Global System for MobileCommunication

Basic Principle

Introduction to GSMGSM OverviewMobile communication market of IndiaGSM System ArchitectureGSM Frequencies AllocationMultiple-Access TechniquesGSM Channels structureGSM Key technologiesGSM Network FunctionsGSM Numbering PlanGSM Frequency Reuse TechnologyGSM development

Contents

• Mobile communication existed half a century ago, but it was in the 1980’s that it was really developed 。The main goal of mobile communication is to realize communication among any objects at any time, and in any place.

Land cellular mobile communication

system (PLMN) has gone through 3 stages:

1. First Generation --Analog Mobile Telephone System

2.Second Generation---Digital Mobile Communication System

3. Third Generation---IMT-2000

Evolution of Mobile Communication

AMPS （ America ）NMT （ North Europe ）

TACS （ U.K. ）

Analog

Digital

D － AMPS PDCGSM

CDMA

Evolution

Development of Mobile Communication

• Analog cellular mobile communication system has following fatal weaknesses:

A) There is no public air interface between various systems;

B) It can not adapt itself to the digitization of fixed networks, and digital bearer services are hard to develop;

C) It has a low frequency availability, thus unable to meet large capacity requirements;

D) It has a low degree of safety, thus easy to be eavesdropped, and easy to be “copied” with “false” handsets.

First Generation-Analog Mobile Telephone System

Development of Mobile Communication

Disadvantages of First Generation Analog Mobile Communication System

• Not standard interface

• No Mobile Data Services

• Less efficiency of the Freq

• No roaming automatically

• Lower security

Second Generation - Digital Mobile

Communication System

• Due to the various defects of analog systems such as TACS, mobile telephone systems were developed in the 1990’s embodied by digital transmission, TDMA and narrow-band CDMA, which are called the second generation mobile telephone system.

Types of TDMA Systems• The comparatively mature and most typical system in the

TDMA series are: the pan-European GSM, American D-AMPS and the Japanese PDC.

1 ） D–AMPS was formally launched into commerical application in 1993 after the American Electronic Industry Association (EIA) completed its technical standardization in 1989

• 2 ） The Japanese JDC (now renamed as PDC) had its technical standards completed in 1990. It was put into service in 1993, but is restricted to Japan only.

• 3 ） The special mobile communication group (SMG) of CEPT laid down the phase 1 standard of GSM in 1988, with the working frequency band around 900MHz. It was launched into commercial use in 1990.

GSM System Requirements

Commercial Standard of GSM:Great than or equal to 2 Operators in a county to get best

coexist and competition.

Must be an open system for equipment providers to get best

coexist and competition.

Has no effect to PSTN.

System Standard of GSM ： The system must be Pan-European.

The system must have and keep good Voice Quality.

The system must have a high frequency efficiency.

The system must have enough capacity.

The system must be compatible with other communication standard.

The system must have good security.

Advantages of GSM Systems

The advantages of GSM standard system are as

follows: Can bear more inter-cell interference.

Can get better average voice quality than Analog Cellular System.

Supports data transmission.

User information security can be guaranteed.

Compatible with ISDN and can support new service.

International roaming is possible in all GSM deploying countries.

Low investment and usage price

GSM Services

GSM Services

Bearing Services

Telecom Services

Basic bearing services

Complementary services

Complementary services

Short message

Voice

Data

most important

Overview of Mobile Communication Market of India

Brief History of India telecom Market

India Telecom Circles

Mobile Subscriber’s Growth

Indian telecom market share

GSM System Architecture

GSM System Architecture

O&M

BSC

BTS900

BTS1800

BTS1900

BTS900/1800/1900

A Interface

MSC/VLR

SMU/TCU

Ater Interface

Abis Interface

Um Interface

OMC

PCM/DDN/X.25 O&M

PSTN/PLMN

PSPDN/ISDN

HLR/AUC

EIR

SMC

Gb Interface

PCU

SGSN

NMC

IP Network

Q3 Interface

IP IP NetworkNetwork

• BSS: Base Station Subsystem

• BSC: Base Station Controller

• BTS: Base Transceiver Station

• MSC:Mobile Switching Center

• OMC:Operation and Maintenance Center

• AUC:Authentication Center

• EIR:Equipment Identification Register

Elements of GSM System

• HLR:Home Location Register

• VLR:Visitor Location Register

• MS:Mobile Station

• ISDN:Integrated Services Digital Network

• PSTN:Public Switched Telephone Network

• PSPDN:Packet Switched Public DataNetwork

• PLMN Public Land Mobile Network

Elements of GSM System

GSM Subsystem

GSM includes 3 subsystems

Abis

Open interface

Open interface

Air A

O & M

• Mobile stations are not fixed to one subscriber. On any mobile station in the system, we can identify the subscriber with the SIM card (Subscriber Identity Module). The personal identification number (PIN) can be used to prevent unauthorized use of the SIM card.

