GO NA01 E1 1 GSM Basic Principle-45

7/28/2019 GO NA01 E1 1 GSM Basic Principle-45

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GSM Basic Principle



Objective

At the end of this course, you will be able to: Understand GSM system architecture and function

State GSM common events

Describe basic calling process



Content

GSM System Overview

Voice transmission process

Radio key technology

Radio channel



AMPS

TACS

NMT

Others

1G

Analog

GSM

CDMAIS95

TDMAIS-136

PDC

2G

Digital

Market

Driving

3G

IMT-2000

UMTS

WCDMA

CDMA

2000

Market

Driving

TD-SCDMA

Mobile Telecommunication Technology Evolution



GSM system architecture

BTS

BSC

MSC

VLR HLR AuC EIR

PSTN, ISDN...

OMC OMC

NMC X.25 links

GSM interfaces

Voicemail Serv

er

SM-SC

MS (Mobile Station)

BSS (Base Station System)

NSS(Network Switching

Subsystem)

OMS(Operations & MaintenanceManagement)

MS

http://www.nokia-asia.com/nokia/0,,48192,00.html



GSM network entities

MS (Mobile Station)：

Mobile Equipment

Subscriber Identity Module (SIM)

BTS (Base Transceiver Station)：

Provide radio channels

BSC (Base Station Controller)： Radio resource management

Transcoder




HLR (Home Location Register)：

Database：

Subscriber data

Subscriber location info.

VLR (Visitor Location Register)：

Database：

MSRN (Mobile Station Roaming Number)

TMSI (Temporary Mobile Subscriber Identification)

Location area code（LAC）

Subscriber data related to supplementary service




MSC (Mobile service Switching center)：

Circuit switching

AUC (Authenticate Center) :

Authenticate subscriber access

EIR (mobile station Equipment Identity Register) :

Identify terminal equipment

OMC (Operation and Maintenance Center)：

Provide MMI to control and monitor system



GSM service area

GSM Service Area

PLMN Service Area

MSC Service Area

Location Area

Cell



GSM interfaces

MS BTS BSC MSC

VLR VLR

HLR

MSCEIR

Sm

Um

Abis A B

D

C

E F

G



GSM operation band

SYSTEM P-GSM 900 E-GSM 900 GSM 1800 GSM 1900

Frequencies

- Uplink- Downlink

890 - 915 MHz935 - 960 MHz

880 - 915 MHz925 - 960 MHz

1710 - 1785 MHz1805 - 1880 MHz

1850 - 1910 MHz1930 - 1990 MHz

Wavelength ~33 cm ~33 cm ~17 cm ~16 cm

Bandwidth 25 MHz 35 MHz 75 MHz 60 MHz

Duplex Distance 45 MHz 45 MHz 95 MHz 80 MHz

Carrier Separation 200 kHz 200 kHz 200 kHz 200 kHz

Radio Channels 125 175 375 300



Absolute radio frequency channel Number （ ARFCN）

GSM900： Fu (n) = 890 + 0.2n MHz

Fd (n) = Fu(n) + 45 MHz，01 n 124

GSM1800：

Fu (n) = 1710.2 + 0.2(n-512) MHz

Fd (n) = Fu(n) + 95 MHz，512 n 885



Multiple Access Technology (MAT)

Many subscribers share commontelecommunication lines without interference to

each other.

MAT

GSM

FDMA

TDMA

CDMA



FDMA

FDMA： Identify by frequency

Time

Frequency

FDMA



TDMA

TDMA： Identify by time

Time

Frequency

TDMA



CDMA

CDMA： Identify by code

Time

Frequency

CDMA

Code



Content

GSM System Overview

Voice transmission process


Radio channel



Voice Processing in the GSM System

A/D

D/A

Voice

codingChannel

coding

Interle

avingEncryption

Burst pulse

formingModulation

Voice

decoding

Channel

decodingDeinterleaving Decryption

Burst pulse

disassembleDemodulation

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



Voice encoding

RPE-LTP (Rule Pulse Excitation-Long TermPrediction )

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

Parameter encoding



Channel coding

Channel coding serves to improve transmissionquality and overcome the negative impact of

interferences on signals.

Commonly used channel coding methods are:

Convolution coding

Fire coding

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

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 7

8 9 10 11 12 13 14 15

1 2 3 4 5 6 7 8

456 bit

0 1 2 3 4 5 6 7

8 9 10 11 12 13 14 15

1 2 3 4 5 6 7 8

456 bit

0 1 2 3 4 5 6 7

8 9 10 11 12 13 14 15

1 2 3 4 5 6 7 8

456 bit

0 1 2 3 4 5 6 7

8 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

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

GMSK is a special digital FM modulation mode The modulation rate is 270.833 kilobauds.

The Frequency Shift Keying (FSK) modulation

with bit rate four times of frequency offset (67.708

kHz )is called MSK (Minimum Shift-frequency

Keying).

Gaussian demodulation filter is used to further

reduce the modulation spectrum.



The GMSK can be expressed by a I/Q diagram



Content

GSM System Overview Voice transmission process


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 transmissionquality.



Frequency Hopping (FH)

Type Baseband

Synthesized

Function Frequency diversity

Interference

diversity

Parameters HSN

MAIO



Diversity receiving

The diversity reception technology is usually introduced tothe 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



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



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 me

By one TA in advance

Time delayTA



Timing Advance（TA）

BTS calculate TA Send by SACCH to MS

MS Dedicated mode

Range: 0-63Bits

Distance: 0-35Km



Content

GSM System Overview Voice transmission process


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)



GSM Frame structure



Physical and logical channel

Physical Channels –

the path used to carryinformation between an MS and a BTS

Logical Channels – different information carried on

the physical channels



FCCH

SCH TDMA#

BCCH

Hey. I’m a GSM xmitter !

GSM?

GSM!!!

MCC...MNC...Cl…

Ok…ok

Broadcast Channel (BCH)



PCH downlink only

Hello! You have a call.

RACH uplink only

Hello! I have to set

up a call.

I need SDCCH.

AGCH downlink only

Ok. Use SDCCH.

Common Control Channel (CCCH)



SDCCH

SACCH/TCH

MS power

FACCH/TCHhandover

On SDCCH:-call set up signaling

-SMS

-etc…..

On SACCH

-SMS

-MS power

Don’t shoutat me.

Dedicated Control Channel (DCCH)



Channel Mapping

Item Configuration Combination

1 TCHFull TCH/F + FACCH/F + SACCH/TF

2 TCHHalf TCH/H)+FACCH/H+ SACCH/TH

3 TCHHalf2 TCH/H + FACCH/H+ SACCH/TH+ TCH/H

4 MainBCCH FCCH + SCH + BCCH + CCCH

5BCCHCombined

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

SACCH/C4

6 BCH BCCH + CCCH

7 SDCCH SDCCH/8+ SACCH/C8

8 BCCHwithCBCHFCCH+SCH+BCCH+CCCH+ SDCCH/4+

SACCH/C4 + CBCH

9 SDCCHwithCBCH SDCCH/8+SACCH/C8+CBCH



Structure of 26-Frame Traffic 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£ºSDCCH

A£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

GO NA01 E1 1 GSM Basic Principle-45

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