Konsep Kanal Fisik Dan Logik Pada GSM

Jaringan Telekomunikasi dan Informasi Konsep kanal fisik dan lojik pada GSM Susmini I. Lestariningati, M.T

Jartelinfo

@lestariningati

GSM: Physical and Logical Channel •

GSM uses a mix of Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA).

•

FDMA parts involves the division by frequency of the 25 MHz bandwidth in to 124 carrier frequencies (Also called ARFCN) spaced 200 KHz for GSM-900. For GSM-1800 frequency spectrum of 75 MHz bandwidth is divided in to 374 carrier frequencies spaced 200 KHz.

•

TDMA further divides each carrier frequencies in to 8 time slots such that each carrier frequency is shared by 8 users.

•

So in GSM, the basic radio resource is a time slot with duration of 577 μs. 8 Time slots of 577 μs constitutes a 4.615 ms TDMA Frame. GSM uses Gaussian Minimum Shift Keying (GMSK) modulation scheme to transmit information (data and signalling) over Air Interface.

Teknik Telekomunikasi

2

Jartelinfo

@lestariningati

Alokasi Kanal MS Transmit Band Uplink

890

BTS Transmit Band 915 MHz

Downlink

935

CH 1 CH 2

CH 1 CH 2

CH 124

CH 124 200 kHz

Teknik Telekomunikasi

960 MHz

200 kHz

3

Jartelinfo

@lestariningati

ARFCN (Absolute Radio-Frequency Number) In GSM cellular networks, an absolute radio-frequency channel number (ARFCN) is a code that specifies a pair of physical radio carriers used for transmission and reception in a land mobile radio system, one for the uplink signal and one for the downlink signal.

ARFCN Table for common GSM systems

Teknik Telekomunikasi

4

Jartelinfo

@lestariningati

Mencari frekuensi uplink dan downlink https://www.cellmapper.net In order to obtain the ARFCN/UARFCN/EARFCN, you will need to enter "Field Test Mode" in your phone. This varies greatly from phone to phone. In general, all involve "calling" certain numbers to bring up the hidden options

Some common ones are:

Samsung (Android): *#*#197328640#*#* or *#0011#

iPhone (all): *3001#12345#*

HTC (Android): *#*#7262626#*#*

Teknik Telekomunikasi

5

Jartelinfo

@lestariningati

https://www.cellmapper.net

Teknik Telekomunikasi

6

Jartelinfo

@lestariningati

Contoh tentang ARFCN

Sumber: https://julitra.wordpress.com/2009/01/24/melihat-kembali-alokasi-frekuensi-operator-gsm/

Teknik Telekomunikasi

7

Jartelinfo

@lestariningati

Standarisasi GSM

Air interface

Air Interface distandarkan! Mobile Station

Vendor bebas mengembangkan handset dengan keunggulan masingmasing selama bisa berkomunikasi melalui interface yang sudah distandarkan

Teknik Telekomunikasi

Base Station Pada GSM adalah sebagaimana berikut

‣ struktur dari TDMA memiliki 8 timeslot per RF carrier

‣ sebesar 0.577 ms per timeslot

‣ Interval frame=8 timeslot = 4.615 ms

‣ menggunakan skema modulasi GMSK, BT = 0.3

‣ Slow frequency Hopping (217 hops/s)

Vendor bebas mengembangkan sub system, misalnya ningkatkan sensitivitas dan sebagainya

8

Jartelinfo

@lestariningati

Spesifikasi Air Interface Band Frequency

: Uplink = 890 - 915 MHz

Downlink = 935 - 960 MHz

Access Method

: FDMA - TDMA

Basic Duplexing

: FDD (Frequency Division Duplex)

Duplex Spacing

: 45 MHz

Carrier Spacing

: 200 KHz

Modulation

: Gaussian Minimum Shift Keying (GMSK)

Transmission Rate

: 270 Kbps

Speech Coder

: RPE LPC 13 Kbps

Teknik Telekomunikasi

9

Jartelinfo

@lestariningati

The GSM Air Interface

FDMA 174 frequencies with 200kHz spacing (GSM 900)