Mobile Station

• Each mobile station has its own identification number, i.e., the international mobile equipment identifier (IMEI). IMEI mainly consists of the type permission code and the related manufacturer product number.

• Each mobile subscriber has its own international mobile subscriber identifier (IMSI), which is stored in the SIM card and in HLR.

Mobile Station

BSS System

BSS including: BSC

BTS

TC

BSS functions:

Radio resources control and

managements

Speech code switching

Signal and data processing of

Air interface

BTS

TC

BSC

BSC

TCBTS

BTS

It is the radio tranmission part of the base station system. Controlled by BSC, it serves cell radio transceiver equipment, handles conversion between BSC and radio channels, and performs radio transmission between BTS and MS via air interfaces as well as related control functions.

Base Transceiver Station (BTS)

As the control part of BSS, BSC performs the switching function in BSS.

- BSC may be connected with multiple BTSs at one end, and MSC and OMC at the other end. BSC mainly manages radio network and radio resources, supervises and manages radio base station, controls the establishment, connection and disconnection of radio links in MS and BTS and the location updating, hand-over and paging of mobile station, provides functions such as voice encoding, transcoding, rate adaptation, as well as the operation and maintenance functions of BSS.

Base Station Controller(BSC)

TC mainly completes voice conversion between the 16kbit/s RPE-LTP (regular pulse excited long-term prediction) codes and 64kbit/s A-law PCM codes. In a typical application pattern, ZXG10-TC is located between MSC and BSC.

16kbit/s RPE-LTP 64kbit/s A-law PCM codes

Transcoder (TC)

• The network and switching sub-system mainly includes switching functions of the GSM system, and database functions used for subscriber data and mobility management as well as safety management. It manages the communications among GSM mobile subscribers and those between GSM mobile subscribers and other communication network subscribers.

Network and Switching Subsystem (NSS)

MSC

VLR

B

MSC

VLR

B

G E

EIR

HLR/AUC

BSCBTS

NSS

A

BSS

F

C

D

Network and Switching Subsystem （ NSS ）

• The network sub-system is divided into six function units:

• Mobile Service Switching Center (MSC)• Home location Register (HLR)• Visitor Location Register (VLR)• Authentification Center (AUC)• Equipment Identification Register (EIR)• Operation and Maintenance Center (OMC)

NSS Architecture

• As the core of a network, MSC provides switching functions, and connects mobile subscribers with fixed network subscribers, or with mobile subscribers. Thus, it provides interfaces to fixed networks (such as PSTN, ISDN, etc.) and interfaces for interconnection with other MSCs.

Mobile Services Switching Center (MSC)

• MSC obtains all the data for processing subscriber call requests from 3 types of databases (HLR, VLR and AUC).

• MSC can provides a series of services for subscribers: • -Telecom services, such as phone, sms, and emergent calls• - Bearer services

• -Supplementary services, such as call transfer, call restriction and videoconferencing.

Functions of MSC

• VLR stores all related information of mobile subscribers having entering into its coverage area, which enables MSC to set up incoming/outgoing calls. It can be taken as a dynamic subscriber database. VLR obtains and stores necessary data from the HLR of a mobile subscriber. Once a mobile subscriber leaves the coverage area of this VLR, it will be re-registered in another VLR, the temporarily recorded data of this mobile subscriber stored in the original VLR will be deleted.

Visitor Location Register （ VLR ）

• As the central database of the GSM system, HLR stores the related data of all existing mobile subscribers controlled by the same HLR. One HLR can control several mobile switching areas or the whole mobile communication network and the important static data of all subscribers are stored in the HLR, including IMSI, access capability, subscriber type and supplementary services. Furthermore, HLR also stores and provides MSC(A) with (dynamic) information of the MSC(B) area into which a mobile station has roamed, so that any incoming call is immediately sent to the called subscriber on a selected path.

Home Location Register （ HLR ）

• As a function unit of HLR, AUC is specially used for security management of the GSM system. AUC stores authentication information and encryption keys for subscriber authentication, encryption of voice, data, signaling messages on radio interfaces, preventing unauthorized subscribers access and guaranteeing the safety of mobile subscriber communication.

• Authentication Center （ AUC ）

• EIR stores the international mobile equipment identifier (IMEI) of mobile equipment. By checking 3 types of lists, i.e., white lists, black lists, and gray lists, it respectively lists the mobile equipment identifiers that are authorized, that should be monitored in case of faults, and that are unauthorized in case of theft. Service operators can use such information to locate the location of a stolen mobile station and block it.

