Gsm Call Sequence

Fahreddin Sadıkoğlu 1

External networks NSS BSS MS Users

Mobile Station (MS), Base Station Subsystem (BBS), Network and Switching Subsystem (NSS), Operation Management Subsystem (OMS).

BSSNSS

OMS

GSM

MSExternalnetworks

User

Operator

GSM ARCHITECTURE


OMSOMS

MSCMSC

EIREIRVLRVLR

ASASPSTNPSTN

ISDNISDN

PSDNPSDN

PLMNPLMN

NSS

BSS

HLRHLR

BTSBTS

BSCBSC

MS SIMUm interface

Abis interface

Asub interface


BTS

BSC NSS

OSS

Figure 4.12

Message

SignallingRadio interface (Um)

Abis interface

Asub interface

BTS

BTS

BSS components and interfaces


BSC

TRXn

.

.TRX2

TRX1

Base Station


VCO Synthesizer Channel Codec

Signaling

Transmitter AD

Receiver AD

EqualizerMod./Dem.

Speech 8/13 bitCodec 13/8 bit

Burst buildingMultip./Dem.

Speech 8/13 bitCodec 13/8 bit

ControlUnit

13 kbits

16 kbits

64kbits

64 kbits

64 kbits

A law

A-bis

BTS BSC

BLOCK DIAGRAM OF A BASE STATION


890-915 MHz for uplink, MC to BS

935-960 MHz for downlink, BS to MS

fup(n)=(890+0,2xn) MHz (with,ARFCN 1≤n≤124)

fdown(n)=fup(n)+45MHz

Radio frequency channel spacing: 200 kHz; Duplex spacing: 45 MHz

Radio Frequency channels for GSM D900

CHANNEL DISTRIBUTION FOR D900

890 890.2 914.8 915 935 935.2 959.8 960200 kHz Channel spacing

Duplex spacing 45 MHz

Uplink Downlink

001 002 123 124 001 002 123 124


GSM 18001710-1785 MHz for uplink; 1805-1880 MHz for downlink

Duplex spscing is 95 MHz with 374 channels 200 kHz spacing

Numberd with 512-885

fup(n)=(1710+0,2xn) (n-511) (with,ARFCN 512≤n≤885

fdown(n)=fup(n)+95MHz

GSM EXTENDED BAND (E-GSM 900)

880-915 MHz for uplink ; 925-960 MHz for downlinkWith FDMA 124 (174 for extended band )

Fup(n)=(890+0.2 x n)MHz (with ARFCN 0≤n≤124 ) andfup(n)=(890+0,2xn) (n-1024) (with ARFCN 975≤n≤1023)

fdown (n)=fup (n)+45 MHz

Radio frequency channel spacing: 200 kHz; Duplex spacing: 45 MHz


3 57 1 26 1 57 3 8.25

156.25 bits

Duration 0.57692 ms

Duration 120 ms

Duration 6.12 s

Duration 3.48 s0 1 2047

0 1 504948474645444342

Hyper Frame

Super Frame

0 1 17 18 19 20 21 22 23 24 24Multiframe

0 1 2 3 4 5 6 71250 bits; Duration 4.615ms

25

Time Slot ST Data S Training S Data SP G

ST:Start BitsS:Stealing BitSP:Stop BitsG:Guard Bits

TB Data SF T SF Data TB G

3 57 1 26 1 57 3 8.25 TB:Tail BitsS:Stealing BitSP:Stop BitsG:Guard Bits

GSM FRAME STRUCTURE

Normal burst


CCH ( Control Channels )

DCCH

SDCCH ACCH

FACCH SACCH

CCCH

RACH CBCH

PCH/AGCH

BCCH

BCCH Synch.

