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Copyright 2010 Huawei Technologies Co., Ltd. All rights reserved.

GSM Principles


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Copyright 2010 Huawei Technologies Co., Ltd. All rights reserved. Page2

Objectives

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

Grasp basic idea of GSM system such as frequency spectrum,

frequency reuse etc.

Grasp the structure of the GSM system and the protocol used.

Grasp certain numbers that refer to BSS

Grasp the 4 kinds of channel combination and understand the idea

of multi-frame.

Know some radio techniquesGet the idea of EDGE


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References

BSS Feature Description

BSS Signaling Analysis Manual

BSC Technical Manual


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Contents

1. GSM System Overview

2. GSM Network Structure

3. Service Area and Number Planning

4. Channels on the Wireless Interface

5. Radio Techniques

6. GPRS & EDGE Introduction


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Contents





5. Radio Techniques



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GSM system overview

The GSM system is a frequency- and time-division cellular system,each physical channel is characterized by a carrier frequency and a

time slot number

Cellular systems are designed to operate with groups of low-power

radios spread out over the geographical service area. Each group ofradios serve MSs presently located near them. The area served by eachgroup of radios is called a CELL

Uplink and downlink signals for one user are assigned different

frequencies, this kind of technique is called Frequency Division Duplex

(FDD)

Data for different users is conveyed in time intervals called slots ,

several slots make up a frame. This kind of technique is called Time

Division Multiple Access (TDMA)


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Cell Technique

Macro Cell and Micro Cell A certain radio coverage area formed by a set of transceivers that

connected to a set of antennas is called a CELL.

Macro Cell

In the beginning , High-Power BTSs are adopted to provide services. TheBTS covers a wider area , but its frequency utilization is not efficient. So , it

can only provide a few channels for subscribers.

Micro Cell

Later the Low-Power BTS joins the system for getting a better service areawith high capacity . At the same time it adopts the frequency reuse

technique to improve the efficiency of the frequency utilization and also

the whole capacity of the network.


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Multiple Access Technique

Multiple Access Technique allows many subscribers touse the same communication medium.

There are three kinds of basic Multiple Access Technique :

FDMA , TDMA and CDMA.GSM system adopt FDD-TDMA (FDMA and TDMA

together).


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FDMA

FDMA uses different frequencychannels to accomplish

communication.

The whole frequency spectrum

available is divided into many

individual channels (for

transmitting and receiving)

every channel can support thetraffic for one subscriber or some

control information.

Frequency

Time


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TDMA

TDMA accomplishes thecommunication in different

timeslot.

A carrier is divided into

channels based on time.

Different signals occupy

different timeslots in certain

sequence , that is , manysignals are transmitted on the

same frequency in different

time.

Time

Frequency


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CDMA

CDMA accomplishes thecommunication in different code

sequences.

Special coding is adopted before

transmission, then different

information will lose nothing

after being mixed and

transmitted together on thesame frequency and at the same

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



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FrequencySpectrum

Range(MHz) Uplink Frequency

FrequencyPoint

Available

DownlinkFrequency

GSM 450

450.4~457.6

460.4~467.

6

Fu(n)=450.6+0.2(n-259) 259


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Frequency Reuse

The frequency resource of mobile system is very limited.

The different Subscribers can use the same frequency in

different places.

The quality of communication must be ensured.


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Frequency Reuse

7(Site)X 1(Cell) reuse

2

1

2

3

4

5

6

7


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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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Cell Types

Omni

1

120degree

12

3

Omni-directional Cell

120 Degree Cell


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Contents





5. Radio Techniques



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Interface Between Different Entities

GSM /GPRS BSS

BTS

BSC

BTS

BSC

PCU SS7

SMS system

PSTNISDN

Internet,Intranet

MSC/VLR GMSC

HLR/AUC

SGSN

CG BG

GGSN

GPRS backbone

Other PLMN

A

Gb

Gi

Gp

C/D/Gs

Gr/Gs/Gd/Ge Gc

Ga

Abis

Um

MS

MS

OMC


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Mobile Station MS

International Mobile Equipment Identity

(IMEI) Mobile Equipment

MS=ME+SIM

International Mobile Subscriber Identity (IMSI)

Subscriber Identity Module


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Subscriber Identity Module SIM

International Mobile SubscriberIdentity (IMSI)

Temporary Mobile Subscriber

Identity (TMSI)Location Area Identity (LAI)

Subscriber Authentication Key (Ki)

SIM


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BTS

BSC

TC/SMBSS

MSC

Base Station Subsystem BSS

The Base Station Controller BSC

The Base Transceiver Station

BTSThe Trans-coder TC and

Sub multiplexer (SM)


