gsm technology - standards & implementation

7/30/2019 GSM TECHNOLOGY - Standards & Implementation

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10/4/99 1Company Confidential

GSM900DCS1800

GSM TECHNOLOGY -Standards & Implementation


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Introduction to Cellular


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Omni-directional Cell

BTS

Sectorial Cell

BTS

Cell Configuration


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GSM uses concept of cells

One cell covers small part of network

Network has many cells Frequency used in one cell can be used

in another cells This is known as

F=1F=2

F=3

F=4,8F=5,9

F=6,10F=7

F=1F=2

F=3F=4,8

F=5,9F=6,10

F=7F=1

F=2F=3

F=4,8F=5,9

F=6,10

F=7

F= 1,2,3,4,5,6,7,8,9,10

Clusters

Co-Channel ( Re-use ) Cells

Frequency Reuse


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MS

BTS

BTS

BTS

BTSBTS

BTS

BTS

BTS

BSC

BSC

PSTN

VLR

TRAUHLR

EIR

OMC

SMSC

BC

AUC

VMSC

MSC

A

OML

GSM Network Architecture


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MSISDN : Human Identity used to call a Mobile Station

IMEI: Serial number unique to every Mobile Station

IMSI : Network Identity unique to a SIM

3 digits 2 digits 10 digits

TMSI : Identity unique in a LAI

MSRN : Mobile Station Roaming No

CC NDC SN

98 XXX 12345

MCC MNC MSIN

404 XX 12345

TAC FAC SNR S

6 digits 2 digits 6 digits 1 digit

Mobile Station Identities


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VLR

HLR/AUC

EIR

PSTN GMSC GSMSC

VLR

HLR/

AUC

Abis A

BC

F

E

G

D

SS7/R2

MSCBSC

BTSOML

OMC

A,B,C,D,E,F,G,H,I = SS7Abis = LAPDOML = X.25

SUPPI

H

GSM Signaling Interfaces


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Separate Bands for Uplink and Downlink Down link : 935 - 960 MHz ( E-GSM 925 - 960 MHz )

Uplink : 890 - 915 MHz ( E-GSM 880 - 915 MHz)

TDMA and FDMA Multiplex 124 Frequency Channels (ARFCN) for GSM900

1 to 124 for current band

975 to 1023 for E-GSM

200kHz Channels

8 Mobiles share ARFCN by TDMA

0.3 GMSK Modulation 270.833 kbits/sec. rate

Variable Tx Power and Timing

GSM Air Interface


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Time

Frequency

Amplitude

The GSM Burst


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20ms

Speech Coder

260 bits

50 132 78

1a 1b 11

Channel Coder

456 bits

13 kbps

22.8 Kbps

Tranceiver ( BTS )

22.8 Kbps

456 bits

260 bits13 kbps

Transcoder Handler

260 + 60 = 320 bits16 kbps

TRAU Frame

Abis

Speech coding Process


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UPLINK

ADJACENTCELL

BCH

DOWNLINK

RXLEV RXLEV RXLEV RXLEV RXLEV

Measuring Adjacent Cell BCH Power


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Mobile is commanded to change its Transmit Power

Change in Power is proportionate to the Path Loss Change is Power is done in steps of 2 dbs

Tx Level5

67.

14

15

Power dBm33

3129.

15

13

Mobile Power Control


13/24


TDMA approach requires signals to arrive at BTS at the correct

time. They must not overlap

BTS

Timing Advance


14/24


ARFCN

( 200Khz )

BCCH

FCH

SCH

Broadcast Channel

SDCCH

SACCH

FACCH

Dedicated Control Channel

PAGCH

AGCH

RACH

CBCH

NCH

Common Control Channel

Control Channel

Full Rate TCH Half Rate TCH

Traffic Channel

Logical Channels

Physical Channel

Logical Channels

TO

C T T T T T T T

T1 T2 T3 T4 T5 T6 T7

Physical and Logical Channel


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Traffic Channels

Traffic Channels carry either encoded speech or user data Two forms of Traffic Channels are defined :

-- Full rate Traffic Channel : Carries encoded information at gross rate of 22.8Kbps

-- Half rate Traffic Channel : Carries encoded information at gross rate of 11.4 Kbps

Speech Traffic Channels

Full rate Traffic Channel for speech : Speech out of encoded information is at 13 kbpsHalf rate Traffic Channel for speech : Speech out of encoded information is at 6.5 kbps

Data Traffic Channels

Full rate Traffic Channel for 9.6 kbps user data

Full rate Traffic Channel for 4.8 kbps user data

Full rate Traffic Channel for < 2.4 kbps user data

Traffic Channels Modes

Circuit Switching mode ( transparent connection to a service like telephony ) Packet Swithching mode ( as per recommendation X.25 or other standardised protocols)

