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
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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
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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
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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
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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
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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
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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
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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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