38228984 GPRS EDGE Radio Network Optimization

GPRS Principles

www.huawei.com

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

1

Forewordz

GPRS principle is the basic part of the whole GPRS system and the succeeding products learning.

z

This slide will help us to understand the GPRS system networking and wireless subsystem etc.


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Objectivesz

Upon 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


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Contents1. GPRS System Overview 2. GPRS Architecture 3. GPRS Network Interfaces & Protocols 4. GPRS Wireless Subsystem 5. GPRS Location Area


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Circuit Switch (CS)ACS CS

G

B H CCS

I

D E

J

K FCS CS

L


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5

Packet Switch (PS)PS PS11 2 3

A

PS2 3

31 2

C3

1

2

2

3 2 1

BPS

PS

2 1 3

1 2 3

PS

PS

D


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GSM Development Evolution3G UMTS384 Kb/s

2.75 G

ECSD38.8 Kb/s

EGPRS EDGE59.2 Kb/s

2.5 G

HSCSD14.4 Kb/s

GPRS21.4 Kb/s

CS

2G

GSM

9.6 Kb/s

PS


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What is GPRS and EDGE?z z

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)

z

z z

EGPRS (Enhanced GPRS)

EGPRS supports wireless access rate of up to 473.6Kbps.

ECSD (Enhanced CSD, Enhanced HSCSD-High Speed Circuit Switched Data)


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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 RateKbps

60.00 50.00 40.00 30.0021.4 22.4 17.6 14.8 8.8 11.2

59.2 54.4

GPRS EGPRS29.6

44.8

20.0013.4

15.6

10.00 0.00

9.05

CS-1

CS-2

CS-3

CS-4

MCS-1

MCS-2

MCS-3

MCS-4

MCS-5

MCS-6

MCS-7

MCS-8

MCS-9

GMSK

8PSK


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Adjustments to GSM Network

BSSPb

A

CS Core NetworkGs

PCU

Gb

PS Core Network NSS

BSS


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Most Popular GPRS Applicationsz z z z z z z z

E-mail Web Browsing Information Services Moving Images Still Images Remote LAN Access File Transfer Job DespatchFile Transfer Still Images Moving Bank Stock Market Live News Sport Report Public Information Weather Forecast Service Traffic Information

Personal Information Service

Email

Web Browsing


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Advantages and Disadvantages of GPRSz

Advantages

Share resource with GSM High resource utilization Fast transmission rate Always on line Short access time

z

Disadvantages

Slower data rates in practice than anticipated in theory Suboptimal modulation techniquePage11


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CS & PS Logic StructureC

GMSCE D CS A

PSTN

MSC/VLR Gs Gb SGSN Gr HLR AUC GPRS Register

B T S

Abis

TRAU

BSC

PCU

PS

G-Abis

Pb

BSSGn Gc GGSN Gi Internet

CNCopyright 2009 Huawei Technologies Co., Ltd. All rights reserved. Page13

14

GPRS System StructureMSC/VLR SMS-GMSC SMS-IWMSC HLR EIR

SS7WAP Gateway BSS MS

Gs

Gd

Gr Gn

Gf

GcGGSN

BSC

Firewall

Gb

Gi

Intranet/InternetRADIUS

Abis BTS PCUSGSN

GPRS BackboneATM/DDN/ISDN/Ethernet, etc

Ga

CG

GiX.25

GnBSS MS

BSCGb

SGSN GGSN CNCN-PS DNS BG Other PLMN

Abis BTS PCU

Gp


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GPRS MSz

Class A

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

z

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.

z

Class C

The MS is attached to either GPRS or other GSM services. Alternate use only. services are selected manually or default selected service.Page15


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Functions of PCU (Packet Control Unit)z

Packet wireless resource management function (RLC/MAC protocol function)

Wireless resource management functions of GPRS BSS Circuit paging coordination

z

G-Abis interface processing function

Function related with GPRS BTS


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Functions of PCU (Packet Control Unit)z

Pb interface processing function

LAPD link between BSC and PCU Layer-3 signaling between BSC and PCU

z

Gb interface processing function

Data packet relay on wireless interface and Gb interface Mobility management (cell updating procedure) Downlink traffic control (wireless QoS guarantee)


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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)z z z z z

Packet routing MS Session management Authentication and Ciphering Mobility management Billing information collection


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Functions of GGSN (Gateway GPRS Support Node)z z z z z

Interface between GPRS backbone and external PDNs. PDP Conversion and context management IP address assignment management Packet routing to/from SGSNs Billing information collection


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Functions of CG (Charging Gateway)z z z z

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


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Functions of MSC/VLRz z

When Gs interface is installed, MSC/VLR can support Establishment and maintenance of the association between SGSN and MSC/VLR. GPRS combined mobility management procedure.

z

Combined IMSI/GPRS attachment/detachment. Combined location area/routing area updating.

z

Circuit paging coordination function.

z

The wireless resource usage can be greatly improved.


