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Intorduction to GSM Air interface. Channels transport on air interface.
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GSM-GPRS Operation
GSM Air Interface
Module 2
Outline
Introduction & Review GSM Frequency Band GSM Channel Numbering Physical Channel Logical Channel Mapping Logical Channel on to Physical
Channel
Air Interface = Um Interface
Major problems at air interface In GSM network, it is about Um interface
Air interface
Arsitektur Jaringan GSM
Mobileterminal device
BSSBase StationSubsystem
NSSNetwork Switching
Subsystem
control/switching ofmobile services
BSSBase StationSubsystem
BSSBase StationSubsystem
PLMNPublic Land Mobile Network
PSTNPublic Switched
Telephone Network
ISDNIntegrated Services
Digital Network
PDNPublic Data
Network
MSMobileStation
Mobilecomponents
Fixed networkcomponents
UmAir Interface
Fixednetwork
GSM 900 MHz Frequency Band
200 kHz
CH 1 CH 2
CH 124
200 kHz
CH 1 CH 2
CH 124
890 915 MHzUplink
MS Transmit Band
25 MHz
935 960 MHzDownlink
MS Transmit Band
25 MHz
Penomoran Kanal GSM GSM900
FU(n) = 890 + 0.2n (MHz)FD(n) = Fu(n) + 45 (MHz) 1 n 124
E-GSM900FU(n) = 890 + 0.2(n-1024) (MHz) 974 n 1023FD(n) = Fu(n) + 45 (MHz)
GSM1800Fu(n) = 1710.2 + 0.2(n-512) (MHz)
FD(n) = FU(n) + 95 (MHz) 512 n 885
374 channels
n disebut Absolutely Radio Frequency Channel Number (ARFCN)
GSM Frequency Allocation In Indonesia
SATELINDO (INDOSAT) : 890 – 900 MHz (10 MHz)
TELKOMSEL : 900 – 907 MHz (7.5 MHz)
EXCELKOMINDO : 907.5 – 915 MHz (7.5 MHz)
GSM : [890+nx0.2] MHz up to 915MHzDCS 1800 : [1710+nx0.2] MHz up to 1785MHz
890 915
Tx
Indosat Telkomsel Excelcomindo
900
Operators share bandwidth
Frequency Allocation Per-Cell
1 2 3 4 5 6 7
1710 1732
f
Selanjutnya...bandwidth displit di dalam sel-sel
1
1
23
2
4
5
6
7
3
4
5
6
71
Spesifikasi RF
F1 F2 F1' F2'
Frequency
1
2
3
4
5
6
7
8
45 MHz
BS Transmission Band : 935 – 960 MHZ
MS Transmission Band : 890 – 915 MHZ
Year Introduced 1990
Access method TDMA
Channel Bandwidth
200 kHz
Number of duplex channels
125
Users per channel 8
Speech coding bit rate
13 kbps
Data coding bit rate
12 kbps
Frame size 4.6 ms
GSM-GPRS Operation
Kanal Fisik
TDMAframe4.615ms
time
TS4
TS5
TS6
TS7
TS0
TS1
TS2
TS3
Frequency [MHz]
••• •••
Duplex distance: 45 MHz
200 kHz
Example:GSM900
890 915 935 960
UL DL
TS577s
Physical channel (Um)Physical channel (Um)
Radio Interface (Layer 1)
Struktur Sinyal GSM GSM carrier selebar 200 kHz. Pada arah downlink BTS,
timeslot berbeda digunakan untuk masing-masing MS – MS mendengar hanya pada TS yg dialokasikan untuknya Pada TS yg tidak digunakan,
MS dapat menggunakannya utk pengukuran sinyal berguna utk Handover
Pada arah uplink, MS transmit hanya pada timeslot yg dialokasikan untuknya Transmit MS terjadi berbeda 3
TS dari TS transmit BTS untuk mencegah transmit-terima simultan pada MS (membutuhkan duplekser)
3 timeslot
