Ch1 gsm – global system for mobile communication

GSM – GLOBAL SYSTEM FOR

MOBILE COMMUNICATIONS

BY: ENG. Waleed Elsafoury

Copyright © 2013 Waleed Elsafoury

HISTORY OF COMMUNICATION

- CONTENT- communication systems overview- Introduction to Cellular Fundamentals- Network Architecture- GSM Air Interface- Digital Mobile Elements- GSM Network Protocols- Understanding GPRS & EDGE


• Communication systems


Voice Communications


Basic Communications System Elements

● Source

● Destination

● Transmission Medium

Source DestinationTransmission Medium


Transmission Medium

Wired Wireless

• Transmission Medium


Long Distance Communications

Telecommunication is the process of long distance communications.

Early telecommunications involved smoke, flags, drums, and other such methods

to relay messages and information.


TelegraphThe first wire line communications was the telegraph. Invented in the mid 19thcentury, it opened a new era in long-distance telecommunication.


TelephoneWhen we talk over the telephone, our voice is converted to a electronic signal bythe microphone in the handset. This signal is then transmitted over telephone wires.


Telephone Networks Early Switching DevicesSwitches are devices that cause a connection between two transmitting/receiving devices.Modern Switching DevicesToday many different types of automated switches are used which make it possible for fast placement of calls.


Wired VS Wireless• Losses• Mobility• Security• Bandwidth• Cost

Cellular FUNDEMENTALS

Transition from analog to digital

• Capacity

• Cost

• Quality

• Security


1 0 0 0 1 1 00 1 0 0 1 0 10 0 1 0 0 1 10 0 0 1 1 1 1

G =

1 1 0 1 1 0 01 0 1 1 0 1 00 1 1 1 0 0 1

H =

C = D G = ( 1 0 1 1 : 0 0 1 (

D = ( 1 0 1 1 )

THIS IS SENT OVER THE CHANNEL

CHECK AT THE RECIVER

S = C H T = ( 0 0 0 )

S = C H T = ( 1 0 1 ) =

IF WE RECIVER ERROR AT BIT No. 5 C = ( 1 0 0 1 : 0 0 1 )

5

Some techniques used in wireless communication:

FDM

TDM

FDMA

TDMA


FDM


TDM


Freq

uenc

y FDMA

FDMA is the division of each bandwidth (RX,TX) into many frequency bands (channels)


TDMA It allows several users to share the same radio frequency (RF)by dividing it into different timeslots

Time

Freq

uenc

yCellular FUNDEMENTALS

TDMA/FDMA


Time

Freq

uenc

y

Cellular FUNDEMENTALS• Types of telephones

Fixed (PSTN) telephones

Cordless Telephones

Mobile Telephones

Handset The base

Modes OF Transmission in wireless

Simplex communication system Example:

Television , radio

TX RXCommunication is possible in one direction only


Half – Duplex communication system Example :

Police radio

TX+RX TX +RX Two-way communication on the same channel.

At any given time a user can only transmit or receive


Full – Duplex communication system Example :

GSM mobile radio

TX+RX TX +RX

• simultaneous two-way communication• Two simultaneous but separate channels are

provided for communication to and from the terminals


Simple growth was the single transmitting/receiving station

- heavy, bulky and expensive- no switching between regions- low quality- limited capacity- rapid market saturation- power hungry transceiver - power level was not safe

MS

High transmitted power Up link

Down link



First generation cellular system- Introduction of analog cellular systems in the late 1970s and 1980s- analog system- incompatible systems- limited to voice service- no encryption- FM modulation- FDMA transmission technology- suffer from capacity saturation


NMT 900

TACS

JTACS/NTACS

820 830 840 850 860 870 880 890 900 910 920 930 940 950

MCS

AMPS/NAMPS

960

820 830 840 850 860 870 880 890 900 910 920 930 940 950 960

Uplink Downlink

824 849 869 894

Uplink Downlink

905 935

885

Downlink

925

Uplink

Uplink

915 935

Downlink

Downlink

885 925

Uplink

MHz

1G Frequency Bands


Systems of first generation

SystemYear of

Introduction RegionAccess Mode/Modulation

MCS-L2 1988 (1979) Japan FDMA/PMNMT 450 1981 Scandinavia FDMA/FMNMT 900 1986 Scandinavia FDMA/FMAMPS 1983 North America FDMA/FMNAMPS 1991 North America FDMA/FMTACS 1985 United Kingdom FDMA/FMETACS 1988 United Kingdom FDMA/FMJTACS 1989 Japan FDMA/FMNTACS 1991 Japan FDMA/FMC450 1985 Germany FDMA/FMRadioCom 1985 France FDMA/FM


