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
HISTORY OF COMMUNICATION • Communication systems Click to edit Master text styles Second level ● Third level ● Fourth level ● Fifth level
HISTORY OF COMMUNICATION Voice Communications
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HISTORY OF COMMUNICATION Basic Communications System Elements ● Source ● Destination ● Transmission Medium Transmission Medium Source
Destination
HISTORY OF COMMUNICATION • Transmission Medium
Transmission Medium
Wired
Wireless
HISTORY OF COMMUNICATION Long Distance Communications Telecommunication is the process of long distance communications. Early telecommunications involved smoke, flags, drums, and other such methods to relay messages information.
and
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HISTORY OF COMMUNICATION Telegraph The first wire line communications was the telegraph. Invented in the mid 19th century, it opened a new era in long-distance telecommunication.
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HISTORY OF COMMUNICATION Telephone When we talk over the telephone, our voice is converted to a electronic signal by the microphone in the handset. This signal is then transmitted over telephone wires. Click to edit Master text styles Second level ● Third level ● Fourth level ● Fifth level
HISTORY OF COMMUNICATION Telephone Networks Early Switching Devices Switches are devices that cause a connection between two transmitting/receiving devices. Modern Switching Devices Today many different types of automated switches are used which make it possible for fast placement of calls. Click to edit Master text styles Second level ● Third level ● Fourth level ● Fifth level
HISTORY OF COMMUNICATION Wired VS Wireless • Losses • Mobility • Security • Bandwidth • Cost Click to edit Master text styles Second level ● Third level ● Fourth level ● Fifth level
Cellular FUNDEMENTALS Transition from analog to digital
• Capacity • Cost • Quality • Security
Cellular FUNDEMENTALS 1000 110 G =
0100 101 0010 011
1101 100 H =
1011 010 0111 001
0001 111 D = ( 1 0 1 1 )
C = D G = ( 1 0 1 1 : 0 0 1 ( THIS IS SENT OVER THE CHANNEL CHECK AT THE RECIVER S = C H T = ( 0 0 0 ) IF WE RECIVER ERROR AT BIT No. 5 C = ( 1 0 0 1 : 0 0 1 ) S = C H T = ( 1 0 1 ) =
5
Cellular FUNDEMENTALS
Some techniques used in wireless communication: –
FDM
–
TDM
–
FDMA
–
TDMA
Cellular FUNDEMENTALS FDM
Cellular FUNDEMENTALS
TDM
Cellular FUNDEMENTALS FDMA FDMA is the division of each bandwidth (RX,TX) into many frequency bands (channels)
Frequency
ď ą
Cellular FUNDEMENTALS
TDMA
Frequency
ď ą It allows several users to share the same radio frequency (RF) by dividing it into different timeslots
Time
Cellular FUNDEMENTALS
Frequency
TDMA/FDMA
Time
Cellular FUNDEMENTALS • Types of telephones Fixed (PSTN) telephones
Cordless Telephones Handset
Mobile Telephones
The base
Cellular FUNDEMENTALS Modes OF Transmission in wireless
Simplex communication system
Example: –
TX
Television , radio
Communication is possible in one direction only
RX
Cellular FUNDEMENTALS
Half – Duplex communication system
Example : –
Police radio
TX+RX
Two-way communication on the same channel. At any given time a user can only transmit or receive
TX +RX
Cellular FUNDEMENTALS
Full – Duplex communication system
Example : –
GSM mobile radio
•
TX+RX
•
simultaneous two-way communication Two simultaneous but separate channels are provided for communication to and from the terminals
TX +RX
Cellular FUNDEMENTALS 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
Up link
Down link
MS
High transmitted power
Cellular FUNDEMENTALS
Cellular FUNDEMENTALS 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
Cellular FUNDEMENTALS 1G Frequency Bands 820
830
840
850
860
870
MCS
880
890
900
910
920
Downlink
930
940
925
NMT 900
Uplink
Downlink 915
Uplink 824
935
Downlink 849
894
869
Uplink
TACS
Downlink 935
905
JTACS/ NTACS 820
Downlink
Uplink
885
830
840