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Functions of HLR/AUCz z z

Saving 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.

z

Subscriber tracing (optional)


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Functions of SMS-GMSC/SMS-IWMSCz

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.

z

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.

z

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

MS

SGSN

SMS-IWMSC SMS-GMSCPage23


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)z

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

z z z

It is normally based on routers It can be combined with GGSN in physical. BG does not exclusively belong to the GPRS network.Gp GSNPLMN AR RR R

BG

BG

PLMN B

GSN


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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)z

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 Server

z

DNS does not exclusively belong to the GPRS network.SGSN GPRS BackbonePage25

SGSN


DNSDomain 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)z

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

z

The RADIUS server stores the authentication and authorization information of subscribers.

z

It also performs subscriber identity authentication in the case of non-transparent access.

z

RADIUS Server does not exclusively belong to the GPRS network.


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Contents3. GPRS Network Interfaces & Protocols3.1 Interface and Protocol Stack 3.2 Um Interface 3.3 G-abis/Pb Interface 3.4 Gb Interface 3.5 Gs Interface


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Network interface typesSGSN SGSNIP interface SS7 interface Gc

GPRS backbone networkGn

GGSN GGSN

Gi

SGSN SGSNGb Gr MT Gs Gd

PDP network (IP/X.25)

TE

Um

A

BSS

MSC

HLR

SMSGMSC

MS


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Interface in GPRS NetworkInterface R Um Gb Gc Gd Gi Gn Gp Gr Gs Gf Description The reference point between the Mobile Terminal (MT) (for example, mobile phone) and the Terminal Equipment (TE) (for example, the portable computer). The interface between MS and GPRS network side The interface between the SGSN and BSS. The interface between the GGSN and HLR (optional). The interface between SMS and GMSC The interface between SMS-IWMSC and SGSN The reference point between the GPRS and external packet data The interface between SGSNs and between SGSN and GGSN in the PLMN. The interface between GSNs of different PLMNs. The interface between the SGSN and HLR. The interface between the SGSN and MSC/VLR (optional). The interface between the SGSN and EIR (optional).Page30


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Data transmission planeApplication

IP/X.25 SNDCP LLC RLC MAC Physical Layer MSz z z

IP/X.25

IP/X.25

relaySNDCP

GTP

GTP UDP/TCP IP L2 Physical Layer Physical Layer GGSN L2 (MAC)

LLCRLC

UDP/TCP IP L2 Physical Layer

relay

BSSGP

BSSGP Network Service Physical Layer

MAC Physical Layer

Network Service Physical Layer

Um

BSSz z z

Gb

SGSN

Gn

Gi

MAC: Media Access Control RLC: Radio Link Control LLC: Logical Link Control

BSSGP: BSS GPRS Protocol SNDCP: Sub-Network Dependency Convergence Protocol GTP: GPRS Tunneling ProtocolPage31


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 planeGMM/SM LLCrelay Relay

GMM/SM LLC RLC MAC GSM RF Um BSS BSSGP Network Service L1bis Gb BSSGP Network Service L1bis SGSN

RLC MAC GSM RF MSz z

GMM: GPRS Mobility Management SM: Session ManagementPage32


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: 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 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

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

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Contents3. GPRS Network Interfaces & Protocols3.1 Interface and Protocol Stack 3.2 Um Interface 3.3 G-abis/Pb Interface 3.4 Gb Interface 3.5 Gs Interface


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Protocol Layer of Um InterfaceGMM/SMz

SNDCP

z

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.Page34

LLC RLC MACPhysical Link

z

z

RFz

z


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.

SMS35

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

MM State>GMM context is not established; MS is not reachable.IDLE

Data transmission to and from the mobile subscriber as well as the paging of the subscriber are not possible

STANDBY

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

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.

