GBC_002_E1_1 GSM Radio Interface Technology

ZTE UniversityGSM-BSS D&T Team

Objectives

At the end of this course, you will be able to: Understand GSM speech transmission process Understand GSM radio key technology Grasp the function of various logical channels Describe the channel mapping pattern

Content

Voice transmission process

Radio key technology

Radio channel

Voice Processing in the GSM System

Voice transmission process

A/D

D/A

Voice coding

Channel coding

Interleaving Encryption Burst pulse

formingModulation

Voice decoding

Channel decoding Deinterleaving Decryption Burst pulse

disassemble Demodulation

260bit/20ms 456bit/20ms 33.8kbit/s 270kbit/s

Content

Voice transmission process

Radio key technology

Radio channel

Discontinuous Transmission （ DTX） Two aims can be achieved by adopting DTX mode.

Lower the total interference level in the air

Save transmitter power.

The DTX mode and the normal mode are optional, since

the former will slightly lower the transmission quality.

Radio key technology

Frequency Hopping (FH)

Type

Baseband

Synthesized

Function

Frequency diversity

Interference diversity

Parameters

HSN

MAIO

Radio key technology

Diversity receiving

The diversity reception technology is usually introduced to the GSM

system to receive on several tributaries the signals with little relativity

but carrying the same information and then output the signals after

they are combined.

In this way, the impact of fading on the stability of receiving signals can

be decreased.

Types:

Space Diversity

Frequency Diversity

Time Diversity

Polarization Diversity

Radio key technology

Dynamic power control

Target: On the basis of certain service quality

Lower the total interference level in the air

Save transmitter power

Power control command sent by SACCH

MS: Dedicated mode

Static 6 level, Dynamic 15 level

Step: 2dBm

A B

Radio key technology

Timing Advance （ TA） In the GSM, because TDMA is adopted in the air

interface, the MS must employ the TSs allocated to it

only, and remain inactive in other TSs. Otherwise, it may

affect the MSs using other TSs on the same carrier.

It does not work,Let MS send meBy one TA in advance

Time delayTA

Radio key technology

Timing Advance （ TA）

BTS calculate TA

Send by SACCH to MS

MS Dedicated mode

Range: 0-63Bits

Distance: 0-35Km

Radio key technology

Content

Voice transmission process

Radio key technology

Radio channel

Frame1

1 2 3 4 5 760RF

Frame0

1 2 3 4 5 760

Frame N

1 2 3 4 5 760

Channel 0

Channel 1

Channel 7

Time Division Multiple Access (TDMA)

Radio channel

Physical and logical channel

Physical Channels – the path used to carry information between

an MS and a BTS

Logical Channels – different information carried on the physical

channels

Radio channel

Logical channels

Broadcast Channels

Logical Channels

Control Channels

Common Control

Channels

Traffic Channels

Dedicated Control

Channels

FCCH

SCH

BCCH

RACH

AGCH

PCH

SDCCH

SACCH

FACCH

Radio channel

FCCH

SCH TDMA#

BCCH

Hey. I’m aGSM xmitter!

GSM?

GSM!!!

MCC...MNC...Cl…

Ok…ok

Broadcast Channel (BCH)

Radio channel

PCH downlink only

Hello! You have a call.

RACH uplink only

Hello! I have to setup a call.

I need SDCCH.

AGCH downlink only

Ok. Use SDCCH.

Common Control Channel (CCCH)

Radio channel

SDCCH

SACCH/TCHMS power

FACCH/TCHhandover

On SDCCH:-call set up signaling-SMS-etc…..

On SACCH-SMS-MS power

Don’t shout at me.

Dedicated Control Channel (DCCH)

Radio channel

Channel Mapping

Item Configuration Combination1 TCHFull TCH/F + FACCH/F + SACCH/TF2 TCHHalf TCH/H)+FACCH/H+ SACCH/TH3 TCHHalf2 TCH/H + FACCH/H+ SACCH/TH+ TCH/H4 MainBCCH FCCH + SCH + BCCH + CCCH

5BCCHCombined FCCH+SCH+BCCH+CCCH+SDCCH/4+

SACCH/C46 BCH BCCH + CCCH7 SDCCH SDCCH/8+ SACCH/C8

8BCCHwithCBCH FCCH+SCH+BCCH+CCCH+ SDCCH/4+

SACCH/C4 + CBCH9 SDCCHwithCBCH SDCCH/8+SACCH/C8+CBCH

Radio channel