Separate bands for uplink and downlink

Divided between operators

TDMA 8 timeslots per frequency band (one user per timeslot)

Modulation 271 kbit/s GMSK

Teknik Telekomunikasi

10

Jartelinfo

Teknik Telekomunikasi

@lestariningati

11

Jartelinfo

@lestariningati

Struktur Air Interface

Teknik Telekomunikasi

12

Jartelinfo

@lestariningati

Frequency Division Duplex •

Frequency division duplex (FDD) is a technique where separate frequency bands are used at the transmitter and receiver side.

•

Because the FDD technique uses different frequency bands for send and receive operations, the sending and receiving data signals don't interfere with each other. This makes FDD a better choice than Time Division Duplex (TDD) for symmetric traffic such as voice applications in broadband wireless networks

•

Examples of FDD systems include the following:

•

Asymmetric digital subscriber line (ADSL) and very-high-bitrate digital subscriber line (VDSL)

•

Cellular systems, including the UMTS/WCDMA Frequency Division Duplexing mode and the CDMA2000 system

•

IEEE 802.16 WiMax Frequency Division Duplexing mode

Teknik Telekomunikasi

13

Jartelinfo

@lestariningati

GSM : Physical and Logical Channels •

GSM uses number of channels to carry data over Air Interface, these channels are broadly divided in to following two categories:

•

Physical Channels

•

Logical Channels

Teknik Telekomunikasi

14

Jartelinfo

@lestariningati

Physical Channels •

A physical channel is determined by the carrier frequency or a number of carrier frequencies with defined hopping sequence and the Time Slot number.

•

8 Time Slots (1 Time Slot = 1 Physical Channel) of 577 μs constitutes a 4.615 ms TDMA Frame. In GSM standard data on a time slot transmitted in bursts, so time slot is often expressed in BP (Burst Period). 1 BP represents 1 TS. TDMA frame (4.615 ms of 8 TS) further structured in to multiframes. There are two types of multiframes in the system:

•

•

26 TDMA Multiframe: Consists 26 TDMA frames with duration of 120 ms and used to carry the Logical Channels TCH, SACCH, FACCH etc.

•

51 TDMA Multiframe: Consists 51 TDMA frames with duration of 234.5 ms and used to carry the Logical Channels FCCH, SCH, BCCH, CCCH, SDCCH, SACCH etc.

These multiframes further structured in to Superframe and Hyperframe.

•

SUPERFRAME: Superframe consists of 51*26 TDMA frames with duration of 6.12 sec. This is corresponding to the smallest cycle for which the organisation of all channels is repeated.

•

HYPERFRAME: Hyperframe consists 2048 superframes (2048*51*26 TDMA frames) with duration of 3 hrs, 28 min, 53 sec and 760 ms. It is in particular smallest cycle for frequency hopping, cyphering.

Teknik Telekomunikasi

15

Jartelinfo

@lestariningati

21 Multiframe

Teknik Telekomunikasi

51 Multiframe

16

Jartelinfo

@lestariningati

Frame Hierarchy is used for Synchronization Between BTS and MS The frame hierarchy is used for synchronization between BTS and MS.

Multiframes in GSM

3. LOGICAL CHANNELS

Teknik Telekomunikasi

Logical Channels are determined by the information carried within the physical channel. Logical channels

17

Jartelinfo

@lestariningati

Struktur Frame GSM 1 multiframe for signalling 51 TDMA frame = 235.38 ms

0

1

2

1 multiframe for speech/data 26 TDMA frame = 120 ms

49

50

0

1

2

24

25

8 TS = 1 TDMA frame = 4.615 ms

0

1

2

3

4

5

6

7

1 TS

BURST = Contents of Time Slot 156.25 bit = 576.88 µs ( 1 bit = 3.692 µs )

Teknik Telekomunikasi

18

Jartelinfo

Teknik Telekomunikasi

@lestariningati

19

Jartelinfo

@lestariningati

Logical Channels •

Logical Channels are determined by the information carried within the physical channel. Logical channels used to carry data and signalling information. Different logical channels are mapped in either direction on physical channels.