• Equipment Identification Register （ EIR ）

NMS System

NMS functions : Network element and function

monitoring:

Fault management

Configuration management

Function management

Wireless coverage area structure

Cell

Location Area

MSC Service Area

PLMN Service Area

GSM Service Area

Cell is a smallest radio coverage area in the network

Cell

Location area is group of cells It is the largest area in which mobile station may roam without updating its locationServed by one or more BSC but only one MSCThe area within which paging message are sent out to all the mobile subscriber.

LA

MSC Service Area

PLMN

A Public Land Mobile Network is : A group of MSC/VLR service areas The largest geographical service area served by one

network operator PLMN area for example area covered by Airtel or BSNL.

The GSM service area is the collection of PLMNs in which you can use one mobile station

GSM service Area

GSM Frequencies Allocation

GSM Working Frequency

GSM

System

Uplink/ MHz Downlink/

MHz

Bandwidth/

MHz

Duplex

Isolation/ MHz

Channel

(ARFCN)

GSM900 890 ~ 915 935 ~ 960 2 ×25 45 124

GSM900E 880 ~ 915 925 ~ 960 2 ×35 45 174

GSM1800 1710 ~ 1785 1805 ~ 1880 2 ×75 95 374

GSM1900 1850~1910 1930~1990 2 ×60 80 299

GSM900 ：890~915MHZ (upward) 935~960MHZ (downward)Duplex interval is 45MHZ, working bandwidth is 25MHZ, and carrier frequency interval is 200KHZ. GSM （ DCS ） 1800 ：1710-1785MHZ (upward) 1805-1880MHZ (downward) Duplex interval is 95MHZ, working bandwidth is 75MHZ, and carrier frequency interval is 200kHZ.EGSM900: 880~915MHZ (upward)925~960MHZ (downward)

GSM working frequency

GSM working frequency

Channel Isolation 200 KHz per carrier ， TDMA and 8 physical channels

Channel Configuration GSM900MHz ：

fu(n)=890.2MHz+(n-1)*0.2MHz

fd(n)= fu(n)+45MHz

GSM1800MHz ： fu(n)=1710.2MHz+(n-512)*0.2MHz

fd(n)= fu(n)+95MHz

fu(n) ： Uplink frequency ， MS transmitting , BTS receiving

fd(n) ： Downlink frequency ， BTS transmitting , MS receiving

1800MHz

1900MHz

900MHz

Single Band Network

Single Band

Dual Band

Triple Band

In a sense, the network determines the handsets can be selected.But nowadays, most handsets support dual band.

Frequency Resources

Cell coverage radius :

The higher the propagation frequency

The higher the propagation loss

The smaller the cell coverage radius.

900MHz

1800MHz

1900MHz

Single Band Network

We know

Propagation characteristic

Frequency Vs Distance

Multiple-Access Techniques

Multiple Access Techniques ：Users share the public communication resource and have no

interferences to others.

Multiple Access Techniques

GSM Technique

FDMA

TDMA

CDMA

Multiple Access Techniques

FDMA ：Channels are differentiated by frequencies

Multiple Access Techniques - FDMA

TDMA ：Channels are differentiated by time slots

Multiple Access Techniques - TDMA

CDMA ：Channels are differentiated by codes

Multiple Access Techniques - CDMA

TDMA Channels

TDMA Channels

Physical Channel Logic channel

Service channel Control channel

One slot is defined as a physical channel

Logic channel is based on different message type, it is mapped to different time slots.

Timeslot in Time-domain

and Frequency-domain

Physical Channel: TS

B T S

... ...

Bursts from Mobile Station

One Time Slot

Time frame

Types of Burst Pulse(1)

NB(Normal Burst): Used for traffic channel and control channels except for RACH, SCH, FCCH.

AB(Access Burst): Transmitted on RACH channel and used as access request made by MS to BTS. AB is the sole short BP sequence defined by GSM protocol.

SB (Synchronization Burst): Transmitted on SCH channel and used for initial synchronization seizing by MS.

FB (Frequency Correction Burst) : Used for carrier frequency correction of MS.

DB (Dummy Burst): Has the same format with NB, mainly used for bit filling

Types of Burst Pulse

GSM Channels Structure

Channel types

In a GSM system, channels are divided into logical and physical channels. Time slots are basic physical channels; thus each carrier frequency contains 8 physical channels. Physical channels of radio sub-systems support logical channels which can be subdivided funcationally into traffic channels (TCH) and control channels (CCH).