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BTS

BSC

TC/SM

BSS

MSC

Packet Control Unit-----PCU

Packet dataswitching

Bridge between

SGSN and BSCProvide Pb and Gb

interface GPRSBackbone

PCU SGSN


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Mobile-service Switching Center

MSCHome Location Register HLRVisitor Location Register VLREquipment Identity Register EIRAuthentication Center AUCEcho Cancellor EC

AUCHLR

MSC/VLR

PSTN

NSSEIROMC

BSS

EC

The Network Switching System


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Mobile-service Switching Center MSC

Call Processing

Operations and Maintenance Support

Interface management

Inter-network & Inter-working

Billing


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Home Location Register HLR

Subscriber ID (IMSI and MSISDN)

Current subscriber VLR (current location)

Supplementary service information

Subscriber status (registered/deregistered)

Authentication key and AuC functionality


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Visitor Location Register VLR

Mobile Status (IMSI attached / detached / busy / idle etc.)

Location Area Identity(LAI)

Temporary Mobile Subscriber Identity(TMSI)

Allocating the Roaming Number


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IMEI is Checked In White List

IMEI is Checked in Black/Grey List

If NOT found

EIR focus on theequipment , not thesubscriber!

Equipment Identity Register EIR

White List

Black List

Grey List


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OMC Functional Architecture

OS

MMI

DB

Event/AlarmManagement

SecurityManagement

ConfigurationManagement

PerformanceManagement

FaultManagement


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Contents

1. GSM System Overview2. GSM Network Structure


4. Channels on the Wireless Interface5. Radio Techniques



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Service Area

PLMN service area

......

Service Area

MSC service area...

Location area...

cell

PLMN service area PLMN service area

MSC service area...

Location area...

cell


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LAI

Location Area Identification

The LAI is the international code for a location area.

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: 460-00-0011

MCC MNC LAC


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CGI

The CGI is a unique international identification for a cell

The format is LAI+CILAI: Location Area IdentificationCI: Cell Identity. This code uses two bytes hex code to

identify the cells within an LAI.

For example : 460-00-0011-0001

CGI: Cell Global Identification


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BSIC

NCC: PLMN network color code. It comprises 3 bit. Itallows various neighboring PLMNs to bedistinguished.

BCC: BTS color code. It comprises 3 bit, used todistinguish different cells assigned the samefrequency!

NCC BCC

BSIC

BSIC Base Station Identification Color Code)


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CC: Country Code. For example: The CC of China is "86".NDC: National Destination Code. For example: The NDC of

China Telecom is 139, 138, 137, 136, 135.

SN: Subscriber Number. Format:H0 H1 H2 H3 ABCDExample: 86-139-0666-1234

MSISDN

CC NDC SNNational (significant)

Mobile number

Mobile station international

ISDN number


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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 Telecom is "00"

MSIN: Mobile Subscriber Identification Number. H1H2H3 S ABCDEFFor example: 666-9777001

NMSI: National Mobile Subscriber Identification MNC and MSINform it together.

For Example of IMSI : 460-00-666-9777001

Not more than 15 digits 3 digits 2 digits

IMSI

MCC MNC MSIN

NMSI

IMSI


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TMSI

The TMSI is assigned only after successful subscriber

authentication.The VLR controls the allocation of new TMSI numbersand notifies them to the HLR.

TMSI is used to ensure that the identity of the mobile

subscriber on the air interface is kept secret.The TMSI consists of 4 bytes( 8 HEX numbers) anddetermined by the operator.

TMSI: Temporary Mobile Subscriber Identification)


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IMEI

TAC FAC SNR SP

IMEI

IMEI: International Mobile Station Equipment Identification

TAC: Type approval code, 6 bit, determined by the type approval centerFAC: Final assembly code, 2 bit, It is determined by the manufacturer.SNR: Serial number, 6 bits, It is issued by the manufacturer of the MS.

SP: 1 bit , Not used.Check the IMEI in your MS : *#06#


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Contents






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2 30 16 74 52 3

The physical channel is the medium over which theinformation 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 information carried

over the physical channels

TDMA FRAME


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Two types of Logical Channel

Traffic Channel (TCH) :Transmits traffic information, include dataand speech.

Control Channel (CCH) :Or Signaling Channel, transmits all kinds ofcontrol information.


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Traffic Channel (TCH)

TCHTraffic Channels

Speech

TCH/FS

Data

TCH/HSTCH/9.6 TCH/2.4

TCH/4.8

TCH Traffic ChannelTCH/FS Full rate Speech ChannelTCH/HS Half rate Speech ChannelTCH/9.6 Data Channel 9.6kb/sTCH/4.8 Data Channel 4.8kb/sTCH/2.4 Data Channel 2.4Kb/s


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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 DCCHAssociated Control Channel ACCH

Control Channel (CCH)


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CCH

BCH

BCCHSynch.