960
Uplink
885
AMPS/ NAMPS
950
850
860
870
880
890
925
900
910
920
930
940
950
960
MHz
Cellular FUNDEMENTALS Systems of first generation System MCS-L2 NMT 450 NMT 900 AMPS NAMPS TACS ETACS JTACS NTACS C450 RadioCom
Year of Introduction
Region
1988 (1979) 1981 1986 1983 1991 1985 1988 1989 1991 1985 1985
Japan Scandinavia Scandinavia North America North America United Kingdom United Kingdom Japan Japan Germany France
Access Mode/ Modulation FDMA/PM FDMA/FM FDMA/FM FDMA/FM FDMA/FM FDMA/FM FDMA/FM FDMA/FM FDMA/FM FDMA/FM FDMA/FM
Cellular FUNDEMENTALS 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
Cellular FUNDEMENTALS - Worldwide GSM Networks in Service
Countries with GSM service Countries without GSM service
Cellular FUNDEMENTALS Third generation cellular system - Multimedia services - W-CDMA transmission technology - Large BW - Higher Bit Rate - More Services
FUNDAMENTAL OF CELLULAR SYSTEM Cluster size=7
FUNDAMENTAL OF CELLULAR SYSTEM • Cell shape
FUNDAMENTAL OF CELLULAR SYSTEM
Area Map
Elevations
Traffic Distribution
Simulation
Design parameters Effect
Drive Test (Optimization )
Drive Test readings
FUNDAMENTAL OF CELLULAR SYSTEM cell sectorization
FUNDAMENTAL OF CELLULAR SYSTEM cell sectorization
Sector 1 Sector 3 Sector 2
FUNDAMENTAL OF CELLULAR SYSTEM
F1
F1
F1
F1
F1
F1
F1
FUNDAMENTAL OF CELLULAR SYSTEM cell sectorization Sector 1
Sector 6
Sector 2
Sector 5
Sector 3
Sector 4
FUNDAMENTAL OF CELLULAR SYSTEM cell sectorization
FUNDAMENTAL OF CELLULAR SYSTEM adaptive power control - as cellular mobile moves power seen at Bs changed - so we use adaptive power control to maintain it
P1
P2
FUNDAMENTAL OF CELLULAR SYSTEM
FUNDAMENTAL OF CELLULAR SYSTEM cell types - macrocell - microcell - picocell
Very small cells
FUNDAMENTAL OF CELLULAR SYSTEM
BS
Microcell
Macrocell
BS
Microcell
BS
FUNDAMENTAL OF CELLULAR SYSTEM Pico Cell
FUNDAMENTAL OF CELLULAR SYSTEM
Global Suburb an Urban & rural
In-building
Pico-Cell
Satellite Macro-Cell Micro-Cell Pico-Cell
FUNDAMENTAL OF CELLULAR SYSTEM 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
2,5,8
2,5
1,4,7
1,4
3,6,9
Fixed
Dynamic
3,6
Hybrid
FUNDAMENTAL OF CELLULAR SYSTEM channel characteristics - Multipath fading
τ1
τ2 τ3
FUNDAMENTAL OF CELLULAR SYSTEM - It gives a Rayleigh fading distribution -
Rayleigh fading is frequency selective
FUNDAMENTAL OF CELLULAR SYSTEM •
To overcome multipath fading we use : - Microscopic diversity and combining techniques - Frequency hopping - Error correction - Interleaving technique - adaptive power control
FUNDAMENTAL OF CELLULAR SYSTEM - Microscopic diversity techniques : 1-Time diversity technique
2-Frequency diversity technique
FUNDAMENTAL OF CELLULAR SYSTEM 3-Space diversity technique
FUNDAMENTAL OF CELLULAR SYSTEM -Space diversity technique
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FUNDAMENTAL OF CELLULAR SYSTEM - Combining techniques : 1-Selective technique 2-Maximal ratio technique 3-Equal gain technique
comparator
Receiver
FUNDAMENTAL OF CELLULAR SYSTEM - 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 .
FUNDAMENTAL OF CELLULAR SYSTEM - Co-channel interference
Dc
FUNDAMENTAL OF CELLULAR SYSTEM - Adjacent channel interference Signal level (dB)
Filter
Adjacent channel interference
Required ch.
Frequency
FUNDAMENTAL OF CELLULAR SYSTEM - Channel management
7,14,21 6,13,20
2,9,16 1,8,15
5,12,19
Amplitude
3,10,17 4,11,18
Frequency (MHz)
FUNDAMENTAL OF CELLULAR SYSTEM - Delay Spread (Time dispersion) - Due to multipath fading - To overcome this we use delay equalizer Path 1
1
2
3
4
5
6
Path 2 τ1
τ2 τ3
1
2
3
4
5
6
FUNDAMENTAL OF CELLULAR SYSTEM - Distance between MS and BS - This makes Time alignment Problem - To overcome this system should respond to this delay
T1
T2
T3
A B
A
B
FUNDAMENTAL OF CELLULAR SYSTEM
-
Path loss
Pr α Pt Rβ
Signal level (dB)
β=3~4
Distance
FUNDAMENTAL OF CELLULAR SYSTEM - Combined signal loss
Signal level (dB)
Path loss Rayleigh fading
Shadowing
Log d