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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).
BSSNSS
OMS
GSM
MSExternalnetworks
User
Operator
GSM ARCHITECTURE
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OMSOMS
MSCMSC
EIREIRVLRVLR
ASASPSTNPSTN
ISDNISDN
PSDNPSDN
PLMNPLMN
NSS
BSS
HLRHLR
BTSBTS
BSCBSC
MS SIMUm interface
Abis interface
Asub interface
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BTS
BSC NSS
OSS
Figure 4.12
Message
SignallingRadio 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 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
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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 960200 kHz Channel spacing
Duplex spacing 45 MHz
Uplink Downlink
001 002 123 124 001 002 123 124
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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
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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
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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 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
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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
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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 ==
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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
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Convolutional Coding
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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.
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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
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
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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 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