>MS can implement data transmission.READY

The MS performs MM procedures to provide the network with the actual selected cell.

SGSN performs the MM on cell level.


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

36

MM State ModelGPRS Attach READY timer expiry or Force to STANDBY

MM State Model of MS

IDLEGPRS Detach

READY

STANDBYPDU transmission READY timer expiry or Force to STANDBY or Abnormal RLC condition

GPRS Attach

MM State Model of SGSN

IDLE

READYGPRS Detach or Cancel Location

STANDBYPDU reception

Implicit Detach or Cancel Location


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RLC/MAC Block GenerationNetwork Layer Subscriber IP packet (N-PDU)

SNDCP Layer

SNDCP PDU(SN-PDU)

LLC Layer

LLC frame

RLC/MAC Layer

RLC/MAC block

Subscriber data

SNDCP head

LLC head

LLC FCS

RLC/MAC head


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Physical Channelz z z z z z

The same as in GSM The same frequency The modulation mode The same TDMA frame definition The same burst pulse definition IP/X25 SNDCP LLC RLC MAC Physical Layer MS RLC MAC Physical Layer BSS Relay Frame relay Physical LayerBSSGP

Application

z z z z

The differences between GPRS and GSM The Multi-frame structure The channel coding


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Packet Logic ChannelsPacket Logic ChannelPacket service channel Packet control channel

PBCCH

PCCCH

PDCCH

BCCHPDTCH/U PDTCH/D PPCH PRACH PAGCH PACCH PTCCH/U PTCCH/D

TCH

PNCH

PCH, RACH, AGCH,NCH

SACCHz

The specific type of PDCH (except PRACH) is determined by RLC/MAC head and RLC/MAC control message type.Copyright 2009 Huawei Technologies Co., Ltd. All rights reserved. Page39

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Channel Abbreviationz z z z z z z z z z z z

Packet Data Traffic CHannel Uplink - PDTCH/U Packet Data Traffic CHannel Downlink - PDTCH/D Packet Broadcast Control CHannel - PBCCH Packet Common Control CHannel - PCCCH Packet Dedicated Control Channel - PDCCH Packet Paging CHannel - PPCH Packet Random Access CHannel - PRACH Packet Access Grant CHannel - PAGCH Packet Notification CHannel - PNCH Packet Associated Control CHannel - PACCH Packet Timing advance Control CHannel Uplink - PTCCH/U Packet Timing advance Control CHannel Downlink PTCCH/DPage40


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PDTCH (Packet Data Traffic CHannel)z

All packet data traffic channels are uni-directional.

Uplink (PDTCH/U) for a mobile originated packet transfer.

Packet service channel

Downlink (PDTCH/D) for a mobile terminated packet transfer.

PDTCH/U

PDTCH/D


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PBCCH (Packet Broadcast Control CHannel)z

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.

Packet control channel

z

PBCCH

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.


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PCCCH (Packet Common Control CHannel)z

PPCH

Downlink only, used to page MS.

z

PRACH

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

PCCCH

z

PAGCH

Downlink only, used to allocate one or several PDTCHs.

z

PNCH

PPCH

PRACH

PAGCH

PNCH

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

z

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.


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PDCCH (Packet Dedicated Control Channels)z

PACCHPDCCH

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

z

PTCCH/U

PACCH

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

z

PTCCH/D

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


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Combinations of Packet Logic ChannelMode 1: PBCCH+PCCCH+PDTCH+PACCH+PTCCH Mode 2: PCCCH+PDTCH+PACCH+PTCCH

Mode 3: PDTCH+PACCH+PTCCH

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

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.


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Packet Wireless Channel Configurationsz

Reason of adopting static PDCH

To enable that GPRS MS is constantly online in the cell. To ensure certain QoS of GPRS services.

z

Reason of adopting dynamic PDCH

GPRS 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.


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Packet Wireless Channel Configurationsz

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.


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Mapping of Packet Logic Channelz

A radio block is a 4-normal-burst sequence that carries a RLC/MAC PDU (Protocol Data Unit).

