GSM Fundamentals

Wireless Curriculum Development SectionWireless Curriculum Development SectionWireless Curriculum Development SectionWireless Curriculum Development Section

ISSUEISSUE 3.23.2

GSM FundamentalsGSM FundamentalsGSM FundamentalsGSM Fundamentals

Security Level: InternalConfidential Information of Huawei. No Spreading without Permission.

Contents Contents

Basic Concepts of Cellular Mobile SystemBasic Concepts of Cellular Mobile System

Service Area and Number Planning

GSM Network Components

Channels on The Air Interface

Radio Technologies


ObjectivesObjectives

Name the two different cell types and understand why and when each would be used.

Get the concept of frequency reuse.

Name the frequency spectrum used in GSM

Name the two different cell types and understand why and when each would be used.

Get the concept of frequency reuse.

Name the frequency spectrum used in GSM

On completion of this section you will be able to:


CELLCELL

Omni

1

120degree

1

23

Omni-Directional CellsOmni-Directional Cells

120 Degree Sectors120 Degree Sectors


Cell conceptCell concept

HighwayHighway

TownTownSuburbSuburb

RuralRural

• Flexible network planning based on location nature Flexible network planning based on location nature

• Smooth Handover (no service degradation while subscriber moves)Smooth Handover (no service degradation while subscriber moves)

• Frequency reuse (same group of frequencies used in different cells)Frequency reuse (same group of frequencies used in different cells)

Signal Signal strengthstrength

distancedistance

• Cell : basic service area that can be efficiently managed by the network

• One base station (equipment to switch, transmit and receive calls) per cell for comm. between MS and the network

• Cell boundaries are defined by BS signal strength


25 MHz Uplink (MS to BS)

25 MHz Downlink (BS to MS)

f

200 KHz

915 MHz890 MHz

……

960 MHz935 MHz

45 MHz duplex spacing

Frequency Spectrum GSM 900Frequency Spectrum GSM 900

……

For DCS1800: uplink from 1710 to 1785MHz, downlink is from 1805 to 1880MHz 75Mhz each / 374 RF carriers . 95MHz duplex spacing.

t

f

200 KHz

……

200 KHz x 125 = 25 MHz

1 TDMA frame = 0.577 m

s x 8 TS

……

915 MHz

890 MHz

Physical channelsPhysical channels


Contents Contents


Service Area and Number Planning


Channels on The Air InterfaceChannels on The Air Interface

Radio Technologies


Understand the structure of multiframes

On completion of this section you will be able to:


Name the 4 most commonly used channel combinations

Identify the types of physical channels and logical channels


Logical channels Logical channels

Logical ChannelsLogical ChannelsLogical ChannelsLogical Channels

CCHCCHCCHCCHTCHTCHTCHTCH DATADATADATADATASPEECHSPEECHSPEECHSPEECH

TCH/HRTCH/HR7kbps7kbps

TCH/HRTCH/HR7kbps7kbps

TCH/FRTCH/FR13kbps13kbps

TCH/FRTCH/FR13kbps13kbps

2.4/4.8kbps2.4/4.8kbps((FR&HR)FR&HR)2.4/4.8kbps2.4/4.8kbps((FR&HR)FR&HR) 9.6kbps 9.6kbps FRFR9.6kbps 9.6kbps FRFR

Logical traffic channelsLogical traffic channels

logical channels consist of the information carried over the physical channel.logical channels consist of the information carried over the physical channel.


Logical control channelsLogical control channels

CCHCCHCCHCCH

BCHBCHBCHBCHDCHDCHDCHDCH CCCHCCCHCCCHCCCH

SCHSCHSCHSCH

FCCHFCCHFCCHFCCHPCHPCHPCHPCH AGCHAGCHAGCHAGCH RACHRACHRACHRACHSDCCHSDCCHSDCCHSDCCH

BCCHBCCHBCCHBCCH

•Power Control indicator•cell ID , LAI , PLMN code •List of neighboring cells

SACCHSACCHSACCHSACCH

Power & timing controlRSSI & link quality

FACCHFACCHFACCHFACCH

Auth. and HO.