Traffic channel carries encoded speech or subscriber data, including full-rate traffic channel and half-rate traffic channel:

Speech channel

TCH/FS ： TCH/Full speed 13Kbit/s

TCH/HS ： TCH/Half speed 5.6Kbit/s

Data channel

TCH/F9.6 ： TCH/Full 9.6Kbit/s

TCH/F4.8 ： TCH/Full 4.8Kbit/s

TCH/H4.8 ： TCH/Half 9.6Kbit/s

TCH/H2.4 ： TCH/Half <=2.4Kbit/s

TCH/F2.4 ： TCH/Full <=2.4Kbit/s

Traffic Channel (TCH)

Control Channel

Control channelSignal bearing

Synchronous dataControl channel

CCH

DCCH

SDCCH ACCH

SACCH FACCH

CCCH

RACH CBCH

PCH/AGCH

BCH

BCCH SCH

FCCH

NB

ABNB NB

NB

FB

SBNB/DB

BCCH: Broadcast control channel

BCCH, system information broadcasting ：Current cell frequency

Neighbor cell BCCH frequency

LAI

CCCH and CBCH

management

Controlling and selecting

parameters

BCH is only Downlink BCH is only Downlink

FCCH, bearing information of frequency

correction ， using for MS to locate the cell

and other system information for carrier

synchronization

SCH ， bearing synchronous information ,TDMA

frame number and BSIC for frame synchronization

CCCH: Common Control Channel

CCCH is assigned for all the MS in one cell

PCH －－－ Downlink channel ， one

point to multipoint

Bearing paging information in one LAC,

is used by system to call MS

AGCH －－－ Downlink channel ， one

point to multipoint

Bearing DCCH information to assign

resources to t MS such as SDCCH

channel.

CBCH －－－

Downlink channel ， one

point to multipoint

RACH －－－ Uplink

channel, one point to one

point

Broadcasting short massage and other

information of the cell to all MSs within a cell

Bearing information of random access requirement

used by MS to gain access to system

DCCH: Dedicated Control Channel

SDCCH －－－ bi-direction channel , support

transfer of data to and from MS during call setup

and validation.

Information for call setup.