0

25

51

B0

B1

B2 T B3

B4456 bits

B5 I B6

B7

B8 T B9

B10 B11 I

01234 567

012 34 567 01234 567 1 TDMA frame

01234 56 7

I = Idle frame T = Frame used for PTCCH B0 ~ B11 = Radio blocks


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Mapping of Packet Logic Channel0 50

BCCH 0

F S B B B B C C C C F S C C C C C C C C F S C C CC C C C C F S C C C C C C C C F S C C C C C C C C

I

112 25 51

PDCH

2 B0 3

B1

B2 T B3

B4

B5 I B625

B7

B8 T B9

B10 B11 I

TCH

4T T T T T T T T T T T TSTT T T T T T T T T T T I 5 6 7


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Transmission Principle of Data Packet on Um InterfaceSubscriber IP packet SNDCP PDU

LLC PDU

RLC/MAC blockN B N B N B N B

Physical layer

B0 B1 B2 T B3 B4 B5 I B6 B7 B8 T B9 B10 B11 ISubscriber data SNDCP head LLC head LLC FCSPage50

RLC/MAC head


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Allocation of Wireless Packet ResourcesTS 0 B0 B1 B2B3 B4

B5

B6

B7

B8

B9

B1 0

B1 1

TS 1

B0

B1

B2

B3

B4

B5

B6

B7

B8

B9

B1 0

B1 1

TS 2

B0

B1

B2

B3

B4

B5

B6

B7

B8

B9

B10

B11

MS1z

MS2

MS3

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.

z


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Basic Conceptions about Radio Blockz

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.F=4 US U =4 SF F=4 US

I

z

The USF field is three bits in lengthDLU =1 SF F=2 US F=3 US

I

F=3 US

F=3 US

US

T F=3

T

F=2 US

U

=1 SF

U

=1 SF

F=1 US

B0

I

B B1 1

10

B

B 9T

8

B7UL

5 I B B6

B4

T B3

B2

B1

B0

I

USF=1

MS1

USF=2

MS2

USF=3

MS3

USF=4

MS4


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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.

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Basic Conceptions about Radio Blockz

TBF (Temporary Block Flow)

A Temporary Block Flow (TBF) is a physical connection used by the two RR entitiesthe 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.

z

TFI (Temporary Flow Identity)

Each TBF is assigned a Temporary Flow Identity (TFI) by the network. The TFI field is five bits in length.


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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.

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Contents4. GPRS Wireless Subsystem4.1 Packet Channels 4.2 Medium Access Modes 4.3 MS Multi-TS Ability 4.4 Power Control 4.5 Network Control Modes


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Medium Access Modesz

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.

z

Downlink resource allocation mode

Dynamic allocation and fixed allocation.


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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

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MS Multi-TS Abilityz

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)

z

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


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Power Controlz

Power control can improve the spectrum usage and system capacity as well as reduce MS power consumption.

z

As there is no continuous bi-directional connection in the packet data transmission process, GPRS power control is very complicated.

z

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

z

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.


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Network Control Modesz

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

z

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


Page61

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.

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Network Control ModesMS NC0 MS NC1

The MS shall send measurement reports to the network

The MS shall perform autonomous cell re-selection

The MS shall perform autonomous cell re-selection

NC2 MRThe MS shall not

MSCell re-selection command

BTS

perform autonomous cell re-selection


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Relationship among Location AreasSGSN1 SGSN2 BSC1 BSC3

BSC2 CELL CELL CELL CELL CELL CELL CELL RA2 CELL RA1 LA1 LA2 CELL RA3


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LAI (Location Area Identification)z

MCCMobile Country Code, it consists of 3 digits. For example: The MCC of China is "460" MNCMobile Network Code, it consists of 2 digits. For example: The MNC of China Mobile is "00" LACLocation Area Code, it is a two bytes hex code. The value 0000 and FFFF is invalid For example: 460008C90

z

z

z

MCC

MNC Location Area Identification

LAC


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66

RAIz

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

z

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

MCC

MNC

LAC

RAC

Location Area Identification Routing Area Identification


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CGIz

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

z z z

MCC

MNC

LAC

RAC

CI

Location Area Identification Routing Area Identification CGI


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Relationship among location areasz

LAI

MCC+ MNC+ LACLAI

z

RAI

MCC+ MNC+ LAC+RACRAI

z

CGI /CellID

MCC+ MNC+ LAC+{RAC}+CICGI


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Summaryz z z z z

GPRS System Overview GPRS Architecture GPRS Network Interfaces & Protocols GPRS Wireless Subsystem GPRS Location Area


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Thank youwww.huawei.com

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GPRS EDGE Mobile Management Algorithmwww.huawei.com


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Forewordz

GPRS 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.


