gsm

04/17/23 [email protected] 1

E. Sicard - Introduction to GSM

Part 3 - Introduction to GSM



Contents

• History• Present• Specifications level 1• Transmission• Data Transfer• Voice compression• One-chip GSM• GPRS• Conclusion



1st wireless telephone invented by Bell System

1st analog cellular network AMPS in Chicago

1st digital cellular network RITA

1st analog french cellular network, Radiocom 2000

GSM network started in Europe

DCS 1800 network started in Europe

Universal Mobile Telecom.System

2 billion subscribers GSM

SFR started 3G+

1940

1978

1981

1985

1993

1996

2003

2005

2008

1985

1. History

Mobile phone History



The International Union of Telecoms allocates 900MHz

Sub bands fixed to 890-915 tx, 935-960 rx

Group Special Mobile created for planification

MARATHON project started at CNET to support GSM

The European Commission choose GSM standard

Time Domain Multiplexing validated

In France, call for 4 operators: France télécom & SFR

1979

1982

1983

1984

1985

1987

1988

1. History

A zoom at GSM history (1/2)



In France, Itinéris and SFR networks start

GSM becomes Global System for Mobiles

Adaptation Digital Cellular au 1800 MHz

GSM phase 2

100 Million subscribers

GSM 2+ (services, WAP)

General Packet Radio Service (GSM+IP)

One Billion GSM subscribers

Two Billion GSM subscribers

One billion mobile phones manufactured

1991

1992

1993

1995

1997

1998

1999

2002

2005

2007

March 2003 - SFR

1. History

A zoom at GSM history (2/2)



1997

500

1000

2000

1000

2003

1500

400

2005

2000

2500

2007

Global mobile-phone subscribers hit 2B (Oct 05)

More mobiles than fixed phones in France (Oct 01)

3000

Subscribers (Millions)

UMTS 100 Million

1. History

3500

UMTS 250 Million

Global mobile-phone subscribers hit 3B (Oct 08)

2008



End June 2008, from http://www.gsmworld.com/news/statistics/

2. Present



System Band Uplink (MHz) Downlink (MHz) Channel Number

T-GSM-380 380 380.2–389.8 390.2–399.8 Dynamic

T-GSM-410 410 410.2–419.8 420.2–429.8 Dynamic

GSM-450 450 450.4–457.6 460.4–467.6 259–293

GSM-480 480 478.8–486.0 488.8–496.0 306–340

GSM-710 710 698.0–716.0 728.0–746.0 Dynamic

GSM-750 750 747.0–762.0 777.0–792.0 438–511

T-GSM-810 810 806.0–821.0 851.0–866.0 Dynamic

GSM-850 850 824.0–849.0 869.0–894.0 128–251

P-GSM-900 900 890.0–915.0 935.0–960.0 1–124

E-GSM-900 900 880.0–915.0 925.0–960.0 975–1023, 0-124

R-GSM-900 900 876.0–915.0 921.0–960.0 955–1023, 0-124

T-GSM-900 900 870.4–876.0 915.4–921.0 Dynamic

DCS-1800 1800 1710.0–1785.0 1805.0–1880.0 512–885

PCS-1900 1900 1850.0–1910.0 1930.0–1990.0 512–810

Tetra=police, ambulances, military P=Primary, R=Railway, E= extended

2. Present



2. Present

• Mobile economy : 1.8% of global economy• Largest Mobile Phone Markets :

– China 530 Million subscribers (GSM)– USA 250 Million (non-GSM)– India 240 Million– Russia 180 Million– Brasil 120 Million– Japan 11 Million (85% 3G)

• 8,000,000,000 (Billion) SMS per day since 1992’s “merry xmas”

Worldwide



2. Present

• 234 Milliards € invested since 2002 for 2 G and 3 G infrastructures• Average Revenue Per User (ARPU) : 20 €

Worldwide



2. Present

Europe



2. Present

http://www.arcep.fr (Autorité de Régulation des Com.)

