Huawei PS-GPRS-EDGE Radio Network Optimization

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Copyright © 2009 Huawei Technologies Co., Ltd. All rights reserved.

GPRS Principles

1

Page1Copyright © 2009 Huawei Technologies Co., Ltd. All rights reserved.

ForewordGPRS principle is the basic part of the whole GPRS system

and the succeeding products learning.

This slide will help us to understand the GPRS system

networking and wireless subsystem etc.

2


ObjectivesUpon completion of this course, you will be able to:

Know the GPRS system structure

Describe the GPRS important interfaces

Understand the GPRS channel structures

Master the GPRS relevant numbering

3


Contents1. GPRS System Overview

2. GPRS Architecture

3. GPRS Network Interfaces & Protocols

4. GPRS Wireless Subsystem

5. GPRS Location Area

4


Circuit Switch (CS)

CS

F

CS

CS CS

CS

A

B

C

D

E

G

H

I

J

K

L

5


Packet Switch (PS)

PS

PS

PS

1 2 3

12

3

13

2

2

1 3

2 2

1 3

1 2 3

12

3

PS

PS

PS

PS

PS

PS

PS

1 2 3

12

3

13

2

2

1 3

2 2

1 3

1 2 3

12

3

PS

PS

PS

AC

B D

6


GSM Development Evolution

GSM 9.6 Kb/s

GPRS21.4 Kb/s

EGPRS59.2 Kb/s

384 Kb/s UMTS

2 G

2.5 G

2.75 G

3 G

HSCSD14.4 Kb/s

ECSD38.8 Kb/s

CS

PS

EDGE

7


What is GPRS and EDGE?Abbreviation of General Packet Radio Service.

GPRS is an end-to-end packet switching technology

provided on the basis of GSM technology.

It has much interactive services with the existing GSM

circuit switching system.

GPRS supports wireless access rate of up to 171.2Kbps.

EDGE (Enhanced Data Rates for GSM Evolution) EGPRS (Enhanced GPRS)

EGPRS supports wireless access rate of up to 473.6Kbps.

ECSD (Enhanced CSD, Enhanced HSCSD-High Speed Circuit

Switched Data)

•GPRS is the abbreviation of General Packet Radio Service.•GPRS network introduces packet switching functional entities in the GSM network to implement data transmission in the packet mode.•GPRS can be regarded as the service expansion based on the GSM network for supporting mobile subscribers access the Internet of other packet data networks via packet data mobile terminal. Making full use of the existing GSM network,small investment and quick rewarding,all of these benefit to protect the existing investment and obtain maximum benefits for the operators.

8


GPRS&EDGE Coding Rate

8PSKGMSK

9.0513.4

15.6

21.4

8.811.2

14.817.6

22.4

29.6

44.8

54.4

59.2

0.00

10.00

20.00

30.00

40.00

50.00

60.00

CS-1 CS-3 CS-4 MCS-1 MCS-2 MCS-3 MCS-4 MCS-5 MCS-6 MCS-7 MCS-8 MCS-9

Kbps

GPRS

EGPRS

CS-2

9


Adjustments to GSM Network

BSS CS Core Network

A

PS Core Network

PCU

BSS NSS

Gb

Pb

Gs

10


Most Popular GPRS Applications

E-mail

Web Browsing

Information Services

Moving Images

Still Images

Remote LAN Access

File Transfer

Job Despatch

Traffic Information

Sport Report

Weather Forecast

Stock Market

PublicInformation

Service

Email

Web Browsing

Still Images

File Transfer

Moving Bank

Live News

PersonalInformation

Service

11


Advantages and Disadvantages of GPRS

Advantages

Share resource with GSM

High resource utilization

Fast transmission rate

Always on line

Short access time

Disadvantages

Slower data rates in practice than anticipated in theory

Suboptimal modulation technique

12







13


CS & PS Logic Structure

HLRAUC

GPRSRegister

MSC/VLR

BSCAbis

D

C

CS

GMSC PSTN

BTS

BSS

CN

E

A

PS Gs

SGSN

GGSN

Gb

Gn

Gc

Gr

Gi

Internet

G-Abis Pb

PCU

TRAU

14


Gf

GiGn

Gc

Gp

Gs

MSC/VLR

Gr

SGSN

Gd

SMS-GMSCSMS-IWMSC

GGSN

EIR

SGSN

Gn

GPRSBackbone

ATM/DDN/ISDN/Ethernet, etc

CNCN--PSPSGGSN

GiCG

GPRS System Structure

Gb

SS7

HLR

Ga

Intranet/InternetFirewall

RADIUS

WAP Gateway

Other PLMN

BTS

BSCBSSBSS

AbisPCU

Gb

BTS

BSCBSSBSS

AbisPCU

X.25

DNS BG

MS

MS

15


GPRS MSClass A

The MS is attached to both GPRS and other GSM services and the MS supports simultaneous operation of GPRS and other GSM services.

Class B The MS is attached on GPRS network and GSM network simultaneously but not enabling circuit switching and packet switching services at the same time.

services are selected automatically.

Class CThe MS is attached to either GPRS or other GSM services. Alternate use only.

services are selected manually or default selected service.

16


Functions of PCU (Packet Control Unit)

Packet wireless resource management function (RLC/MAC

protocol function)

Wireless resource management functions of GPRS BSS

Circuit paging coordination

G-Abis interface processing function

Function related with GPRS BTS

17


Functions of PCU (Packet Control Unit)

Pb interface processing function

LAPD link between BSC and PCU

Layer-3 signaling between BSC and PCU

Gb interface processing function

Data packet relay on wireless interface and Gb interface

Mobility management (cell updating procedure)

Downlink traffic control (wireless QoS guarantee)

Provides physical and logical data interface out of the BSS for packet data traffic

LLC layer PDU segmentation/reassembly of RLC blocks

Packet data transfer scheduling

ARQ functions

Radio channel management function

18


Functions of SGSN (Serving GPRS Support Node)

Packet routing

MS Session management

Authentication and Ciphering

Mobility management

Billing information collection

19


Functions of GGSN (Gateway GPRS Support Node)

Interface between GPRS backbone and external PDNs.

PDP Conversion and context management

IP address assignment management

Packet routing to/from SGSNs

Billing information collection

20


Functions of CG (Charging Gateway)

Real-time collection of GPRS bills

Temporary storage and buffering of GPRS bills

Pre-processing of GPRS bills

Sending GPRS bills to the billing center

21


Functions of MSC/VLRWhen Gs interface is installed, MSC/VLR can support

Establishment and maintenance of the association between SGSN and MSC/VLR.

GPRS combined mobility management procedure.Combined IMSI/GPRS attachment/detachment.

Combined location area/routing area updating.

Circuit paging coordination function.

The wireless resource usage can be greatly improved.

22


Functions of HLR/AUCSaving and updating GPRS subscriber subscription data

User authentication

Providing location/routing information and processing

needed in mobility management and routing, for example:

Saving and updating user service SGSN number and address

GPRS user location deletion indication

Whether MS is reachable.

Subscriber tracing (optional)

23


Functions of SMS-GMSC/SMS-IWMSC

The SMS-GMSC and SMS-IWMSC are connected to the SGSN

via the Gd interface to enable GPRS MSs to send and receive

SMs over GPRS radio channels.

After Gd interface is installed, short messages can be sent via

GPRS, which reduces the occupation on SDCCH and cuts down

the influence on voice services by SMS services.

The operator can select to send SMS via MSC or SGSN.

MS SGSN SMS-IWMSCSMS-GMSC

GdSMS

SMS-IWMSC(Interworking MSC For Short Message Service):A function of an MSC capable of receiving a short message from within the PLMN and submitting it to the recipient SC.For example:The MSC forwards the SM to the SMS-IWMSC, which is responsible for processing SMs submitted by the MS.SMS-IWMSC:The SMS Interworking MSC acts as an interface between the PLMN and a Short Message Service Centre (SC) to allow short messages to be submitted from Mobile Stations to the SC. SMS-GMSC(Gateway MSC For Short Message Service):A function of an MSC capable of receiving a short message from an SC, interrogating an HLR for routing information and SMS info, and delivering the short message to the VMSC of the recipient MSFor example:The SMS system submits the message transfer request to the SMS-GMSC, which is responsible for processing delivered SMs. SMS-GMSC:The SMS Gateway MSC (SMS-GMSC) acts as an interface between a Short Message Service Centre and the PLMN, to allow short messages to be delivered to mobile stations from the Service Centre (SC)。

24


Functions of BG (Border Gateway)BG enables the following protocols necessary for interworking between operators

Security protocol: IPSec and firewall are recommended

Routing protocol: BGP is recommended

Billing protocol: determined by the operators with negotiation; BG might be needed in collecting billing information

It is normally based on routers

It can be combined with GGSN in physical.

BG does not exclusively belong to the GPRS network.

Gp

PLMN AGSN RR

BG RR

BG GSN PLMN B

IPsec (IP security) is a standardized framework for securing Internet Protocol (IP) communications by encrypting and/or authenticating each IP packet in a data stream. A protocol for exchanging routing information between gateway host s (each with its own router ) in a network of autonomous system s. BGP is often the protocol used between gateway hosts on the Internet.

25


Functions of DNS (Domain Name System)The following two types of DNSs may be adopted in the GPRS network:

The DNS between the GGSN and external networks

The DNS on the GPRS backbone network. Provides two types of functions:

a. Resolve the GGSN IP address based on the Access Point Name (APN) in the process of the PDP context activation;

b. Resolve original SGSN IP address based on the original routing area No. in the process of the update of inter-SGSN routing area.

DNS does not exclusively belong to the GPRS network.

GPRS BackboneSGSN

DNS Server

SGSN

DNS（Domain Name System）The following two types of DNSs may be adopted in the GPRS network:

The DNS between the GGSN and external networks: Implements resolution of the domain name of external network, and functions as the ordinary DNS on the Internet.The DNS on the GPRS backbone network. Provides two types of functions:

a. Resolve the GGSN IP address based on the Access Point Name (APN) in the process of the PDP context activation; b. Resolve original SGSN IP address based on the original routing area No. in the process of the update of inter-SGSN routing area. The DNS is not a proprietary entity of the GPRS network.

26


Functions of RADIUS Server (Remote Authentication Dial In User Service Server)

It is a protocol used by Remote Access Server's for user

Authentication.

The RADIUS server stores the authentication and

authorization information of subscribers.

It also performs subscriber identity authentication in the

case of non-transparent access.

RADIUS Server does not exclusively belong to the GPRS

network.

27







28


Contents3. GPRS Network Interfaces & Protocols

3.1 Interface and Protocol Stack

3.2 Um Interface

3.3 G-abis/Pb Interface

3.4 Gb Interface

3.5 Gs Interface

29


Network interface types

GPRS backbone network

SGSNSGSN

SGSNSGSNGGSNGGSNGn

IP interface

SS7 interface

BSS MSCSMS-GMSC

AUm

PDP network(IP/X.25)

Gi

TE

MT

MS

HLR

Gs

Gr

Gd

Gc

Gb

30


Interface in GPRS Network

The interface between MS and GPRS network sideUm

The interface between the SGSN and EIR (optional). GfThe interface between the SGSN and MSC/VLR (optional). GsThe interface between the SGSN and HLR. GrThe interface between GSNs of different PLMNs. GpThe interface between SGSNs and between SGSN and GGSN in the PLMN. GnThe reference point between the GPRS and external packet dataGi

The interface between SMS and GMSCThe interface between SMS-IWMSC and SGSNGd

The interface between the GGSN and HLR (optional). GcThe interface between the SGSN and BSS. Gb

The reference point between the Mobile Terminal (MT) (for example, mobile phone) and the Terminal Equipment (TE) (for example, the portable computer).

R

DescriptionInterface

31


Data transmission plane

MAC: Media Access ControlRLC: Radio Link ControlLLC: Logical Link Control

BSSGP: BSS GPRS ProtocolSNDCP: Sub-Network Dependency Convergence ProtocolGTP: GPRS Tunneling Protocol

Application

IP/X.25 IP/X.25 IP/X.25

SNDCP GTP

LLC LLC UDP/TCP UDP/TCP

RLC BSSGP BSSGP IP IP

MAC MAC NetworkService

NetworkService L2 L2

L2 (MAC)

PhysicalLayer

PhysicalLayer

PhysicalLayer

PhysicalLayer

PhysicalLayer

PhysicalLayer

PhysicalLayer

MS BSS SGSN GGSN

relay

relaySNDCP GTP

Um Gb Gn Gi

RLC

The Relay function provides buffering and parameter mapping between the RLC/MAC and the BSSGP. For example, on the uplink the RLC/MAC shall provide a TLLI. The Relay function shall then make it available to BSSGP.

32


MS-SGSN signaling plane

GMM: GPRS Mobility Management

SM: Session Management

MS BSS SGSN

BSSGP

GMM/SM

LLC

RLC

MAC

GSM RF

GMM/SM

LLC

BSSGP

L1bisUm Gb

NetworkService

RLC

MAC

GSM RF L1bis

NetworkService

Relayrelay

Um interface:

Physical layer: wireless coding/decoding, channel multiplexing and mapping, wireless link control and wireless measurement

RLC/MAC: wireless interface media access and link control function

LLC: providing a reliable logic link between MS and SGSN for data transmission. LLC protocol can support both acknowledged mode and unacknowledged mode. It supports both encryption and decryption modes

SNDCP: Layer-3 transmission protocol. As the transition between the network layer and the subnet layer, it implements segmentation/assembling and compression/decompression on IP/X.25 subscriber data

GMM/SM: Layer-3 signaling protocol

Gb interface:

L1bis: physical transmission layer based on E1 or T1

NS: based on FR; used to transmit BSSGP PDU of the upper layer

BSSGP: On the transmission platform, this protocol is used to provide a connectionless link between BSS and SGSN for unacknowledged data transmission; on the signaling platform, it is used to transmit QoS and routing information related with the wireless section; it is also used to process paging requests and implement traffic control on data transmission

33


Contents3. GPRS Network Interfaces & Protocols

3.1 Interface and Protocol Stack

3.2 Um Interface

3.3 G-abis/Pb Interface

3.4 Gb Interface

3.5 Gs Interface

34


Protocol Layer of Um Interface GMM (GPRS Mobility Management): operates in the signalling plane of GPRS supports mobility management functionality.

SM (Session Management): processes procedure that GPRS MS connects to the external data network.

SNDCP (Subnetwork Dependent Convergence Protocol): Multiplexing of several PDPs, compression / decompression and Segmentation of user data.

LLC (Logical Link Control ): This layer provides a highly reliable ciphered logical link between an MS and its SGSN.

RLC:Segmentation and re-assembly between LLC PDUs and RLC blocks.

MAC: defines the procedures that enable multiple mobile stations to share a common transmission medium.

LLC

RLC

MAC

RF

Physical Link

SND

CP

SMS

GM

M/S

M

GMM (GPRS Mobility Management)This protocol that operates in the signalling plane of GPRS supports mobility management functionality such as GPRS attach, GPRS detach, security, routing area update, location update, roaming, authentication, and selection of encryption algorithms.

SM (Session Management)It is the processing procedure that GPRS MS connects to the external data network. The main function is to support the processing of PDP mobile scenario.

Logical Link Control (LLC): This layer provides a highly reliable ciphered logical link between an MS and its SGSN.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.

35


MM State

IDLE GMM context is not established; MS is not reachable.

MS can implement data transmission.

GMM context is established; MS can receive paging but cannot implement data transmission.

The MS performs MM procedures to provide the network with the actual

selected cell.

SGSN performs the MM on cell level.

READY

STANDBYThe location information in the SGSN MM context contains only the GPRS RAI.

Pages for data or signalling information transfers may be received. It is also

possible to receive pages for the CS services via the SGSN. Data reception

and transmission are not possible in this state.

Data transmission to and from the mobile subscriber as well as the paging of

the subscriber are not possible

The Mobility Management (MM) activities related to a GPRS subscriber are characterised by one of three different MM states.

36


MM State Model

IDLE READY STANDBY

IDLE READY STANDBY

MM State Model of MS

MM State Model of SGSN

GPRS Attach

GPRS Detach

READY timer expiry or

PDU transmission

PDU reception

Implicit Detach or Cancel Location

GPRS Attach

Force to STANDBY

READY timer expiry orForce to STANDBY or

Abnormal RLC condition

GPRS Detach or Cancel Location

37


RLC/MAC Block Generation

RLC/MAC block

Subscriber data RLC/MAC headLLC headSNDCP head LLC FCS

LLC frame

Subscriber IP packet (N-PDU)

SNDCP PDU(SN-PDU)

Network Layer

SNDCP Layer

LLC Layer

RLC/MAC Layer

38


Physical Channel The same as in GSM

The same frequency

The modulation mode

The same TDMA frame definition

The same burst pulse definition

…

The differences between GPRS and GSM

The Multi-frame structure

The channel coding

…

Application

IP/X25

SNDCP

LLC

RLC RLC BSSGP

MAC MAC Framerelay

PhysicalLayer

PhysicalLayer

PhysicalLayer

MS BSS

Relay

39


Packet Logic Channels

The specific type of PDCH (except PRACH) is determined by

RLC/MAC head and RLC/MAC control message type.

TCH

BCCH

PCH, RACH, AGCH,NCH

Packet service channel

PACCH

Packet Logic Channel

Packet control channel

PBCCH

PPCH PRACH PAGCH

PCCCH PDCCH

PDTCH/U PDTCH/D PNCH

PTCCH/U PTCCH/DSACCH

40


Channel AbbreviationPacket Data Traffic CHannel Uplink - PDTCH/UPacket Data Traffic CHannel Downlink - PDTCH/DPacket Broadcast Control CHannel - PBCCHPacket Common Control CHannel - PCCCHPacket Dedicated Control Channel - PDCCHPacket Paging CHannel - PPCHPacket Random Access CHannel - PRACHPacket Access Grant CHannel - PAGCHPacket Notification CHannel - PNCHPacket Associated Control CHannel - PACCH Packet Timing advance Control CHannel Uplink - PTCCH/UPacket Timing advance Control CHannel Downlink -PTCCH/D

41


PDTCH (Packet Data Traffic CHannel)

All packet data traffic channels are

uni-directional.

Uplink (PDTCH/U) for a mobile

originated packet transfer.

Downlink (PDTCH/D) for a mobile

terminated packet transfer.

Packet service channel

PDTCH/U PDTCH/D

42


PBCCH (Packet Broadcast Control CHannel)

The PBCCH broadcasts parameters used by the MS to access the network for packet transmission operation.

The PBCCH also carries the information transmitted via the BCCH to allow circuit switching operation.

The MS in GPRS attached mode monitors the PBCCH only, if PBCCH is available, otherwise, the BCCH shall be used to broadcast information for packet operation.

The existence of the PBCCH in the cell is indicated on the BCCH via SI13.

Packet control channel

PBCCH

43


PCCCH (Packet Common Control CHannel)

PPCH

Downlink only, used to page MS.

PRACH

Uplink only, used to request allocation of one or several PDTCH/Us or PDTCH/Ds.

PAGCH

Downlink only, used to allocate one or several PDTCHs.

PNCH

Downlink only, used to notify MS of PTM-M call.

If no PCCCH is allocated, the information for packet switching operation is transmitted on the CCCH. If a PCCCH is allocated, it may transmit information for circuit switching operation.