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Referencesz

GBSS8.1 BSC6000 Feature Description


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Objectivesz

Upon 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


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Contents1. Overview of GPRS Mobile Management 2. Location Update 3. GPRS Cell Selection & Reselection


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Overview for GPRS Mobile Managementz

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

z

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 MSs current location.

z

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).


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

Data transmission to and from the mobile subscriber as well as the paging of the subscriber are not possible

STANDBY

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

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.

> MS can implement data transmission.READY

The MS performs MM procedures to provide the network with the actual selected cell.

SGSN performs the MM on cell level.


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78

GMM State ModelGPRS Attach READY timer expiry or Force to STANDBY

MM State Model of MS

IDLEGPRS Detach

READY

STANDBYPDU transmission READY timer expiry or Force to STANDBY or Abnormal RLC condition

GPRS Attach

MM State Model of SGSN

IDLE

READYGPRS Detach or Cancel Location

STANDBYPDU reception

Implicit Detach or Cancel Location


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z

z

z

z

By performing GPRS attach, the MS gets into READY state and if the MS does not transmit 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 same way, 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 is not 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 MSs location is known precisely and no paging delay during delivery downlonk packet. Howeverm this consumes much more the uplink radio capacity and battery of the MS.

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GMM State vs Location Informationz

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

z

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

z

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.


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Contents1. Overview of GPRS Mobile Management 2. Location Update2.1 Relationship between Cell, Routing Area & Location Area 2.2 LAI, RAI, CGI 2.3 Signaling flow for Cell Update, RA Update & LA Update

3. GPRS Cell Selection & Reselection


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Relationship among Location AreasSGSN1 SGSN2 BSC1 BSC3

BSC2 CELL CELL CELL CELL CELL CELL CELL RA2 CELL RA1 LA1 LA2 CELL RA3


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z z z

When MS across Location Area border, LAU & RAU is necessary When MS moves within same LA and across Routing Area boarder, RAU is necessary When 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.

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Relationship among Location Areasz

LAI

MCC+ MNC+ LACLAI

z

RAI

MCC+ MNC+ LAC+RACRAI

z

CGI /CellID

MCC+ MNC+ LAC+{RAC}+CICGI


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LAI (Location Area Identification)z

MCCMobile Country Code, it consists of 3 digits. For example: The MCC of China is "460" MNCMobile Network Code, it consists of 2 digits. For example: The MNC of China Mobile is "00" LACLocation Area Code, it is a two bytes hex code. The value 0000 and FFFF is invalid For example: 460008C90

z

z

z

MCC

MNC Location Area Identification

LAC


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RAI (Routing Area Identification)z

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

z

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

MCC

MNC

LAC

RAC

Location Area Identification Routing Area Identification


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CGI (Cell Global Identity)z

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

z z z

MCC

MNC

LAC

RAC

CI

Location Area Identification Routing Area Identification CGI


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Cell Update FlowMS Old Cell New CellPDU (CGI) in BSSGP-PDU

SGSNSGSN received and recorded the cell update

Uplink LLC-PDU [MS ID]

RLC Radio Block

SGSN send the subsequence service to MS through the new cell


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2.

3.

4.

5.

6.

7.

When the MS moves from one cell to another within the same RA and LA, cell update procedure will happen during the READY state. 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. MS make an access in the new cell and send a cell update to the SGSN (transparent to the PCU). SGSN will obtain the cell update (cell change information) from the uplink LLCPDU and record the cell update information and discovers that there was already an ongoing downlink packet transfer. 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. 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. 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.

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Intra-SGSN Routing Area Update FlowMSROUTING AREA UPDATE REQUEST [Old RAI, old P-TMSI, update type]

BSS

SGSNROUTING AREA UPDATE REQUEST [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]


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z

z

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

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Inter-SGSN Routing Area Update FlowMS BSS New SGSN Old SGSN GGSN HLRROUTING AREA UPDATE REQUEST [Old RAI, old P-TMSI, update type] PDP CTT REQ PDP CTT ACK [GGSN address] PDP CONTEXT UPDATE PDP CONTEXT UPDATE ACK

DATABASE UPDATE ROUTING AREA UPDATE ACCEPT INSERT SUBCRIBER DATA

ROUTING AREA UPDATE COMPLETE


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z

z

z

z

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 user HLR about the users 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 MS The old SGSN is requested to transmit the undelivered data to the new SGSN.

