gbc_002_e1_1 gsm radio interface technology-31.ppt [mode de compatibilité]

GBC_002_E1_1 GSM Radio Interface Technology

ZTE University

GSM-BSS D&T Team

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Objectives

At the end of this course, you will be able to:

Ø Understand GSM speech transmission process

Ø Understand GSM radio key technology

Ø Grasp the function of various logical channels

Ø Describe the channel mapping pattern




Content

Voice transmission process

Radio key technology

Radio channel




Voice Processing in the GSM System


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




Voice encoding

n RPE-LTP (Rule Pulse Excitation-Long Term Prediction )

n 260bit/20ms=13Kbit/s voice block

n Parameter encoding





Channel coding

n Channel coding serves to improve transmission quality

and overcome the negative impact of interferences on

signals.

n Commonly used channel coding methods are:

Ñ Convolution coding

Ñ Fire coding

Ñ Parity check coding.





Channel coding

50 bit (Ia) 132 bit (Ib)

78 bit (Ic)

260 bits / 20ms

50 132 783 4

Fire Code

Protection bits

136 bit53 bit

189 bit

CONVOLUTIONAL CODER (1:2)

378 bit

78 bit

456 bit





Channel Interleving

n Target: Change continuous bit errors into discontinuous bit errors

which can be corrected by channel coding

3 41 2 3 41 2 3 41 2 3 41 2

3 41 3 41 2 3 41 2 3 41 2

3 41 2 3 41 2 3 41 2 3 41 2

2

Message block

Interleving

After interleving

Error bits





Two stage interleving

456 bit

0 1 2 3 4 5 6 78 9 10 11 12 13 14 15

1 2 3 4 5 6 7 8

456 bit

0 1 2 3 4 5 6 78 9 10 11 12 13 14 15

1 2 3 4 5 6 7 8

456 bit

0 1 2 3 4 5 6 78 9 10 11 12 13 14 15

1 2 3 4 5 6 7 8

456 bit

0 1 2 3 4 5 6 78 9 10 11 12 13 14 15

1 2 3 4 5 6 7 8

57 1 57 1 57 1 57 1 57 1 57 1 57 1 57 1

Block A Block B Block A+1 Block B+1

116-bit block 116-bit block 116-bit block 116-bit block

Odd N+4 Odd N+5Odd N+6

Odd N+7Even N Even N+1 Even N+2 Even N+3





Encryption/Decryption

n Encryption is accomplished by exclusive or operation of

an encryption sequence (computed by A5 encryption

algorithm via key Kc and frame number) and 114

information bits on a normal burst.





Modulation and Demodulation

n GMSK is a special digital FM modulation mode

n The modulation rate is 270.833 kilobauds.

n The Frequency Shift Keying (FSK) modulation with bit

rate four times of frequency offset (67.708 kHz )is called

MSK (Minimum Shift-frequency Keying).

n Gaussian demodulation filter is used to further reduce the

modulation spectrum.





The GMSK can be expressed by a I/Q diagram





Content



Radio channel




Discontinuous Transmission（DTX）

n Two aims can be achieved by adopting DTX mode.

Ñ Lower the total interference level in the air

Ñ Save transmitter power.

n The DTX mode and the normal mode are optional, since

the former will slightly lower the transmission quality.





Frequency Hopping (FH)

n Type

Ñ Baseband

Ñ Synthesized

n Function

Ñ Frequency diversity

Ñ Interference diversity

n Parameters

Ñ HSN

ÑMAIO





Diversity receiving

n 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.

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

be decreased.

n Types:

Ñ Space Diversity

Ñ Frequency Diversity

Ñ Time Diversity

Ñ Polarization Diversity





Dynamic power control

n Target: On the basis of certain service quality

Ñ Lower the total interference level in the air

Ñ Save transmitter power

n Power control command sent by SACCH

n MS: Dedicated mode

n Static 6 level, Dynamic 15 level

n Step: 2dBm

A B





Timing Advance（TA）

n 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





Timing Advance（TA）

n BTS calculate TA

n Send by SACCH to MS

n MS Dedicated mode

n Range: 0-63Bits

n Distance: 0-35Km





Content



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




GSM Frame structure

Radio channel




Physical and logical channel

n Physical Channels – the path used to carry information

between an MS and a BTS

n 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

5 BCCHCombined FCCH+SCH+BCCH+CCCH+SDCCH/4+ SACCH/C4

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

8 BCCHwithCBCH FCCH+SCH+BCCH+CCCH+ SDCCH/4+ SACCH/C4 + CBCH

9 SDCCHwithCBCH SDCCH/8+SACCH/C8+CBCH

Radio channel




Structure of 26-Frame Traffic Channel

Radio channel




Structure of 51-Frame Control Channel

SF B C

R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R

51 Ö¡

SF C C SF C C SF C C I

R R R R R R R R R R

D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 A2 A3

SF C C

R R R R R R R R R R

III

D0 D1 D2 D3 D4 D5 D6 D7 A4 A5 A6 A7 III

A1 A2 A3 III

A5 A6 A7 III

D0 D1 D2 D3 D4 D5 D6 D7 A0

D0 D1 D2 D3 D4 D5 D6 D7 A4

SF B C SF C C SF D0 D1 SF D2 D3 ISF A0 A1

SF B C SF C C SF D0 D1 SF D2 D3 ISF A2 A3

D3

D3

R R

R R

A2 A3

A0 A1

D2

D2

SF

SF

D0 D1

D0 D1

R R R R R R R R R R R R R R R R R R R R R R R

R R R R R R R R R R R R R R R R R R R R R R R

F£ºFCCH S£ºSCHB£ºBCCH C£ºCCCH£¨CCCH=PCH+AGCH+RACH£©R£ºRACH D£ºSDCCHA£ºSACCH/C I£ºidle

BCCH+CCCH£¨ÏÂÐÐ£©

BCCH+CCCH£¨ÉÏÐÐ£©

8 SDCCH/8£¨ÏÂÐÐ£©

8 SDCCH/8£¨ÉÏÐÐ£©

BCCH+CCCH+4SDCCH/4

£¨ÏÂÐÐ£©

BCCH+CCCH+4SDCCH/4

£¨ÉÏÐÐ£©

(a) FCCH+SCH+BCCH+CCCH

(b) SDCCH/8(0,...,7)+SACCH/C8(0,...,7)

(c) FCCH+SCH+CCCH+SDCCH/4(0,...,3)+SACCH/C4(0,...,3)

R R

R R

Radio channel




gbc_002_e1_1 gsm radio interface technology-31.ppt [mode de compatibilité]

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