- Frequency-correction channel, used for MS frequency correction.- Frequency-correction channel, used for MS frequency correction.- Synchronization channel, used for MS frame synchronization and BS - Synchronization channel, used for MS frame synchronization and BS identification.identification.

Broadcast control channel, used to send cell information.Broadcast control channel, used to send cell information.-Random access channel, for dedicated channels assignment requestRandom access channel, for dedicated channels assignment request-Access grant channel, used to assign dedicated control channels for the MSAccess grant channel, used to assign dedicated control channels for the MS-Paging channel : used to page (alert) MS Paging channel : used to page (alert) MS -Standalone dedicated channel : Supports the transfer of data during connection Standalone dedicated channel : Supports the transfer of data during connection setupsetup-Slow/Fast associated control channels : carrying information associated with the Slow/Fast associated control channels : carrying information associated with the process being carried out on either the SDCCH or the TCH.process being carried out on either the SDCCH or the TCH.


Timeslots and TDMA FramesTimeslots and TDMA Frames

Higher Capacity Cell / more than 1 RF carriermore than 1 RF carrier

Broadcast TrafficDedicated

Traffic00 1 2 3 4 5 6 7

00 1 2 3 4 5 6 7

Low Capacity Cell / 1 RF carrier 1 RF carrier

Combined Traffic

0 1 2 3 4 5 6 7


GSM Logical ChannelGSM Logical Channel

Channel Combination

• Main BCH combination – BCCH + CCCH

• DCH combination – SDCCH8 + SACCH8

• Combined Channel Combination – BCCH + CCCH

+SDCCH4 + SACCH4

• TCH combination – TCH8/FACCH + SACCH


Structure of Logical Channel Combination Frame-Main BCCH

Structure of Logical Channel Combination Frame-Main BCCH

1 multi-frame (51TDMA Frames) 235.38ms Downlink

Group Group1 Group2

Group3,4

(same as

Group2)

Grpup5

Channel F S BX4 CX4 F S CX4 CX4 …… F S CX4 CX4 I

Frame

Number0 1 2-5 6-9 10 11 12-15 16-19 20-39 40 41 42-45 46-49 50

1 multi-frame (51TDMA Frames) 235.38ms Uplink

Channel R R R R R R R R R R R R R R……R R R R R

Frame

Number0 1 2 3 4 5 6 7 8 9 10 11 12 13-46 47 48 49 50

F:FCCH; S:SCH; B:BCCH; C:CCCH; I:IDLE; R:RACH


Structure of Logical Channel Combination Frame-Main SDCCH

Structure of Logical Channel Combination Frame-Main SDCCH


Channel D0×4 D1×4 D2×4 D3×4 D4×4 D5×4 D6×4 D7×4 A0×4 A1×4 A2×4 A3×4 I I I

Channel D0×4 D1×4 D2×4 D3×4 D4×4 D5×4 D6×4 D7×4 A4×4 A5×4 A6×4 A7×4 I I I

Frame

Number0-3 4-7 8-11 12-15 16-19 20-23 24-27 28-31 32-35 36-39 40-43 44-47 48 49 50


