Basics of GSM CHL.ppt

8/10/2019 Basics of GSM CHL.ppt

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R.N.SHARMA

Sr.SDE(NOKIA)

SW-I FACULTY,ALTTC GZB

ALT CENTRE

ALTTC

An Over ViewOf

GSM Channel Concepts


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OBJECTIVES:

Upon completion of this Lecture the Trainees

will be Able to Describe the GSM Logical &Physical Channels.


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1. Introduction

2. Describe the Difference Between Physical & Logical

Channels

3. Describe Various Logical Channels

(I) Broad Cast Channels.

(II) Dedicated Channels

4. Describe mapping of channels in GSM Frame

5. Summery.


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GSM

Uplink & Downlink

Frequency Bands

GSM 900 Mhz

Uplink 890-915Mhz

Down Link 935-960Mhz

BT

S


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GSM Specifications

GSM 900

Mobile to BS (UP-LINK) - 890 to 915 MHz

BS to Mobile (DOWN -LINK) - 935 to 960

MHz

Bandwidth - 25 MHz

GSM 1800

Mobile to Cell (UP-LINK) - 1710 to 1785 MHz

Cell to Mobile (DOWN -LINK) - 1805 to 1880 MHz

Bandwidth - 75 MHz

RF Spectrum :


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GSM - MULTIPLE ACCESS GSM uses both FDMA & TDMA

Freq

Mhz.890.2

1

890.4

2

890.6

3

890.8

4

891.0

5 6

914.8

124

FDMA Access along Frequency axis

Each RF carrier 200khz apart

Total 124 RF Channels available.One or more carrier assigned to each base station

...


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GSM

FDMA

25 MHz 25 MHz

Mobile to Base

0 1 2

890.2 890.4 890.6(MHz)

Base to Mobile

0 1 2

935.2 935.4 935.6

200 kHz45MHz

Channel layout and frequency bands of operation

890 935 960915

200 kHz


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GSM

TDMA

87

65

43

21

87

65

43

21

45 MHz

Frequency

F2F1(Cell transmit)

F2F1(Cell Rx)

Amplitude

Typical TDMA/ FDMA frame structure


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TDMA Frame

Physical Channel

(0.577ms)

The TDMA frame time slot of 0.577ms is known

as physical channel while the contents of physicalchannel according to their roles are called as

logical channel


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Physical and Logical channel

Physical Channel

Each timeslot in TDMA frame is called a physical channel.

There are 8 physical channels per carrier in GSM.

Physical channels may be used to carry speech data or

signaling

information.

Logical Channel

The Information carried by physical channels is known as

logical

channel.

There are a several type of logical channels available in

GSM.


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GSM

LOGICAL CHANNELS

USER INFORMATION( TRAFFIC)

SIGNALLING INFORMATION (CONTROL)


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Logical Channels

Logical

Channels

Dedicated

ChannelsCommon

Channels

Full-Rate

Half-Rate

Common

Control

Channels

Dedicated

Control

Channels

Broadcast

Channels

SDCCH

SACCH

FACCH

RACH

PCH

AGCH

FCCH

SCH

BCCH

Traffic

Channels


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Common channelsare used to broadcast different

information to MS & for setting up signalingchannels between the MSC/VLR & the MS

Common

Channels

Common

Control

Channels

BroadcastChannels


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Broadcast Channels

FCCH (Frequency Correction Channel) Provides the

frequency correction information used by the mobile

station.

SCH (Synchronization Channel) Contains the BaseStation Identity Code (BSIC) and the TDMA frame

number used for synchronization of the mobile station to

the frame structure of a new BTS.

BCCH (Broadcast Control Channel)Used to broadcast

general information, related to network, to all mobile

stations.


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Broadcast Channels.

SCH(Synchronization Channel):- BTS sendsTDMA frame number on SCH by which MS

synchronize it self with GSM system.

SCH

TDMA Frame Number BSIC

BSIC:-N/W color cod & Base Station color cod

Down link


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Broadcast Channels.

Broadcast Control Channel(BCCH):-

1. System Type 900/1800

2. LAI

3. Neighbor Cell BCCH Information

4. Frequency hopping used or not?

5. Type of Training sequence used

6. Max power allowed in cell

Down link


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Broadcast Channels.

BCCH.

7. Paging Group

8. Max Timing advance allowed


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Common Control Channels (CCCH)

PCH (Paging Channel)Used to page the mobile station. PCH

information is transmitted over the downlink It contain IMSI or

TMSI.

RACH (Random Access Channel )Used by a mobile station to

Request access to the system. RACH information is transmitted

over the uplink.

AGCH (Access Grant Channel)Used to assign a SDCCH for

call setup. AGCH information is transmitted over the downlink.


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Dedicated Control Channels (DCCH)

SDCCH (Stand alone Dedicated Control Channel)Carries

signaling information during call setup

SACCH (Slow Associated Control Channel)Transmits callControl data and measurement reports during the call.

FACCH (Fast Associated Control Channel)Carries urgent

Signalling information for handover etc.

.


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GSM

THREE TYPES OF CONTROL CHANNELS

Dedicated control channel DCCH

P - P For Registration SDCCH

,authentication SACCH

& Handover FACCH

Broadcast control channel BCCH

P- MP For Freq Correction FCCH

For Syncronisation SCH

BCCH

Common control channel CCCH

For ACCESS Management PCH

RACH

AGCH


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OPERATIONALCONCEPTS

IDLE MODE

IDLE MODE

ACCESS PROCDURE DEDICATED MODE

MS O/G Call

MS I/C Call

----FCCH---- SCH

----BCCH

----RACH

----AGCH----SDCCH

----TCH

----PCH

----RACH----AGCH

----SDCCH

----TCH


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Common channelsare generally transmitted

on TS0of BCCH carrier frequency

F SB B B B C0 C0 C0 C0

F S C1 C1 C1 C1 C2 C2 C2 C2

F SC3 C3 C3 C3 C4 C4 C4 C4

F SC5 C5 C5 C5 C6 C6 C6 C6

F SC7 C7 C7 C7 C8 C8 C8 C8

I

Down Link


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01 2 3 4 5 6 7

Broadcast/Control Information

Traffic Information

Question

If MS is chandelling calls then how it

can receive SMS


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TCH Structure:-

TTTTTTTTTTTTATTTTTTTTTTTTI12 250

It get SMS on SACCH as it

comes after every 12 TCH


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Conclusion:-

Discussed Frequency Spectrum used in GSM.

Explain Channel Definition & difference b/w

Physical & Logical channel.

Discussed Various Logical Channels.

Discussed over all GSM frame structure


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THANKS !!

Basics of GSM CHL.ppt

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