Location update

Short massage

TCH assignment

DCCH is assigned to a special MSDCCH is assigned to a special MS

SACCH －－－ bi-direction channel , signaling

channel associated with TCH and SDCCH

MS power control information

TA

FACCH －－－ bi-direction channel, associated with TCH

Bearing signaling information, faster than SACCH, handover message

Transferring signaling using 20ms TCH time slot: Frame stealing

Logical Channel

Physical and Logical channel

PCHRACH

BCCH

SCH

FCCH

HALF -RATE

AGCH

FULL –RATE

SDCCHSACCHFACCH

ENHANCED FULL RATE

12 logical channels,3 traffic + 9 Control

PCH

RACH

BCCH

SCH

FCCH

HALF -RATE

AGCH

FULL –RATE

SDCCH

SACCH

FACCH

ENHANCED FULL RATE

Traffic and control channels

PCHRACH

BCCH

SCH

FCCH

HALF -RATE

AGCH

FULL –RATE

SDCCHSACCHFACCH

ENHANCED FULL RATE

FCCH

PCHRACH

BCCH

SCH

FCCH

HALF -RATE

AGCH

FULL –RATE

SDCCHSACCHFACCH

ENHANCED FULL RATE

SCH

PCHRACH

BCCH

SCH

FCCH

HALF -RATE

AGCH

FULL –RATE

SDCCHSACCHFACCH

ENHANCED FULL RATE

BCCH

PCH

PCHRACH

BCCH

SCH

FCCH

HALF -RATE

AGCH

FULL –RATE

SDCCHSACCHFACCH

ENHANCED FULL RATE

PCHRACH

BCCH

SCH

FCCH

HALF -RATE

AGCH

FULL –RATE

SDCCHSACCHFACCH

ENHANCED FULL RATE

RACH

PCHRACH

BCCH

SCH

FCCH

HALF -RATE

AGCH

FULL –RATE

SDCCHSACCHFACCH

ENHANCED FULL RATE

AGCH

PCHRACH

BCCH

SCH

FCCH

HALF -RATE

AGCH

FULL –RATE

SDCCHSACCHFACCH

ENHANCED FULL RATE

SDCCH

PCHRACH

BCCH

SCH

FCCH

HALF -RATE

AGCH

FULL –RATE

SDCCHSACCHFACCH

ENHANCED FULL RATE

SACCH

PCHRACH

BCCH

SCH

FCCH

HALF -RATE

AGCH

FULL –RATE

SDCCHSACCHFACCH

ENHANCED FULL RATE FACCH

PCHRACH

BCCH

SCH

FCCH

HALF -RATE

AGCH

FULL –RATE

SDCCHSACCHFACCH

ENHANCED FULL RATE TCH

Channel Combination

1) tCHFull TCH/F + FACCH/F + SACCH/TF2) tCHHalf TCH/H)+FACCH/H+ SACCH/TH3) tCHHalf2 TCH/H + FACCH/H+ SACCH/TH+ TCH/H4) mainBCCH FCCH + SCH + BCCH + CCCH5) bCCHCombined FCCH+SCH+BCCH+CCCH+ SDCCH/4+ SACCH/C46) bCH BCCH + CCCH7) sDCCH SDCCH/8+ SACCH/C88) bCCHwithCBCH FCCH+SCH+BCCH+CCCH+ SDCCH/4 + SACCH/C4 + CBCH9) sDCCHwithCBCH SDCCH/8+SACCH/C8+CBCH

SF B C

R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R

51 Ö¡

SF C C SF C C SF C C I

R R R R R R R R R R

D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 A2 A3

SF C C

R R R R R R R R R R

III

D0 D1 D2 D3 D4 D5 D6 D7 A4 A5 A6 A7 III

A1 A2 A3 III

A5 A6 A7 III

D0 D1 D2 D3 D4 D5 D6 D7 A0

D0 D1 D2 D3 D4 D5 D6 D7 A4

SF B C SF C C SF D0 D1 SF D2 D3 ISF A0 A1

SF B C SF C C SF D0 D1 SF D2 D3 ISF A2 A3

D3

D3

R R

R R

A2 A3

A0 A1

D2

D2

RR

RR

D0 D1

D0 D1

R R R R R R R R R R R R R R R R R R R R R R R

R R R R R R R R R R R R R R R R R R R R R R R

F£ºFCCH S£ºSCHB£ºBCCH C£ºCCCH£¨CCCH=PCH+AGCH+RACH£©R£ºRACH D£ºSDCCHA£ºSACCH/C I£ºidle

BCCH+CCCH£¨ÏÂÐУ©

BCCH+CCCH£¨ÉÏÐУ©

8 SDCCH/8£¨ÏÂÐУ©

8 SDCCH/8£¨ÉÏÐУ©

BCCH+CCCH+4SDCCH/4£¨ÏÂÐУ©

BCCH+CCCH+4SDCCH/4£¨ÉÏÐУ©

(a) FCCH+SCH+BCCH+CCCH

(b) SDCCH/8(0,...,7)+SACCH/C8(0,...,7)

(c) FCCH+SCH+CCCH+SDCCH/4(0,...,3)+SACCH/C4(0,...,3)

Structure of 51-Frame Control Channel

Structure of 26-Frame Traffic Channel

Small capacity cell with only 1 TRXTN0:FCCH+SCH+CCCH+BCCH+SDCCH/4(0,_,3)+SACCH/C4(0,_,3);TN1_7: TCH/F+FACCH/F+SACCH/TF

The medium-size cell with 4 TRXs1TN0 group: FCCH+SCH+BCCH+CCCH;2 SDCCH/8(0,_,7)+SACCH/C8(0,_,7);29 TCH/F+FACCH/F+SACCH/TF

Channel Assignment inside Cells

Large-size cell with 12 TRXs1 TN0 group: FCCH+SCH+BCCH+CCCH;

1 TN2 group, 1 TN4 group and 1 TN6 group: BCCH+CCCH;

5 SDCCH/8(0,_,7)+SACCH/C8(0,_,7);

87 TCH/F+FACCH/F+SACCH/TF

Channel Assignment inside Cells

GSM Principle

Purpose ： restraining high frequency component, Preventing excessive instantaneous frequency offset, to satisfy coherent demodulation requirement.

requirements ： out-of band radiating power: － 60 ～－ 80dB

Feature: Adding pre-filter on the base of MSK modulator.

Gaussian filter : narrow bandwidth and being deep cutoff.

Lower extra pulse corresponding.

Constant output pulse area.

Application ： GSM system

Gaussian filter

GMSK Modulation

AMR-Adaptive MultiRate Codec

Unlike previous GSM speech codecs(FR, EFR, and HR), which operate at a fixed rate and constant error protection level, the AMR speech codec adapts its error protection level to the local radio channel and traffic conditions.

AMR actually comprises a family of codec's, which greatly increases its flexibility.

In poor network conditions that produce a high amount of errors, more bits are used for error correction to obtain robust coding. However, when transmission conditions are good, fewer bits are needed for sufficient error protection and more can therefore be allocated for speech coding.