ChannelA5×

4A6×4 A7×4 I I I D0×4

D1×

4D2×4 D3×4 D4×4 D5×4 D6×4 D7×4 A0×4

ChannelA1×

4A2×4 A3×4 I I I D0×4

D1×

4D2×4 D3×4 D4×4 D5×4 D6×4 D7×4 A4×4

Frame

Number0-3 4-7 8-11 12 13 14

15-

18

19-

2223-26

27-

3031-34 35-38 39-42 43-46 47-50



Structure of Logical Channel Combination Frame-Combined BCCH

Structure of Logical Channel Combination Frame-Combined BCCH


Group Group1 Group2 Group3 Group4 Grpup5

Channel F SB×

4

C×

4F S

C×

4

C×

4F S

D0

×4

D1

×4F S

D2

×4

D3

×4F S

A0

×4

A1

×4I

Channel F SB×

4

C×

4F S

C×

4

C×

4F S

D0

×4

D1

×4F S

D2

×4

D3

×4F S

A2

×4

A3

×4I

Frame

Number0 1 2-5 6-9 10 11

12-

15

16-

1920 21

22-

25

26-

2930 31

32-

35

36-

3940 41

42-

45

46-

4950


Channel D3×4 R R A2×4 A3×4 R……R D0×4 D1×4 R R D2×4

Channel D0×4 R R A0×4 A1×4 R……R D0×4 D1×4 R R D2×4

Frame

Number0-3 4 5 6-9 10-13 14-36 37-40 41-44 45 46 47-50



Structure of Logical Channel Combination Frame-TCH

Structure of Logical Channel Combination Frame-TCH

T:TCH; I:IDLE ; A:SACCH

1 multi-frame (26TDMA Frames) 120ms

Channel T T T T T T T T T T T.A…T T T T T I

Frame Number 0 1 2 3 4 5 6 7 8 910-12 －

2021 22 23 24 25

.The FACCH is not showed in the diagram as it does not receive its own time allocation. The FACCH steals a time period from the TCH when required. .The 13th frame is used by the SACCH which carriers link control information to and from the mobile and BTS.


Frames hierarchy Frames hierarchy

The hyper frame lasts for over 3 hours, after which ciphering and FH algorithms are restarted.The hyper frame lasts for over 3 hours, after which ciphering and FH algorithms are restarted.


Contents Contents


Service Area and Number PlanningService Area and Number Planning



Radio Technologies


Service AreaService Area

PLMN service area

......

System area

PLMN service area

MSC service area...

Location area...

Base station area...

Radio cell

...... ......

MSC service area...

Location area...

Base station area...

Radio cell

PLMN service area


LAILAI

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 BCD

code(hex). The value 0000 and FFFF is invalid.For example: 460-00-0011

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 BCD

code(hex). The value 0000 and FFFF is invalid.For example: 460-00-0011

MCC MNC LAC


CGICGI

The CGI is a unique international identification for a cell

The format is LAI+CI

LAI: Location Area Identification

CI ： Cell Identity. This code uses two bytes BCD

code(hex) to identify the radio cells within an LAI.

For example : 460-00-0011-0001

The CGI is a unique international identification for a cell

The format is LAI+CI

LAI: Location Area Identification

CI ： Cell Identity. This code uses two bytes BCD

code(hex) to identify the radio cells within an LAI.

For example : 460-00-0011-0001

CGI: Cell Global Identification


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

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

MSISDNMSISDN

CC NDC SN

National (significant)Mobile number

Mobile station internationalISDN number


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

ABCDEF For example: 666-9777001NMSI ： National Mobile Subscriber Identification ， MNC and MSIN

form it together. For Example of IMSI : 460-00-666-9777001

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

ABCDEF For example: 666-9777001NMSI ： National Mobile Subscriber Identification ， MNC and MSIN

form 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 IMSI


The TMSI is assigned only after successful subscriber authentication.

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) and determined by the telecom operator.

The TMSI is assigned only after successful subscriber authentication.

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) and determined by the telecom operator.

TMSITMSI

TMSI: Temporary Mobile Subscriber Identification)


IMEIIMEI

TAC FAC SNR SP

IMEI

TAC ： Type approval code. It is administered by the type approval center.

FAC ： Final assembly code.It is administered by the manufacturer.

SNR ： Serial number.It is issued by the manufacturer of the MS.

SP ： Not used.

TAC ： Type approval code. It is administered by the type approval center.

FAC ： Final assembly code.It is administered by the manufacturer.

SNR ： Serial number.It is issued by the manufacturer of the MS.

SP ： Not used.

IMEI: International Mobile Station Equipment Identification


Contents Contents



GSM Network ComponentsGSM Network Components


Radio Technologies


PSTNPSTN

OtheOther r

GSM GSM

OMCOMC

GSM network architectureGSM network architecture

Permanent data:Permanent data:

-IMSIIMSI

-Suppl. service info .Suppl. service info .

-Authentication key Authentication key

-Roaming & billing info Roaming & billing info

Temporary data:Temporary data:

-MSC/VLR address-MSC/VLR address

Temporary data:Temporary data:

-copy of most of data for -copy of most of data for active subscribers in VLR active subscribers in VLR coverage coverage

-Mobile status-Mobile status

-LAI-LAI

-TMSI-TMSI

Mobile Station : - Mobile Equipment contains IMEI for ME identification Mobile Station : - Mobile Equipment contains IMEI for ME identification - Subscriber Identity module contains IMSI,TMSI,LAI,Auth. key - Subscriber Identity module contains IMSI,TMSI,LAI,Auth. key

Base Transceiver Station : the first access point for mobile stations to access the Base Transceiver Station : the first access point for mobile stations to access the network. The BTS is a radio equipment (transceivers & antennas) needed to serve network. The BTS is a radio equipment (transceivers & antennas) needed to serve each cell in the network. each cell in the network.