•

Logical channels divided in to following two categories:

•

Traffic Channels

•

Signalling Channels/ Control Channel


Teknik Telekomunikasi

20

Jartelinfo

@lestariningati

Keluarga Kanal Logic Pada GSM cell broadcast channel

traffic channel TCH Data or Speech

CBCH

TCH/F TCH/H BCH

FCCH

CCH

DCCH

CCCH

SCH BCCH PCH AGCH

RACH

ACCH SDCCH

Mobile transmits Base station transmits Both transmit

Teknik Telekomunikasi

21

Jartelinfo

@lestariningati

Control Channel •

Kanal logik yang digunakan untuk manajemen komunikasi, manajemen mobilitas, dan manajemen resource (koreksi frekuensi dan sinkronisasi) CCH control channel

broadcast

common control

BCH FCCH

FCCH SCH BCCH PCH AGCH RACH

Teknik Telekomunikasi

SCH

dedicated control DCCH

CCCH BCCH

PCH

AGCH RACH

frequency correction channel sincronization channel broadcast control channel paging channel access grant channel random access channel

ACCH SACCH

ACCH SACCH FACCH SDCCH

SDCCH FACCH

associated control channel slow associated control channel fast associated control channel stand alone control channel 22

Jartelinfo

•

@lestariningati

Terbagi kedalam 3 kelompok besar yaitu :

1. Broadcast Channel (BCH), bersifat diarahkan ke semua MS.

2. Common Control Channel (CCH), bersifat dipergunakan bersamaan oleh MS

3. Dedicated Control Channel (DCCH), bersifat dipergunakan oleh MS yang sudah ditentukan ( sudah ditentukan utk pelanggan tertentu )

Teknik Telekomunikasi

23

Jartelinfo

@lestariningati

1. Broadcast Control Channel (BCH) •

Broadcast Control Channel (BCH)

‣ Terdiri dari Broadcast ControlChannel (BCCH), FCCH ( Frequency Correction Channel),

SCH (Syncronisation Channel)

•

•

FCCH ( Frequency Correction Channel) •

Arah downlink

•

Point to Multipoint

•

Sinkronisasi frekuensi MS (MS Freq Synchronization) untuk menyamakan frek MS pada frek BTS.

•

Gelombang sinus

SCH (Syncronisation Channel) •

Arah downlink

•

Point to Multipoint

•

TDMA frame structure ( untuk sinkronisasi frame)

•

Info BSIC (Base Station Identity Code)

Teknik Telekomunikasi

24

Jartelinfo

•

@lestariningati

BCCH ( Broadcast Control Channel )

•

Arah downlink

•

Point to Multipoint

•

Informasi LAI (Location Area Identity)

•

Informasi power output maksimum MS

•

Informasi BCCH carrier sel yang berdekatan, untuk mengetahui frek tetangga untuk keperluan Handover

FCCH , SCH dan BCCH dipancarkan secara terus menerus Pembacaan FCCH, BCCH, dan SCH harus dilakukan tiap kali MS pindah sel

Teknik Telekomunikasi

25

Jartelinfo

@lestariningati

2. Common Control Channel (BCH) •

Broadcast Control Channel (BCH)

‣ PCH ( Paging Channel )

‣ Arah downlink

‣ Point to Multipoint

‣ Paging message ( IMSI/TMSI )

‣ Test system ( yang mana yang ada, kalau ada IMSI menggunakan IMSI, kalau ada TMSI

menpergunakan TMSI )

‣ RACH ( Random Access Channel )

‣ Uplink

‣ Point to Point ( harus tahu ID User )

‣ MS call set up, untuk minta kanal dipergunakan utk kanal signaling dan authentikasi

‣ AGCH ( Access Grant Channel )

