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External networks NSS BSS MS Users
Mobile Station (MS),
Base Station Subsystem (BBS),
Network and Switching Subsystem (NSS),
Operation Management Subsystem (OMS).
BSS NSS
OMS
GSM
MS External
networks
User
Operator
GSM ARCHITECTURE
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OMS
MSC
EIR VLR
AS PSTN
ISDN
PSDN
PLMN
NSS
BSS
HLR
BTS
BSC
MS SIM
Um interface
Abis interface
Asub interface
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BTS
BSC
NSS
OSS
Figure 4.12
Message
Signalling Radio interface
(Um)
Abis interface
Asub interface
BTS
BTS
BSS components and interfaces
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BSC
TRXn
.
.
TRX2
TRX1
Base Station
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VCO Synthesizer Channel Codec Signaling
Transmitter A
D
Receiver A
D Equalizer
Mod./Dem.
Speech 8/13 bit
Codec 13/8 bit
Burst building
Multip./Dem.
Speech 8/13 bit
Codec 13/8 bit
Control
Unit
13 kbits
16 kbits
64kbits
64 kbits
64 kbits
A law
A-bis
BTS BSC
BLOCK DIAGRAM OF A BASE STATION
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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
890 890.2 914.8 915 935 935.2 959.8 960
200 kHz Channel spacing
Duplex spacing 45 MHz
Uplink Downlink
001 002 123 124 001 002 123 124
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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
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
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3 57 1 26 1 57 3 8.25
156.25 bits
Duration 577 µs
(156x3.9 µs )
Duration 120 ms
Duration 6.12 s
Duration 3.48 hours
0 1 2047
0 1 50 49 48 47 46 45 44 43 42
Hyper Frame
Super Frame
0 1 17 18 19 20 21 22 23 24 24 Multiframe
0 1 2 3 4 5 6 7 1250 bits;
Duration
4.615ms
25
Time Slot ST Data S Training S Data SP G
ST:Start Bits (Tailing bits-000)
S:Stealing Bit
SP:Stop Bits (Tailing bits-000)
G:Guard Bits
ST Data S T S Data SP G
3 57 1 26 1 57 3 8.25
GSM FRAME STRUCTURE
Normal burst
Frame
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CCH
( Control Channels )
DCCH
SDCCH ACCH
FACCH SACCH
CCCH
RACH CBCH
PCH/AGCH
BCCH
BCCH Synch.
SCH FCH
Control Channels
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Speech coding
LPC-PEA
Shufling
Interleaving
Linear Predictive cooding
Rgular Pulse Excitation
Analysis
Long-Term Prediction
Microphone
ADC
Channel cooding
Ciphering
Modulation
Speech Decoding
DeShufling
DeInterleaving
Microphone
ADC
Channel decooding
Deciphering
Demodulation
Channel
Is used to protect data
Ki+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
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Speech and Channel Coding
Linear Predictive Coding and Regular Pulse Extantion –LPC/RPE Long Term Prediction-LTP
A
D
BPF Speech
Encoder
Channel
Coding
A
D
LPF Speech
Decoder
Channel
Decoder
M
To Modulator
From Demodulator
0.3-3.4 kHz fs =8kHz;
13 bits 104 kbs
Block Filters
1
2
3
4
Selection
Sequence with
maximal energy
1 5 . 37
2 6 . 38
3 7. 39
4 8. 40
Every 20 ms
160 samples
13kbs 22.8 kbs
Correlation
analysis
C(Si, Si-k)=max
Β= Si-Si-k
Β Si
Speech Encoder
Channel Encoder
Cyclic Coding
For error
detection
Convolutional
Coding for 1 bit
error correction
189
bits
456
bits
Reordering
Restructuring
Interliving
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GMSK MODULATION
Integrater Gaussian
Filter
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 2cos)(2sin)()(
))(sin()());(cos()( tctQtctI
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AUTHOINTICATION MS
DATA CIPHERING
MS Network Um Interface
A3 Algorithm
Rand Ki
=?
SRES
SRES
Yes/No
A8
Rand
Ki
Kc
A5
MS
Data
Kc
A5
Kc
Data Cipherd
Data
Network Um
Interface
MS
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Convolutional Coding
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Functional Sequence of Basic Call Types
Mobile Originated Call (MOC) to the fixed network
Figure 4.16
1
VLR 2
PST
N
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 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.
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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.
3 VLR
4
8 9
MS1
Calling
subscriber
6 2
5
5
HLR
MSC
7 9 8 8
7
BTS/BSC/TRAU BTS/BSC/TRAU
Called
subscriber
BTS/BSC/TRAU
BSS
NSC
MS2
PLMN
1
1
1
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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 .
8 9 7
5
GMSC
MSC
VLR
VLR 6
4
4 3
1 2
BTS/BSC/TRAU BTS/BSC/TRAU BTS/BSC/TRAU
7 7 9 8 7
MS
BSS
NSC
Called
subscriber
PLMN
Calling
subscriber