AMR Codec Mode

In order to enhance channel anti-interference capacity and transmission quality, special redundancy technologies should be adopted to increase the bulk of transmitted information which can be inserted at a certain pattern (encoding) at the sending end and extracted at an agreed pattern (decoding) at the receiving end. This is called the encoding/decoding process of channels. Commonly used channel coding methods are: 1) convolution coding; 2) Fire coding; 3) parity check coding.

Channel Encoding

De-interleaver

channel

interleaverInner encoder

Inner decoder

Outerencoder

Outer decoder

Speech coder

Speechdecoder

13 kbit/s33.9 kbit/s

22.8 kbit/s

Speech outputs

Speech inputs

Channel Coding

50bi t(I a) 132bi t(I b) 78bi t(I c)

50 3 132 4

1

78

260bi t/20ms

X2 X3 X4

Fi re code

+

+

Protecti onbi ts

456bi t

78bi t

378bi t

Bl ockcodi ng

Convol uti onalcoder

G0

G1

136bi t

189bi t

53bi t

O/E

Convolutional coding

Channel Interleaving In radio telecommunication, error bits often occurs in the burst pulse

sequence because of deep signal fading. Check and correction of errors cannot be efficiently done merely by means of channel encoding mentioned above. Interleaving technique is thus adopted, by which the continuous bits in an information block are segmented and transmitted individually according to certain rules. That is, the originally continuous block in the transmission process becomes discontinuous, forming a group of interwoven message transmitting blocks, which are to be recovered (de-interleaving) into the original information blocks at the receiving end.

Interleave Technique

Interleave technique: Information codes are permutated and combined before transmitting in the TX; information codes are de-permuted and de-combined in the RX; it can decrease BER.

3 41 2 3 41 2 3 41 2 3 41 2

3 41 3 41 2 3 41 2 3 41 2

3 41 2 3 41 2 3 41 2 3 41 2

2

Massage grouping

Interleaving

Massage grouping after interleaving Error

456bit

Block A

08

1

19

2

210

3

311

4

412

5

513

6

614

7

715

8

456bit

Block B

08

1

19

2

210

3

311

4

412

5

513

6

614

7

715

8

456bit

Block A+1

08

1

19

2

210

3

311

4

412

5

513

6

614

7

715

8

456bit

Block B+1

08

1

19

2

210

3

311

4

412

5

513

6

614

7

715

8

57 1 57 1 57 1 57 1 57 1 57 1 57 1 57 1

Even N+3Even N+2Even N+1

Even N

Odd N+4Odd N+5

Odd N+6 Odd N+7

116-bit block 116-bit block 116-bit block 116-bit block

Two aims can be achieved by adopting DTX mode. One is to lower the total interference level in the air, and the other is to save transmitter power. The DTX mode and the normal mode are optional, since the former will slightly lower the transmission quality.

Discontinuous Transmission (DTX)

DTX is also called voice control.

The average speech consumed time is usually less than 40% the channel

consumed time.

DTX function ： Interference reduction ， speech quality improvement ， capacity increase.

Reducing TX time and increasing working time.

Discontinuous Transmission

Power Control

Purpose: using minimum TX power to guarantee the normal service quality, reducing co-channel interference.

Dynamic power control: Power of BTS and MS can be dynamic adjusted according to path loss and signal quality. this will get the minimum signal strength to satisfy system quality requirements.

Diversity Technique

Diversity technique: multipath signals are received and combined to one

signal, this will increase signal quality.

Including: time diversity, space diversity, frequency diversity, polarization

diversity, etc.

Signals sent by a base station on the broadcasting channel help mobile stations to synchronize with the base station. After connection is set up between a mobile station and the base station, the base station will make continuous tests, and provide the time advance (TA) on the SACCH channel to all mobile stations twice every second according to the BS-MS-BS broadcasting delay. Mobile stations will make self-adaptive frame adjustment according to time advance so that the time of mobile station transmission to the base station matches that of base station reception.

Timing Advance (TA)

BTS

BTS transmit at time 0

MS receive at time d/c

MS transmit at time 3+d/c

BTS receives at time 3 +2d/c

TA: Time Advance

MS RX

1 2 3 4 5 6 70

3TSOFFSET

TDMA FRAME N

MS RX

1 2 3 4 5 6 70

3TSOFFSET

TDMA FRAME N

MS TX

1 2 3 4 5 6 70

TDMA FRAME N

MS TX

1 2 3 4 5 6 70

TDMA FRAME N

TIME ADVANCE

To enhance system anti-interference ability, the GSM system adopts the frequency hopping technology. Frequency hopping refers to the hopping of carrier wave frequencies according to a certain sequence in a very wide frequency range. Data of control information are converted into base band signals after modulation, which are then sent into carrier wave modulation. Afterwards, the carrier frequency changes under the control of pseudo-random codes, the sequence of which is frequency-hopping sequence. Finally, when filtered by radio filter, the carrier is transmitted to and radiated by antenna.

