GSM&GPRS Fundamentals

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HUAWEI TECHNOLOGIES CO., LTD. Huawei ConfidentialHUAWEI TECHNOLOGIES CO., LTD.

www.huawei.com

Huawei Confidential

Security Level:7/9/11

GSM/GPRSFundamentals

HUAWEI


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HUAWEI TECHNOLOGIES CO., LTD. Huawei ConfidentialPage 2

Chapter 1 GSM System Overview

Chapter 2 GSM Network Structure

Chapter 3 Channels on the Wireless Interface

Chapter 4 GPRS/EGPRS Fundamentals

Chapter 5 GSM/GPRS Procedure

Contents


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GSM system overview

q The GSM system is a frequency- and time-division cellular system, each physical channel ischaracterized by a carrier frequency and a timeslot number

q Cellular systems are designed to operate withgroups of low-power radios spread out over thegeographical service area. Each group of radiosserve MSs presently located near them. The areaserved by each group of radios is called a CELL

q Uplink and downlink signals for one user areassigned different frequencies, this kind oftechnique is called Frequency Division Duplex(FDD)

q Data for different users is conveyed in timeintervals called slots several slots make u a


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Cell Technique

q A certain radio coverage area formed by a set of

transceivers that connected to a set of antennas is called a

CELL.

q Macro Cell

mIn the beginning , High-Power BTSs are adopted to

provide services. The BTS covers a wider area , but its

frequency utilization is not efficient. So , it can only

provide a few channels for subscribers.

q Micro Cell

mLater the Low-Power BTS joins the system for getting a

better service area with high capacity . At the same

time it adopts the frequency reuse technique to

Macro Cell and Micro Cell


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Multiple Access Technique

q Multiple Access Technique allows many

subscribers to use the same

communication medium.

q There are three kinds of basic Multiple

Access Technique : FDMA , TDMA and

CDMA.

q GSM system adopt FDD-TDMA (FDMA and

TDMA together).


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FDMA

q FDMA uses different frequency

channels to accomplish

communication.

qThe whole frequency spectrumavailable is divided into many

individual channels (for

transmitting and

receiving) every channel can

support the traffic for one

subscriber or some control

information.

Frequency

Time


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TDMA

qTDMA accomplishes the

communication in different

timeslot.

q A carrier is divided into

channels based on time.

Different signals occupy

different timeslots in

certain sequence , that is ,many signals are

transmitted on the same

frequency in different time.

Time

Frequency


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GSM 900

Duplex Separation: 45MHzChannel Bandwidth: 200KHz

The Frequency Spectrum

Uplink

890 915 935 960MHz

Downlink


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Duplex Separation: 95MHzChannel Bandwidth: 200KHz

Base Station Receive

1710 1785 1805 1880MHz

Base Station Transmit

DCS 1800

The Frequency Spectrum


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Frequency Reuse

qThe frequency resource of mobile system is very

limited.

q The different Subscribers can use the same

frequency in different places.

q The quality of communication must be ensured.


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4 site X 3 cells reuse

1

8

9

210

46

5 37

11

12

R

Frequency Reuse


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Contents


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OMC

HLR/AUC/EIR

SMC

MSC/VLR

BSC

MSCBT

S

MS

MS

BTS

BTS

MAP

A-bis

A

PSTN

ISDN

GSM Network Structure


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q The Base StationController BSC

q The Base Transceiver

Station BTS

BTS

BSCBSS

MSC

Base Station Subsystem BSS


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q Packet data

switching

qIntegrated intoBSC

q Provide Gb

interface

BTS

BSC/PCU

BSS

MSC

Packet Control Unit-----PCU

Click to edit Master text

Second level Third level Fourth level

Fifth level

GPRSBackbone

SGSN


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Mobile-service Switching Center MSCHome Location Register HLRVisitor Location Register VLREquipment Identity Register

EIRAuthentication Center AUC

AUCHLR

MSC/VLR

PSTN

NSS

EIROMC

BSS

The Network Switching System


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Contents


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2 30 16 74 52 3

The physical channel is the medium over whichthe information is carried: 200KHz and 0.577ms

0 1

TDMA FRAME

Timeslot The information carried in one timeslot is called a burst

Physical Channel and Logical Channel

The logical channel consists of the informationcarried over the physical channels

TDMA FRAME


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Two types of Logical Channel

Traffic Channel (TCH) :

Transmits traffic information, includedata and speech.