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Contents1. Overview of GPRS Mobile Management 2. Location Update 3. GPRS Cell Selection & Reselection3.1 Cell Reselection Algorithm 3.2 Parameter for Cell Reselection 3.3 Type of Cell Reselection


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GPRS Cell Reselection Algorithmz

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) C2 = C1 CRO C1 = RLA_C RxLev_Acc_Min

when PT=/31 when PT=31

Max((MS_TXPWR_MAX_CCCH P), 0)


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1. 2. 3.

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

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

Cell reselection between different RA/LA: C2(nei) > C2 (serving) + CRH for t>5s


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

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Cell Reselection in Standby Mode

RA 2 RA 1AC2>BC2Cell B Cell A Cell C

CC2>BC2CRH


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Cell Reselection in Ready ModeRA 1BC2>AC2CRHCell A Cell B


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If PBCCH exists, new cell selection & reselection algorithm (C31, C32) is applicable:C31(s) = RLA_P(s) HCS_THR(s) C31(n) = RLA_P(n) HCS_THR(n) GPRS_TO(n)*H(GPRS_PENALTY_TIME-T)*L(n) (Neighbor cell) (Serving cell)

C31 RLA_P HCS_THR GPRS_TO

= signal threshold criterion = actual received level of the GPRS cell = signal level threshold of cell reselection of HCS GPRS = GPRS temporary offset

L = 0; when PRIORITY_CLASS (s) = PRIORITY_CLASS (n) L = 1; when PRIORITY_CLASS (s) =/ PRIORITY_CLASS (n)Copyright 2010 Huawei Technologies Co., Ltd. All rights reserved. Page25

z

z

z z

C31 = signal threshold criterion/ signal level threshold criterion of HCS and is used to judge whether to adopt preference cell reselection HCS_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 cell TO = Temporary offset given to the neighbor when the neighbor cells PRIORITY_CLASS is different from the PRIORITY_CLASS of the serving cell

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If PBCCH exists, new cell selection & reselection algorithm (C31, C32) is applicable:C32(s) = C1 C32(n) = C1 + GPRS_RESELECT_OFF GPRS_TO*H(GPRS_PENALTY_TIME T) * (1-L) (Neighbor cell) (Serving cell)

H(X 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)

C1 = RxLev GPRS_Acc_Level_Min Max( (GPRS_MS_TXPWR_MAX_CCH P), 0)Copyright 2010 Huawei Technologies Co., Ltd. All rights reserved. Page26

z

z

z

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

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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 RAC32(n) = C32(n)

When MS in READY mode, and within the same RAC32(n) = C32(n) - CELL_RESELECT_HYSTERESIS

When MS in READY or STANDBY mode, with different RAC32(n) = C32(n) - RA_RESELECT_HYSTERESIS


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z

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

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Cell Reselection Trigger Conditionz

Cell reselection triggering condition:With C1, C2 criterion 1 2 3 4 C1 < 0 Downlink signaling failure Serving cell is barred Random access attempt is unsuccessful after MAX_RETRANS 5 Better neighbor cell detected: Same RA: C2(n) > C2(s) for t>5s Dif RA: C2(n) > C2(s)+CRH for t>5 With C1, C31, C32 criterion C1 < 0 Downlink signaling failure Serving cell is barred Random access attempt is unsuccessful after MAX_RETRANS Better cell with the highest C32 among: (a) Highest PRIORITY_CLASS, C31>=0 (b) All cell, if no cell fulfils C31 criterion


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Network Control Modez

Cell Attribute -> GPRS Attributes


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z z

z z

Parameter Name: Network Control Mode Description: 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

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Parameter for GPRS Cell Reselectionz

Network Control Mode (NCO)Whether the MS send the M.R No Yes Yes Cell Selection Mode Controlled by MS Controlled by MS Controlled by network

Mode NC0 NC1 NC2

Definition Normal MS Control Mode MS Control with M.R Mode Network Control Mode

MS mode Ready & Standby Only Ready Only Ready


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z

z

z

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.