Logical Channels


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Broadcast Channels ( BCH )

Frequency Correction Channels ( FCCH ) :

Carries Information for frequency correction of the mobile stations. ( Downlink )

Synchronisation Channels ( SCH ) :

Carries information for frame synchronization of the mobile stations and identification of BTS( Downlink )

Contains two pieces of information : BSIC & Reduced Frame Number *

Broadcast Control Channels ( BCCH ) :

Broadcasts various cell parameters and other information required by the mobile to access

the network. ( Downlink)

Logical Channels


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Broadcast Channels ( BCH )

0 1 2 3 4 5 6 7FCCH

SCHBCCHBCCHBCCHBCCHCCCHCCCHCCCHCCCHFCCHSCH

I

TN

FCCH & SCH occurs every 10th frame

BCCH is send in block of 4 frames

BCCH block occurs once in 51 frames

FN 0

FN 10

FN 11

FN 51

Logical Channels


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Common Control Channels

Paging Channel ( PCH ) :

Used to page Mobiles ( Downlink )

Access Grant Channel ( AGCH ) :

Used to for allocation of a dedicated channel ( SDCCH ) ( Downlink )

Random Access Channel ( RACH ) :

Used to request allocation of dedicated channel ( SDCCH ) ( Uplink )

Logical Channels


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CCCH is configured

to AGCH & PCH

either dynamically

or through O & M

AGCH & PCH also

occurs in block of 4

No of AGCH & PCH

in one Multiframe

depends on channelcombinations

FCCH

AGCH

AGCH

AGCH

AGCH

FCCH

SCH

PCH

PCH

PCH

PCH

PCH

PCH

PCH

PCH

FN 0

FN 10

FN 11

FN 51

FN 12

FN 19

0 1 2 3 4 5 6 7

RACHFN 0

FN 51

0 1 2 3 4 5 6 7

DownlinkUplink

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

RACH

Logical Channels


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Dedicated Control Channels

Standalone dedicated control channel ( SDCCH ) :

Used for conveying signaling information ( Downlink & Uplink )

Slow Associated Control Channel ( SACCH ) :

Used for conveying slow information associated with SDCCH

and TCH ( Downlink and Uplink )

Fast Associated Control Channel ( FACCH ) :

Associated with TCH for conveying fast signaling information

( D & U )

Cell Broadcast Control Channel ( CBCH ) :

Subset of SDCCH used for broadcasting cell broadcastmessages ( Downlink )

Logical Channels


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B + D

Mapping of Channel Combinations using Multiframe Concept

F S B C F S C C F S D0 D1 F S D2 D3 F S A0 A1 I

50Downlink0

TN=0F S B C F S C C F S D0 D1 F S D2 D3 F S A2 A3 I

D3 R R A2 A3 R R R R R R R R R R R R R R R R R R R R R R R D0 D1 R R D2

50

D3 R R A0 A1 R R R R R R R R R R R R R R R R R R R R R R R D0 D1 R R D2

0 Uplink

B

F S B C F S C C F S C C F S C C F S C C ITN=00 Downlink 50

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 RR R R R R R R R R R R R R R R R R R R R

500

TN=0

Uplink

Mapping of Logical channels on PCHN


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B + C

I I B C I I C C I I C C I I C C I I C C ITN=0

0 Downlink 50

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 RR R R R R R R R R R R R R R R R R R R R

500

TN=2,4,6

Uplink

D

I

50Downlink0

Uplink

D1 D2 D4 D5 D7 A0 A2 A3D0 D3 D6 A1 I I

ID1 D2 D4 D5 D7 A4 A6 A7D0 D3 D6 A5 I ITN=0

IA6 A7 D1 D2 D4 D5 D7 A0A5 D0 D3 D6I I

IA2 A3 D1 D2 D4 D5 D7 A4A1 D0 D3 D6I ITN=0

0 50



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T

T T T T T T T T T T T T A T T T T T T T T T T T T I

250

TN=0

Downlink

Uplink

T T T T T T T T T T T T A T T T T T T T T T T T T I

250



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1 Burst = 577usecs

0 1 2 3 4 5 6 71 TDMA Frame = 8 bursts = 4.616 ms

Multiframe

1 TCH Multiframe = 26 TF = 120ms 1 CCH Multiframe = 51 TF = 234.6ms

0 1 2 3 2044 2045 2046 2047

1 Hyperframe = 2048 Superframes = 2715648 TDMA Frames

= 3 hrs 28 min 53 sec 760 ms

0

01

1

2

2

4823

49

24

50

25

0 1 2 23 24 25 0 1 2 48 49 50

1 Superframe = 26 CCH MF = 1326 TF = 6.12 sec1 Superframe = 51 TCH MF = 1326 TF = 6.12 sec

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