PPCH PRACH PAGCH

PCCCH

PNCH

44


PDCCH (Packet Dedicated Control Channels)

PACCH

Bi-directional, used to transmit the packet signaling in data transmission.

PTCCH/U

Used to transmit random access bursts to allow estimation of the timing advance for one MS in packet transfer mode.

PTCCH/D

Used to transmit timing advance updates for several MS. One PTCCH/D is paired with several PTCCH/U's.

PACCH

PDCCH

PTCCH/U PTCCH/D

45


Combinations of Packet Logic Channel

Mode 3: PDTCH+PACCH+PTCCH

Mode 1: PBCCH+PCCCH+PDTCH+PACCH+PTCCH Mode 2: PCCCH+PDTCH+PACCH+PTCCH

In case of small GPRS traffic, GPRS and circuit services share the same BCCH and CCCH in the cell. In this case, only combination mode 3 is needed in the cell.

With the increase of traffic, the packet public channel should be configured in the cell. Channel combination mode 1 and mode 2 should be adopted.

Mode 4: PBCCH+PCCCH

(PCCCH=PPCH+PRACH+PAGCH+PNCH）

46


Packet Wireless Channel Configurations

Reason of adopting static PDCHTo enable that GPRS MS is constantly online in the cell.

To ensure certain QoS of GPRS services.

Reason of adopting dynamic PDCHGPRS and GSM share wireless resources.

Wireless resources should be adopted in priority; on the other hand, QoS of voice services should be ensured.

In a cell, the percentage of packet switching services and the percentage of circuit switching services are constantly changing.

Dynamic PDCH is not visible for voice services.

47


Packet Wireless Channel Configurations

General principles The cell should be configured with static PDCH to enable MS to

be normally attached on GPRS network as well as certain QoS of

GPRS services.

Dynamic PDCH should be configured according to the GPRS

traffic forecast, which should be adjusted as TCH or PDCH usable

in the operation process according to the cell traffic status.

Circuit switching services can seize the channel used by GPRS

services.

48


Mapping of Packet Logic Channel A radio block is a 4-normal-burst sequence that carries a

RLC/MAC PDU (Protocol Data Unit).

I = Idle frame T = Frame used for PTCCHB0 ~ B11 = Radio blocks

51250

B0 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11T I T I

456 bits

0 1 2 3 4 5 6 7

1 TDMA frame

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

49


Mapping of Packet Logic Channel

51

4

3

5

6

7

0

1

2 B0 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11T I T I

500

BCCH

PDCH

TCH

S B B B B C C C C F S CC C C C C C C F S C C CCC C C C F S C C C C C CC C F S C C C C C C C C I

T T T T T T T T T T T S T T T T T T T T T T T T IT

F

25

2512

50


Transmission Principle of Data Packet on Um Interface

Subscriber data RLC/MAC headLLC headSNDCP head

Subscriber IP packet

LLC FCS

SNDCP PDU

LLC PDU

RLC/MAC block

Physical layer

B0 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11T I T I

NB

NB

NB

NB

51


Allocation of Wireless Packet Resources

Wireless resource allocation and wireless transmission adopt the wireless block

(BLOCK) as the basic unit.

Each PDCH can be used by several MSs; each MS can use multiple PDCHs at the

same time.

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10

B11

B0

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10

B11

B0

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11B0

MS3MS2

TS 0

TS 1

TS 2

MS1

52


Basic Conceptions about Radio Block

USF(Uplink State Flag) 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

B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0

T

I

T

I

UL

DL

USF=1USF=1

USF=1USF=2

USF=2USF=3

USF=3USF=3

USF=3USF=4

USF=4USF=4

T

I

T

I

USF=1

USF=2

USF=3

USF=4

MS1

MS2

MS3

MS4

USF=1

……

B0 I……

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.

53


Basic Conceptions about Radio Block

TBF (Temporary Block Flow)

A Temporary Block Flow (TBF) is a physical connection used by the

two RR entities（the RR entity of the MS and that of the BSS） to support the unidirectional transfer of LLC PDUs on packet data

physical channels.

A TBF is temporary and is maintained only for the duration of the data

transfer.

TFI (Temporary Flow Identity)

Each TBF is assigned a Temporary Flow Identity (TFI) by the network.

The TFI field is five bits in length.

The same TFI value may be used concurrently for TBFs in opposite directions. The TFI is assigned in a resource assignment message that precedes the transfer of LLC frames belonging to one TBF to/from the MS. The same TFI is included in every RLC header belonging to a particular TBF as well as in the control messages associated to the LLC frame transfer (e.g. acknowledgements) in order to address the peer RLC entities.

54


Contents4. GPRS Wireless Subsystem

4.1 Packet Channels

4.2 Medium Access Modes

4.3 MS Multi-TS Ability

4.4 Power Control

4.5 Network Control Modes

55


Medium Access Modes Uplink resource allocation mode

Dynamic allocation (supported by all MSs and all networks)

The mobile station detecting an assigned USF value for each assigned PDCH and block or group of four blocks that it is allowed to transmit on that PDCH.

Fixed allocation (supported by all MSs and all networks)

Fixed bit mapping is adopted to determine the allocated blocks in the allocation period without an assigned USF.

Extended dynamic allocation (optional for the network)

The mobile station detecting an assigned USF value for any assigned PDCH allowing the mobile station to transmit on that PDCH and all higher numbered assigned PDCHs in the same block or group of four blocks.

Downlink resource allocation mode

Dynamic allocation and fixed allocation.

Three medium access modes are supported:- Dynamic Allocation characterised by that the mobile station detecting an assigned USF value for each assigned PDCH and block or group of four blocks that it is allowed to transmit on that PDCH;- Extended Dynamic Allocation characterised by the mobile station detecting an assigned USF value for any assigned PDCH allowing the mobile station to transmit on that PDCH and all higher numbered assigned PDCHs in the same block or group of four blocks- Fixed Allocation characterised by fixed allocation of radio blocks and PDCHs in the assignment message without an assigned USF. Fixed Allocation may operate in half duplex mode, characterised by that downlink and uplink TBF are not active at the same time. Half duplex mode is only applicable for multislot classes 19 to 29.

Either the Dynamic Allocation medium access mode or Fixed Allocation medium access mode shall

be supported by mobile stations and all networks that support GPRS. The support of Extended

Dynamic Allocation is optional for the network.

The Dynamic Allocation and Fixed Allocation modes shall be supported in all mobile stations. The

support of Extended Dynamic Allocation is mandatory for mobile stations of multislot classes 22, 24,

25 and 27. The support of Extended Dynamic Allocation for mobile stations of all other multislot

classes are optional and shall be indicated in the MS Radio Access Capability.

In the case of a downlink transfer, the term medium access mode refers to the measurement time

scheduling, for the MS to perform neighbour cell power measurements

56



4.1 Packet Channels



4.4 Power Control


57


MS Multi-TS Ability Concept of MS multi-TS ability

Types

Type 1: Non-simultaneous TRX

Type 2: Simultaneous TRX

the multi-TS ability level is 1-29; the bigger the level, the stronger the multi-TS ability.

1~12 (Type 1),up to 4 timeslots in any direction

13~18 (Type 2),ranges between 3~8 timeslots

19~29 (Type 1)

BSS allocates resources according to the MS multi-TS ability, requested QoS and current resource configuration.

58



4.1 Packet Channels



4.4 Power Control


59


Power Control Power control can improve the spectrum usage and system

capacity as well as reduce MS power consumption.

As there is no continuous bi-directional connection in the packet

data transmission process, GPRS power control is very

complicated.

Uplink power control includes open-loop and close-loop power

control.

About downlink power control, there is no specific definition in

protocol. It lies on the BTS and its algorithm needs information

about downlink, so downlink power control needs MS sends

channel quality reports to BTS.

60



4.1 Packet Channels



4.4 Power Control


61


Network Control Modes During the network controlled cell re-selection, the network

may request measurement reports from the MS and control

its cell re-selection. Hence, three types of mode are defined

as follows:

NC0: Normal MS controls

NC1: MS control with measurement reports

NC2: Network control

The network subsystem must support NC0 and should

gradually support NC1 and NC2.

During the network controlled cell re-selection, the network may request measurement reports from the MS and control its cell re-selection. Hence, three types of mode are defined as follows:

NC0: Normal MS controls. The MS shall perform autonomous cell re-selection.NC1: MS control with measurement reports. The MS shall send measurement reports to the network. The MS shall perform autonomous cell re-selection.NC2: Network control. The MS shall send measurement reports to the network. The MS shall not perform autonomous cell re-selection.

The network subsystem must support NC0 and should gradually support NC1 and NC2.

62


Network Control ModesMS NC0 NC1

NC2

The MS shall perform autonomous cell re-selection

MS

The MS shall perform autonomous cell re-selection

The MS shall send

measurement reports

to the network

MS BTS

MR

Cell re-selection

command

The MS shall not

perform autonomous cell

re-selection

63







64


Relationship among Location Areas

CELL

CELL

CELL

CELL

RA1

RA2

CELL

CELL

RA3

CELL

CELL

CELL

SGSN1SGSN2

BSC1

BSC2

BSC3

LA1 LA2

65


Location Area Identification

MCC MNC LAC

LAI (Location Area Identification)MCC：Mobile Country Code, it consists of 3 digits. For example: The MCC of China is "460"

MNC：Mobile Network Code, it consists of 2 digits. For example: The MNC of China Mobile is "00"

LAC：Location Area Code, it is a two bytes hex code. The value 0000 and FFFF is invalid

For example: 460008C90

66


RAIRouting area is the sub-set of the location area. In special cases, the two areas are equal

The division of the routing area is related with traffic distribution and SGSN processing ability


MCC MNC LAC RAC

Routing Area Identification

67


CGICI (Cell Identity): This code uses two bytes hex code to identify the radio cells within a LAI.

RAC is only unique when presented together with LAI.

CI is only unique when presented together with LAI or RAI.

CGI = MCC+MNC+LAC+{RAC}+CI


MCC MNC LAC CI

CGI

RAC


68


CGI

Relationship among location areasLAI

MCC+ MNC+ LAC

LAI

RAI

MCC+ MNC+ LAC+RAC

CGI /CellID

MCC+ MNC+ LAC+{RAC}+CI

RAI

69


SummaryGPRS System Overview

GPRS Architecture

GPRS Network Interfaces & Protocols

GPRS Wireless Subsystem

GPRS Location Area

70

Thank youwww.huawei.com

71

www.huawei.com


GPRS EDGE Mobile Management Algorithm

72


ForewordGPRS Mobility Management is a GPRS signaling protocol that handles mobility issues such as roaming, authentication and selection of encryption algorithms. It is important to enable the network to keep track the current location of the MS in order for the paging to be performed smoothly. With the proper setting of the GMM parameters, we can shorten the access delay of the MS.

73


ReferencesGBSS8.1 BSC6000 Feature Description

74


ObjectivesUpon completion of this course, you will be able to:

Understand the GPRS Mobility Management procedure

Familiar with the GMM state model

Understand the cell reselection algorithm

Recognize the cell update and routing area update flow

Realize the GMM related parameters

75


Contents

1. Overview of GPRS Mobile Management

2. Location Update

3. GPRS Cell Selection & Reselection

76


Overview for GPRS Mobile Management

The main purpose of the mobility management is to keep track of the user’s current location. Thus, the paging can be performed.

MS perform cell selection and reselection when it moves around the coverage area. It also sends the location update message to the SGSN so that the network can be always aware of the MS’s current location.

There are 3 states exist in the GPRS mobility management and different location information is available in each state (please see the following figure – MM State).

77


GMM State

IDLE GMM context is not established; MS is not reachable.

MS can implement data transmission.

GMM context is established; MS can receive paging butcannot implement data transmission.

The MS performs MM procedures to provide the network with the actual

selected cell.

SGSN performs the MM on cell level.

READY

STANDBY

The location information in the SGSN MM context contains only the GPRS RAI.

Pages for data or signalling information transfers may be received. It is also

possible to receive pages for the CS services via the SGSN. Data reception

and transmission are not possible in this state.

Data transmission to and from the mobile subscriber as well as the paging of

the subscriber are not possible

.

78


GMM State Model

IDLE READY STANDBY

IDLE READY STANDBY

MM State Model of MS

MM State Model of SGSN

GPRS Attach

GPRS Detach

READY timer expiry or

PDU transmission

PDU reception

Implicit Detach or Cancel Location

GPRS Attach

Force to STANDBY

READY timer expiry orForce to STANDBY or

Abnormal RLC condition

GPRS Detach or Cancel Location

By performing GPRS attach, the MS gets into READY state and if the MS does nottransmit any packet for a long period of time until the READY timer is expired, the MS will get into STANDBY state.It is possible to transmit data only if the MS is in READY state, thus the MS in STANDBY state can switch back to the READY state, if a PDU transmission occurs and in the sameway, at READY state if the GPRS detach is performed, the MS will be back into IDLE state and all PDP context will be deleted.In STANDBY state, the MS sends the location update message seldom, so its location isnot known exactly and the paging is necessary for every downlonk packet, resulting in a delivery delay.In READY state, the MS updates its location frequently. Consequently the MS‘s locationis known precisely and no paging delay during delivery downlonk packet. Howeverm thisconsumes much more the uplink radio capacity and battery of the MS.

79


GMM State vs Location Information

During GMM IDLE state, MS is detached from GPRS. Thus MS can not receive paging nor data transmission.

During GMM STANDBY state, MS is attached to the GPRS network and it will perform routing area update (RAU), MS-controlled cell reselection and monitor paging. It only report RA changes.

During GMM READY state/ packet transfer mode, MS will perform both routing area update (RAU) and cell update (both MS-controlled and Network-controlled cell reselection). It report the cell changes and RA changes.

80


Contents


2. Location Update2.1Relationship between Cell, Routing Area & Location Area

2.2LAI, RAI, CGI

2.3Signaling flow for Cell Update, RA Update & LA Update


81



CELL

CELL

CELL

CELL

RA1

RA2

CELL

CELL

RA3

CELL

CELL

CELL

SGSN1SGSN2

BSC1

BSC2

BSC3

LA1 LA2

When MS across Location Area border, LAU & RAU is necessaryWhen MS moves within same LA and across Routing Area boarder, RAU is necessaryWhen MS moves within the same LA and RA, cell update may be needed may be needed. It depends on the current state of the MS.a) READY state: MS updates the location every cell change. This strategy ensures that the accurate location of the MS is always known and packet data can be delivered faster as no paging procedure is necessary. However the MS battery is drained more and uplink radio capacity is wasted for cell updates.b) STANDBY state: MS updates the location only when the MS moves to a new routing area (RA). In this strategy, when data packet is sent to the MS, paging is required in order to find out the current location of the MS. Thus, uplink capacity will be wasted for paging response and every downlink packet requires paging of the mobile delay.

82


CGI


LAI

MCC+ MNC+ LACLAI

RAI

MCC+ MNC+ LAC+RAC

CGI /CellID

MCC+ MNC+ LAC+{RAC}+CI

RAI

83


Contents



2.2LAI, RAI, CGI



84



MCC MNC LAC

LAI (Location Area Identification)MCC：Mobile Country Code, it consists of 3 digits. For example: The MCC of China is "460"

MNC：Mobile Network Code, it consists of 2 digits. For example: The MNC of China Mobile is "00"

LAC：Location Area Code, it is a two bytes hex code. The value 0000 and FFFF is invalid

For example: 460008C90

85


RAI (Routing Area Identification)

Routing area is the sub-set of the location area. In special cases, the two areas are equal.

The division of the routing area is related with traffic distribution and SGSN processing ability


MCC MNC LAC RAC


86


CGI (Cell Global Identity)CI (Cell Identity): This code uses two bytes hex code to identify the radio cells within a LAI.

RAC is only unique when presented together with LAI.

CI is only unique when presented together with LAI or RAI.

CGI = MCC+MNC+LAC+{RAC}+CI


MCC MNC LAC CI

CGI

RAC


87


Contents



2.2LAI, RAI, CGI



88


Cell Update Flow

MS Old Cell SGSN

Uplink LLC-PDU

[MS ID]

SGSN received andrecorded the cell update

New Cell

SGSN send the subsequence service

to MS through the new cell

PDU (CGI) in BSSGP-PDU

RLC Radio Block

1. When the MS moves from one cell to another within the same RA and LA, cell update procedure will happen during the READY state.

2. During the READY state/ packet transfer state, MS will keep monitor its current location and cell reselection will happen. When MS discover another better cell according to its own measurement. The MS stops listening to the old cell and start to read the necessary SYSINFO in the new cell.

3. MS make an access in the new cell and send a cell update to the SGSN (transparent to the PCU).

4. SGSN will obtain the cell update (cell change information) from the uplink LLC-PDU and record the cell update information and discovers that there was already an ongoing downlink packet transfer.

5. SGSN will then sends a Flush message to the respective PCU. The Flush message contains the addresses to both the old and new cell as well as the MS identity.

6. The PCU check whether it is responsible for the new cell. In that case all the buffered frames/ the subsequence service will be moved to a queue towards the new cell. The PCU assign new resources to the MS in the new cell and transmission is restarted.

7. If the PCU is not responsible for the new cell, it will delete all the frames destined to the MS ang leave the retransmission to higher layers.

89


Intra-SGSN Routing Area Update Flow

MS BSS SGSN

ROUTING AREA UPDATE REQUEST ROUTING AREA UPDATE REQUEST[Old RAI, old P-TMSI, update type] [Old RAI, old P-TMSI, update type, new CI]

SECURITY FUNCTIONS (optional)

ROUTING AREA UPDATE ACCEPT[P-TMSI, P-TMSI signature]

ROUTING AREA UPDATE COMPLETE[P-TMSI] optional]

1. When MS moves to new RA, it sends RA update request including the RAI of the old RA to its assigned SGSN. When the message arrives at the BSS, the BSS adds the CI of the new cell. Based on the RAI and CI data, SGSN can derived the new RAI. Intra-SGSN routing area update: The MS has moved to an RA, assigned to the same SGSN as the old RA. In this case, the SGSN knows already all necessary user profile, and can assign a new packet temporary mobile subscriber identity (P-TMSI) to the user without the need to inform other network elements.Security function: authentication and ciphering/encrpytion

90


Inter-SGSN Routing Area Update Flow

MS BSSNew

SGSNROUTING AREA UPDATE REQUEST

[Old RAI, old P-TMSI, update type]

Old SGSN GGSN HLR

PDP CTT REQ

[GGSN address]

PDP CTT ACK

PDP CONTEXT UPDATE

PDP CONTEXT UPDATE ACK

DATABASE UPDATE

INSERT SUBCRIBER DATA

ROUTING AREA UPDATE COMPLETE

ROUTING AREA UPDATE ACCEPT

Inter-SGSN routing area update: In this case, the MS has moved to an RA, assigned to a different SGSN, thus, the new SGSN does not have the user profile of the MS. The new SGSN contacts the old SGSN and requests the PDP context of the user. After receiving the PDP context of the user, the new SGSN informs the involved network elements,

GGSN about the new PDP context of the userHLR about the user’s new SGSN

HLR cancels the MS information context in the old SGSN and loads the subscriber data to the new SGSN. New SGSN acknowledges to the MSThe old SGSN is requested to transmit the undelivered data to the new SGSN.