Second Generation cellular system- Introduction of digital cellular systems (90’s) - development of unified international standard for mobile communications- pan-national roaming- digital encryption- enhanced range of services (data + voice)- low power consumption- light weight, compact and pocket size terminals- TDMA transmission technology- huge capacity


- WORLDWIDE GSM NETWORKS IN SERVICE

Countries with GSM serviceCountries without GSM service


Third generation cellular system

- Multimedia services

- W-CDMA transmission technology

- Large BW

- Higher Bit Rate

- More Services


FUNDAMENTAL OF CELLULAR SYSTEM

Cluster size=7


• Cell shape


Area Map

Elevations

Traffic Distribution

Simulation

Design parameters Effect

Drive Test(Optimization )

Drive Test readings


cell sectorization


cell sectorization

Sector 1

Sector 2

Sector 3


F1

F1

F1

F1

F1 F1

F1


cell sectorization Sector 1

Sector 2Sector 3

Sector 4

Sector 5Sector 6


cell sectorization


adaptive power control - as cellular mobile moves power seen at Bs changed - so we use adaptive power control to maintain it

P1P2



cell types- macrocell- microcell- picocell

Very small cells

Macrocell BS

BS

BS

Microcell

Microcell



Pico Cell


Satellite

Global Suburban& rural

Urban

Pico-Cell

Micro-Cell Macro-Cell

In-building

Pico-Cell


cell splitting - as traffic load increases in a cell - to increase channels designer tend to split cell into smaller cells - R decrease Dc decrease so more capacity

FUNDAMENTAL OF CELLULAR SYSTEM channel allocation techniques

- Fixed channel assignment technique (less Ts)

- dynamic channel assignment technique (largest Ts)

- hybrid channel assignment technique (Improved)

1,4,7

2,5,8

3,6,9

1-9 7,8,9

1,4

2,5

3,6

Fixed Dynamic Hybrid


channel characteristics - Multipath fading


- It gives a Rayleigh fading distribution- Rayleigh fading is frequency selective


• To overcome multipath fading we use :- Microscopic diversity and combining techniques

- Frequency hopping

- Error correction

- Interleaving technique

- adaptive power control


- Microscopic diversity techniques : 1-Time diversity technique

2-Frequency diversity technique


3-Space diversity technique


-Space diversity technique


- Combining techniques :

1-Selective technique

2-Maximal ratio technique 3-Equal gain technique

Receiver

comparator


- Shadow fading -The Solution of this problem by using Macroscopic Diversity By selecting a BS which is not shadowed when others are.

FUNDAMENTAL OF CELLULAR SYSTEM- Doppler shift - +ve if the mobile moves toward the BS

- -ve if the mobile moves away from the BS- The Doppler frequency shift should be compensated so that

a correct frequency synchronization is achieved .


- Co-channel interference

Dc


- Adjacent channel interference

Frequency

Signal level (dB)

Filter

Required ch.

Adjacent channel interference


- Channel management

1,8,15

2,9,16

5,12,19

6,13,20

7,14,21

4,11,18

3,10,17

Frequency (MHz)

Amplitude


- Delay Spread (Time dispersion)

- Due to multipath fading

- To overcome this we use delay equalizer

1 2 3 4 65

1 2 3 4 65

Path 1

Path 2


- Distance between MS and BS

- This makes Time alignment Problem

- To overcome this system should respond to this delay

T1 T2 T3

AB

A

B


- Path lossPr α Pt

Rβ

β = 3 ~ 4

Signal level (dB)

Distance


- Combined signal loss

Path loss

Rayleigh fading

Shadowing

Signal level (dB)

Log d

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Ch1 gsm – global system for mobile communication