France

56 millions subscribers 30 june 2008 ( 88,1 % of French Population)

Christams gift effect 1 Billion SMS in 3 months



900 MHzVoice

1G

12 kb/s

900 MHz1800 MHz

Voice

2G

12 kb/s

900-1800 MHzVoice, Camera Tiny Internet

2.5G

100 kb/s

900-1800-1900 MHzSmart Phone

Video, Internet…

2.75G

300 kb/s

2. Present

Generation and associated data rate



2. Present

1,000,000,000 GSM mobiles to be fabricated in 2008 (total 1.25 B)

0

100

200

300

400

500

600

Nokia Samsung Motorola Sony LG Others

2G Mobiles



(*) OSI/ISO= open system interconnection from International Standard Organization

OSI/ISO(*) Title Application to GSM

Layer 7 Application Appl protocols, user-interface

Layer 6 Presentation Appl specific format transfer

Layer 5 Session Connection to process, billing

Layer 4 Transport Flow control point to point

Layer 3 Network Connection, switching of links

Layer 2 Data link Signaling signals, block transfer

Layer 1 Physical Transmission, coding, modul.

These slides

3. Specifications Level 1

OSI levels




mobile station

(MS) base station

(BS)

Um Abis

Abis

Abis

base station controller

(BSC)

BSC

TRAU

Transcoder Rate Adaptor Unit (TRAU)

A

From Joachim Gollerhttp://www2.informatik.hu-berlin.de/~goeller

To Integrated

Service Digital

Network (ISDN)

Home Location Register (HLR)

Visitor Location Register (VLR)

Equipment Identity Register (VLR)

MSC

Mobile Switching

Center (MSC)

GMSC

GatewayMobile

Switching Center (GMSC)

Uplink (Tx)

Downlink (Rx)

2G infrastucture




Name Exchange Description

Um MS - BS Radio interface between mobile and base station

Abis BS - BSC Communication transfer base station - controller

A BSC - MSC Communication transfer controller – switch center

B MSC - VLR Visitor information communication

C GMSC - HLR Request HLR for incoming call

D VLR - HLR Subscriber localization

E MSC - MSC Handover

F MSC - VLR Mobile station identity verification

2G infrastucture



DCS 1800

1710 1785 1805

Tx

1880

Rx f(MHz)

MS=mobile station1-2WattsBS=base

station100-200 Watts

Uplink (Tx)

GSM

890 915 935

Tx

960

Rx f(MHz)

Downlink (Rx)


Frequency-power



GSM : [890+nx0.2] MHz up to 915MHz

DCS 1800 : [1710+nx0.2] MHz up to 1785MHz

Theoretical network capacity

1710 1785

Tx

Operator 1 Operator 2 Operator 3

1732

Operators share bandwidth





• ARFCN = Absolute Radio Frequency Number • GSM : ARFCN=1-124

– Frequency (Downlink) = 935.2 + 0.2*(n-1) MHz, – Frequency (uplink) = 890.2 + 0.2*(n-1) MHz

• DSC 1800 : ARFCN=512-885 – Frequency (Downlink) = 1805.2 + 0.2*(n-512) MHz – Frequency (Uplink) = 1710.2 + 0.2*(n-512) MHz

• Extended GSM : ARFCN=975-1023– Uplink (880.4-890.0 MHz) – Downlink (925.4- 935.0 MHz) – Frequency (Downlink) = 935.2 + 0.2*(n-1024) MHz– Frequency (Uplink) = 890.2 + 0.2*(n-1024) MHz

• SFR 75 - 124, 721-764 channels• ORANGE 1-50, 765 - 809 channels• Bouygues 51-74, 811 – 885 channels

Channel Numbers



1 2 3 4 5 6 7

1710 1732

f

Bandwidth split within cells

1

1

23

2

4

5

6

7

3

4

5

6

7

1


Cellular architecture



1km

At INSA


Cellular architecture

Each BS has a Beacon Channel (BCCH) on channel 0




• 1 cell = ___ communications• 1 cell = ___ x 20 subscribers



935 960

Frequency (MHz)• Scan peaks of energy within the authorized band

•Memorize the 5 most important

•Try to capture the highest


Getting started




•Signal power of less than -102 dB is unusable for a GSM-connection. •GSM channels 3,4,5,6,7, 16, 19, 21, 30 can be used

Spectrum Analysis http://www2.informatik.hu-berlin.de/~goeller/isdn/GSMDmChannels.pdf



BS=base station

MS=mobile station

Sample Code Modulate x

VCO1

DAC Decode Demodulate x

VCO2

4. Transmission

Voice chain



890 Frequency(MHz)

200KHz

Amplitude

Time

R1

T1

577µs

935

890

935

T1

4.61ms

T8

200KHz

Time domain multiple access (TDMA)

Duplex distance45MHz

4. Transmission

Duplex & TDMA



577µs

Frequency (MHz)

4.61ms

Frame TDMA

0 1 2 3 4 5 6 7890.4

890.6

890.8

891.0

TimeNeeds for very precise synchronization

4. Transmission

TDMA Frame



Frequency (MHz)