Base Station Controller : controls one or more BTSs and interfaces BSS to NSS. It is Base Station Controller : controls one or more BTSs and interfaces BSS to NSS. It is a high capacity switch that provides handover, cell configuration data. a high capacity switch that provides handover, cell configuration data. Mobile Switching Center : controls one or more BSCs and manages switching Mobile Switching Center : controls one or more BSCs and manages switching

White list :White list :

Valid mobiles Valid mobiles

Black list :Black list :

Stolen or forbidden Stolen or forbidden

Gray list :Gray list :

Faulty mobilesFaulty mobiles


Subscriber Identity Module – SIMSubscriber Identity Module – SIM

NSS MS

Authentication Process

Air interface

HLR AUC SIM

BSS

Authentication Algorithms





Transcoder and submultiplexerTranscoder and submultiplexer

30 x 64k voice channels = 120 x 16k compressed/combined = 2Mbps PCM link


Mobile to Landline callMobile to Landline call

MS BSS MSC VLR HLR CHANNEL REQUEST <RACH>

<AGCH>DCCH ASSIGN

<SDCCH>

SIGNALING LINK ESTABLISHED

REQ. FOR SERVICECR

CC

AUTHENTICATION

SET Cipher MODE

SET-UP <SDCCH>

Call Info EQUIP. ID REQ.

COMPLETE CALL

CALL PROCEEDING <SDCCH>

PSTN

SFOC

services Auth.


Mobile to Landline callMobile to Landline call

ASSIG. COMMAND<SDCCH>

ASSIG. COMPLETE

Address Complete(ACM)

Alerting

<FACCH>

Answer (ANS)Connect

TCH connect

<TCH>

Initial and Final Address Message (IAM)

MS hears ring tone from land phone

<FACCH>

Ring tone stops

MS BSS MSC VLR HLR PSTN

Connect Acknowledge<FACCH>

BILLINGBILLING

ISUP (IAM)ISUP (IAM)

(ACM) (ACM)

+ alerting + alerting

ANSANS

Conn.

Conn. ack


Contents Contents



GSM Network ComponentsGSM Network Components


Radio TechnologiesRadio Technologies


On completion of this section you will be able to know about the following radio technologies :

VAD, DTX, DRX

Diversity

Frequency Hopping



Battery LifeBattery Life

Power ControlPower Control

Voice Activity Detection – VAD

Discontinuous Transmission – DTX

Discontinuous Reception – DRX


VAD & DTXVAD & DTX

Encoding the speech silences at a rate of 500 bit/s rather than the full 13Kb/s.

If the mobile does not transmit during ‘silence’ there is a reduction in the overall power output requirement

Without DTX

With DTX

Comfort Noise


DRXDRX

PCH is structured so that MS knows when it needs to check for a paging signal. In the time between paging signals, the mobile can go into sleep mode, when almost no power is used.

P P P P P P BCCH P P

BCCH Multiframe P = Paging Channel

MS Being paged

MS in listen mode

MS receive System

information

MS in listen mode


DiversityDiversity

When diversity is implemented two antennas are situated at the receiver. These antennas are placed several wavelengths apart to ensure minimum correlation between the two receive paths.

The two signals are then combined, this ensures that a low signal strength is less likely to occur.

Compare oradd signals

Resultant Signal

Approx. 10 wavelengths


Frequency HoppingFrequency Hopping

Synthesizer Hopping:each timeslot on a given transceiver can transmit at a different frequency

Baseband Hopping: each transceiver stays at the same frequency and the data is switched to the appropriate transceiver.

Each time the BTS or mobile transmits a burst, it does so on a different RF carrier frequency.

time

frequency


Subscriber Identity Module – SIMSubscriber Identity Module – SIM

GSM Fundamentals

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