Channel Allocation Algorithm tends to separate EDGE TBFs and GPRS TBFs on different RTSL to avoid multiplexing, if only one PS Territory exists in the cell or there is high load. The algorithm checks the need for re-allocation every TBF_LOAD_GUARD_THRSHLD (more information is available in [2]), in order to separate sessions.
The detailed description of TBF allocation and reallocation can be found in [9].5.3.2.6 UL Power Control
Theoretically (the test results below are actually real results, not theory)optimized Uplink Power Control can achieve higher signal level as well.
The following graph shows the function of MS output power and DL Rx Lev.
Figure 22 Effect of gamma and alpha 0.8
With lower values of Gamma the MS output power is increased, when the user is closer to the BTS. This can help to reduce retransmissions in the UL and improve the performance. The drawback would be that with lower values of Gamma interference in the UL is increased too.
Practically it is not so easy to measure the impact of PC on signal level and finally on data rate.
5.3.2.6.1 MeasurementsThe following KPIs can be used to observe the effect of UL PC functionality.
Uplink GPRS CS1 ratio rlc_54b
Uplink GPRS CS2 ratio rlc_32
Uplink GPRS CS1 retransmission ratio rlc_10e
Uplink GPRS CS2 retransmission ratio rlc_11f
Uplink EGPRS RLC throughput trf_234
Uplink EGPRS coding scheme selection rlc_56
Uplink EGPRS retransmission ratio rlc_20b
Uplink EGPRS BLER rlc_60
LLC throughput for 4 timeslot capable EDGE MS (pr QoS class) llc_6
LLC throughput for other than 4 timeslot capable EDGE MS (pr QoS class) llc_5
LLC throughput for GPRS MS (pr QoS class) llc_4
Low UL PS power gives bad performance, high UL PS power with low PS traffic gives good performance and high UL PS power with high UL PS traffic gives bad performance. Yes, this is what we expect but not verified yet, so maybe a bit softer statement would be in orderCSW RX Qual must be checked on those TRXs, where (E)GPRS traffic is generated.
5.3.2.6.2 Parameters
Alpha and Gamma parameters have impact on UL PC functionality:
Recommended settings should provide good UL throughput in a case where maximum of -105 dBm level interferer is present.
Still, in strong signal conditions, MS output power is limited to avoid unnecessary UL interference generation especially in high altitude locations.
In practice, estimating impact of possible additional interference caused by higher mobile output power is very difficult. This impact is anyway considered clearly a secondary issue compared to improved UL throughput.
This should provide an improvement to UL throughput in all Nokia supplied networks that still use previous default values.
5.3.3 Multislot Usage MaximizationWhen the TSL data rate is maximized, the next optimization step is to maximize the PSW territory. The aim of this maximization is to provide the required TSLs based on multislot capability of MS.
The multislot usage can be limited by:
TSL Unavailability
CSW traffic and HSCSD
Free TSL setting
5.3.3.1.1 TSL unavailability
The TSL unavailability (for any traffic due to fault on normal TRXs) can be checked by ND226 - uav_13.
5.3.3.1.2 CSW traffic and HSCSD
Average CS traffic on normal TRXs can be checked by trf_97. This KPI includes all types of CS traffic (single TCH, HSCSD) on normal TRXs.
In principle CSW has always priority over PSW and the share between HSCSD and (E)GPRS makes it possible for one multislot HSCSD user to block many (E)GPRS users from the service.Protection of (E)GPRS is needed based on dedicated GPRS capacity, MinHSCSDcapacity and DefaultGPRScapacity. The Table 4 shows the service with different parameter: Is the table correct, or should it be dedicatedGPRScapacity?
Table 6 Prioritization between HSCSD and (E)GPRS
5.3.3.1.3 Territory Downgrade
The territory downgrade heavily depends on the size of dedicated and default territory. There are two types of downgrades: Territory downgrade due to CSW traffic rise (Downgrade request below Default territory because of rising CSW (c1179)) Territory downgrade due to less PSW traffic (Downgrade request back to the default territory when there is no need for additional channels anymore (c1181))5.3.3.1.4 Territory Upgrade Request Rejection
Territory upgrade request rejection also limits the data rate: Territory upgrade request rejection beyond default territory. Upgrade request beyond Default territory for additional resources, which can be rejected because of (c1174):1. PCU and EDAP capacity limitation (256 Abis TSL per PCU)
2. High CSW load
3. No (E)GPRS capable resource left (no (E)GPRS enable TRX or the maximum (E)GPRS capacity reached). In practice, no! Because there will not be any territory upgrade requests if the max capacity has been reached5.3.3.1.5 Free TSLs
The BSC attempts to keep one or