91


Contents


2. Location Update

3. GPRS Cell Selection & Reselection3.1Cell Reselection Algorithm

3.2Parameter for Cell Reselection

3.3Type of Cell Reselection

92


GPRS Cell Reselection Algorithm

If no PBCCH exists, the GPRS cell selection &

reselection is basically the same as GSM cell

selection & reselection (C1, C2):

C2 = C1 + CRO – TO*H(PT-T) when PT=/31

C2 = C1 – CRO when PT=31

C1 = RLA_C – RxLev_Acc_Min –

Max((MS_TXPWR_MAX_CCCH – P), 0)

1. C1 = RLA_C - RxLev_Access_Min - Max((MS_TxPwr_MAX_CCH - P), 0)2. C2 = C1 + CRO - TO * H(PT-T) when PT=/313. C2 = C1 - CRO when PT= 31

93


GPRS Cell Reselection Algorithm If no PBCCH exists, the GPRS cell selection & reselection is basically the same as GSM cell selection & reselection (C1, C2) excepts for the following conditions:a) When MS in STANDBY mode,

Cell reselection within the same RA/LA:

C2(nei) > C2 (serving) for t>5s

Cell reselection between different RA/LA:

C2(nei) > C2 (serving) + CRH for t>5s

b) When MS in READY mode,Cell reselection within the same RA/LA:


Cell reselection between different RA/LA:


1. C1 = RLA_C - RxLev_Access_Min - Max((MS_TxPwr_MAX_CCH - P), 0)2. C2 = C1 + CRO - TO * H(PT-T) when PT=/313. C2 = C1 - CRO when PT= 31

94


Cell Reselection in Standby Mode

RA 1RA 2

Cell A

Cell B

Cell C

AC2>BC2 CC2>BC2＋CRH

95


Cell Reselection in Ready Mode

BC2>AC2＋CRH

RA 1

Cell A

Cell B

96



If PBCCH exists, new cell selection & reselection algorithm (C31, C32) is applicable:C31(s) = RLA_P(s) – HCS_THR(s) (Serving cell)

C31(n) = RLA_P(n) – HCS_THR(n) –

GPRS_TO(n)*H(GPRS_PENALTY_TIME-T)*L(n) (Neighbor cell)

C31 = signal threshold criterion

RLA_P = actual received level of the GPRS cell

HCS_THR = signal level threshold of cell reselection of HCS GPRS

GPRS_TO = GPRS temporary offset

L = 0; when PRIORITY_CLASS (s) = PRIORITY_CLASS (n)

L = 1; when PRIORITY_CLASS (s) =/ PRIORITY_CLASS (n)

C31 = signal threshold criterion/ signal level threshold criterion of HCS and is used to judge whether to adopt preference cell reselectionHCS_THR = Hierarchical Cell Structure signal level threshold of cell reselection of HCS GPRS. It is broadcast on PBCCH of the service cell. RLA_P = Received level of the GPRS cellTO = Temporary offset given to the neighbor when the neighbor cell’s PRIORITY_CLASS is different from the PRIORITY_CLASS of the serving cell

97



If PBCCH exists, new cell selection & reselection algorithm (C31, C32) is applicable:C32(s) = C’1 (Serving cell)

C32(n) = C’1 + GPRS_RESELECT_OFF –

GPRS_TO*H(GPRS_PENALTY_TIME – T) * (1-L) (Neighbor cell)

H(X<0) = 0; T > GPRS_PENALTY_TIME

H(X>0) = 1; T < GPRS_PENALTY_TIME

L = 0; when PRIORITY_CLASS (s) = PRIORITY_CLASS (n)

L = 1; when PRIORITY_CLASS (s) =/ PRIORITY_CLASS (n)

C’1 = RxLev – GPRS_Acc_Level_Min – Max( (GPRS_MS_TXPWR_MAX_CCH – P), 0)

C32 = Perfection of C2 applied to GSM. It applies the offset and the delay value to the cell reselection which needs execution of cell update program or route update program. When the PBCCH channel does not exist in the service cell, the MS will execute cell reselection according to the C2 algorithm. T = timer with initial value =0. When a cell is recorded by the MS into the 6 strongest cell, the counter corresponding to this cell, T will begin to count at a precision of one TDMA frame (4.62ms). When this cell is removed from the 6 strongest cell list, the timer is reset.GPRS TO = temporary offset, which counts from the counter T. T to the

98



In additional, it is necessary to consider the routing area for

the serving cell and adjacent cell:

When MS in STANDBY mode, and within the same RA

C32’(n) = C32(n)

When MS in READY mode, and within the same RA

C32’(n) = C32(n) - CELL_RESELECT_HYSTERESIS

When MS in READY or STANDBY mode, with different RA

C32’(n) = C32(n) - RA_RESELECT_HYSTERESIS

C32’(n) = Final calculated/ actual value of the C32 criterion after consider the routing area of the serving cell and neighbor cell.

99


Cell Reselection Trigger Condition

Cell reselection triggering condition:

Random access attempt is unsuccessful

after MAX_RETRANS

Random access attempt is

unsuccessful after MAX_RETRANS

4

5

3

2

1

With C’1, C31, C32 criterionWith C1, C2 criterion

C’1 < 0C1 < 0

Downlink signaling failureDownlink signaling failure

Better cell with the highest C32 among:

(a) Highest PRIORITY_CLASS, C31>=0

(b) All cell, if no cell fulfils C31 criterion

Better neighbor cell detected:

Same RA: C2(n) > C2(s) for t>5s

Dif RA: C2(n) > C2(s)+CRH for t>5

Serving cell is barredServing cell is barred

100


Contents


2. Location Update




101


Network Control Mode

Cell Attribute -> GPRS Attributes

Parameter Name: Network Control ModeDescription:In the cell reselection required by the network, the network requests the MS to send measurement reports to control its cell reselection. There are three network control modes. nc0: Normal MS control. The MS performs automatic cell reselection.nc1: MS control with measurement reports. The MS sends measurement reports to the network and performs automatic cell reselection.nc2: Network control. The MS sends measurement reports to the network but does not perform automatic cell reselection. GUI Value Range: [nc0,nc1,nc2]Default Value: nc0

102


Parameter for GPRS Cell Reselection

Network Control Mode (NCO)

Controlled by networkOnly ReadyYesNetwork Control

ModeNC2

Controlled by MSOnly ReadyYesMS Control with

M.R ModeNC1

Controlled by MS

Ready & StandbyNoNormal MS

Control ModeNC0

Cell Selection

ModeMS mode

Whether the MS send the

M.RDefinitionMode

NC0: MS performs autonomous cell reselection without sending measurement reports to the network.NC1: MS performs autonomous cell reselection and sends measurement reports to network.NC2: Network controls cell reselection and MS sends measurement reports to the network.

103


Support NC2

Cell Attributes ->

Other Attributes

Parameter Name: Support NC2Description:This parameter specifies whether the cell supports the Network Control 2 (NC2) function. In NC2, the MS reports the measurement report of the reference cell and neighbor cells to the BSC. The BSC controls cell reselection (including normal reselections and load-based reselections) of the MS.GUI Value Range: [No,Yes]Default Value: No

104


NC2 Support in External Neighbour Cell

BSC6000 -> Configure

2G External Cell

Parameter Name: NC2 Support in External Neighbour CellDescription:This parameter specifies whether the GSM external cell supports NC2.GUI Value Range: [Not Support,Support]Default Value: Not Support

105


Parameter for GPRS Cell Reselection

Cell Attributes -> GPRS Attributes -> Advanced -> Ps

Other Parameters

Parameter Name: Cell Urgent Reselection AllowedDescription: This parameter specifies whether enabling the critical cell reselection algorithm is allowed.GUI Value Range: [Forbid,Permit]Default Value: Permit

Parameter Name: Cell Load Reselection AllowedDescription: This parameter specifies whether enabling the cell load-based reselection algorithm is allowed.GUI Value Range: [Forbid,Permit]Default Value: Permit

Parameter Name: Cell Normal Reselection AllowedDescription: This parameter specifies whether enabling the normal cell reselection algorithm is allowed.GUI Value Range: [Forbid,Permit]Default Value: Permit

106


Support NACC

Cell Attributes ->

Other Attributes

Parameter Name: Support NACCDescription:This parameter specifies whether the cell support the Network Assisted Cell Change (NACC) function.In network control mode NC0, NC1, or NC2, when the MS is in the packet transmission mode, the network informs the MS of the system information about neighbor cells in advance. Therefore, the cell reselection of the MS is accelerated.GUI Value Range: [No,Yes]Default Value: No

107


Contents


2. Location Update




108


GPRS Cell Reselection Type

There are 3 type of cell reselections:

MS controlled cell reselection

Network controlled cell reselection

Network assisted cell reselection

109


MS-Controlled Cell Reselection

MS-Controlled Cell Reselection MS periodically measures the RX levels of all the BCCH carriers of the

serving cell and its neighboring cells.

With no PBCCH configured, MS calculates C2 value.

With PBCCH configures, MS calculates C31/C32 value.

Based on the calculated value, MS decided whether to reselect a new

serving cell.

Also call as autonomous cell reselection.

Parameter setting:Support NC0/ NC1 to YES

110


Network-Controlled Cell Reselection

Network-Controlled Cell ReselectionMS periodically sends measurement reports to the BSC based on the

parameters in the SYSINFO broadcast in the cell.

Based on the measurement reports and neighboring cell load, BSC

sends a cell change command to the MS if all conditions are met, leading

the MS to a suitable cell.

Parameter setting:Support NC2 to YES

111


Network-Controlled Cell Reselection (NC2)

MS BSSPACKET MEASUREMENT REPORT

PACKET CELL CHANGE ORDER

PACKET CELL CHANGE FAILURE

[P-TMSI] optional]

PACKET NEIGHBOR CELL DATA

NC2 Cell Reselection Algorithm

PACKET ENHANCED MEASUREMENT REPORT

1. MS in the GMM Ready mode state periodically sends PACKET MEASUREMETN REPORT to the BSC.

2. After receive the MR, NSC process the MR. According to the NC2 cell reselection algorithm, BSC determines whether to perform cell reselection.

3. If BSC determines to initiate a cell reselection, it send PACKET CELL CHANGE ORDER to MS to instruct MS to reselect the target cell. If NACC support, PACKET NEIGHBOR CELL DATA containing SYSINFO will be sent before the PACKET CELL CHANGE ORDER so that the reselection can be accelerated.

4. If cell reselection fails, MS sends PACKET CELL CHANGE FAILURE message to BSC. After receive this message, BSC subtracts CELL PENALTY LEVEL from the RxLev of the target cell.

112



The NC2 cell reselection algorithm follows the priority

sequence in descending order of:

Urgent reselection algorithm

Load reselection algorithm

Normal reselection algorithm

Urgent reselection is based on the receive quality of the radio link on the Um interface. If BER increases, the possible reason is that the signal level is too low or there is interference on the channel. In the network, load in some cells are heavy and some are light. To balance the load in these cells, load reselection is performed. In load reselection procedure, MS in heavy-loaded cell are directed to light-loaded cell. MS in neighbouring cell should not be reselected to the heavy-loaded cell.Normal reselection is based on Receive Level. When urgent reselection an load reselection are not met, normal reseelction is started to handover MS to a neighboring cell with higher signal strength if the RxLev (serving cell) < [Min Access Level Threshold]

113



Yes Yes

Yes Yes Yes

Yes Yes

No

No No

NoNoNo

No

Yes

No

Measure RxLev & RxQualMS in the MR

[Cell Urgent Reselection Allowed]?

MS RxQualdeterioration ratio >

[MS Rx Qual Worsen Threshold]

[Cell Load Reselect Allowed]?

[Cell Normal Reselect Allowed]?

Channel multiplexing rate>[Load Reselect

Start Thres]

Any MS RxLev<[Load Reselect Level Thres]

Receive Level (serving cell) < [Min Access

Level Thres]Satisfy P/N?

Trigger urgent cell reselection and select cell with the highest priority in

cell list.

End

Continue

Begin

NC2 cell reselection algorithm follow the priority of:urgent reselection -> load reselection -> normal reselectionEach type of reselection have different trigger condition.

114



YesYesYes

Yes

No

NoNo

NoRxLev>MAX(RxLev(s),

[Min_Acc_Level_Thres])+ [Cell Reselect Hyst] AND

non-congestion state

Ec/No>[PS FDD EcNoQuality Thres] or

RSCP>[PS FDD RSCP Quality Thres]

RSCP>[PS FDD RSCP Quality Thres]

Cell reselection successful?

Trigger urgent cell reselection and select cell with the highest priority in cell list.

[Cell Penalty Level] given to target cell with [cell Penalty

Last Time]

For GSM Cell For FDD Cell For TDD Cell

Continue

End

End

The priority of the target cell is determined by receive level and the characteristics information such as cell type, cell priority, support for EDGE, and load status.Different cell type will need to fulfill the specified condition to be the candidate cell.When cell reselection fails, penalty is given to the target cell. If penalty time within [Cell Penalty Last Time (s)], [Cell Penalty Level] is subtracted from the receive level of the target cell.

115



Serving cell is

GSM cell, target

cell is UTRAN

Different BSC,

both GSM cell

Same BSC

Serving cell &Target cell position

Highest priority in the cell list.Intra-BSC

Condition

Cell Reselection Type

For FDD cell : Ec/No>[PS FDD EcNo Quality Thres] or RSCP>[PS FDD RSCP Quality Thres]

For TDD cell: RSCP>[PS TDD RSCP Quality Thres]

GSM to

UTRAN

RxLev (Ext nei) = RxLev (n) – MAX(2, [Cell Reselection Hyst/2])

Inter-BSC

Each NC2 cell reselection algorithm contains three NC2

cell reselection type:

Intra-BSC cell reselection:Serving cell and target cell are controlled by same BSC. The selected target cell is the one that has highest priority in the cell list.Inter-BSC cell reselection:Serving cell and target are in different BSC and both is GSM cell. The priority for the external neighbouring cell is lower. Thus,

RxLev (Ext nei) = RxLev (n) – external cell reselection offsetRxLev (Ext nei) = RxLev (n) – MAX(2, [Cell Reselection Hyst/2])

GSM to UTRAN cell reselection:Serving cell is GSM cell and target cell is UTRAN cell. The 3G MR and the 2G/3G cell priority strategy should be processed during the cell reselection.

For FDD cell: Ec/No>[PS FDD EcNo Quality Thres] or RSCP>[PS FDD RSCP Quality Thres]

For TDD cell: RSCP>[PS TDD RSCP Quality Thres][2G/3G Cell Reselection Strategy] : Preference for 2G cell, Preference for 3G cell

116


Network-Assisted Cell Reselection

Network-Assisted Cell ReselectionIt is also known as NACC, Network Assisted Cell Change.

MS originates a cell change notification (CCN) procedure, and the BSC

sends the system information (SYSINFO) about the neighboring cell to

the MS before the cell reselection.

NACC accelerates the cell reselection and shortens the service

disruption time during cell reselection.

Parameter setting:Support NC0/ NC1/ NC2 to YES

Support NACC to YES

117


Network Assisted Cell Change (NACC)

Purposes:

MS is able to request BSC to send the target cell’s SYSINFO

during the cell reselection.

Advantages:

According to the SYSINFO, MS accelerates the packet service

access in the target cell.

Reduce the period of packet service disruption during a cell

reselection .

118



Cell A Cell B

Receive System information of cell B before reselection

119



MS can initiate an NACC procedure only when autonomous cell

reselection is triggered:

In NC0/ NC1 mode and packet transfer mode:

C1 <0

C2/ C23 is met

Downlink signaling reception fails

Authentication fails

NACC procedure is not initiated when:

In GMM standby state

In DTM mode

120



The system supports:

Intra-BSC NACC

Inter-BSC NACC

UTRAN to GERAN NACC (Gb must support RIM procedure)

The system does not support the GERAN to UTRAN NACC

procedure.

When PBCCH exists in target cell, the system does not

support NACC procedure or the PACKET SI STATUS

procedure.

GERAN : GPRS EDGE Radia Access NetworkRIM : RAN Information ManagementRIM procedure refer to the procedure of getting SYSINFO about the external neighboring cell from the serving cell 2 types of RIM procedures in the inter-BSC and UTRAN to GERAN NACCa) Inter RAN SYSINFO request procedure: initiated by controlling BSC/RNC to request the SYSINFO about the serving BSCb) Inter RAN SYSINFO update procedure: initiated by the serving BSC to ask the controlling BSC/RNC to update SYSINFO about the external neighboring cellRIM association between a cell in the serving BSS and the controlling BSS that requests the application information about this cell. It consists of 3 identities: a) ID of the cell in the controlling BSSb) ID of the cell in the serving BSSc) RIM application identity

121


Intra-BSC NACC Flow

MS BSS

PACKET CELL CHANGE NOTIFICATION

PACKET CELL CHANGE CONTINUE

PACKET SI STATUS

PACKET SERVING CELL DATA

[P-TMSI] optional]


Obtain system messages of the target cell

1. After MS determines to initiate an autonomous cell reselection, it enter CCN mode. But the MS does not change the cell immediately, it sends a PACKET CELL CHANGE NOTIFICATION to BSC to request SYSINFO about the target cell.

2. When BSC received PACKET CELL CHANGE NOTIFICATION, it sends a PACKET NEIGHBOUR CELL DATA that contains SI1, SI3, SI13. Then BSC send PACKET CELL CHANGE CONTINUE to ask the MS to proceed the cell reselection.

3. After receive PACKET NEIGHBOUR CELL DATA, MS save the SYSINFO. After receive the PACKET CELL CHANGE CONTINUE, MS changes from CCN mode to NC0/NC1 mode and continue cell reselection.

4. After MS changes the cell, the MS uses the SYSINFO for initial packet access procedure.

5. If target cell support PACKET SI STATUS (YES), MS does not receive all SYSINFO. MS needs to send PACKET SI STATUS message to request the SYSINFO. After BSC received PACKET SI STATUS, it sends PACKET SERVING CELL DATA which contain the SYSINFO of the serving cell.

6. Then MS saves the SYSINFO in the PACKET SERVING CELL DATA.

122


Inter-BSC NACC Flow

MSControl

BSS/RNC

PACKET CELL CHANGE NOTIFICATION

PACKET CELL CHANGE CONTINUE

PACKET SI STATUS

PACKET SERVING CELL DATA


Obtain system messages of the target cell

Serving BSS

RIM Procedure

1. After MS determines to initiate an autonomous cell reselection, it enter CCN mode. But the MS does not change the cell immediately, it sends a PACKET CELL CHANGE NOTIFICATION to BSC to request SYSINFO about the target cell.

2. When BSC received PACKET CELL CHANGE NOTIFICATION, it sends a PACKET NEIGHBOUR CELL DATA that contains SI1, SI3, SI13. Then BSC send PACKET CELL CHANGE CONTINUE to ask the MS to proceed the cell reselection.

3. After receive PACKET NEIGHBOUR CELL DATA, MS save the SYSINFO. After receive the PACKET CELL CHANGE CONTINUE, MS changes from CCN mode to NC0/NC1 mode and continue cell reselection.

4. After MS changes the cell, the MS uses the SYSINFO for initial packet access procedure.

5. If target cell support PACKET SI STATUS (YES), MS does not receive all SYSINFO. MS needs to send PACKET SI STATUS message to request the SYSINFO. After BSC received PACKET SI STATUS, it sends PACKET SERVING CELL DATA which contain the SYSINFO of the serving cell.

