Modul 2 gsm air interface

GSM-GPRS Operation

GSM Air Interface

Module 2

kris.sujatmoko@gmail.com 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

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

Indosat Telkomsel Excelcomindo

Operators share bandwidth

Frequency Allocation Per-Cell

1 2 3 4 5 6 7

1710 1732

Selanjutnya...bandwidth displit di dalam sel-sel

Spesifikasi RF

F1 F2 F1' F2'

Frequency

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

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

Frequency [MHz]

••• •••

Duplex distance: 45 MHz

200 kHz

Example:GSM900

890 915 935 960

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

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

01234567

012345

202122232425

4344454647484950

RFC124

Frequency

UserTraffic

Signaling

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

Logical Channel

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

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!!

Information57

Training Seq.26

GP8.25

Information57

0 1 2 3 4 5 6 7

RFC123

RFC124

••• •••

UL: 890 MHz 915 MHz

GMSKModulation 200 kHz

270.833kbit/s

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

Modul 2 gsm air interface

Education

GSM DIALLER AND INTERFACE INTERFACE Y AVISADOR TELEFONICO

GSM Air Interface - Mpirical

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