Channels

SCH FCCH

The information carried on the BCCH

is monitored by the MS

periodically when it is in idle modeBCCH: Broadcast Control Channel

FCCH: Frequency Correction Channel

SCH: Synchronization Channel

Broadcast Control Channel BCCH


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CCH

CCCH

RACHuplink

CBCH

downlink

PCH/AGCHdownlink

The CCCH is responsible fortransferring control informationbetween all mobiles and thenetwork.

RACH: Random Access Channel

PCH: Paging Channel

AGCH: Access Granted Channel

CBCH: Cell Broadcast Channel

Common Control Channel CCCH


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CCH

DCCH

SDCCH

FACCH SACCH

DCCH is assigned to a singlewireless connection formeasurement and handoverpurpose.

SDCCH: Stand-alone DedicatedControl Channel

ACCH: Associated Control ChannelSACCH: Slow Associated

Control Channel

FACCH: Fast Associated ControlChannel

ACCH

Dedicated Control Channel DCCH


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RACH CCCHCCH

SDCCH

SACCH

FACCH

TCH/F

TCH/H

DCCH

TCH

DCH

Uplink Logical channel


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FCCH

SCH

BCCH

PCH

AGCH

BCCH

CCCH

CCH

SDCCH

SACCH

FACCH

TCH/F

TCH/H

DCCH

TCH

DCH

Downlink Logical channel


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Allocate signaling channel

FCCHSCHBCCH

PCHRACH

AGCHSDCCH

SDCCHTCHFACCH

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 messageSend access burst

Set up the call

Allocate voice channel

Conversation

Release the call


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Packet logic channel

Packet data channel (PDCH)Comprising packet service channel and packet control

channel

Packet service channel (PDTCH)Combined into the single-directional service channel

Packet control channel

Broadcast control channel: PBCCHPublic control channel: PPCH, PRACH, PAGCH

Private control channel: PACCH, PTCCH

TCH

BCCH

SACCH

CCCH

TCH


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C bi i f k l i


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Combination of packet logicchannel

Packet logic channels (PDCH) can be combined via thefollowing three modes

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

Mode 2: PCCCH+PDTCH+PACCH+PTCCH;

Mode 3: PDTCH+PACCH+PTCCHIn case of small GPRS traffic, GPRS and circuit services use thesame BCCH and CCCH in the cell. In this case, only combinationmode 3 is needed in the cell

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


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GSM Multi-frames

TDMA Frames

0 1

0 1 2 4 3 21 22 23 2524

26 Frame Multi-frames

0 1 10

TRAFFICCHANNELS

2 3 4 5 6 7 2 3 5 764


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Power Control

Saves battery power

Reduces co-channel and

adjacent channel interference

8W

0.8W

5WBoth Uplink and Downlinkpower settings can becontrolled independently andindividually.

BCCH -------Does not attend Power

control


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DTX and VAD

Voice Activity Detection VAD

Discontinuous Transmission DTX

Battery SavingInterference reduction


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Timing Advance (TA)

Transmission delay t

Transmission delay t

TA

The mobile phone should

send the signal in advance!


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Multi-path Fading

Diversity Frequency Hopping

Time Dispersion


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Diversity Whats Diversity?

Receive diversity provides an effective technique for bothovercoming the impact of fading across the radio channel

and increasing the received signal to interference ratio.

The former is achieved by ensuring uncorrelated (i.e.

low enough correlated) fading between antenna

branches i.e. not all antennas experience fades at the

same time.


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Kinds of DiversityTime diversity

Coding, interleaving

Frequency diversity

Frequency hopping

Space diversityMultiple antennas

Polarization diversity

Dual-polarized antennas

Multi-path diversity

Equalizer

t

f


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Frequency HoppingFrequency

f 0

Frame

f 1

f 2

f 3

f 4

Time


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Contents






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57.6 kbps

115 kbps

384 kbps

2 Mbps

GSM

HSCSD

GPRS

EDGE

IMT-2000

9.6 kbps

2G

2.5G

3G

GSM Development Evolution


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Data rate of EDGE and GPRS

8PSKGMSK

9.0

13.415.6

21.4

8.811.2

14.817.6

22.4

29.6

44.8

54.4

59.2

0.0

10.0

20.0

30.0

40.0

50.0

60.0

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

Kbps

P R S

P R S


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Huawei EDGE Test Result

Downlink, 4 TS, MCS-9


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Summary

The basic idea of GSMThe frequency spectrum used in GSM

The structure of GSM

Certain service area and numbers

Some radio techniques used in GSM

Evolution of GSM


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