Control Channel (CCH) :

Or Signaling Channel, transmits all

kinds of control information.


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Traffic Channel (TCH)

TCHTraffic Channels

TCH Traffic ChannelTCH/FS Full rate SpeechChannelTCH/HS Half rate SpeechChannelTCH/9.6 Data Channel9.6kb/s

TCH/4.8 Data Channel4.8kb/s

Speech

TCH/FS TCH/HS

Data

TCH/9.6 TCH/2.4

TCH/4.8


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FCCHSCH

CCH (Control Channels)

DCCH

SDCCH

BCH

BCCH Synch. CH.ACCH

SACCHFACCH CCCH

RACH CBCH

PCH/AGCH

Broadcast Control Channel BCCHCommon Control Channel CCCHDedicated Control Channel

Control Channel (CCH)


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Allocate signaling channel

FCCH

SCH

BCCH

PCH

RACH

AGCH

SDCCH

SDCCH

TCH

FACCH

Power-off

Idle mode

Dedicated mode

Idle mode

How to use these channels?

Search for frequency correction burst

Search for synchronous burst

Extract system information

Monitor paging message

Send access burst

Set up the call

Allocate voice channel

Conversation

Release the call


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GSM Logical Channel Combination

Main BCCH combination FCCH + SCH + BCCH +

CCCH

SDCCH combination SDCCH/8 + SACCH/8

Combined BCCH BCCH + CCCH +SDCCH/4 +

SACCH/4

TCH/FR combination TCH/F + FACCH/F + SACCH/F

TCH/HR combination TCH/H + FACCH/H + SACCH/H


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TDMA Frames

0 1

0 1 2 43 46 47 48 5049

51 Frame Multi-frames

0 1 10

CONTROL CHANNELS

2 3 4 5 6 7 2 3 5 764

GSM Multi-frames


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GSM Multi-frames

TDMA Frames

0 1

0 1 2 43 21 22 23 2524

26 Frame Multi-frames

0 1 10

TRAFFIC CHANNELS

2 3 4 5 6 7 2 3 5 764


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Contents


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What is GPRS?

General Packet Radio Service

An end-to-end packet switched service on the basis of GSM

The maximum reuse of the existing GSM network

infrastructure

Providing efficient utilization of radio resources

Interaction with the existing GSM switched circuit system

Based on a standard open interface


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GPRS Structure and Network Interfaces

GPRSbackbone

network

SGSN

SGSNGGSNGn

IP interface

SS7 interface

BSS MSC SMS-GMSC

AUm

PDP network

(IP/X.25)

GiInternet

TE

MT

MS

HLR

Gs

Gr

Gd

Gc

Gb


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Data Transfer Plane

Application Application

IP/X25 IP/X25 IP/X25

SNDCP GTP

LLC LLC UDP/TCP UDP/TCP

RLC RLC (BSSGP) (BSSGP) IP IP

MAC MACFramerelay

Framerelay

L2 L2

L2 (MAC)

Physical

Layer

Physical

Layer

Physical

Layer

Physical

Layer

Physical

Layer

Physical

Layer

Physical

Layer

MS BSS SGSN GGSN

relay

relaySNDCP

GTP

Um Gb Gn Gi

MAC: Media Access Control

RLC: Radio Link Control

LLC: Logical Link Control

l BSSGP: BSS GPRS Protocol

l SNDCP: Sub-Network Dependency

Convergence Protocol

l GTP: GPRS Tunneling Protocol

MS BSS/SGSN Si li Pl


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MS-BSS/SGSN Signaling Plane

BSSGP

GMM/SM

LLC

RLC

MAC

GSM RF

GMM/SM

LLC

BSSGP

L1bisUm G

b

NetworkService

RLC

MAC

GSM RF L1bis

NetworkService

Relayrelay

Physical layer: radio coding and decoding, channelmultiplexing and mapping, radio link control and radiomeasurementRLC/MAC: media access and link control of radiointerface

LLC: Provision of a reliable logical link betweenMS andSGSN for data transfer. LLC protocol supportsacknowledgement and non-acknowledgement modes,and encryption and non-encryption modes.SNDCP: Lay 3 transfer protocol, atransition betweennetwork layer and subnet layer,segmentation/packaging andcompression/decompression of IP/X.25 subscriber dataGMM/SM: Layer 3 Signaling Protocol

