01 go_na01_e1_1 gsm basic principle-45

8/6/2019 01 GO_NA01_E1_1 GSM Basic Principle-45

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GSM Basic Principle


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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


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Content

GSM System Overview

Voice transmission process

Radio key technology

Radio channel


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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


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GSM network entities

MS (Mobile Station)

Mobile Equipment

Subscriber Identity Module (SIM)

BTS (Base Transceiver Station)

Provide radio channels

BSC (Base StationController)Radio resource management

Transcoder


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HLR (Home LocationRegister)

Database

Subscriber data

Subscriber location info.

VLR (VisitorLocationRegister)

Database

MSRN (Mobile Station Roaming Number)

TMSI (Temporary Mobile Subscriber Identification)

Location area codeLAC

Subscriber data related to supplementary service


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MSC (Mobile service Switchingcenter)

Circuit switching

AUC (Authenticate Center) :

Authenticate subscriber access

EIR (mobile stationEquipment Identity Register) :

Identify terminal equipment

OMC (Operationand Maintenance Center)

Provide MMI to control and monitor system


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GSM service area

GSM Service Area

PLMN Service Area

MSC Service Area

LocationArea

Cell


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GSM interfaces

MS BTS BSC MSC

VLR VLR

HLR

MSC

EIR

Sm

Um

Abis A B

D

C

E F

G


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GSM operation band

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

Fre en ie

- pin- o nin

890 - 915 MHz935 - 960 MHz

880 - 915 MHz925 - 960 MHz

1710 - 1785 MHz1805 - 1880 MHz

1850 - 1910 MHz1930 - 1990 MHz

Waeen t ~33 ~33 ~17 ~16and idt 25 MHz 35 MHz 75 MHz 60 MHzpex i tan e 45 MHz 45 MHz 95 MHz 80 MHz

Carrier Separation 200 Hz 200 Hz 200 Hz 200 Hzadio C anne 125 175 375 300


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Absolute radio frequency channel NumberAR CN

GSM Fu (n) = + . vn M

Fd (n) = Fu(n) + M 01e n e 124

GSM1800

Fu (n) = 1710.2 + 0.2v(n 12) M

Fd (n) = Fu(n) + M 512e n e 885


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Multiple Access Technology (MAT)

Many subscribers share commontelecommunication lines without interference toeach other.

MAT

GSM

FDMA

TDMA

CDMA


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FDMA

FDMA Identify by frequency

Time

Frequency

FDMA


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CDMA

CDMA Identify by code

Time

Frequency

CDMA

Code


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Content

GSM System Overview



Radio channel


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Voice Processing in the GSM System

A/D

D/A

Voice

codingChannel

coding

Interle

avingEncryption

Burstpulse

formingModulation

Voice

decoding

Channel

decodingDeinterleaving Decryption

Burstpulse

disassembleDemodulation

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

/s


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Voice encoding

RPE LTP (Rule Pulse E citation Long TermPrediction )

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

Parameter encoding


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Channel coding

Channel coding serves to improve transmissionquality and overcome the negative impact ofinterferences on signals.

Commonly used channel coding methods are: Convolution coding

Fire coding

Parity check coding.


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Channel coding

50bit (Ia) 132bit

(Ib)

78bit (Ic)

260bits /

20ms

50 132 783 4

Fire

Code

Protection

bits

136 bit53 bit

189

bit

CONVOLUTIONAL

CODER (1:2)

378

bit

78bit

456

bit


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Channel Interleving

Target: Change continuous bit errors intodiscontinuous bit errors which can be corrected bychannel 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

Afterinterleving

Errorbits


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Encryption/Decryption

Encryption is accomplished by e clusive oroperation of an encryption sequence (computedby A5 encryption algorithm via key Kc and framenumber) and 114 information bits on a normalburst.


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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 (67.708k )is called MSK (Minimum Shift frequencyKeying).

Gaussian demodulation filter is used to further

reduce the modulation spectrum.


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Content

GSM System Overview



Radio channel


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Discontinuous TransmissionDTX

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.


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Frequency opping (FH)

Type Baseband

Synthesi ed

Function Frequency diversity

Interferencediversity

Parameters HSN

MAIO


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Diversity receiving

The diversity reception technology is usually introduced tothe GSM system to receive on several tributaries thesignals with little relativity but carrying the sameinformation and then output the signals after they arecombined.

In this way, the impact of fading on the stability of receivingsignals can be decreased.

Types: Space Diversity

Frequency Diversity

Time Diversity

Polari ation Diversity


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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


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Timing AdvanceTA

In the GSM, because TDMA is adopted in the airinterface, the MS must employ the TSs allocatedto it only, and remain inactive in other TSs.Otherwise, it may affect the MSs using other TSs

on the same carrier.

Itdoesnot work,

LetMSsendme

Byone TAinadvance

TimedelayTA


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Timing AdvanceTA

BTS calculate TA Send by SACCH to MS

MS Dedicated mode

Range: 0-63Bits Distance: 0-35Km


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Content

GSM System Overview



Radio channel


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Frame1

1 2 3 4 5 760RF

Frame0

1 2 3 4 5 760

Frame N

1 2 3 4 5 760

Channel0

Channel 1

Channel7

Time Division Multiple Access (TDMA)


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Physical and logical channel

Physical Channels the path used to carryinformation between an MS and a BTS

Logical Channels different information carried onthe physical channels


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Logical channels

Broadcast

Channels

Logical

Channels

Control

Channels

Common

ControlChannels

Traffic

Channels

Dedicated

ControlChannels

FCCH

SCH

BCCH

RACH

AGCH

PCH

SDCCH

SACCH

FACCH


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FCCH

SCH TDMA#

BCCH

Hey. Im a

GSM xmitter!

GSM?

GSM!!!

MCC...MNC...Cl

Okok

Broadcast Channel (BCH)


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PCHdownlink only

Hello! You have acall.

RACHuplink only

Hello! I have to set

up acall.

I need SDCCH.

AGCHdownlink only

Ok. Use SDCCH.

Common Control Channel (CCCH)


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SDCCH

SACCH/TCH

MS power

FACCH/TCHhandover

On SDCCH:

-call set up signaling

-SMS

-etc..

On SACCH

-SMS

-MS power

Dont shoutat me.

Dedicated Control Channel (DCCH)


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Structure of26-Frame Traffic Channel


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01 go_na01_e1_1 gsm basic principle-45

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