Adaptive frame alignment:Mencegah pengiriman/penerimaan
secara bersamaan/simultanUL/DL di delay 3 TS
76543210
76543210 DL
UL
Timing Advance TA: Kompensasi delay propagasi
BTS memerintahkan MS mengirim lebih lambat:2 x waktu propagasi MS - BTS
Adaptive Frame Alignment / Timing Advance (TA)
TDMAframe
Frames
RFC3
RFC2
RFC1
01234567
012345
202122232425
4344454647484950
Time
RFC124
Frequency
0
1
2
3
4
5
6
7Time
FDMA
UserTraffic
Signaling
cyclical repetitionof certain contents
cyclical repetitionof certain contents
• TDMA-• Multi-• Super-• Hyper-
Multi-Frames
Konsep Frame
1 Signalling Multiframe =51 TDMA frames 235,4 ms
1 TCH Multiframe =26 TDMA frames = 120 ms
TimeStructure Hyperframe =
2048 Superframes 3h 29 min
0 1 2 3 4 5 6 7
0 1 2 3 24 25 0 1 2 3 49 50
0 1 2 3 4950
0 1 2 3 24 25
1 Superframe =51 x 26
TDMA frames 6.12 ms
Numbering Periode.g. repetition of • frequency hopping• ciphering
Channel organisationscheme
Repetition schemefor TCH / Signalling
BURST = TS content
1 TDMA frame= 8 TS = 4,615 ms
1 Burst = 156,25 bit = 576,88 us(1 bit = 3,6923 us)
GSM-GPRS Operation
Kanal Logik
GSM-GPRS Operation
Mapping Kanal Logik ke Kanal Fisik
Kanal logik GSM harus dipetakan ke kanal fisik, artinya : informasi pada kanal logik harus ditempatkan pada kanal fisik dengan format burst tertentu untuk ditransmisikan
Analogi pemetaan kanal logika pada kanal fisik...
Tipe burst pada kanal fisik dapat dianalogikan sebagai ‘tipe gerbong’ pada rangkaian kereta api. Orang makan malam berada pada gerbong restorasi. Demikian pula pada kanal logik, penempatan kanal logika pada ‘gerbong’ burst tergantung dari fungsi kanal logik tersebut beserta sifat-sifat fisisnya.
FCCH BurstSCH Burst
SynchronizationChannel
FrequencyCorrectionChannelDedicated
ControlChannels
TrafficChannel
Normal Burst
Mapping
FCCH BurstSCH Burst
SynchronizationChannel
FrequencyCorrectionChannelDedicated
ControlChannels
TrafficChannel
Normal Burst
Kanal RF selebar 200 kHz Rel kereta
Kanal logik Isi gerbong kereta
Kanal fisik (timeslot) Gerbong kereta
Burst Tipe/jenis gerbong
Kasus analogi di GSM
Mapping
512 513 514 808 809 810
299 200kHz Radio Channels
FDMA
FDD
0 1 2 5 6 7
8 0.57ms Time Slots
3 4TDMA{
Burst - Transmission Quantum in GSM
1 Frame
Burst Burst Burst Burst Burst Burst Burst Burst
Frame Train on Frequency Track…an analogy
For GSM 1900... U D
60 MHz 60 MHz
ARFCNNumbers
Multiplexing
Membutuhkan sinkronisasi yg sangat tepat!!
TB3
Information57
S1
Training Seq.26
S1
TB3
GP8.25
Information57
0 1 2 3 4 5 6 7
RFC1
RFC2
RFC3
RFCi
RFC123
RFC124
••• •••
UL: 890 MHz 915 MHz
FDMA
GMSKModulation 200 kHz
270.833kbit/s
TDMA
1 TDMA Frame: 4.615 ms / 1250 bit
1 TS: 33.85 kbit/s
1 Normal Burst: 576.9 s / 156.25 bit
1 Bit = 3.6923 s
24.7 kbit/s = 22.8 kbit/s TCH data (incl. redundancy) + 0.95 kbit/s SACCH + 0.95 kbit/s “Idle”
Physical Channel / GSM Data Rates
GSM-GPRS Operation
End of Section 2
GSM Air Interface