L1bis: Physical Transport LayerNS: transmission of upper-layerBSSGPPDU, based on frame relay/IPBSSGP: Provision ofa connectionless link betweenBSS and SGSN for non-acknowledgementdata transfer on the transport platform. Transmission of QoS and routinginformation related to radio on the signalingplatform, paging request processing, andflow control of data transfer


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q Packet Data Channel (PDCH)

q Packet Data Traffic Channel and Packet Data Control Channel

q Packet Data Traffic Channel (PDTCH)

q Unidirectional traffic channel

q Packet Data Control Channel

q Packet Broadcast Control Channel (PBCCH)

q

Common Control Channel: PPCH, PRACH, PAGCH, PNCH

q Dedicated Control Channel: PACCH and PTCCH

Packet Data Logical Channel


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q Packet logic channels (PDCH) can be combined via the

following three modes

qMode 1: PBCCH+PCCCH+PDTCH+PACCH+PTCCH;

qMode 2: PCCCH+PDTCH+PACCH+PTCCH;

qMode 3: PDTCH+PACCH+PTCCH

q In case of small GPRS traffic, GPRS and circuit services use the

same BCCH and CCCH in the cell. In this case, only combination

mode 3 is needed in the cell

q 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

Combination of packet logic channel


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Radio-Packet Resource Allocation

q The basic unit of radio resource allocation and radio transmission is data

block.

q One PDCH can be used by multiple MSs; One MS can use multiple PDCHs

simultaneously.

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11B0

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11B0

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11B0

MS3MS2

TS 0

TS 1

TS 2

MS1


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qRouting Area: a subset of location area

qMobility Management Entities: SGSN, HLR, and MS

qGMM Status

qIdle: GMM context is not set up; MS is not reachable.

qStandby: GMM context is set up; MS can receive paging, but

cannot transfer data.

qReady: MS can transfer data.

Concept of Mobility Management


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GMM State Model


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What is EDGE?

EDGE: Enhanced Data Rates For GSM Evolution.

EDGE consists of EGPRS and ECSD.

EGPRS: Enhanced GPRS, applied in more and more GSM

networks. Introduce the 8PSK modulation mode, Adopt

MCS-1~9 encoding modes and Modifies RLC/MAC protocols

ECSD: Enhanced HSCSD, not applied


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qNew modulation method: 8PSK

qBit rate on physical layer is three times higher than GMSK.

qUnder poor radio conditions, likelihood of misinterpretation of

the 8PSK symbols is higher than GMSK.

qNew channel coding methods: MCS1~MCS9

qEach has different amount of error-correcting coding.

qShould be used with different modulation method.

EGPRS Enhancement strategy1


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Increasedcapacityandspectral efficiency

Data21.4Kvoicevoicevoice voice

Data21.4K

Data21.4K

voicevoicevoice voice

Standard GSM/GPRS Radio Interface

EDGE Radio Interface

voice voice

voice

Data59.2K

Data59.2K

Additional!

Higher Spectral Efficiency than GPRS


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8PSK Modulation Mode

Modulating

bits

D3i, d3i+1,

d3i+2

Symbol

parameter

l

(1,1,1) 0

(0,1,1) 1

(0,1,0) 2

(0,0,0) 3

(0,0,1) 4

(1,0,1) 5

(1,0,0) 6

(1,1,1) 7

qEDGE introduces 8PSK(8-phase shift keying)

qModulation mode, which expresses symbols bythe phase of the signal and the symbol has 8

types and each symbol is mapped to 3 bits.

Hence, EDGE data rate can reach 3 times GSM

data rate.


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qLink Adaptation

qLA can select appropriate MCS and modulation method

according to radio link quality.

qIf a packet is received incorrectly, it will be retransmitted.

qIncremental Redundancy

qIR uses higher MCS without consideration for the actual radio

link quality.

qIf a packet is received incorrectly, additional error-correcting

coding will be transmitted.

EGPRS Enhancement strategy 2

Li k Q lit C t l


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Link Quality Control

qLink Adaptation Scheme

Selects appropriate modulation and codingscheme according to link quality

For GPRS, retransmission with another CS isimpossible

For EGPRS, retransmission with another MCSis possible

qIncremental Redundancy Scheme

Information sent with little coding

If decoding succeeds, high bit rate isachieved

If decoding fails, additional coded bits aresent and combined with previous info in thereceiver


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Contents


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GPRS GMM Procedure


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GPRS GMM Procedure

GPRS TBF Establishment


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GPRS TBF Establishment

qTBF Temporary Block Flow

qTFI Temporary Flow Identity

qUSF Uplink State Flag


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