Ch1 gsm – global system for mobile communication

GSM – GLOBAL SYSTEM FOR

MOBILE COMMUNICATIONS

BY: ENG. 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

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

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 )

Some techniques used in wireless communication:

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

yCellular FUNDEMENTALS

TDMA/FDMA

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

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

JTACS/NTACS

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

AMPS/NAMPS

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

Downlink

Uplink

915 935

Downlink

885 925

Uplink

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

Sector 1

Sector 2

Sector 3

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

cell types- macrocell- microcell- picocell

Very small cells

Macrocell BS

Microcell

Pico Cell

Satellite

Global Suburban& rural

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)

1-9 7,8,9

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

- 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

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

- Path lossPr α Pt

β = 3 ~ 4

Signal level (dB)

Distance

- Combined signal loss

Path loss

Rayleigh fading

Shadowing

Signal level (dB)

Ch1 gsm – global system for mobile communication

wireless communication

mobile communicationsby

radio frequency rfby

radio txrxcommunication

bandwidth rx

transmittingreceiving

telephone wires

wire line communications

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