0 1 2 3 4 5 6 7890.4

890.6

890.8

891.0

Time

Frequency jump

• Improved transmission• Increased confidentiality

0 1 2 3 4 5 6

4. Transmission



0

F0Frequency

9dB

18dB

41dB

51dB

+600K+200 +400

Signal level (dB)

Noise level

The mobile phone must be highly selective

4. Transmission

Interference with other mobiles



0 1 2 3 4 5 6 7

« Burst » description

Data bits Data bits (same)

3 bits 58 bits 26 bits 58 bits 3 bits

546 µs Training sequence00100 10111 000010 00100 10111

BS000010

GSM data rate

5. Data Transfer



Gain control

Gain

MicroAmplifier

Filter300Hz-3KHz

Analog to Digital

converter 12 bit

Clock

Serial data

8000Hz

96 Kbit/s

High data rate not compatible with GSM

5. Data Transfer

Voice sampling - example



Regular Pulse Excitation (60 parameters, 188 bits)

Parameter computing

F0Long Term Prediction (8 parameters, 26 bits)

Short term prediction (8 parameters, 36 bits)

Compression 1/10

2080 bits 260 bits

20 ms of sampled signal

6. Voice Compression

LTE-RTP Algorithm – University of Berkeley, USA



Linear Predictive Coder for short term (20ms) prediction of the sound

20ms


LTE-RTP Algorithm – Short term



Fréquence (Hz)

1000 20000

Energie Filtre 1/(1-a0z-1-a1z-2)

Filtre 1/(1-a0z-1-a1z-2- a2z-3-a3z-4- -..a7z-8)

In GSM: 8th order polynom for short term prediction

Short term prediction


LTE-RTP Algorithm – Short term



Long term prediction: accounts for the variations of F0

Filter 1/(1-bz-N)N on 7 bitsb on 2 bits

F0

Updated 4 times in the 20ms period (4x9=36 bits)


LTE-RTP Algorithm – Long term



260 bits

50 b 132 b 132 b

• filter coefs• block amplitude• LTP params

• RPE pointers• RPE pulses• 2nd LTP params

• 2nd RPE pulses• 2nd filter params

50 b 132 b 132 b3 4

114 b

convolution

114 b 114 b 114 b


Encryption



PCM

PLL

Jtag

SDIDMA

Exchange buffers

Exchange controls

PRAM

PROM

Timers Verbiti Cipher

DSP DRAM

Registers

Fifo GSMK

Rx ADC

AFC

Tx Buffer

SPW

PLL IF

GPRS

MMU

IT & Timer

Conf registers

ARM732 bits

Boot

CSGen

RTC SIM KPad Aux LCD ADC

7. One chip GSM

One big chip

analog

DSP

exchange

CPU

interface



Power management

Battery

CAN

Codec audio

Reset

SIM

Supply Peripherals

One-chip GSM

CPU

DSP

Codec RF

RF ampli (GaAs)

VCO

RF Receiver

RF Emitter

Power Ampli

BluetoothBluetooth

One-chip bluetooth

16-64Mb16-64Mb

External Flash

CCD module

Camera

7. One chip GSM

LCDMemory

Discrete components

50 components – 50$ min.



7. One chip GSM

Electronique International Sept 08



Memory

ScreenDsp

CCD

Audio

Passives

Batt Pack

GSM 2 G: 30 euro

GSM 2.75 G : 75 euro

Memory

Screen

Dsp

Pass

BattPack

Audio

7. One chip GSM



TimeTx890MHz

Rx 935MHz

TDMA frame

General Packet Radio Service: allocate more than one slot

Half duplex: emit then transmit (Class 1-12)Full duplex: simulateous emit/transmit (Class 19-29)Much more complex mobile phoneImproves data rate up to 4x10kbit/s

8. GPRS



• GSM radio compatibility (Low cost)• Reliability Classes : Loss probability 10-9 10-4 10-2

• Delay classes: <0,5s, <5s, <50s, no limit• Data rate classes 1 to 18 (0,22bit/s up to 111Kb/s)

Question: GSM data rate with 8 slots: only 80kb/s

4 different coding scheme

4 different data rate

Strong protection

Weak protection

8. GPRS

GPRS - Classes



Conclusion

• History of GSM to become a legend• 3 billion subscribers in 2008• GSM level one described, corresponding to physical layer• Data sampling and compression introduced• 50 components, 30 € for a GSM• GPRS introduced featuring enhancing data rate

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