Gsm Architecture

GSM ARCHITECTURE Operator OMS External networks

BSS

NSS

MS

GSM User

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

External networks ÅÆ NSS ÅÆ BSS ÅÆ MS ÅÆ Users Fahreddin Sadıkoğlu

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PSTN PSTN ISDN ISDN

AS AS VLR VLR

PSDN PSDN

HLR HLR

NSS EIR EIR

MSC MSC

PLMN PLMN

OMS OMS Asub interface BSC BSC

BSS

Abis interface BTS BTS Um interface

MS

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SIM

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BSS components and interfaces BTS

OSS BTS BSC BTS

NSS Asub interface

Abis interface Radio interface (Um)

Message Signalling

Figure 4.12

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Base Station TRXn . BSC

. TRX2 TRX1

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BLOCK DIAGRAM OF A BASE STATION A-bis 64 kbits

Receiver

A

Speech 8/13 bit Codec 13/8 bit

Equalizer Mod./Dem.

D

A law 13 kbits

VCO Synthesizer

Control Unit

64kbits

Channel Codec

Signaling 16 kbits

Transmitter

A D

Burst building Multip./Dem. BTS

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Speech 8/13 bit Codec 13/8 bit

64 kbits

BSC

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Radio Frequency channels for GSM D900 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

CHANNEL DISTRIBUTION FOR D900 Uplink 001

002

Downlink 123

890 890.2

124

914.8 915

001

002

935 935.2

123

124

959.8 960

200 kHz Channel spacing Duplex spacing 45 MHz Fahreddin Sadıkoğlu

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GSM EXTENDED BAND (E-GSM 900) 880-915 MHz for uplink ; 925-960 MHz for downlink With FDMA 124 (174 for extended band ) Fup(n)=(890+0.2 x n)MHz (with ARFCN 0≤n≤124 ) and fup(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

GSM 1800 1710-1785 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 Fahreddin Sadıkoğlu

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GSM FRAME STRUCTURE Hyper Frame

0

2047

1

Duration 3.48 s 0

Super Frame

42

1

43

44

45

46

47

48

49

50

Duration 6.12 s Multiframe

0 0 3

Time Slot

ST

17

1 1

2

3

57 Data

4 1

18

5

6

26 Training

S

19

20

21

22

23

24

1

57 S

Data

3

25

Duration 120 ms

1250 bits; Duration 4.615ms

7

24

8.25

SP

156.25 bits

G

ST:Start Bits S:Stealing Bit SP:Stop Bits G:Guard Bits

Duration 0.57692 ms

Normal burst 3

TB

57

1

Data SF

26

T

1

57

SF

Data

3

8.25

TB G

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TB:Tail Bits S:Stealing Bit SP:Stop Bits G:Guard Bits

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Control Channels

CCH ( Control Channels )

DCCH

SDCCH

FACCH

BCCH

ACCH

SACCH

BCCH

Synch.

SCH

FCH

CCCH

RACH

CBCH

PCH/AGCH Fahreddin Sadıkoğlu

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GSM PHYSICAL LAYER

Microphone ADC

Microphone ADC

LPC-PEA

Linear Predictive cooding Rgular Pulse Excitation Analysis Long-Term Prediction

Shufling Interleaving

Decreases possibility of distortion of consecitive bits in radio channel

Speech coding

Channel cooding

Cyclic and Convolutional codes for error detection and correction purpose

Ciphering

Is used to protect data Ki+Rand A8 Kc

Modulation

GMSK

Speech Decoding

DeShufling DeInterleaving Channel decooding

Deciphering

Demodulation

Channel Fahreddin Sadıkoğlu

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Speech and Channel Coding 0.3-3.4 kHz

BPF

M

fs =8kHz; 13 bits 104 kbs

A

Speech Encoder

D

13kbs

To Modulator Channel Coding

22.8 kbs

From Demodulator LPF

A

Speech Decoder

D

Speech Block Filters

1 5 . 37

1 2 3 4

2 6 . 38

Every 20 ms 160 samples

3 7. 39 4 8. 40

Channel Decoder

Encoder Selection Sequence with maximal energy

Linear Predictive Coding and Regular Pulse Extantion –LPC/RPE

Channel Cyclic Coding For error detection

189 bits

Si

Correlation analysis C(Si, Si-k)=max Β= Si-Si-k

Β

Long Term Prediction-LTP

Encoder Convolutional Coding for 1 bit error correction

456 bits

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Reordering Restructuring Interliving 11

GMSK MODULATION Sin 2πfct I(t) COS(c(t)) d(t)

Integrater

di(t)

Gaussian Filter

X

+

C(t) Q(t) Sin(c(t))

m(t)

X Cos 2πfct

I ( t ) = cos( c ( t ));

Q ( t ) = sin( c ( t ))

m ( t ) = I ( t ) sin 2 π fct + Q ( t ) cos 2 π fct

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AUTHOINTICATION MS Network

Um Interface

MS

SRES

Rand

Ki A3 Algorithm

=? SRES

Yes/No

DATA CIPHERING Ki

MS

MS Kc

Rand A8

Data

A5

Network

Um Interface Kc Cipherd Data

A5

Data

Kc Fahreddin Sadıkoğlu

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Convolutional Coding

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

Before an MOC begins a location registration and with it an authentication must have taken place.The MS sends the 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.

Calling subscriber MS 1

Called subscriber BSS

BTS/BSC/TRAU

1 VLR

2

NSC MSC

3

PSTN PST N PLMN

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Figure 4.16

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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.

MS2

MS1

Called subscriber

Calling subscriber

1

8 7

1 BTS/BSC/TRAU

BTS/BSC/TRAU

8

9

BTS/BSC/TRAU 8

BSS

7

9

1 MSC 2 3

VLR 4

NSC

6 5 5

HLR

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PLMN

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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 called subscriber 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 .

Called subscriber

MS 8

7

BTS/BSC/TRAU

BTS/BSC/TRAU 7

4

8

7

VLR

6

3 VLR

9

9

BTS/BSC/TRAU 7

BSS NSC

MSC 5

2

GMSC

Calling subscriber

1

4 PLMN

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