6. Then MS saves the SYSINFO in the PACKET SERVING CELL DATA.

123


SummaryWe have understand the below from this training:

GPRS Mobility Management procedure

Cell reselection algorithm

Cell reselection and routing area update flow

Parameters related to GMM.

124


125

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GPRS EDGE Radio Network Optimization Parameters

126


ForewordThe PCU performance parameters are essential to the

GPRS network. Proper setting of such parameters can

improve performance of the packet services.

127


Contents

GPRS Cell Parameters

GPRS Power Control

GPRS Cell Reselection

Performance Parameters

128



NOM

T3168

T3192

DRX_TIMER_MAX

BS_CV_MAX

PAN

N3101

N3103

N3105

129


Network Operation Mode

PCHPCHCCCHCCCH

PPCHPCHYesNoIII

CCCHCCCHPCHPCHNoNoII

-PACCH

PCHPCH PACCHPCCCH

Or CCCH

PPCHPPCH

YesYesI

Idle ModeGPRS Paging

Channel

Channel for circuit paging

Configure PCCH

ConfigureGs

Network Mode

130


T3168T3168 is used to set the maximum duration for the

MS to wait for the packet uplink assignment messagePCU

PACKET CHANNEL REQUEST

PACKET UPLINK ASSIGNMENT/ IMMEDIATE ASSIGNMENT COMMAND

PACKET RESOURCE REQUEST

20005%<BLER<10%Bad10002%<BLER<5%Good500BLER<2%Very Good

T3168 recommendation（ms）BLERCondiction

T3168 PACKET UPLINK ASSIGNMENT

The timer T3168 is used to set the maximum duration for the MS to wait for the packet uplink assignment message. The MS should start the timer T3168 to wait for the packet uplink assignment message after sending the packet resource request message. If the MS receives the packet uplink assignment message before timeout of T3168 and gets into the status of waiting for packet uplink assignment message, the MS will reset T3168; if T3168 times out, the MS will trigger the packet access process again until this process repeats for 4 times. Then the MS will believe that TBF establishment failure occurs. If the value of this paramter is smaller, the period of the MS determining failure of TBF establishment will be shorter, and the average time of packet access will be shorter. However, in severe wireless conditions, that will make the TBF establishment success rate lower. Moreover, too low values will make the MS increase the probability of retransmitting the packet access requests, which will increase the probabilty of the PCU performing repeated assignment and lead to waste of system resources. On the other hand, if this value is higher, the period of the MS determining failure of TBF establishment will be longer, and the average delay of the packet access will be longer.Value range: This parameter value is measured in 500ms, and its range is: 500ms, 1000ms, 1500ms… 4000ms.The recommended value is 500ms.

131


T3192The timer is for the MS to wait for TBF release after receiving

the last data block.PCU

T3192

PACKET DOWNLINK ACK/NACK （FAI=1）

PACKET DOWNLINK ASSIGNMENTTFI

Final ACKIdentifier

20016012080015001000500value（ms）

After receiving the RLC data block which contains the Final Block Identifier (FBI) and confirming that all RLC data blocks in TBF are received, the MS should send the packet downlink acknowledgement/unacknowledgement message, set its Final Acknowledgement Identifier (FAI) to 1 and start T3192. If T3192 times out, the MS will stop all allocated listening tasks on PDCH, begin to listen to the paging channel and get into the packet idle status. If this parameter value is greater, the time for the MS to reserve the TFI and timeslot assigned by the system will be longer, and the risk of congestion will be higher. On the other hand, if this value is smaller, the MS will release TBF quickly. If new downlink packet data comes to the network, the network will have to originate the paging again or assign the program promptly, which prolongs the time of establishing the downlink TBF greatly. Value range: This parameter value is measured in 500ms, and its range is: 0ms, 80ms, 120ms, 160ms, 200ms, 500ms, 1000ms and 1500ms. The recommended value is 500ms.

132


DRX_TIMER_MAXThe MS request keeps the maximum value of non-

DRX mode.

Packet transmission mode

Non_DRX DRX

Packet idle mode

Non_DRX

DRX_TIMER_MAX (s)

64321684210Value（Sencond）

Packet idle mode

Set the maximum value of the duration for MS to execute the non-DRX mode when shifting from the packet transmission mode to the packet idle mode. This parameter value is measured in seconds. Values: “0” – Get into the DRX mode immediately after the transmission mode, “1s” - 1 second, “2s” - 2 seconds, “4s” – 4 seconds… “64s” – 64 seconds. The typical value is “4s". If the value is higher, the TBF establishment duration will be shorter, but the MS power consumption will increase. If the value is lower, the battery consumption is lower, but the paging process will be longer, the system signaling load will be heavier and the data transmission delay will be longer.

133


Packet Signaling Processing

PACKET DOWNLINK ACK/NACK （FAI=1）

RLC DATA BLOCK (FBI)

RLC DATA BLOCK

T3192=500ms

Non DRX mode= 4s

DRX mode

DRX mode

Ready Mode

134


BS_CV_MAX

PCU

T3198

RLC DATA BLOCK

CV=X

RLC DATA ACK

RLC DATA BLOCK

CV=X

Timeout

设BS_CV_MAX=10

200ms

Set BS_CV_MAX. It is a parameter used for the MS to calculate the Countdown Value (CV). If the PBCCH channel does not exist, this parameter will be broadcast in the system message 13. When the RLC data block to be sent is the last but (x-1) data block, if x<= BS_CV_MAX, CV=x; otherwise CV=15. Ensure that the last RLC data block is being sent in case CV=0.Value range of BS_CV_MAX: 0~15When the MS sends an RLC data block, the MS starts the timer T3198. After timeout of the timer, the MS will allow the status of this RLC data block to be “unacknowledged”and retransmit the data block. The default value of T3198 is duration of BS_CV_MAX blocks. The duration of each block is 20ms.The empiric value of transmission delay between MS and PCU is 100ms, so T3198 value > 100ms, i.e., BS_CV_MAX >5.1. If the BS_CV_MAX value is higher, the efficiency of the slide window program will be lower; 2. If the BS_CV_MAX value is lower, the probability of retransmission will be higher, and more wireless resources will be occupied.

135


BS_CV_MAX

PCU

MS buffer – UL RLC blocks

CV=0 CV=1 CV=2 CV=3 CV=15 CV=15 CV=15 CV=15

CV=0 CV=1 CV=2More data CV=3 CV=15 CV=15

suppose BS_CV_MAX=

3

The default value of the MS-side timer T3198 is duration of BS_CV_MAX RLC blocks. The T3198 begins counting after the MS sends the RLC block. After timeout of T3198, the block is marked as “unacknowledged” and needs to be retransmitted.

To retransmit the erroneous RLC Block as soon as possible, the value of the BS_CV_MAX should be as small as possible, but cannot be less than the delay of transmission from MS to PCU. According to empiric values, the BS_CV_MAX value should be over 5.

136


PANPAN_DEC

Set the decrease step length of the N3102 counter of the MS

PAN_INC

Set the increase step length of the N3102 counter of the MS

PAN_MAX

Set the maximum value of the N3102 counter of the MS

137


PAN

Packet Uplink Ack/NackN3102

PAN_MAX

- PAN_DEC+ PAN_INC

Abnormal Release

T3182

T3182

T3182 T3182

T3182

Perform Cell Re-selection

This parameter is used to avoid unpredictable link failure. It is used together with the MS-side counter N3102, and consists of three sub-parameters. PAN_DEC: Decrementalvalue of PAN counter PAN_INC: Incremental value of PAN counterPAN_MAX: Maximum value of PAN counter The MS sets the counter N3102 according to PAN_MAX. When the MS receives a Packet ACK/NACK message, the N3102 increases by PAN_INCWhen N3102=PAN_MAX, the MS starts the timer T3182If the MS still receives no acknowledgement message upon timeout of T3182, the MS will decrease N3102 by PAN_DEC. In case N3102<=0, the MS will execute exception release of this TBF, and trigger cell reselection.

138


PAN

PCU

N3102+2

RLC DATA BLOCK

PACKET DATA ACK

Timeout

设PAN_INC=2

RLC DATA BLOCK

PACKET DATA ACKT3182

设PAN_DEC=1

N3102- 1

139


N3101

PCU

RLC DATA BLOCK/PACKET UPLINK ASSIGNMET (valid USF)

RLC DATA ACKN3101+1

POLLING REQUEST

If N3101 expires, the network release the uplink TBF.

140


N3103

PCU

PACKET UPLINK ACK/NACK (FAI=1)

PACKET CONTROL ACKN3103+1

PACKET UPLINK ACK/NACK (FAI=1)


141


N3105

PCU

RLC DATA BLOCK (RRBP)

PACKET DOWNLINL ACK/NACKN3105+1

RLC DATA BLOCK (RRBP)


142


Case 1Phenomenon Description:

Three cells of a satellite transmission BTS under a BSC are

unable to access the network through GPRS. View the cell

status and channel status. They are all normal. The PCU traffic

measurement, Um interface and cell signaling tracing, and

configuration data are collected on site.

The possible causes are as follows: 1. The configuration data of the PCU and BSC is incorrect.2. The PCU version is incorrect.3. The cell is exceptional for various reasons.4. The parameter related to satellite transmission is not properly set.

5. Handling Process:a. Check the data. No exception occurs in other cells and the satellite transmission parameter on the PCU is set to Yes.

6. b. View the traffic measurement. The traffic measurement item "number of uplink assignment successes on PACCH" is 0. The traffic measurement item "number of uplink TBF establishment successes" is also 0 and the basic cause value is "uplink TBF establishment failures owing to no response from the mobile station".

7. c. View signaling messages. There are only a large number of RACK_RES_REQ and PACK_UL_ASSI messages over the air interface. This is obviously abnormal.

8. d. Analyze the traffic and signaling messages. After the MS sends a RACK_RES_REQ message and the PCU returns a PACK_UL_ASSI message, the MS makes no response and continues sending a RACK_RES_REQ message.5. Check the GPRS table about the PCU cell data. Timer T3168 is set to 500 ms, which is the same as that for other GPRS cells of terrestrial transmission. 6. Run the mt sattrans show delay command to view the transmission delay of the satellite transmission cells. The transmission delay is 725 ms.7. Find the cause. After the MS sends a RACK_RES_REQ message, timer T3168 is started. If the timer expires before a PACK_UL_ASSI message is received, the MS resends a RACK_RES_REQ message for four times at most. The duration of the onsite timer T3168 is less than the delay of

143


Contents


GPRS Power Control



144


GPRS Power Control GPRS Power Control Purpose

Save the power

Reduce the interference of the network

GPRS Power Control is complex than GSM for discontinuous

transmission.

Normally now just uplink power control is implemented.

Because for the downlink blocks, it is not only contained TFI for downlink but also USF which may be is for another MS. The two subscribers perhaps one is near the BTS, one is far away. So downlink power control is not implemented for GPRS.

145


GPRS Power Control According GPRS principle, GPRS MS output power as

below：

Pch = Min〔 Ro - Rch – a*( C+48) , Pmax〕

Pmax: GPRS MS max transmitting power

a：ALPHA，normally is 1

Ro：39dBm for 900M cell, and 36dBm for 1800M cell

Rch：GAMMA

C：MS receiving level

146


GPRS Power Control

The ALPHA parameter is used by the MS to calculate the output power value PCH of its uplink PDCHFor open loop power control, it should be set to 1.0.

GAMMA:Expected receiving signal strength at the BTS side when the MS GPRS dynamic power control is activeValue range: 0~62dB, default value is 14

147


Contents


GPRS Power Control



148



During ready and standby mode, MS will occur cell

reselection

Cell reselection will be triggered upon the following 5

kinds conditions.current serving cell is prohibited

down link fails

C1 of serving cell is lower than 0 last 5s

Neighbor cell C32 and C31 higher than serving cell last 5S

MS starts a cell reselection if the access times exceed the MAX

retrans.

If the C2 value of the target cell is higher than that of the serving cell by at least the value of CRH for longer than 5 seconds, a location update process and the cell reselection process will be performed.Only after the PBCCH is configured, C31 and C32 will be worked.

149


NETWORK_CONTROL_ORDER

Controlled by networkOnly ReadyYesNetwork Control

ModeNC2

Controlled by MSOnly ReadyYesMS Control with M.R

ModeNC1

Controlled by MS

Ready & StandbyNoNormal MS Control

ModeNC0

Cell Selection ModeMS mode

Whether the MS send the M.R

Definition

150


NETWORK_CONTROL_ORDER

151


Serving cell A

Neighbor cell B

Neighbor cell c

change to cell C

NC2 Feature

For MS receiving level of cell B is higher than cell C, but the load of cell B is too higher. So PCU will make the MS cell change to cell C instead of cell B. NC2 is just like load handover.

152


GPRS Cell ReselectionIf PBCCH no exists, the cell reselection is basically the

same as GSM cell reselection

When the two cells locates in the different routing areas or the

MS is in READY mode, the NC2 must be greater than

SC2+CRH (>5s)

When the two cells locates in the same routing area and the

MS is in STANDBY mode, the NC2 must be greater than SC2

(>5s)

Two consecutive cell reselections caused by C2 have a time interval of 15 seconds. In other words to say, if because of C2 a MS reselected to a cell, then the MS cannot reselect to another cell by the cause of C2 within 15 seconds.

153


Cell Reselection in Standby Mode

RA 1 RA 2

Cell A

Cell B

Cell C

AC2>BC2 CC2>BC2＋CRH

154


Cell Reselection in Ready Mode

BC2>AC2＋CRHRA 1

Cell A Cell B

155


NACC

Cell ACell B

System information of cell B

In network control mode NC0, NC1, or NC2, when the MS is in the packet transmission mode, the network informs the MS of the system information about neighbor cells in advance. Therefore, the cell reselection of the MS is accelerated.

156


NACC

NACC (Network Assisted Cell Change): shorten the duration of cell reselection NACC will be used during packet transmission mode, network will inform neighbor cell system information to make the cell reselection quickly.NC0:Before the cell reselection decision, MS will send “PACKET CELL CHANGE NOTIFICATION” to BSC, which carry ARFCN and BSIC of target cell. If serving cell support NACC, BSC will send the SI1,SI3 and SI13 of target cell .

Before the GBSS8.1 version, just support intra-BSC NACC; GBSS8.1 or later version also can support inter BSC or inter RNC NACC.For Inter-BSC NACC,BSC and core network should support RIM （RAN Information Management）to get external cell system information.RIM flow means BSS requires the target cell system information from target BSC/RNC through core network. BSC implements RIM flow during provider service, and stores all the external cell system information. BSC also will update these external cell system information periodical. And during the inter-BSC NACC, if BSS did not find the target cell system information, it will trigger RIM flow.

157


Contents


GPRS Power Control



158


Dynamic PDCH Channel Conversion

When dynamic PDCH conversion will be triggered?

PDCH required failure (such as reach the max threshold)

No meet the multiple timeslot

The TBF numbers higher than ”Uplink (Downlink) Multiplex

Threshold of Dynamic Channel Conversion”

Parameter Name Uplink Multiplex Threshold of Dynamic Channel ConversionDescription This parameter specifies the uplink multiplex threshold of dynamic channel conversion.When the number of subscribers carried over the channel reaches the threshold/10, dynamic channels are used.GUI Value Range [10,70]Default Value 20Configuration Policy If this threshold is high, it is difficult to seize dynamic channels. If this threshold is low, it is easy to seize dynamic channels.

Parameter Name Downlink Multiplex Threshold of Dynamic Channel ConversionDescription This parameter specifies the downlink multiplex threshold of dynamic channel conversion.When the number of subscribers carried over the channel reaches the threshold/10, dynamic channels are used.GUI Value Range [10,80]Default Value 20

159



Which channel will be convert to dynamic PDCH

TCH/F channels can be converted to dynamic PDCH, the

maximum dynamic PDCH number will be restricted by reasons

listed below：

The max PDCH number restricted by License

Maximum Ratio Threshold of PDCHs in a Cell

Maximum PDCH numbers of carrier

Reservation Threshold of Dynamic Channel Conversion

Maximum PDCHs number in a Cell= ( TCH/F channels number + PDCH channels number) * Maximum Ratio Threshold of PDCHs in a Cell

160



When the dynamic PDCH channel will be converted to TCH

channel?

Timer of Releasing Idle dynamic Channel

CS services preemption

All dynamic channels can be preempted

Control channels cannot be preempted

Dynamic channels carrying services cannot be preempted

161



Parameter Name Maximum Ratio Threshold of PDCHs in a Cell

Description This parameter specifies the maximum ratio of PDCHs in a cell. The total number of TCHs and PDCHs available in a cell is fixed. The PDCH ratio is equal to PDCHs / (TCHs + static PDCHs). This parameter determines the proportion of PDCHs to the total number of TCHs + PDCHs.

GUI Value Range [0,100]

Default Value 30

Configuration Policy If this parameter is set to an excessive value, there are excessive PDCHs and insufficient TCHs. This affects CS services. If this parameter is set to a modest value, there are insufficient PDCHs and excessive TCHs. This affects PS services.

Parameter Name PDCH Uplink Multiplex Threshold

Description This parameter specifies the PDCH uplink multiplex threshold.The uplink PDCH can carry a maximum of (threshold/10) TBFs.

GUI Value Range [10,70]

Default Value 70

Configuration Policy If this parameter is set to a lower value, the TBFs established on the PDCH and the subscribers are fewer, and the uplink bandwidth for each subscriber is higherIf this threshold is set to a higher value, the TBFs established on the PDCH and the subscribers are more, and the uplink bandwidth for each subscriber is lower.

Parameter Name PDCH Downlink Multiplex Threshold

Description This parameter specifies the PDCH downlink multiplex threshold.The downlink PDCH i f (th h ld/10) TBF

162

Parameter Name Level of Preempting Dynamic ChannelDescription This parameter specifies the levels of dynamic channels preempted by CS services and PS services. Only full-rate TCHs are the dynamic channels that can be preempted. All dynamic channels can be preempted: It indicates that the CS services can preempt all the dynamic channels.Control channels cannot be preempted: It indicates that the CS services can preempt all the dynamic channels except for the control channels.Dynamic channels carrying services cannot be preempted: It indicates that the CS services cannot preempt the dynamic channels that carry services.GUI Value Range [Preempt all dynamic TCHFs,No preempt of CCHs,Nopreempt of service TCHF]Default Value All dynamic channels can be preempted

Parameter Name Reservation Threshold of Dynamic Channel ConversionDescription This parameter specifies the number of channels reserved for the CS services.GUI Value Range [0,8]Default Value 2Configuration Policy If this parameter is set to an excessive value, the PS services are affected.If this parameter is set to a modest value, the CS services are affected when there are too many PS services.

Parameter Name Maximum PDCH numbers of carrierDescription This parameter specifies the maximum number of PDCHsallocated to a TRX. GUI Value Range [0,8]Default Value 8

163


GPRS Channel Priority Type

Value Range GPRS Channel, EGPRS Normal Channel, EGPRS Priority Channel, EGPRS Special Channel, None-GPRS Channel

Default Value When Channel Type is set to non-PDTCH, the default value is None-GPRS Channel. When Channel Type is set to PDTCH and the cell does not support EDGE services, the default value is EGPRS Normal Channel. When Channel Type is set to PDTCH and the cell supports EDGE services, the default value is EGPRS Normal Channel.