Frequency Hopping(1)

Frequency hopping is to avoid external interference. In other words, it is to prevent or greatly reduce co-channel interference and frequency selective fading effect by converting frequencies to an extent that interference cannot catch up with

There are two frequency hopping modes: base band frequency hopping and radio frequency hopping.

Frequency Hopping(2)

Reason: counteract Rayleigh Fading scatter interference among multiple calls Types: Base band frequency hopping

keeps the transmission and receiving frequency of each carrier unit unchanged, but merely sends FU transmission data to different carrier units at different FN moments.

radio frequency hoppingcontrols the frequency synthesizer of each transceiver, making it hop according to different schemes in different time slots.

Frequency Hopping Technique

GSM Network Functions

Overview

GSM network functions

Communication services

Supports basic and supplementary

services to guarantee the

communication between users.

Mobile managements

Supports all mobile related function

including location update, handover

and roaming.

Security managements

Supports Authentication, signaling and

user data encryption.

Additional call

processing functions

Supports call rebuilding,

queuing, DTX and so on.

Emphasis！

Location Update

HLR

VLR

MSC (old)

VLR

MSC (new)

LocationUpdate

Initiated by the MS.

The current location information is

stored in the SIM.

MS will initiate the location update

when the current location is different

with that in the SIM.

Location Update

Location Types:Startup & Shutdown

IMSI ATTACH/DETACH

Location register

MS startup & shutdown

General location update

LAC is changed

Periodic location update

The period is set by operators

MS will initiate the location

update when the period is

exceeded.

VLRMSC

LA 2LA 1

ON

Purpose:Continuous communication in the moving.

Increasing service quality:

Decrease call drop rate

Decrease congestion rate

Network elements participating the handover:MS 、 BTS 、 BSC 、 MSC

MS ： measurements of downlink signal quality and adjacent cell signal

strength.

BTS ： Monitoring uplink signal quality and interference, sending results to

BSC.

BSC ： Handover judgment.

MSC ： Handover judgment between BSS or MSC handover.

Handover

Trigger condition:

Power budget handover

Rescuing signal handover

Rescuing quality handover

Distance handover

Traffic handover

Time advance:

Synchronous handover

Asynchronous handover

Location:

Intra-cell handover

Intra-BTS handover

Intra –BSC handover

Inter –BSC handover

Inter –MSC handover

Handover Type

Air A

TCBTS BSC

Intra-cell Handover

A ir A

T CB T S

B T S

B S C

O ld C e ll / B T S N ew C e ll / B T S

Intra-BSC Handover

A ir A

B T S

O ld C ell / B T S

N ew C ell / B T S

B T S

B S C T C

B S C T C

VL RM SC

Inter-BSC Handover

A ir A

B T S

O ld C ell / B T S

N ew C ell / B T S

B T S

B S C T C

B S C T C

VLRM SC

VLRM SC

Inter-MSC Handover

GSM Numbering Plan

GSM LAC

PLMN Area

MSC Area

LAC Area BTS

Area

CELL AreaGSM Service

Area

Numbering System

International mobile subscriber identification number (IMSI)

International mobile subscriber identification number (IMSI)

It identifies a unique international universal number of a mobile subscriber, which consists of MCC+MNC+MSIN.

1) MCC: country code, 4602 ） MNC: network code, 00 or 013 ） MSIN: subscriber identification, H1H2H3H4 9XXXXXX, H1H2H3H4: subscriber registering place H1H2: assigned by the P&T Administrative Bureau (operator )to different provinces, to each province

H3H4: assigned by each province/city

the IMSI of user will be written into the SIM card by specific device and software and be stored into the HLR with other user information.

It is the subscriber number commonly used. China uses the TDMA independent numbering plan:

CC+NDC+ H1H2H3H4 +ABC

CC: country code, 86NDC: network code, 135—139, 130H1H2H3H4: HLR identification code ABCD: mobile subscriber number inside each HLR

Mobile subscriber ISDN number （ MSISDN ）Mobile subscriber ISDN number （ MSISDN ）

International Mobile Equipment Identification code(IMEI)

International Mobile Equipment Identification code(IMEI)

It will uniquely identify a mobile station. It is a decimal number of 15 digits. Its structure is:

TAC+FAC+SNR+SP

TAC=model ratification code, 6 digitsFAC=factory assembling code, 2 digitsSNR=sequence code, 6 digitsSP=reserved, 1 digit

Mobile subscriber roaming number (MSRN)Mobile subscriber roaming number (MSRN)

The MSRN is temporarily distributed to the subscriber by the VLR according to the request by the HLR when this subscriber is called. The MSRN is released and can be assigned to other subscriber later.