‣ Downlink

‣ Jawaban dari RACH

‣ Point to Point

‣ Menyediakan kanal signalling (SDCCH) Teknik Telekomunikasi

26

Jartelinfo

@lestariningati

PCH, RACH dan AGCH dipancarkan tergantung permintaan

Teknik Telekomunikasi

27

Jartelinfo

@lestariningati

3. Dedicated Control Channel (DCCH) DCCH

U/D

-  DCCH digunakan untuk signalling dan kontrol setelah pembangunan hubungan

ACCH associated control

channel U/D SACCH

U/D FACCH

U/D SDCCH stand alone dedicated control channel -  untuk authentikasi

-  slow access grant channel

-  fast access grant channel

-  selalu dikaitkan dengan TCH atau SDCCH

-  digunakan untuk handover

-  digunakan untuk membawa informasi yang bersifat umum Teknik Telekomunikasi

-  location update -  digunakan sebelum alokasi pada TCH tertentu -  untuk informasi penempatan pada TCH -  independen, tidak dihubungkan pada TCH

28

Jartelinfo

•

•

@lestariningati

SDCCH ( Stand Alone Dedicated Control Channel ) •

Arah downlink dan uplink

•

Point to Point

•

Call set up

•

Authentication

•

Location Updating

•

Kirim Short message dan Cell Broadcast (ditujukan untuk semua user yang berada pada cell tersebut)

•

Menyediakan TCH

SACCH ( Slow Associated Control Channel ) •

Downlink dan uplink

•

Point to Point

•

Uplink : MS measurement data

•

Trafik voice mode ( Dengan adanya Burst, sehingga ada waktu kosong yang dipergunakan oleh SACCH )

•

Downlink :

•

MS power output

•

Timing advanced

Teknik Telekomunikasi

29

Jartelinfo

•

@lestariningati

FACCH ( Fast Associated Control Channel )

•

Downlink dan uplink

•

Point to Point

•

Digunakan pada waktu Handover,menggunakan kanal trafik yang kosong

•

Stealing mode ( pengganti sementara TCH, mencari 1 kanal suara digunakan untuk permintaan handover)

Pada saat HO, TCH digantikan dengan FACCH untuk meminta HO

Teknik Telekomunikasi

30

Jartelinfo

Teknik Telekomunikasi

@lestariningati

31

Jartelinfo

@lestariningati

Studi Kasus : Pengkanalan Pada GSM Mapping GSM Logical Channel onto Physical Channel Kanal logik GSM harus dipetakan ke kanal fisik, artinya : informasi pada kanal logik harus ditempatkan pada kanal fisik dengan format burst tertentu untuk ditransmisikan Logical Channel Mapping Analogy... 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. Dedicated Control Channels

Traffic Channel

Normal Burst Teknik Telekomunikasi

Synchronization Channel

SCH Burst

Frequency Correction Channel

FCCH Burst

32

Jartelinfo

@lestariningati

Analogi Dedicated Control Channels

Traffic Channel

Normal Burst

Synchronization Channel

SCH Burst

Frequency Correction Channel

FCCH Burst

Kasus analogi di GSM Kanal RF selebar 200 kHz !" Rel kereta Kanal Logic !" Isi gerbong kereta Kanal Fisik ( TimeSlot) !" Gerbong kereta Burst !" Tipe/jenis gerbong

Teknik Telekomunikasi

33

Jartelinfo

@lestariningati

GSM Duplexing and Multiplexing Techniques... 60 MHz

60 MHz

For GSM 1900...

FDD

U

D

299 200kHz Radio Channels

FDMA 512 513 514

808 809 810

ARFCN Numbers

8 0.57ms Time Slots

0

1

2

3

4

5

6

1 Frame

7

{

TDMA

Burst - Transmission Quantum in GSM Frame Train on Frequency Track…an analogy Burst

Burst

Burst

Burst

Burst

Burst

Burst

Burst

PT3163-TekJarNirKab-MODUL:06

Teknik Telekomunikasi

34