Description When Channel Type is set to non-PDTCH, the default value is None-GPRS Channel.When Channel Type is set to PDTCH and the cell does not support EDGE services, the default value is EGPRS Normal Channel.When Channel Type is set to PDTCH and the cell supports EDGE services, the default value is EGPRS Normal Channel.

164



TRX2

EGPRS

Normal

EDGE MS GPRS MS

EGPRS normal channel can support GPRS MS and EDGE MS at the sametime. But sometimes it will decrease the EDGE MS speed.

165



TRX2

EGPRS

Priority

EDGE MS

×reject

EGPRSPriority

GPRS MSGPRS MS

EGPRS normal channel can support GPRS MS and EDGE MS at the sametime. But sometimes it will decrease the EDGE MS speed.

166


GPRS&EDGE Coding Scheme

8PSKGMSK

9.0513.4

15.6

21.4

8.811.2

14.817.6

22.4

29.6

44.8

54.4

59.2

0.00

10.00

20.00

30.00

40.00

50.00

60.00

CS-1 CS-3 CS-4 MCS-1 MCS-2 MCS-3 MCS-4 MCS-5 MCS-6 MCS-7 MCS-8 MCS-9

Kbps

GPRS

EGPRS

CS-2

167


Appendix

1+31+21+11+0Idle timeslot

MCS9

MCS8

MCS7

MCS6

MCS5

MCS4

MCS3

MCS2

MCS1

CS4CS3CS2CS1Codec

168


Appendix

169


In this course, we have learned:

The function of GPRS cell parameters

The function of GPRS cell reselection parameters

The function of GPRS performance parameters

Summary

170


171

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GPRS EDGE Build-in PCU Packet Radio Resource Management Algorithm and Parameters

172


ForewordRadio resource management (RR) is an important protocol in the

GSM system.

The channel management and load control is a part of the GPRS

resource management.

The appropriate channel management and load control algorithm can

improve the PS assignment success rate, decrease the congestion

ratio, provide proper service resources for subscribers, and improve

the network service quality.

This document describes the specific algorithms and parameters of

the GPRS/EDGE channel management and load control.

173


Objectives

After studying this course, you will:Understand the purposes of the PS resource management and load control.

Master the procedure for allocating channels and main factors to be considered.

Master the percentage of each factor in the channel allocation and adjustment method.

Master the dynamic channel allocation and release algorithm principles.

Be familiar with the main parameters of the dynamic channel allocation and release algorithm.

174


Contents1. Packet Radio Resource Management Algorithm Overview

2. Packet Channel Assignment Algorithm

3. Packet Channel Conversion Algorithm

4. Packet Channel Release Algorithm

175


Overview of PS Resource Management Algorithm

Phase 2 access on CCCH/PCCCH

Phase 1 access on CCCH/PCCCH

Establishment of the uplink

TBF on the PACCH

Establishment of the downlink

TBF on the PACCH

Establishment of the downlink

TBF on the CCCH/PCCCH

Conversion algorithm of dynamic PDCHPDCH allocation algorithm

TBF reassignment/timeslot re-configuration

Idle dynamic PDCH released

For CS service, no idle radio channel resources available for preemption

For CS service, no idle Abis resources available

for preemption

Dynamic PDCH releasealgorithm

The PS resource management algorithm is intended to guarantee the load balance between channels by allowing a single subscriber to obtain a high throughput rate simultaneously, thus improving the channel usage efficiency of the entire network.Upon the receipt of the service application from a subscriber, the BSS allocates appropriate resources to the subscriber after the processing through the PS resource management algorithm. The PS resource management algorithm consists of the following parts:

PS channel allocation algorithm Dynamic channel conversion algorithm Dynamic channel release algorithm

176


Basic Concepts of PS Resource Management Algorithm

Abistimeslot resource

RLC/MACBlock

resource

TAIresource

TFIresource

USFresource

PS resource management

Radio channel resource

Radio channel resources For the PDCH resources of a cell, one TBF can occupy multiple channels. At least one timeslot among the timeslots occupied by the uplink/downlink TBF of the same subscriber is shared. Multiple MSs can be multiplexed on the same channel. Available channel resources in the cell can be taken into account on the basis of these conditions.

Abis resource In Fix Abis mode, the channel is fixedly bound to an active link (16 kbps) after configuration. After code adjustment, the idle timeslots can be bound. Flex mode

For static PDCHs, the description is the same as the preceding description.

The active link is not bound after the dynamic PDCH is configured. The active link is bound after the activation of the channel. A proper idle timeslot is applied for the binding. When no Abis resources are available, the channel cannot be allocated.

Block resource One block budget is required for every 60 blocks. For a guaranteed bit rate (GBR) subscriber, the maximum number of occupied blocks is specified according to the TBF rate threshold/100 of the GBR. For other types of subscribers, the maximum number of blocks is allocated according to the priority of remaining blocks.

177

The GBR service can be applied for through registration. If the GBR attribute is subscribed to during registration, the service rate is guaranteed. For streaming subscribers, the rate is fixed. The corresponding resource is provided according to rate evaluation. The rate requirement is met after evaluation.

USF resource The uplink status flag is used to control multiple MSs to use radio channels in dynamic allocation mode. The USF has three bits in total, labeling eight (0-7) uplink subscribers in total. For Huawei devices, the setting of USF to 7 is reserved. For example, if the USF of the RRBP block is set to 7, seven (0 – 6) USFs are left for allocation to subscribers. The USF applies to data transmission. The RRBP subscribers make response to corresponding data, for example, Ack or Nack.

TFI resourceTFI is an identity of the TBF. The TBF is uniquely identified through the TFI and data transmission direction. The TFI has five bits in total, identifying subscribers of 0-31 bits. There are 32 independent TBFs at the uplink and downlink respectively.

Different channels of the same TRX can use the same TFI value.

Any TFI value of the same channel at the same time belongs to a unique uplink or downlink TBF.

The uplink and downlink TBFs of the same MS can use different TFIs or the same TFI.

TAI resource

A total of 16 TAIs are available for allocation to subscribers for the TA adjustment.

178


Basic Concepts of PS Resource Management Algorithm

PDCH types - by configuration mode

Static channel: fixedly unconvertible in the case of use by PS service

Dynamic channel: applies to CS or PS services

PDCH types - by PS service bearer capability

GPRS channel: applies to only GPRS services

EGPRS normal channel: applies to both GPRS and EGPRS services

EGPRS priority channel: preferentially applies to EGPRS services

EGPRS special channel: applies to only EGPRS service

179


Data Configuration

Common EGPRS channelGPRS and EGPRS subscribers can use this channel, with the same priority. Therefore, GPRS subscribers and EGPRS subscribers may exist in this channel at the same time. The modulation mode corresponding to the channel encoding used by these subscribers must be the GMSK. Therefore, the configuration may affect the high speed performance of the EDGE.

EGPRS preferred channelThe GPRS service can use this channel when it is idle. When the EGPRS service is available on this channel, the GPRS service is swapped and relevant resources are allocated for the EGPRS subscribers. If no channel is available for the GPRS service in the case of swap, call drop occurs in the GPRS service. Therefore, only GPRS subscribers or EGPRS subscribers can use this channel at the same time. This channel is allocated for EGPRS subscribers with priority.

The GPRS channel assignment is initiated by MSs, which is similar to the GSM channel assignment. One channel may be applied for signaling and data transmission, which is similar to the early assignment in the GSM system. Alternatively, one PDCH is applied for and then PS resources are applied for on the basis of this PDCH. This is similar to the immediate assignment and then assignment in the GSM.

180






181


PS Channel Assignment ProcessTRX:0

Main BCCHSDCCH

TCHSDCCH

TCHTCH

PDTCHPDTCH

TRX:1SDCCH

TCHTCHTCH

PDTCHPDTCH

TCHTCH

TRX:2TCHTCHTCHTCHTCHTCHTCHTCH

TRX:3TCH/HTCH/HTCH/HTCH/HTCH/HTCH/HTCH/HTCH/H

RACH-Channel RequestCause: PS access, random number

AGCH-Imm Assignment(random number, PDCH channel description)

PDCH-Packet Resource Request(TLLI, pre-emption decision)

Imm Assignment decision

Packet assignment decision

PDCH-Packet Assignment(TLLI)

The GPRS channel assignment is initiated by the MS, which is similar to channel assignment in the GSM system. One channel may be applied for signaling and data transmission, which is similar to early assignment in the GSM system. Alternatively, one PDCH is applied for and then PS resources are applied for on the basis of this PDCH, which is similar to the immediate assignment in the GSM.

182


PS Channel Assignment Process

Channel assignmentpre-processing

Yes

Immediate assignment request

Assignment request on the PACCH

Reassignmentrequest

PS channel allocation algorithm

Is the channel assignment successful?

Processing after the initial assignment failure

End

No

According to the received assignment request, the BSS checks the assignment request type during channel assignment pre-processing to determine the channel type of the assignment and assignment process. The PS channel allocation algorithm is used to find the proper TRX, channel group, and calculation weight for the allocation processing. If once assignment is successful, the assignment process ends. If no appropriate channel is used for the assignment, it is subject to the processing after the initial assignment failure. The dynamic channel conversion and twice assignment are performed until the assignment is complete after the initial assignment failure.

183


General Process of PS Channel Allocation Algorithm

Obtain the assignable channel group

Obtain the assignableTRX

Is the assignable TRX available?

Start

Calculate the weight of the assignable channel group

Maximum channel group of the allocation weight

End

Yes

No

Is the assignablechannel group

available?

Yes

No

The PS channel allocation algorithm includes four steps: Obtaining the assignable TRX information. Obtaining the assignable channel group information from the assignable TRX. Performing the weight calculation for all assignable channel groups to obtain the appropriate channel group. Selecting the channel group with the greatest weight for allocation.

184


Obtaining the Allocable TRX

Double-timeslot extension cell?

Start

Yes

Multi-band cell or nor?

Is the MS band support capability known?

Main BCCH TRX band and TRX of the band being compatible with the main

BCCH TRX Bands supported by the MS

Select the double-timeslot extension TRX

TA>63?

Concentric cell or not?

Specify the TRX of the concentric subcell attribute

TRX supporting the EGPRS

Do the MS and cell support the EGPRS?

End

YesNo

Yes

No

Yes

No

No

Yes

No

Yes

No

Yes

No

Specify the overlaid subcell or underlaid

subcell?

The procedure for obtaining the assignable TRX is as follows: TRX requirement: To allocate the PDCH for MSs, check whether the cooperative TBF exists according to the ingress TRX index. If yes, allocate the PDCH for the MS on the specified TRX. For a multi-band cell, the capability of the MS supporting the frequency bands must be taken into account when assigning the PDCHs.

If the BSC does not know the radio access capability of the MS, only the PDCHs over the main BCCH frequency band and the frequency bands compatible with the main BCCH frequency band should be assigned.

If the BSC knows the radio access capability of the MS, only the PDCHs over the frequency bands supported by the MS are assigned.

If the cell is a double timeslot extended cell as defined by the cell attribute parameter 【Cell Ext Type】, and if the TA reported by the MS is greater than 63, then the PDCHs on a double timeslot extended TRX should be assigned to the MS.If the cell is a concentric cell as defined by the cell attribute parameter 【Cell Type】, and if the BSC specifies the overlaid subcell or underlaid subcell upon a PDCH request, then the PDCHs on an overlaid TRX or underlaid TRX should be assigned accordingly. If the overlaid subcell or underlaid subcell is not specified, the PDCHs on a concentric TRX should be assigned without specific tendency.In the case of applying for the allocation of channels, the service type (EDGE or GPRS service, or EDGE + GPRS service) is contained. According to the TRX attribute parameter 【TRX capability】, the TRX supporting the EGPRS is selected if the MS and cell support the EGPRS.

185


Obtaining the �Allocable ChannelStart

Yes

Is the idle PDCH with normal status &

available Abis timeslot & channel priority meeting the

service requirement available?

Does the number of MSs multiplexed on the PDCH

reach the threshold?

The corresponding PDCH isunavailable

Allow E Down G Up Switch?

Perform processing related to Prohibit E Down G Up Switch?

End

Yes

No

Perform polling for all PDCHs

Match the service type to the channel priority type

No

YesYes

No

To obtain the assignable channels, do as follows: Check whether the channel type of the sub timeslot is PDCH. Check whether the valid status of the PDCH is configured, that is, whether the location occupied by the channel can be replaced. If it is not configured, it is unavailable. If it is configured, it is available. Obtain the management status of the current channel. Check the channel management status. If the channel is in the blocked state, do not perform the processing. Check the resource status recorded through 8 bits on the left and the control status recorded through 8 bits on the right. Make sure that they are normal. Check whether the main control status of the channel is in the idle state. Check whether the channel recorded in the radio resource management module is available. Make sure that the number of available Abis is not zero. Check whether the channel priority meets the service type.

For GPRS services, the GPRS channel group, EGPRS normal channel group, and EGPRS priority channel group can be allocated.

For EDGE services, the EGPRS special channel group, EGPRS normalchannel group, and EGPRS priority channel group can be allocated.

186

According to the cell attribute parameter 【 PDCH Uplink/Downlink Multiplex 】Threshold, make sure that the number of MSs multiplexed on the channel does not reach the upper threshold.

For the PBCCH or PCCCH, the number of MSs multiplexed on the channel must be smaller than 7. Otherwise, the number of MSs multiplexed on the uplink PDTCH should be equal to or smaller than 7, and the number of MSs multiplexed on the downlink PDTCH should be equal to or smaller than 8. In the latest version, the downlink PDTCH supports 16 MSs.

Match the service type with the channel priority type: The GPRS services cannot occupy the EGPRS special channels.If an EGPRS priority channel bears the EGPRS services, the EGPRS priority channel cannot be assigned to the GPRS services.

Make decision according to the BSC attribute parameter 【 Allow E Down G Up Switch 】. If the switch is off (that is, the EGPRS OFF GPRS ON is prohibited),

If a channel carries the EGPRS downlink services, the channel cannot be assigned to the GPRS uplink services.If a channel carries the GPRS uplink services, the channel cannot be assigned to the EGPRS downlink services.

Obtain the assignable channel groups. If an available channel exists according to the preceding decision, obtain all channel groups that can be allocated to MSs based on the MS multi-timeslot capability.

187


Data Configuration

PDCH Uplink Multiplex ThresholdDescription: This parameter specifies the PDCH uplink multiplex threshold.Theuplink PDCH can carry a maximum of (threshold/10) TBFs.Value Range: [10,70] Default Value: 70Configuration Policy: If this parameter is set to a lower value, the TBFsestablished on the PDCH and the subscribers are fewer, and the uplink bandwidth for each subscriber is higherIf this threshold is set to a higher value, the TBFs established on the PDCH and the subscribers are more, and the uplink bandwidth for each subscriber is lower.

PDCH Downlink Multiplex ThresholdDescription: This parameter specifies the PDCH downlink multiplex threshold.The downlink PDCH can carry a maximum of (threshold/10) TBFs.Value Range: [10,160] Default Value: 80Configuration Policy: If this parameter is set to a lower value, the TBFsestablished on the PDCH and the subscribers are fewer, and the downlink bandwidth for each subscriber is higher.If this threshold is set to a higher value, the TBFs established on the PDCH and the subscribers are more, and the downlink bandwidth for each subscriber is lower.

188


Data Configuration

Allow E Down G Up SwitchDescription: This parameter specifies whether to enable the multiplexing of EDGE download and GPRS upload onto the same channel. If this parameter is set to Open, the EDGE download and GPRS upload can use the same channel;If this parameter is set to Close, the EDGE download and GPRS upload cannot use the same channel.In dynamic allocation or extended dynamic mode, the downlink block must use the GMSK coding scheme (including CS1-4, MCS1-4) to detect the USF assigned for the uplink by the GPRS MS. Then, the downlink cannot use the high-rate coding scheme, thus decreasing the EGPRS rate.If the Allow E Down G Up Switch is set to Open, this can prevent the EGPRS downlink and GPRS uplink from multiplexing the same channel to ensure the EGPRS rate. However, the channel needs to be properly allocated, the GPRS channel configured is to prevent decreasing the access of the GPRS MS due to no GPRS channel.If the Allow E Down G Up Switch is set to Close, the downlink uses the GMSK coding scheme, thus decreasing the EGPRS rate.At present, this parameter is usually set to Open.Value Range: [Open,Close] Default Value: Open

189


BITMAP Mapping of Available Channel

GPRS service BITMAP mapping: 00011101

EGPRS service BITMAP mapping: 00001111

User multiplexing

is full.

The EGPRS subscriber is available and the multiplexing is

not full.

GPRS service BITMAP mapping: 00010100

EGPRS service BITMAP mapping: 00000111

Allow E Down G Up Switch is OFF. The EGPRS downlink multiplexing is not

full.

Uplink GPRS service BITMAP mapping: 00010101

Downlink GPRS service BITMAP mapping: 00011101

76543210

B SD TF GS EN EN EPES

76543210

B SD TF GS EN EN EPES

76543210

B SD TF GS EN EN EPESEGPRS service BITMAP mapping:

00001111

Channel type:

B: BCCH channel

SD: SDCCH channel

TF: TCH full rate channel

GS: GPRS special channel

EN: EGPRS normal channel

ES: EGPRS special channel

EP: EGPRS priority channel In the case of the existing channel resources, generate the corresponding available channel BITMAP according to the service type. See the preceding example.

In the case of the request for allocating uplink channel, the allocation fails when the number of the multiplexed uplink TBFs on the channel is equal to or greater than 【PDCH Uplink Multiplex Threshold】. In the case of the request for allocating downlink, the allocation fails when the number of the multiplexed downlink TBFs on the channel is equal to or greater than 【PDCH Downlink Multiplex Threshold】. The EGPRS special channel cannot be allocated for the GPRS request. The GPRS channel cannot be allocated for the EGPRS request. The EGPRS priority channel occupied by the EGPRS (including the uplink and downlink) cannot be allocated for the GPRS. When 【Allow E Down G Up Switch】 is off, if the EGPRS downlink is available, the resource should be allocated to the GPRS uplink. If the GPRS uplink is available, the resource cannot be allocated to the EGPRS downlink.

All available channel groups are generated through the AND and OR operations among the BITMAP mapping of available channels and all possible BITMP tables of

190


Obtaining the Assignable Channel GroupThe bitmap mapping of multi-timeslot ability. For example for 4 multi-timeslots ability

Enable “Allocate Continuous Timeslot Switch” (by default )

Disable “Allocate Continuous Timeslot Switch”

“Allocate Continuous Timeslot Switch” can not be configured.

191


Obtaining the Downlink Channel Group

Consecutivetimeslot

TAI/TFIResource

Frequency Hopping Parameter

Receive/send Sharing

Timeslot

Cooperation TBF

EDAFunction

Number of Channels Contained

in the ChannelGroup/

MS Multi-timeslot Capability

Obtain the

�downlink channel

group

After obtaining the allocable channel group, attempt to obtain available uplink or downlink channel group of a TRX according to the service status. The method for obtaining the downlink channel group is as follows:

If the number of channels contained in the assignable channel group in the TRX is smaller than or equal to the MS multi-timeslot capability channel group, these channel groups can be used for the allocation.