　　 CC + NDC + 00 + M1M2M3 + ABC　　 CC: country code, 86　　 NDC: mobile network code, 135—139, 130 　　 M1M2: same as the H2H3 of MSISDN　　 ABC: 000 -- 999

Temporarily Mobile Subscriber Identification Number (TMSI)

Temporarily Mobile Subscriber Identification Number (TMSI)

To insure the IMSI security, the VLR will assign an unique TMSI number for the accessed subscriber. It is used locally only and is a 4-byte TMSI number BCD code.

GSM Numbering PlanLAI

LAI: Location Area Identity

Definition ： The area where MS need not to update location when moving. It

includes one or more cells.

The paging area of the system.

MSC >= LA >= Cell

Function ： Location update monitoring and handover request.

MCC MNC LAC

LAI

3 bits 2 bits maximum16bit

LAC ： Location Area Code ， identification of a GSM Location Area. It is defined by operator.

GSM Numbering PlanBSIC

BSIC :Base Station Identity Code

To identify adjacent BTS in different countries, it is a 6 bits code.

NCC ： PLMN Color Code ， to identify different operators.

BCC ： BTS Color Code ， assigned by operator to cells with the same frequency.

NCC BCC

BSIC

3bit 3bit

CILACMNC

LAI

CGI

MCC

Cell Global Identity （ CGI ）

MCC resource is allocated and managed by ITU. The MCC of China is 460 （ decimal).

MNC is usually allocated by the relevant telecommunication administration department of a country.

The LAC encoding mode is specified correspondingly by every country. Usually, the location area should be as large as possible***.

Two or more cells in the same location area are not allowed to share the same CI.

Setting of CGI

CGI

MCC （ Mobile Country Code ） : consists of 3 decimal digits, and the value range is the decimal 000 ～ 999.

MNC （ Mobile Network Code ） : consists of 3 decimal digits, and the value range is the decimal 00 ～ 99.

LAC （ Location Area Code ） : The range is 1-65535.

CI （ Cell Identity ） : The range is 0-65535.

Role of CGI

The CGI information is sent along the system broadcasting information in every cell. When the MS receives the system information, it will extract the CGI information from it and determines whether to camp on the cell according to the MCC and MNC specified by the CGI. In the meantime, it judges whether the current location area is changed, then determines whether to take the location updating process. During the location updating process, the MS will report the LAI information to the network so that the network is fully aware of the cell where the MS is currently located.

GSM Frequency Reuse Technology

Types of Interference

Interference Protection Ratio

Carrier interference ratio C/I Definition ：

The ratio between useful signal and useless signal.

Co-channel interference protection ratio C/I ：The inter-cell interference when using the same frequency.

Standard requirement ： C/I>=9dB.

Engineering requirement ： C/I>=12dB.

Adjacent channel interference protection ratio C/A ：The inter-cell interference when using adjacent frequency.

Standard requirement ： C/I>= － 9dB.

Engineering requirement :C/I>= － 6dB.

The interference protection ratio with 400Khz isolation: C/I>=-

41dB

Frequency reuse

Frequency reuse is the process of reusing the same frequencies over

and over again within the network as long as they are separated

geographically.

C1 C1

f1

P0

f1

P0R R

C/I=¦ Ã C/I=¦ Ã

D

Frequency reuse ：Users in different locations can use the same frequency,

which will increase the spectral efficiency.

Frequency reuse should be designed carefully, unreasonable

design may course interference.

Frequency Reuse Technique

(D/R)2=3*K D - Frequency reuse distance R – Cell radius K – Frequency reuse mode

Frequency Re-use Mode

4/12 Clusters

3/9 Cluster

GSM Development

1 k

1 M

2 M

Bit/s

MessagingSMS

Voice

Graphics

text

Medium quality

High quality

Mobile Office

VideoUMTSUMTS

GPRSGPRS

2002

2000

GSMGSM10 k

1999 56 k

EDGEEDGE 2001

115 k

384 k

Always-on

Mobile Communication Development

SMSInformationServices Chat

RoomE-Mail

m-stock trading

m-bankingm-cash

Picture Mail

Route planning

Multi-playerGames

Mobile OfficeSchedule ManagementWork flow ManagementElectronic ConferenceFile Sharing

Radio

Music

Video Mail

Video streaming

Web

Interactive TVTV Conference

WAPWAP

GPRSGPRS

3G3G

Data Services Development

High date rate

Low data rate

GSM/CDMA/UMTS market share