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Support NC2z

Cell Attributes -> Other Attributes


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z z z

z z

Parameter Name: Support NC2 Description: 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 loadbased reselections) of the MS. GUI Value Range: [No,Yes] Default Value: No

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NC2 Support in External Neighbour Cellz

BSC6000 -> Configure 2G External Cell


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z z

z z

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

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Parameter for GPRS Cell Reselectionz

Cell Attributes -> GPRS Attributes -> Advanced -> Ps Other Parameters


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z z

z z

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

z z

z z

z z

z z

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Support NACCz

Cell Attributes -> Other Attributes


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z z

z z

Parameter Name: Support NACC Description: 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

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GPRS Cell Reselection Typez

There are 3 type of cell reselections:

MS controlled cell reselection Network controlled cell reselection Network assisted cell reselection


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MS-Controlled Cell Reselectionz

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.

z

Parameter setting:

Support NC0/ NC1 to YESPage38


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Network-Controlled Cell Reselectionz

Network-Controlled Cell Reselection

MS 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.

z

Parameter setting:

Support NC2 to YES


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Network-Controlled Cell Reselection (NC2)MSPACKET MEASUREMENT REPORT PACKET ENHANCED MEASUREMENT REPORT NC2 Cell Reselection Algorithm

BSS

PACKET NEIGHBOR CELL DATA

PACKET CELL CHANGE ORDER

PACKET CELL CHANGE FAILURE

[P-TMSI] optional]


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3.

4.

MS in the GMM Ready mode state periodically sends PACKET MEASUREMETN REPORT to the BSC. After receive the MR, NSC process the MR. According to the NC2 cell reselection algorithm, BSC determines whether to perform cell reselection. 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. 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.

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NC2 Cell Reselection Algorithmz

The NC2 cell reselection algorithm follows the priority sequence in descending order of:

Urgent reselection algorithm Load reselection algorithm Normal reselection algorithm


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z

z

z

z

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]

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NC2 Cell Reselection AlgorithmBegin Measure RxLev & RxQual MS in the MR

[Cell Urgent Reselection Allowed]?

Yes

MS RxQual deterioration ratio > [MS Rx Qual Worsen Threshold]No

Yes

No

[Cell Load Reselect Allowed]?No

Yes

Channel multiplexing rate>[Load Reselect Start Thres]No

Yes

Any MS RxLev load reselection -> normal reselection Each type of reselection have different trigger condition.

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NC2 Cell Reselection AlgorithmContinue Trigger urgent cell reselection and select cell with the highest priority in cell list.

For GSM Cell

For FDD Cell

For TDD Cell

RxLev>MAX(RxLev(s), [Min_Acc_Level_Thres])+ [Cell Reselect Hyst] AND non-congestion stateNo Yes

Ec/No>[PS FDD EcNo Quality Thres] or RSCP>[PS FDD RSCP Quality Thres]Yes

No

RSCP>[PS FDD RSCP Quality Thres]No Yes

End

No

Cell reselection successful?

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

Yes

End


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z

z z

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.

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NC2 Cell Reselection Algorithmz

Each NC2 cell reselection algorithm contains three NC2 cell reselection type:Cell Type Intra-BSC Inter-BSC Serving cell Condition position Same BSC Different BSC, both GSM cell GSM to UTRAN Serving cell is cell is UTRAN Highest priority in the cell list. RxLev (Ext nei) = RxLev (n) MAX(2, [Cell Reselection Hyst/2]) For FDD cell : Ec/No>[PS FDD EcNo Quality Thres] Reselection &Target cell

GSM cell, target or RSCP>[PS FDD RSCP Quality Thres] For TDD cell: RSCP>[PS TDD RSCP Quality Thres]Page44


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 offset RxLev (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

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Network-Assisted Cell Reselectionz

Network-Assisted Cell Reselection

It 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.

z

Parameter setting:

Support NC0/ NC1/ NC2 to YES Support NACC to YESPage45


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Network Assisted Cell Change (NACC)z

Purposes:

MS is able to request BSC to send the target cells SYSINFO during the cell reselection.

z

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 .


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Network Assisted Cell Change (NACC)

Receive System information of cell B before reselection

Cell A

Cell B


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Network Assisted Cell Change (NACC)z

MS can initiate an NACC procedure only when autonomous cell reselection is triggered:

In NC0/ NC1 mode and packet transfer mode:

C1

38228984 GPRS EDGE Radio Network Optimization

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