If the MS multi-timeslot capability is unknown, up to one PDCH is allocated. If the MS multi-timeslot capability is known, the maximum number of channels supported by the MS multi-timeslot capability is allocated.

The channel group supports multi-timeslot capability meeting the MS. For type 1 or 2 MS, check the following (for type 1 MS, the simultaneous receiving and transmitting is not allowed. For type 2 MS, the simultaneous receiving and transmitting is allowed).

Calculate the number of received and transmitted timeslots of a TDMA frame. Check whether the number of received and transmitted timeslots meets the multi-timeslot capability.

For the MSs with the multi-timeslot levels from 1 to 12, check whether the timeslot sum of the receiving and transmitting is in the range [1, Sum]. Make sure that the transmitting timeslot does not exist between two receiving timeslots in a TDMA frame. Make sure that the receiving timeslot does not exist between two transmitting timeslots in a TDMA frame.

192

Check whether the Tta, Ttb, Tra, and Trb conditions of multi-timeslot capability are met, that is,

Time of the channel group supporting the MS from neighbor cell power measurement to transmitting (number of timeslots) Tta

Time of the channel group supporting the MS transmitting (number of timeslots) Ttb

Time of the channel group supporting the MS from neighbor cell power measurement to receiving (number of timeslots) Tra

Time of the channel group supporting the MS receiving (number oftimeslots) Trb

193


Obtaining the Uplink Channel Group (Non-EDA Mode)

ConsecutiveTimeslot

TAI/TFIResource

Frequency Hopping Parameter

MS multi-timeslot

Capability

Cooperation TBF

Number of Channels Contained

in the Channel Group

Obtain the �Uplink Channel Group

In non-EDA mode, consider the following factors when obtaining the uplink channel group: The number of channels contained in the channel group is less than or equal to the maximum number of assignable channels.The timeslots that carry the channels must be consecutive.For the cooperation TBF, consider the following items:

If the cooperation TBF does not exist, the channel with the largest timeslot number in the uplink channel group must able to be assigned to the downlink.

If the cooperation TBF exists, the control channel of the channel group must be the same as the control channel of the cooperation TBF, and the control channel of the cooperation TBF must have TAI resources. If there are m timeslots allocated to the channel group and n timeslots allocated to the cooperation TBF, there should be Min (m, n) timeslots for transmission and reception.

The frequency parameters (MAIO, HSN) of the channels in the channel group must be the same.The channel group assigned to the MS must match the multislot capability of the MS.The TFI and TAI resources are available for assignment.

194


Obtaining the Uplink Channel Group (EDA Mode)

Downlink Channel

TAI/TFI Resource

Frequency Hopping

Parameters

EDA Function

Cooperation TBF

Channel Group

including Channel Number

Obtainingthe Uplink Channel

Group

When the BSC software parameter 【Support EDA】 is set to “Support”, and if the MS supports EDA, then only one channel should be assigned on the downlink. Note this channel corresponds to the timeslot numbered smallest of the uplink channel group.If the cooperation TBF exists, the control channel of the channel group must be the same as the control channel of the cooperation TBF, and the control channel of the cooperation TBF must have TAI resources. If there are m timeslots allocated to the channel group and n timeslots allocated to the cooperation TBF, there should be Min (m, n) timeslots for transmission and reception.

Note: The uplink (or downlink) TBF of the MS is the cooperation TBF of the downlink (or uplink) TBF.

If the number of receiving timeslots of the MS is m and the number of transmitting timeslots of the MS is n, there must be Min (m, n) same timeslots in the transmitting and receiving timeslots. The frequency parameter (MAIO, HSN) of the channel in the channel group must be the same. If the frequency parameter of the channel in the channel group is different, the channel group cannot be allocated. The TFI and TAI resources exist in the channel group. The timeslots that carry the channels must be consecutive.

195


Data Configuration

Support EDADescription：This parameter specifies whether the EDA is supported.Value Range：[Not Support,Support]Default Value：Not Support

Allow EDA MultiplexDescription：This parameter specifies whether the EDA multiplexing is allowed.Value Range：[Not Allow,Allow] Default Value：Not Allow

196


Calculating the Weight of the Allocable Channel

Higher priority

Extended weight tableWeight table

Lower priority

Weight table

Priority of service type

Priority of non-double timeslot

channels

Priority of number of channels in the channel group

Priority of the load of

channel groups

31 30 29-27 26-20

Priority of numberof estimated downlink

channels

19-17

Priority of the channel group

bandwidth

16-1

Reserved

0

Extended weight table

Reserved Priority of the

downlink bandwidth of the estimated channel group

31 30-15

Priority of channel type

14-10

Priority of the channel group

timeslot ID

9-6

Reserved

5-0

If there are channels groups available for assignment, their weight must be calculated to select the optimal channel group for the MS. The following describes the channel weight table and channel extension weight table.After comparing the weights of the assignable channel groups on the basis of the channel weight table and channel extension weight table, the optimal channel group for assignment is determined.The channel extension weight table is used only when two channel groups have the same weight.The following describes the factors listed in the channel weight table.

Bit 31 service type priority: When the EGPRS service is requested, the EGPRS channel is allocated with priority and is set to 1. Bit 30 Non- double timeslot channel priority: Check whether it is the double timeslot channel. According to the situation of the actual TA, set the weight of the non double-timeslot channel and double-timeslot channel. If TA is larger than 63, it indicates the high priority for the double timeslot TRX. Otherwise, it indicates the high priority for the common TRX. Bits 29 to 27 (priority of the number of channels in the channel group): This field specifies the number of channels in a channel group.Bit 26-30 channel group load priority: It indicates the total number of MSs multiplexed on the channel. The larger the total number of MSs, the lower the assigned value and the priority. Bit 19-17 number of estimated downlink channels priority: For the uplink TBF, the number of allocable channels can be estimated when the service type is neutral or downlink priority. The larger the number of downlink channels, the higher the priority.

197

Bits 16 to 1 (priority of the bandwidth of the channel group): The higher the bit rate provided by a channel group, the higher the priority of the channel group.

When the BSC software parameter 【Support EDA】 is set to 【Support】, and if the MS supports EDA and uplink service is preferred, the rules for determining the uplink channel group are as follows:

The number of channels contained in the channel group is less than or equal to the maximum number of assignable channels.The number of channels contained in the channel group is greater than or equal to 3.If the cooperation TBF does not exist, the downlink channel corresponding to the timeslot numbered smallest of the uplink channel group must be assignable; that is, the uplink threshold is not exceeded.Only one channel is assigned on the downlink, and the timeslot number of the timeslot that carries the channel must be the smallest.If the BSC software parameter 【Allow EDA Multiplex】 is set to 【Not Allow】, then any channel in the channel group cannot be multiplexed with other MSs.The frequency parameters (MAIO, HSN) of the channels in the channel group must be the same.The TFI and TAI resources are available for assignment.

198






199


Triggering Conditions of Dynamic Channel Application

Failure to allocate the

PDCH

Multi-timeslot

capability is not met

Channel load exceeding

the threshold Channel reserved

Apply for the dynamic channel

Failure to assign a

single block

EGPRSpreemption

In the case of applying for dynamic channels, check whether the cell is allowed to trigger the dynamic channel conversion to increase the number of PDCHs according to the cell channel resource, CPU load, and license. The number of PDCHs does not increase by triggering the dynamic channel conversion in the cell when one of the following cases occurs.

Channel resources

The number of PDCHs activated in the cell is greater than the upper threshold of the maximum PDCH ratio.

The number of convertible TCHs in the cell is equal to or smaller than the number of reserved TCHs (specified by the Reservation Threshold of Dynamic Channel Conversion).

EGPRS MSs occupy the GPRS channel. CPU load: If the CPU utilization is high, the dynamic channel conversion is stopped. License: In the case of the license control, the dynamic channel conversion is not triggered if the activated PDCH channel is available (that is, the current logical type is PDCH).

When any of the preceding conditions is not met, cell conversion is allowed. According to the triggering condition of the dynamic channel conversion, determine whether the subscriber needs to triggers the dynamic channel conversion. That is, dynamic channel application is triggered when any of the following conditions occurs:

Multi-timeslot capability

The assignment of the PDCHs to the MS fails.

The assignment of the PDCHs to the MS succeeds, but the PDCHs do not meet the multislot capability requirement of the MS.

Load

Failure to assign a single block for MSs 200


Data Configuration

Maximum Ratio Threshold of PDCHs in a CellDescription：This parameter specifies the maximum ratio of PDCHs in a cell. The total number of TCHs and PDCHs available in a cell is fixed. The PDCH ratio is equal to PDCHs / (TCHs + static PDCHs). This parameter determines the proportion of PDCHs to the total number of TCHs + PDCHs.Value Range：[0,100] Default Value：30 Unit：%Configuration Policy：If this parameter is set to an excessive value, there are excessive PDCHs and insufficient TCHs. This affects CS services. If this parameter is set to a modest value, there are insufficient PDCHs and excessive TCHs. This affects PS services.

Uplink Multiplex Threshold of Dynamic Channel ConversionDescription：This parameter specifies the uplink multiplex threshold of dynamic channel conversion.When the number of subscribers carried over the channel reaches the threshold/10, dynamic channels are used.Value Range：[10,70] Default Value：20Configuration Policy：If this threshold is high, it is difficult to seize dynamic channels. If this threshold is low, it is easy to seize dynamic channels.

201

Downlink Multiplex Threshold of Dynamic Channel ConversionDescription：This parameter specifies the downlink multiplex threshold of dynamic channel conversion.When the number of subscribers carried over the channel reaches the threshold/10, dynamic channels are used.Value Range：[10,80] Default Value：20

Level of Preempting Dynamic ChannelDescription：This parameter specifies the levels of dynamic channels preempted by CS services and PS services. Only full-rate TCHs are the dynamic channels that can be preempted. Preempt all dynamic TCHFs: It indicates that the CS services can preempt all the dynamic channels.No preempt of CCHs: It indicates that the CS services can preempt all the dynamic channels except for the control channels.No preempt of service TCHF: It indicates that the CS services cannot preempt the dynamic channels that carry services.Value Range：[Preempt all dynamic TCHFs,No preempt of CCHs,No preempt of service TCHF] Default Value：Preempt all dynamic TCHFs

Reservation Threshold of Dynamic Channel ConversionDescription：This parameter specifies the number of channels reserved for theCS services.Value Range：[0,8] Default Value：2

202


Process of Dynamic Channel Application

Obtain the weight maximum TRX

Obtain the number of applied dynamic channels

Is the convertible TRX available?

Start

Obtain the convertible dynamic channel

End

Yes

No

When the condition for triggering dynamic channel application is met, start the dynamic channel application process. The procedure is as follows:

Obtain the number of dynamic channels through calculation. Calculate the TRX weight and obtain the highest TRX of the weight. Locate the dynamic channel bitmap on the TRX and start to apply for the appropriate dynamic channel.

203


Obtaining the �Number of Applied Dynamic Channels

Multi-timeslot capability:

Fail to allocate the PDCH. The MS multi-timeslot capability is

unknown.

The allocation of the PDCH for the MS is successful. The MS multi-

timeslot capability is not met.

Load:

The load reaches Uplink/Downlink Multiplex Threshold of Dynamic

Channel Conversion

Pre-application for the PDCH

Failure to assign a single block for terminals

The method for obtaining the number of dynamic channels for request conversion is as follows: Multi-timeslot capability

If the assignment of the PDCH to the MS fails, and if the multislot capability of the MS is unknown, then the number of dynamic channels requested for conversion is 1; if the multislot capability of the MS is known, the number of dynamic channels requested for conversion is equal to the number of timeslots supported by the MS.If the assignment of the PDCHs to the MS succeeds, but the PDCHs do not meet the multislot capability of the MS, then the number of dynamic channels requested for conversion is: maximum number of channels supported by the multislot capable MS – number of channels assigned to the MS.The channel conversion type of the preceding two causes is the multi-timeslot capability.

Load The dynamic channel conversion is triggered due to the restriction by【Uplink/Downlink Multiplex Threshold of Dynamic Channel Conversion】, to request for calculating the number of converted dynamic channels. The method is as follows:

Assume that the number of dynamic channels requested for conversion is X, the multiplexing dynamic channel conversion threshold is H, total number of uplink TBFs of the cell downlink PDCH channels is S, and the number of downlink PDCHs in the cell is M. The formula is as follows:X = S × 10/H – M + 1This formula is used to check whether the channel resources are sufficient. The dynamic channel can be applied for when the multiplexing dynamic channel conversion threshold is exceeded. The number of dynamic channels applied for is equal to the number of the part of load

204


Obtaining the Convertible TRX

Double-timeslot extension cell?

Start

Yes

Multi-band cell?

Is the MS band support capability known?

Main BCCH TRX band and TRX of the band being compatible with the

main BCCH TRX Bands supported by the MS

Select the double-timeslot extension TRX

TA>63?

Concentric cell ornot?

Specify the TRX of the concentric subcell attribute

Specify the overlaid subcell or underlaid

subcell?

Select the TRX corresponding to the service of triggering dynamic

channel application

End

YesNo

Yes

No

Yes

No

No

Yes

No

Yes

No

Select the TRX where the number of PDCHs is smaller than

Maximum PDCH number of carrier.

Obtain the convertible channel bitmap on the

TRX

The TRXs that carry the dynamic channels must be specified prior to the dynamic channel conversion. The rules for determining the TRXs are as follows:For a multi-band cell, the band supported by MSs must be taken into account.

If the MS radio access capability is unknown, only the main BCCH band and the frequency bands compatible with the main BCCH band is selected.If the MS radio access capability is known, only the band supported by the MS is selected.

For a double timeslot extended cell, if the TA reported by the MS is greater than 63, the double timeslot extended TRXs should be selected.For a concentric cell, the concentric attribute of the TRX carrying the dynamic channels must be taken into account when performing dynamic channel conversion. The cell attribute parameter concerned is 【Dynamic Channel Conversion Parameter of Concentric Cell】. See the following table for details.

If the overlaid subcell or underlaid subcell is specified when requesting PDCH assignment, and if the channel assignment on the specified subcell fails, then the dynamic channel conversion in the specified subcell is triggered.

The TRX of supporting the service is selected according to the service type. For the dynamic channel conversion triggered by the EDGE service, the minimum type of the converted dynamic channel is EGPRS TRX TCH. For the dynamic channel conversion triggered by the GPRS service, the minimum type of the converted dynamic channel is GPRS TRX TCH.

Select the TRX on which the number of PDCHs carried is less than that specified by the TRX attribute parameter 【Maximum PDCH numbers of carrier】.Obtain the convertible channel bitmap on the TRX for selecting the optimal dynamic channel (group). If the dynamic channel conversion type is the multi-timeslot capability, the convertible channel bitmap on the TRX consists of the TCH channel and available PDCH channel. If the dynamic channel conversion type is load, the convertible channel

205


Obtaining the �Weight Maximum TRX

Higher priority

Weight table

TRX conversion weight table

Lower priority

031 2 12930

Priority of main BCCH

TRX

Priority of the number

of PDCHs

Priority of the number of

static PDCHs

Priority of number of convertible

dynamic channels

19 18-15 14-12 11-9

Priority of number of maximum consecutive convertible dynamic

channels

8-6

Distance priority

5-3

Band priority

2-0

Concentric cell

priority

Priority of double timeslot

TRX

Priority of theEDGE TRX

Priority of conversion

request satisfaction

29 28 27 26

Priority of the dynamic

PDCH channel

25-24

Frequency hopping priority

23

Interferencepriority

22-2031-30

Priority of power amplifier

Switch

The TRX with the highest weight should be selected as the optimal TRX for conversion. The following describes the factors listed in the TRX extension weight table:

Bits 31 and 30 (priority of the TRX power amplifier switch): If the switch of the power amplifier of a TRX is turned on, the priority of the TRX is higher; if the switch of the power amplifier of a TRX is turned off, the priority of the TRX is lower.Bit 29 (Subcell priority): When the requested subcell attribute and the TRX subcell attribute are the same, the value is 1. Otherwise, the value is 0. If the subcell attribute is not specified or the access is initial, the underlaid subcell is preferred. Bit 28: Double-timeslot TRX priority. For the single timeslot TRX, the priority is high. For the double timeslot TRX, the priority is lower. Bit 27: EDGE TRX priority (valid only for BTS in the earlier versions such as BTS312 and BTS3012). For the EGPRS TBF, the EGPRS TRX is preferred. For the GPRS TBF, the GPRS TRX is preferred. Bit 26 (priority indicating whether the TRX meets the conversion request): If the number of convertible dynamic channels on the TRX is equal to or greater than the number of dynamic channels for request conversion, it is set to the higher priority. Bit 25 to 24 (TRX dynamic PDCH attribute priority): The highest priority in the channel attribute priority of all TRX traffic channels (including the converted or configured static PDCHs) is the priority of the TRX. For the EGPRS TBF, the priorities of the PDCH attributes from the high to low is {EGPRS special channel, EGPRS priority channel, EGPRS normal channel, and GPRS channel}, with the corresponding weights 3, 2, 1, and 0 respectively. For the GPRS TBF, the priorities of the PDCH attributes from the high to low is {GPRS channel, EGPRS normal channel, EGPRS priority channel, EGPRS special channel}, with the corresponding weights 3, 2, 1, and 0 respectively.

206


Please refer to the notes

Bit 23 (frequency hopping attribute priority): The priority of the TRX without involving the TRX is higher. Bit 22 to 20 (TRX interference priority): The priority of the TRX with lower interference is higher. Bit 19 (priority indicating whether the TRX is the main BCCH TRX): The priority of the main BCCH TRX is higher. Bit 18 to 15 (PDCH quantity priority over the TRX): The more the PDCH quantity is, the higher the priority is (the weight is valid when the number of convertible dynamic channels over the TRX is equal to or greater than 1).Bit 14 to 12 (static PDCH quantity priority over the TRX): The more the static PDCH is, the higher the priority is (the weight is valid when the number of convertible dynamic channels over the TRX is equal to or greater than 1). The maximum value is 7. Bit 11 to 9 (priority of the number of convertible dynamic channels on the TRX): The more the convertible dynamic channels are, the higher the priority is (When the number of convertible dynamic channels on the TRX is smaller than the number of dynamic channels requested for the conversion, the weight is valid). Bit 8 to 6 (priority of the maximum number of consecutive convertible dynamic channels on the TRX): The larger the maximum number of consecutive convertible dynamic channels is, the higher the priority is. Bit 5 to 3 (priority of distance between the maximum number of consecutive convertible dynamic channels on the TRX and other convertible dynamic channel groups): The shorter the distance is, the higher the priority is. Bit 2 to 0 (TRX band priority): The priority of the band differing from the main BCCH TRX band is high. Otherwise, the priority is low. The priority of two sets of main BCCH same band or main BCCH different band are as follows (from high to low):

900M band: P band < E band < R band

1800M/1900M band: Only 1800M band or 1900M band exists on a network. Therefore, only one priority needs to be defined.

850 band

450 band

480 band

207


Obtaining the �Convertible Dynamic ChannelSelect the timeslot where the initial configuration is set to TCHF

You are not allowed to adjust the timeslot where the initial configuration is set to

TCHH.

Consider the value of 【Whether to Allow to Re-adjust the PDCH】

When the value is set to Not allow, select only the idle TCHF or the timeslot

where two TCHHs of the same timeslot are idle.