SCH FCH

Control Channels


Speech codingLPC-PEA

ShuflingInterleaving

Linear Predictive coodingRgular Pulse Excitation

AnalysisLong-Term Prediction

MicrophoneADC

Channel cooding

Ciphering

Modulation

Speech Decoding

DeShuflingDeInterleaving

MicrophoneADC

Channel decooding

Deciphering

Demodulation

Channel

Is used to protect dataKi+Rand A8 Kc

Decreases possibility of distortion of consecitive bits in radio channel

Cyclic and Convolutional codes for error detection and correction purpose

GMSK

GSM PHYSICAL LAYER


Speech and Channel Coding

Linear Predictive Coding and Regular Pulse Extantion –LPC/RPE Long Term Prediction-LTP

AD

BPF SpeechEncoder

ChannelCoding

AD

LPF SpeechDecoder

ChannelDecoder

M

To Modulator

From Demodulator

0.3-3.4 kHz fs =8kHz; 13 bits 104 kbs

Block Filters1234

Selection Sequence with maximal energy

1 5 . 372 6 . 38

3 7. 394 8. 40

Every 20 ms 160 samples

13kbs 22.8 kbs

Correlation analysisC(Si, Si-k)=maxΒ= Si-Si-k

ΒSi

Speech Encoder

Channel EncoderCyclic CodingFor error detection

Convolutional Coding for 1 bit error correction

189bits

456bits

ReorderingRestructuring

Interliving


GMSK MODULATION

Integrater GaussianFilter

COS(c(t))

+

X

X

Cos 2πfct

Sin 2πfct

C(t)

Sin(c(t))

m(t)

Q(t)

I(t)

d(t) di(t)

fcttQfcttItm π+π= 2cos)(2sin)()(

))(sin()());(cos()( tctQtctI ==


AUTHOINTICATION MS

DATA CIPHERING

MS NetworkUm Interface

A3 Algorithm

RandKi

=?SRES

SRES

Yes/No

A8

Rand

Ki

Kc

A5

MS

Data

Kc

A5

KcDataCipherd

Data

NetworkUm Interface

MS


Convolutional Coding


Functional Sequence of Basic Call TypesMobile Originated Call (MOC) to the fixed network

Figure 4.16

1

VLR2

PSTN

3

BTS/BSC/TRAU

MS

BSS

NSC

Calling subscriber

MSC

1

PSTN

Called subscriber

PLMN

Before an MOC begins a location registration and with it an authentication must have taken place.The MS sendsthe call setup information dialed by the mobile subcriber to the MSC (1). The MSC requests call information

from the VLR (mainly about any relevant restictions) concerning the mobile subscriber identified by the IMSI (2). After assigning a traffic channel, the MSC then informs PSTN.


Mobile Internal Call (MIC) The MS1 sends the call setup information dialed by the mobile subscriber (MSISDN) to the MSC (1).The MSC requests informaton about the calling mobile subscriber MS2 from the VLR (2). The MSC

uses the dialling information (MSISDN) to establish the HLR and sets up signalling connection to it (3). The HLR sends a request to the VLR in whose area the called mobile subscriber MS2 is currently roaming (4). The VLR sends the requested MSRN back to the HLR. The HLR forwards the MSRN to the MSC (5). Steps (6) to (9) are the same as steps (6) to (9) in Figure 7.17.

3 VLR

4

8 9

MS1

Callingsubscriber

62

5

5

HLR

MSC

7 988

7

BTS/BSC/TRAU BTS/BSC/TRAU

Calledsubscriber

BTS/BSC/TRAU

BSS

NSC

MS2

PLMN

1

1

1


Mobile Terminating Call (MTC) From The Fixed Network A call for mobile subscriber arrives at the GMSC (1). The GMSC uses the dialing information (MSISDN) to es

tablish the HLR and sets up a signaling connection to it (2). The HLR sends a requested VLR in whose area the calledsubscriber is currently roaming (3). The VLR sends the requested MSRN back to the HLR. The HLR forwards the MSRN

to the GMSC (4). On the basis of the MSRN the GMSC sets up the connection request to the MSC, i.e. the MSC in whose area the mobile subcriber is roaming at this point in time (5).

As the MSC does not know the mobile subscriber up to this point, the MSC requests the mobile subscriber information for the call setup from ıts VLR (6). The MS is now called by means of paging to all BTS/BSCs in the locatıon area, as the radio cell in which the MS is located is not known to the MSC (7). If there is a response to the paging, this information is transmitted to the MSC (8). Finally the connection to the MS is set up (9).Figure7.17 shows the call sequence of an MTC .

8 97

5

GMSC

MSC

VLR

VLR6

4

4 3

12

BTS/BSC/TRAU BTS/BSC/TRAUBTS/BSC/TRAU

7 7987

MS

BSS

NSC

Called subscriber

PLMN

Calling subscriber

Documents

Gsm Call Sequence