When the value is set to Allow, all timeslots of the TCH type can be selected,

regardless of whether the TCHH or TCHF of this timeslot is occupied.

If an independent GPRS request triggers the dynamic conversion, the EGPRS

special channel is not selected. If an independent EGPRS request triggers the

dynamic channel conversion, the GPRS channel is not selected.

When multiple dynamic channels are selected for the conversion, the

conversion is performed according to the sequence of the timeslot numbers 6, 5,

7, 4, 3, 2, 1, and 0.

After selecting the optimal conversion TRX, select the convertible dynamic channel on the TRX according to the requirement. The dynamic channel is not converted when any of the following occurs:

The number of channels to be converted is equal to or smaller than the number of channels being converted. The number of Abis timeslots on the TRX is greater than or equal to the number specified by the TRX attribute parameter MaxAbisTSOccupied.The number of PDCHs on the TRX is greater than or equal to the number specified by the TRX attribute parameter Maximum PDCH numbers of carrier.The number of PDCHs in a cell is greater than or equal to the maximum number of PDCHs allowed in a cell.The maximum number of PDCHs allowed in a cell can be calculated on the basis of the cell attribute parameter Maximum Ratio Threshold of PDCHs in a Cell. The formula is as follows:

Maximum number of PDCHs allowed in a cell = Maximum Ratio Threshold of PDCHs in a Cell x number of TCHs and PDCHs in a cell/100

CS Repacking function is controlled by PDCH reforming. When PDCH reforming is set to Allow, the CS Repacking is functional. That is, it is functional when the dynamic PDCH applying for the conversion is occupied by CS services. If the local cell has the idle TCH resources, these CS services are switched to the idle TCH. If the idle TCH is unavailable and Level of Preempting Dynamic Channel is set to All dynamic channels carrying services not-preempted, the system initiates the forcible release for the CS service. As a result, the CS calls are dropped. If Level of Preempting Dynamic Channel is set to All dynamic channels preempted or control channel not-preempted, the application for converting the dynamic PDCH fails.

208


Data Configuration

Maximum PDCH numbers of carrierDescription：This parameter specifies the maximum number of PDCHsallocated to a TRX. Value Range：[0,8] Default Value：8

MaxAbisTSOccupiedDescription：This parameter specifies the maximum number of Abis timeslots occupied by the PDCHs on a TRX. Value Range：[0,32] Default Value：32

209






210


General Process of Dynamic Channel Release

Release the channel with the highest priority

Obtain the TRX of releasing dynamic channels

Is the TRX obtained successfully?

CS channels areinsufficient and

CECHM receives the request for releasing

channels

Recall the dynamic PDCH with load Release the PDCH resource

End

Yes

No

When CS services are busy, the CS services may preempt the dynamic channel of the PS according to the data configuration because the TCH of the CS is deficient. As a result, the preceding process is triggered. The first step to release channel is to obtain the appropriate TRX of dynamic channel, with considering the requirements of the band and concentric cell.

The band must be available and the congestion cannot occur. The frequency bands supported by the TRX must be the same as requested by the CS services.For the concentric cell, the overlaid/underlaid subcell attribute of the TRX must meet the requirement of the CS services on the overlaid/underlaid subcell.

When the CS requests the overlaid subcell or underlaid subcell, only the overlaid subcell or underlaid subcell can be selected.

When the CS requests the preferred underlaid subcell, the priority of the underlaid TRX is higher.

When the CS requests the preferred overlaid subcell, the priority of the overlaid TRX is higher.

Determine the TRX to release the dynamic channel information. Release the weight ratio for the target TRX. Then select the channel with the maximum weight for initiating the release. In another case, the timing release of the idle dynamic channel is controlled by Timer of Releasing Idle Dynamic Channel.

If the value is large, the idle channel fails to be released. As a result, resource is wasted. If the value is small, the dynamic channel can be released easily. The conversion may be triggered if required. As a result, the conversion is performed repeatedly.

211


Obtaining the Dynamic Channel to be Released

Higher priority

Weight table

Channel release weight table

Lower priority

031 2 12930

Priority of the number of fixed

channels

Priority of thenumber

of PDCHs

19-17 16-14

Priority of channel type

12-11

Priority of timeslot

ID sequence

10-8

Reserved

7-0

Concentric cell priority

Priority of idle dynamic channels

31-30 29


control channels

28-25

Priority of reserved channels

24


dynamic TBFs

23-20

13

Priority of TRX type

Whether to release the channel is specified by 【Level of Preempting Dynamic Channel】.

When the value is set to 【Preempt all dynamic TCHFs】, the dynamic PDCH can be released. When the value is set to 【No preempt of CCHs】, the dynamic PDCH of the control channel cannot be released. When the value is set to 【No preempt of service TCHF】, the channels cannot be preempted if a service exists on this channel. If this channel is idle, the resource is released actively after relevant PS timers expire when 【PDCH reforming】 is set to Allow.

Release the dynamic channel with the highest priority. To select the optimal dynamic channel, calculate the priority of each dynamic channel in the TRX of the dynamic channel to generate the dynamic channel release weight table. See the preceding table. The factors in detail to be considered are as follows (select the dynamic channel with the greatest weight value for the release):

Bits 31 and 30: priority of the concentric cell attributeBit 29 (priority of the idle dynamic channel): An idle dynamic channel has a higher priority of being released.

212

Bits 28 to 25 (priority of the number of control channels): The less number the dynamic channels are used as control channels, the higher the priority of the dynamic channels are being released.Bit 24 (priority of reserved channels): During the PDCH pre-application conversion, the priority of the pre-applied channel is low. Bits 23 to 20 (priority of the number of TBFs on the dynamic channel): If fewer TBFs are multiplexed on a dynamic channel, the priority of the dynamic channel being released is higher.Bits 19 to 17 (priority of the number of fixed channels on the TRX): If fewer fixed channels are carried on the TRX that carries a dynamic channel, the priority of the dynamic channel being released is higher.Bits 16 to 14 (priority of the number of PDCHs on the TRX): If fewer PDCHs are carried on the TRX that carries a dynamic channel, the priority of the dynamic channel being released is higher.Bit 13 (priority of the TRX type): The dynamic channel carried on the GPRS capable TRX has a higher priority of being released.Bits 12 and 11 (priority of channel type): The release priority in descending order is as follows: GPRS channel, EGPRS normal channel, and EGPRS priority channel. Bits 10 to 8 (priority of the timeslot sequence): The priorities of the dynamic channels being released are decreased in the following order: TS0, TS1, TS2, TS3, TS4, TS7, TS5, and TS6.

213


Data Configuration

Timer of Releasing Idle Dynamic ChannelDescription：This parameter specifies the timer set to release the idle dynamic channel after all TBFs on the dynamic channel are released.If all TBFs on a dynamic channel are released, the dynamic channel is not released immediately. Instead, a timer is started when the channel is idle.Before the timer expires, if there are new services, the dynamic channel continues to be used and the timer is stopped. When the timer expires, the dynamic channel is released.Value Range：[10,3600] Default Value：20Unit：SecondsConfiguration Policy：If this parameter is set to an excessive value, the dynamic channel resources may be wasted when there are no services for a long time. If this parameter is set to a modest value, it is possible that a dynamic channel is requested immediately after being released. Therefore, the dynamic channel request is sent frequently.

214


Data Configuration

PDCH reformingDescription：This parameter specifies whether the PS services are allowed to preempt the ongoing channel for CS services when "Level of Preempting Dynamic Channel" is set to "No preempt of service TCHF".This parameter must be used together with "Level of Preempting Dynamic Channel", the condition as follows:1. When "Level of Preempting Dynamic Channel" is set to "No preempt of service TCHF" and "PDCH Reforming" is set to Yes, PS services can preempt the CS channel.2. When "Level of Preempting Dynamic Channel" is set to "No preempt of service TCHF" and "PDCH Reforming" is set to No, PS services cannot preempt the CS channel.Value Range：[No,Yes]Default Value：NoCaution：When this parameter is used:1. "Level of Preempting Dynamic Channel" must be set to "No preempt of service TCHF"; otherwise this parameter is invalid.2. The number of TCH/F of current TRX must be more than the value of the Reservation Threshold of Dynamic Channel Conversion parameter.3. "Maximum Ratio Threshold of PDCHs in a Cell" must be set properly; otherwise the TCH/F can not be changed to the PDCH because of the low ratio.2 and 3 are optional.

215


Summary

After studying this course, you will learn:

PS channel allocation algorithm

Dynamic channel conversion algorithm

Dynamic channel release algorithm

By learning the three algorithms, you should master the PS

channel management algorithm and load control policy of

the BSC6000.

216


217

www.huawei.com


GPRS EDGE Radio Network Optimization Problem Analysis

218

Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved. Page 1

Objectives

Upon completion of this course, you will :

Be familiar with the common problems arising in GPRS and

EDGE network optimization

Master the common troubleshooting measures for the

problems discovered during GPRS and EDGE network

optimization

219


Contents

1. Low TBF Setup Success Ratio

2. Low Downloading Rate

220


TBF Setup Success Ratio

Formula

Common Analysis Method

221


Uplink TBF Setup Success Ratio Formula 1 – Air Interface Measured

A9004: Number of Failed Uplink GPRS TBF Establishments due to MS No Response

A9001: Number of Uplink GPRS TBF Establishment Attempts

Uplink GPRS TBF setup success ratio =

X 100%1 -

A9204: Number of Failed Uplink EGPRS TBF Establishments due to MS No Response

Uplink EGPRS TBF setup success ratio =

X 100%1 -A9201: Number of Uplink EGPRS TBF Establishment Attempts

The formula of the TBF setup success ratio varies with the measured objects.

If the measured object is the air interface, the preceding formulas are used.

For uplink TBF assignment: If the first uplink data block from the MS is not received at the network side after an assignment command is sent from the network side, an uplink TBF setup failure due to no response from MS is counted.

All the preceding counters are cell-level counters. The system also supports BSC-level counters as follows:

ZA9001: uplink GPRS TBF setup attempts within the BSC

ZA9004: uplink GPRS TBF setup failures due to no response from MS within the BSC

ZA9201: uplink EGPRS TBF setup attempts within the BSC

ZA9204: uplink EGPRS TBF setup failures due to no response from MS within the BSC

For particular values of the preceding counters, see the GPRS and EDGE traffic statistics.

222


Downlink TBF Setup Success Ratio Formula 1 – Air Interface Measured

A9104: Number of Failed Downlink GPRS TBF Establishments due to MS No Response

A9101: Number of Downlink GPRS TBF Establishment Attempts

Downlink GPRS TBF setup success ratio =

x 100%1 -

A9301: Number of Downlink EGPRS TBF Establishment Attempts

A9304: Number of Failed Downlink EGPRS TBF Establishments due to MS No Response

Downlink EGPRS TBF setup success ratio =

x 100%1 -


If the measured object is the air interface, the preceding formulas are used.

For downlink TBF assignment: If no Packet Control Acknowledgement message from the MS is received at the network side after an assignment command is sent from the network side, a downlink TBF setup failure due to no response from MS is counted.


ZA9101: downlink GPRS TBF setup attempts within the BSC

ZA9104: downlink GPRS TBF setup failures due to no response from MS within the BSC

ZA9301: downlink EGPRS TBF setup attempts within the BSC

ZA9304: downlink EGPRS TBF setup failures due to no response from MS within the BSC


223


Uplink TBF Setup Success Ratio Formula 2 – Resources Measured

A9003: Number of Failed Uplink GPRS TBF Establishments due to No Channel



x 100%1 -


A9203: Number of Failed Uplink GPRS TBF Establishments due to No ChannelX 100%

A9201: Number of Uplink EGPRS TBF Establishment Attempts1 -


If the measured object is the channel resources, the preceding formulas are used.

For uplink TBF assignment: If the network side sends an assignment rejection message upon the channel request from the MS due to lack of channel resources (including channels, TFI, and USF), an uplink TBF setup failure due to lack of channel resources is counted.



ZA9003: uplink GPRS TBF setup failures due to lack of channel resources within the BSC


ZA9203: uplink EGPRS TBF setup failures due to lack of channel resources within the BSC


224


Downlink TBF Setup Success Ratio Formula 2 – Resources Measured

A9103: Number of Failed Downlink GPRS TBF Establishments due to No Channel


x 100%A9101: Number of Downlink GPRS TBF Establishment Attempts

1 -



A9303: Number of Failed Downlink EGPRS TBF Establishments due to No Channelx 100%1 -


If the measured object is the channel resources, the preceding formulas are used.

For downlink TBF assignment: If the downlink TBF setup fails due to lack of channel resources (including channels, TFI, and USF) at the network side, a downlink TBF setup failure due to lack of channel resources is counted.



ZA9103: downlink GPRS TBF setup failures due to lack of channel resources within the BSC


ZA9303: downlink EGPRS TBF setup failures due to lack of channel resources within the BSC


225


Uplink TBF Setup Success Ratio Formula 3 –Both Air Interface and Resources Measured


x 100%A9002: Number of Successful Uplink GPRS TBF Establishments


A9201: Number of Uplink EGPRS TBF Establishment Attempts

A9202: Number of Successful Uplink EGPRS TBF Establishments


x 100%


If the measured object are the air interface and the channel resources, the preceding formulas are used

For uplink TBF assignment: Both the uplink TBF setup failures due to no response from MS and those due to lack of channel resources are counted as uplink TBF setup failures.



ZA9002: uplink GPRS TBF setup successes within the BSC


ZA9202: uplink EGPRS TBF setup successes within the BSC


226


Downlink TBF Setup Success Ratio Formula 3 –Both Air Interface and Resources Measured

A9102: Number of Successful Downlink GPRS TBF Establishments

A9101: Number of Downlink GPRS TBF Establishment Attempts


x 100%

A9302: Number of Successful Downlink EGPRS TBF Establishments



x 100%


If the measured object are the air interface and the channel resources, the preceding formulas are used.

For downlink TBF assignment: Both the downlink TBF setup failures due to no response from MS and those due to lack of channel resources are counted as downlink TBF setup failures.



ZA9102: downlink GPRS TBF setup successes within the BSC


ZA9302: downlink EGPRS TBF setup successes within the BSC


227


TBF Setup Success Ratio

Formula

Common Analysis Method

228


Low TBF Setup Success Ratio– Common Analysis Process

Start

Analyze causes for the low TBF setup success ratio

Is the Abis interface faulty?

Is the assignment message delivered

normally?

Is the air interface normal?

Is a response to the assignment and

polling available?

End

Check transmission

Other incorrect parameter settings

Errors of important message

Unbalanced uplink and downlink

Inappropriate power control parameter

settings

CCCH overload

No channel

Check traffic statistics

Perform a CQT

Yes

No

No

No

No

Yes

Yes

High rate coding scheme

Check CS domain parameters

229


Low TBF Setup Success Ratio – Abis Interface Transmission

Check whether the Abis link is faulty.

The downlink TBF setup might fail due to transmission problems such as out-

of-synchronization frames and intermittent interruption of the Abis link.

Locate the transmission problems of the Abis interface by checking the G-Abis

frame error rate (FER) in the traffic statistics.

RL9A08: FER = ([L9A02: number of received out-of-synchronization frames] + [L9A03: number of received check error TRAU frames]) x {100}/([L9A02: number of received out-of-synchronization frames]+[L9A03: number of received check error TRAU frames] + [L9A01: number of received normal TRAU frames] + [L9A07: number of received information TRAU frames])

The number of received information TRAU frames equals the number of empty TRAU frames.

1. In normal cases, the FER is lower than 10e-5 (that is, one out of ten thousand) and one error frame occurs every four minutes in each channel. In this case, the link quality is high and the MSs transfer data stably.

2. If the FER is lower than 10e-4 (one out of one thousand), one to three error frames occur every minute and the link quality degrades. In this case, the affected MSs easily suffer rate drop, longer transmission delay, or even call drops due to error frame bursts.

3. If the FER is higher than 10e-4, the transmission link is unstable and might easily suffer out-of-synchronization. The number of out-of-synchronization frames increases. In this case, the MSs support services with low data traffic (such as high-layer signaling and low-volume WAP) only. Transmission of large-volume data (such as the FTP service) is not supported.

If a leased link (for example, microwave satellite) is used, an FER lower than 5‰ is acceptable because the link quality is not controlled by the mobile operator. If the FER of a cell remains high for a long time, it is regarded as a transmission problem and the transmission link needs to be checked and optimized. 230


Low TBF Setup Success Ratio – Abis Interface Transmission

The transmission

quality of the Abis

interface can also

be monitored

through the

maintenance

console.

Monitoring BER

Monitoring port

fault seconds

Function supported by both monitoring options:

Monitor the BER of the E1/T1 ports and optical ports, thus learning the operation conditions of the transmission link and ports.

Definition of fault seconds:

If one or more block errors are detected in a certain second, the second is called a fault second.

Differences between the two monitoring options:

The Monitor BER function requires that remote loopback needs to be enabled at the opposite end of the monitored port. The Monitor Port Fault Secondsfunction, however, does not require remote loopback at the opposite end of the monitored port.

The unit sampling time of the Monitor BER function is configurable (ranging from 30 to 1000 milliseconds), while that of the Monitor Port Fault Seconds function is fixed to 1 second.

231


Low TBF Setup Success Ratio – the Assignment Message Fails to Be Delivered

The assignment message might fail to be delivered due to the following cause:

CCCH overload

Refer to the following counters:

– L3188A: number of reported DELETE IND messages of the Abis interface

– L3188D: number of reported PACKET CCCH LOAD IND messages of the Abis interface

– L3188E: number of reported OVERLOAD (CCCH overload) messages of the Abis interface

To remove CCCH overload, add CCCH channels, split the location area, or modify the CCCH load threshold and the T3168 timer.

L3188A: number of reported DELETE IND messages of the Abis interface

If the BTS deletes the IMM ASS CMD message sent by the BSC due to downlink CCCH overload of the cell, the BTS reports a DELETE IND message to the BSC. This counter is used to measure the number of the DELETE IND messages received by the BSC from the measured cell.

L3188D: number of reported PACKET CCCH LOAD IND messages of the Abis interface

The BTS stores the paging messages sent through the downlink CCCH (PCH channel) for circuit services and those for packet services in two different receive buffer queues. If the length of either receive buffer queue exceeds the specified threshold, it is indicated that downlink CCCH overload occurs. In this case, the judges whether the overload is caused by excessive downlink packet services or excessive circuit services. If the overload is caused by excessive circuit services, the BTS reports a CCCH LOAD IND message to the BSC. If the overload is caused by excessive packet services, the BTS reports a PACKET CCCH LOAD IND message to the BSC. The BSC then forwards the PACKET CCCH LOAD IND message to the PCU. This counter is used to measure the number of PACKET CCCH LOAD IND messages received by the BSC from the BTSs within the measured cell.

L3188E: number of reported OVERLOAD (CCCH overload) messages of the Abis interface

If the BTS detects the CCCH overload, the BTS reports an OVERLOAD (cause: CCCH overload) message and a CCCH LOAD IND message to the BSC. This counter is used to measure the OVERLOAD (cause: CCCH overload) messages

232


Low TBF Setup Success Ratio – the Assignment Message Fails to Be Delivered

The assignment message might fail to be delivered due to the following cause:

No channel is available (including insufficient channel resources and hardware faults).

Check whether the hardware is faulty by referring to the following counters:– RR307: TCH availability

– RK3255: TRX carrier availability

Check whether channel resources are insufficient by referring to the following counters (take the uplink GPRS TBF setup as an example):

– A9003: uplink GPRS TBF setup failures due to lack of channel resources

– A9010: uplink GPRS TBF abnormal releases due to lack of channel resources

– AA9013: average number of concurrent uplink GPRS TBF

– R9343: callbacks of dynamic PDCH

– R9344: callbacks of loaded dynamic PDCH

Channel resources are insufficient in any of the following cases:

1. The cell is configured with a small number of channels when heave traffic of packet services exists. As a result, the channels reach the maximum capacity of MS multiplexing. To solve the problem, add more dynamic and static channels or set the PDCH uplink multiplexing threshold in the PS domain channel management parameters to a higher value.

2. Check whether the resources are insufficient because voice services preempt the dynamic PDCHs. If counters A9343 (callbacks of dynamic PDCH) and A9344 (callbacks of loaded dynamic PDCH) record high values, in indicates that circuit services preempt the channel resources of data services due to heavy traffic. To solve the problem, add more dynamic PDCHs or set Dynamic Channel Preemption Level to Control Channel Preemption Forbidden.

3. If the uplink GPRS TBF setup success ratio is low due to lack of channel resources but the uplink EGPRS TBF setup success ratio is high, check whether the GPRS channels are insufficient due to the configuration of dedicated or preferred EGPRS channels. If dedicated or preferred EGPRS channels are configured, modify some of them into common EGPRS channels and, if necessary, turn on the EGPRS Downlink and GPRS Uplink Allowed switch.

233


Low TBF Setup Success Ratio – Air Interface Abnormal

The MS might fail to receive the downlink assignment message or

polling message due to poor quality of the air interface.

Check the BEP distribution based on the following traffic statistics:

Number of different 8PSK_MEAN_BEP values

Number of different GMSK_MEAN_BEP values

Locate the problem through a CQT.

Locate the air interface problem through the traffic statistics of the CS

domain.

If the air interface suffers severe interference, adjust the frequency points to improve the quality of the air interface.

234


Question

What are the CS domain traffic statistics items that help to

locate air interface problems?

Answers:

Measurement report — interference band measurement (carrier)

Measurement report — full-rate channel Rx level measurement (carrier)

Measurement report — half-rate channel Rx level measurement (carrier)

Measurement report — Rx quality measurement (carrier)

Measurement report — radio link exception measurement (carrier)

Measurement report — measurement of TA-based distribution of radio link exceptions (carrier)

Measurement report — measurement of TA-based RQI distribution (carrier)

Measurement report — RQI distribution measurement (carrier)

Measurement report — Rx quality distribution measurement (carrier)

……

235


Low TBF Setup Success Ratio – No Response from the MS

Check the following counters to determine whether the MS responds to the assignment or polling message:

A9004: uplink GPRS TBF setup failures due to no response from MS

A9104: downlink GPRS TBF setup failures due to no response from MS

A9204: uplink EGPRS TBF setup failures due to no response from MS

A9304: downlink EGPRS TBF setup failures due to no response from MS

The MS might fail to respond to an assignment or polling message due to any of the following causes:

High rate uplink coding scheme

Inappropriate settings of uplink power control parameters

Inappropriate settings of other parameters

Incorrect cells in the assignment message

Unbalanced uplink and downlink

Inappropriate CS domain parameters

When the radio environment is poor, the BLER is extra high and the uplink data blocks cannot be decoded correctly at the network side if a high rate uplink coding scheme is used.

If the uplink power control parameters are configured improperly, the MS supports low Tx power and the uplink data blocks cannot be decoded correctly at the network side.

Other parameters that might be configured improperly are as follows:

Downlink reassignment attempts (affecting the downlink TBF setup): During the setup process of a downlink TBF, the network side fails to receive a valid Packet Control Acknowledge message on the reserved uplink RLC block and then re-sends a downlink assignment message. This parameter specifies the maximum number of downlink reassignment attempts. If the downlink reassignment attempts exceed the value of this parameter, the network side releases the downlink TBF.

Polling retransmission times (affecting the downlink TBF setup): This parameter specifies the maximum number of polling messages retransmitted by the network side during the setup process of a downlink TBF.

Check whether the important cells in the assignment message are incorrect, including frequency hopping parameters and uplink power control parameters.

Frequency hopping parameters: Check whether GPRS Mobile Allocation in the SI 13 message and the Frequency Parameters in the assignment message are consistent with the actual configurations.

Uplink power control parameters: Check whether the Alpha and GAMMAt i I di t A i t C d P k t U li k

236

Unbalanced uplink and downlink: If the uplink and the downlink are unbalanced, the uplink or downlink signals might fail to be received at the edge of coverage, thus resulting in a failure of TBG setup.

To verify whether the uplink and the downlink are balanced, check the uplink Rx level and the downlink Rx level in the measurement report. Refer to the measurement unit in Huawei traffic statistics: measurement report — uplink and downlink balance measurement (carrier).

Usually, the uplink and the downlink are regarded as unbalanced (the downlink signals are too weak or the uplink signals are too strong) if the sum of the percentage of uplink and downlink balance level 1 plus the percentage of uplink and downlink balance level 2 is higher than 15%.

The uplink and the downlink are regarded as unbalanced (the downlink signals are too strong or the uplink signals are too weak) if the percentage of uplink and downlink balance level 11 is higher than 30%.

The low TBF setup success ratio might also result from incorrect settings of CS domain parameters. Check the KPI of the CS domain to identify any exceptions. The relevant CS domain parameters include the call drop rate, congestion rate, assignment success ratio, balance between uplink and downlink, and call setup success ratio.

237


Question

What are the respective solutions to the exceptions that

prevent the MS from responding to an assignment or polling

message?

Answers:

If a high rate uplink coding scheme is used, modify the default uplink MCS and the maximum value of the counter N3101.

Inappropriate settings of uplink power control parameters: Modify the Alpha parameter and the initial power class.

Inappropriate settings of other parameters: Modify the number of downlink reassignment attempts and the number of polling retransmissions.

If the uplink and the downlink are unbalanced, check the following factors:

Installation of antenna feeder: Usually, a small antenna, lightning arrester, conversion connector, grounding solder connection, and antenna (and a power splitter in some cases) are installed between the BTS top interface and the antenna. The installation of such components might affect the receiving and transmitting performance of the BTS. For example, a loosened jumper connector results in severe influence on the uplink Rx level but no significant influence on the downlink level. This is because the transmitted signals are often strong (usually 30 dBm inside the feeder) while the received signals are weak (usually 80 dBm).

Installation of the tower amplifier: Tower amplifiers are active components that amplify uplink signals only. If a tower amplifier is installed, the Tower Amplifier Attenuation Factor parameter is configured as follows at the RF front end of Huawei BSC6000: If the actual gain of the tower amplifier is G, the tower amplifier attenuation factor equals G minus 4 (4 dB here is the estimated compensation for the feeder loss). Therefore, the value of downlink level minus uplink level in the uplink/downlink balance measurement report decreases by 4 dB if an uplink tower amplifier is installed. Particularly, the uplink level increases by 4 dB.

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Contents

1. Low TBF Setup Success Ratio

2. Low Downloading Rate

239


Downloading Rate Measurement

Measurement methods

CQT

Drive test (DT)

The maximum downloading rate at the application layer

under idle conditions is as follows:

225 kbit/s

CQT: Call Quality TestThe CQT is often performed in a good radio environment where the C/I seldom fluctuates. The CQT in idle hours can verify whether all NEs and transmission from the Um interface to the Gi interface are faulty. In this case, the CQT reflects the equipment performance directly and accurately. The CQT in busy hours can also verify the performance of the resource (such as channels, Abis resources, and Gb resources) management algorithms. The CQT in busy hours, however, features randomness. For example, the tested downloading rate might be severely affected if another subscriber is also downloading data during the CQT. In this case, the CQT cannot reflect equipment performance accurately because the test results are significantly related to the quantity of configured resources. Therefore, the CQT in busy hours is used only for performance comparison before and after migration.

DT: Drive TestCompared with the CQT, the DT faces severe C/I fluctuation and cell reselection. Differing from the CQT, the DT can measure radio coverage and interference, performance of the coding scheme adjustment algorithm, and system processing in the case of cell reselection (since PS handover is not really supported yet). The DT, however, also feature randomness. For example, the radio conditions (high C/I or deep fading point) at the location where the testing vehicle waits for traffic light affect the tested average rate obviously.

The maximum downloading rate at the application layer under idle conditions is as follows: 59.2 Kbit/s x (4 -2%) x 95.52% = 225.06 Kbit/s

The items in the equation are defined as follows:59.2 Kbit/s: the theoretical rate of a single channel when the MCS-9 coding scheme is used4: the assumed number of channels for transmission2%: the minimum ratio of control messages in a single channel to all messages in the channel95.52%: LLC layer efficiency (The efficiency is lower than 100% due to frame header overhead in each layer)

240


An Example of Idle Conditions

Differing from the CQT, the DT faces cell reselection and change of the coding scheme due to C/I fluctuation (The link quality control algorithm achieves a compromise between higher coding scheme and fewer retransmissions. The bandwidth of the air interface changes as the coding scheme changes). Compared with downloading of large files, the downloading of small files features severer influence brought by the slow start process upon setup of the TCP connection. Therefore, to locate the cause for a low downloading rate, download large files in idle hours at a place where the C/I is high.

Slow start means that the data is delivered slowly to avoid network congestion when the TCP layer is not aware of the transmission bandwidth and quality or when it is known that the transmission bandwidth decreases or the transmission quality degrades. Therefore, the amount of initially delivered data is insufficient. In addition, loss of packets, frames, or blocks needs to be minimized in all stages (including IPBB, core network, GB interface, PCU, G-Abis interface, BTS, and Um interface).

If control blocks (actually dummy blocks) exist in a non-control channel or a high percentage of control blocks exist in the control channel, it indicates that the system transmits dummy control blocks because no data needs to be sent.

Dummy control block: The system sends a block every one millisecond (transmission priorities: NACK block > VS block > PACK block). If none of those blocks is available, the system sends dummy control blocks that are counted by the TEMS as control blocks. That is to say, the control blocks counted by the TEMS include control messages and dummy control blocks.

NACK block: the block that the MS fails to receive as indicated in the Packet Downlink ACK/NACK message

241


Common Causes for a Low Downloading Rate

Common causes

Degrading the QoE of customers

Insufficientchannel

occupation

Lowcoding

rate

Highblock

error rateAbnormal

TBF release

Highpercentageof control

blocks

Unmatchedrate

betweenthe RLClayer and

the applicationlayer

Quality-of-experience (QoE) describes the system-level activities focusing on the joint optimization of experienced multimedia quality and energy consumption in wireless multimedia systems.

242


Insufficient Channel OccupationTo check the number of channels occupied by MSs, check the latest Packet

Downlink Assignment or Packet Timeslot Reconfiguration message, as shown in the

following figures.

The figure on the left shows the Packet Downlink Assignment message, while that on the right shows the Packet Timeslot Reconfiguration message.

243


Insufficient Channel Occupation

The possible causes for insufficient channel occupations are as follows:

Symptom 1: Failing to assign multiple channels

Cause 1: The channel resources are insufficient.

Cause 2: The MS does not support sufficient multi-slot capability.

Cause 3: The channels suffer out-of-synchronization.

Cause 4: The Abis interface resources are insufficient.

Symptom 2: Failing to occupy multiple channels stably

Cause 1: The channels are preempted by voice services.

Cause 2: The channels suffer out-of-synchronization.

To verify whether the channel resources are sufficient, check the channel configuration.

To verify whether the MS supports sufficient multi-slot capability, check the Packet Resource Request massage for two-stage access or the 11-bit access request and Attach message (for 8-bit one-stage access, the MS indicates its multi-slot capability in the Attach request message) for one-stage access.

To verify out-of-synchronization, check the alarms by running the relevant commands. For example, run the mt pdch show state <cell ID> all command to check the status of all PDCHs in the specified cell if the external PCU is used. If the built-in PCU is used, run the DSP PDCH command to check the channels status.

To verify whether the Abis interface resources are sufficient, check the idle timeslot configurations.

To verify channel preemption of voice services, check the following traffic statistics:

R9343: callbacks of dynamic PDCH

R9344: callbacks of loaded dynamic PDCH

No channel preemption of voice services is detected during a test in idle hours.

244


Abis Interface Timeslots Required by Different Coding Schemes

4MCS8–MCS9

3MCS7

2CS3–CS4MCS3–MCS6

1CS1–CS2MCS1–MCS2

Number of Required Abis Interface 16 bit/s Timeslots

GPRSEGPRS

245


Low Coding Rate

The possible causes for a low coding rate are as follows:Symptom 1: using low-rate coding schemes

Cause 1: insufficient timeslots at the Abis interface

Cause 2: poor quality of the air interface

Cause 3: inappropriate initial coding rate or inappropriate conversion threshold for coding schemes

Cause 3: EDGE services not used

Cause 4: limited license

Symptom 2: changing coding schemes

Cause 1: error bits at the G-Abis interface

Cause 2: inappropriate conversion threshold for coding schemes (for GPRS services only)

Solutions to insufficient timeslots at the Abis interface:

If Flex Abis is not used, configure all Abis interface timeslots that are not configured as idle timeslots.

Increase the multiplexing ratio of signaling links to improve the Abis transmission capacity.

Use Flex Abis.

Expand the transmission capacity.

Solutions to bit errors at the G-Abis interface:

Transmission problems: Perform local loopback and remote loopback at the TMU side to locate the problems.

Faults of the interface board

246


Air Interface Requirements of Different Coding Schemes

30>= –86MCS-9

28.5>= –90.5MCS-8

23.5>= –93MCS-7

20>= –96MCS-6

19>= –97MCS-5

18>= –98MCS-4

16.5>= –99MCS-3

15>= –101MCS-2

13>= –102MCS-1

TU3 C/I (dB)Rx Level of MS (dBm)Coding Scheme

TU3: The speed is 3 km/h in typical urban scenarios.

247


Question

Where can we check the block error rate?

Answers:

1. The figure in page 43 shows that the BLER/TS(%) parameter indicates the block error rate calculated by the TEMS based on a certain number of received blocks.

2. For fixed MSs, the Packet Downlink ACK/NACK message also indicates the block error rate.

The message shows that starting sequence number (SSN) is 64 and that a bitmap exists. This indicates that block 63 is not received. Check the blocks following block 64 (1 indicates that the block is received, while 0 indicates that the block is not received). The message shows that blocks 63, 65, 66, 68, 69, and 71 to 84 are not received.

248


High Block Error Rate

The possible causes for a high block error rate are as

follows:

Bit errors at the air interface

A large number of error frames and out-of-synchronization

frames at the G-Abis interface

The MS performs another process such as decoding neighbor

cell messages.

If a large number of neighbor cells are configured, the block error rate often increases because the MS needs to update the system messages of neighbor cells frequently. According to the relevant protocol, the MS must decode the BCCH data of a new carrier in 30 seconds. If the signal strength fluctuates and a large number of neighboring cells are configured, the MS has to parse the system messages of neighboring cells frequently. To solve this problem, reduce the number of neighboring cells and eliminate unnecessary neighboring cell configurations.

249


High Percentage of Control Blocks

The possible causes for a high percentage of control blocks

are as follows:

The contracted peak rate is not high enough.

The LLC layer adopts the acknowledged mode.

The transmission window stops.

The bandwidth at the Gb interface is insufficient.

The system assigns only one bidirectional control channel for the MS. Therefore, the same timeslot is occupied as the control channel in both the uplink and the downlink. In this way, the control channel can be located.

The PDP context shows the contracted peak rate. As shown in the following figure, the peak rate is 128000 octets/s = 128000 x 8/1024 = 1000 Kbit/s that exceeds the theoretical maximum rate.

250

If the LLC layer uses the acknowledged mode, the next frame is not sent until the current frame is acknowledged by the opposite end. In addition, the LLC layer connection needs to be set up and released, thus resulting in more signaling transmissions in the LLC layer. In a word, the downloading rate decreases significantly if the LLC layer uses the acknowledged mode.

You can also check the MS's PDP context in the TMES to view the operation mode of the LLC layer . If the LLC uses the acknowledged mode, modify it to the unacknowledged mode at the SGSN and modify the subscription information of the SIM card.

Usually, the transmission window stops only in the GPRS network because the GPRS system supports 64-block window only. If an error block occurs, the RRBP delay is about 200 ms regardless of the cause for the error block. When the MS reports the reception of the error block, 200 ms passed. If the MS occupies four timeslots, the system has transmitted 40 blocks (200 ms/(20 ms/block)). In this case, the transmission window may stop.

To verify whether the transmission window stops, check whether the amount of data received at the Gb interface is larger than the amount of data delivered by the system within a certain period.

If the traffic at the Gb interface exceeds 70% of the actual bandwidth, it indicates that the bandwidth is insufficient.

To view the traffic at the Gb interface, check the Downlink data kbytes sent to FR per NSVC item measured at the SGSN.

251


Abnormal TBF Release

The possible causes for abnormal TBF release are as follows:

The uplink TBF is released exceptionally when timers N3101 and

N3103 expire.

The downlink TBF is released exceptionally when timer N3105 expires.

The TBF is released exceptionally when the control channel is

preempted.

The TBF is released exceptionally due to cell reselection.

The TBF is released exceptionally due to some internal processing.

Loss of packet is not a necessary result of abnormal TBF release, because the PCU stores the data that the MS has not transmitted and that the MS has transmitted without acknowledgement within 30 seconds after the TBF is released exceptionally. Usually, the MS initiates TBF re-setup soon. In this case, the TLLI remains unchanged. Therefore,the context of the MS can be detected according to the TLLI and then the data stored by the PCU is sent to the MS.

According to the TBF release process, the MS sets the FAI bit in the Packet Downlink ACK/NACK message to 1 if the download TBF is released normally. The system sets the FAI bit to 1 in the Packet Uplink ACK/NACK message if the uplink TBF is released normally. To verify whether a TBF is released exceptionally, check whether the FAI bit in the relevant message is set to 1. If the network side sends a Packet TBF Release message, the TBF is released exceptionally (the TBF is released exceptionally because timer N3105 expires if the cause value is normal release).

The abnormal TBF release decreases the rate because data transmission is not supported during the abnormal release.

252


Unmatched Rate Between the RLC Layer and the Application Layer

This problem often results from careless operations of the relevant

test engineers.

How to identify the software applications and services that support

automatic connection to the network?

This problem often results from careless operations of the relevant test engineers. The software applications and services (such as automatic update) that support automatic connection to the network must be disabled during the test. If such software applications or services are not disabled, the rate at the application layer decreases when they connect to the network automatically.

How to identify the software applications and services that support automatic connection to the network:

After the test, check whether all the packets captured by the Ethereal software are the data interacted with the IP address of the server. If data interacted with another IP address exists, enter the IP address into the IE to identify the connected network.

253


Summary

The GPRS/EDGE network optimization focuses on the

downloading rate and the TBF setup success ratio. Pay

attention to the relevant parameters and configurations.

Traffic statistics and signaling analysis help to solve the

problems discovered in GPRS/EDGE network optimization

more quickly.

254

www.huawei.comThank you

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Date post:	22-Oct-2015
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Huawei PS-GPRS-EDGE Radio Network Optimization

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