Ch1 gsm “ global system for mobile communication
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Transcript of Ch1 gsm “ global system for mobile communication
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HISTORY OF COMMUNICATION
- CONTENT
-communication systems overview
- Introduction to Cellular Fundamentals
- Network Architecture
- GSM Air Interface
- Digital Mobile Elements
- GSM Network Protocols
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HISTORY OF COMMUNICATION
• Communication systems
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HISTORY OF COMMUNICATION
Voice Communications
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HISTORY OF COMMUNICATION
Basic Communications System Elements
● Source
● Destination
● Transmission Medium
Source Destination Transmission Medium
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HISTORY OF COMMUNICATION
Transmission Medium
Wired Wireless
• Transmission Medium
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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.
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HISTORY OF COMMUNICATION
Wired VS Wireless • Losses
• Mobility
• Security
• Bandwidth
• Cost
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FUNDAMENTAL OF CELLULAR SYSTEM
Transition from analog to digital
• Capacity
Compression in digital gives more channels
• compatibility with other systems
As ISDN (Integrated service Digital Network)
• Cost
• Quality
• Security
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Some techniques used in wireless communication:
FDM
TDM
FDMA
TDMA
Cellular FUNDEMENTALS
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FDM
Cellular FUNDEMENTALS
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TDM
Cellular FUNDEMENTALS
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Fre
qu
en
cy
FDMA
FDMA is the division of each bandwidth (RX,TX) into
many frequency bands (channels)
Cellular FUNDEMENTALS
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TDMA
It allows several users to share the same radio frequency (RF)
by dividing it into different timeslots
Time
Fre
qu
en
cy
Cellular FUNDEMENTALS
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TDMA/FDMA
Cellular FUNDEMENTALS
Time
Fre
qu
en
cy
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Cellular FUNDEMENTALS
• Types of telephones
Fixed (PSTN) telephones
Cordless Telephones
Mobile Telephones
Handset The base
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Modes OF Transmission in wireless
Simplex communication system
Example: Television , radio
TX RX Communication is possible in one direction only
Cellular FUNDEMENTALS
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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
Cellular FUNDEMENTALS
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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
Cellular FUNDEMENTALS
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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
Cellular FUNDEMENTALS
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Cellular FUNDEMENTALS
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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
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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
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Third generation cellular system - Multimedia services
- W-CDMA transmission technology
- Large BW
- Higher Bit Rate
- More Services
Cellular FUNDEMENTALS
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FUNDAMENTAL OF CELLULAR SYSTEM
The cellular structure
- area divided into small zones (cells)
- cells grouped into clusters
- this gives less power usage
- enable frequency reuse
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FUNDAMENTAL OF CELLULAR SYSTEM
Cluster size=7
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Good Coverage requires high number
of Sites and Cells
Area Coverage 83%
Population Coverage 99,5%
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FUNDAMENTAL OF CELLULAR SYSTEM
• Cell shape
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FUNDAMENTAL OF CELLULAR SYSTEM
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FUNDAMENTAL OF CELLULAR SYSTEM
cell sectorization
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FUNDAMENTAL OF CELLULAR SYSTEM
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FUNDAMENTAL OF CELLULAR SYSTEM
cell sectorization
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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
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FUNDAMENTAL OF CELLULAR SYSTEM
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FUNDAMENTAL OF CELLULAR SYSTEM
cell types
- macrocell
- microcell
- picocell
Very small cells
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Macrocell BS
BS
BS
Microcell
Microcell
FUNDAMENTAL OF CELLULAR SYSTEM
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FUNDAMENTAL OF CELLULAR SYSTEM
Pico Cell
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FUNDAMENTAL OF CELLULAR SYSTEM
Satellite
Global
Suburban & rural
Urban
Pico-Cell
Micro-Cell Macro-Cell
In-building
Pico-Cell
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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
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FUNDAMENTAL OF CELLULAR SYSTEM
cell splitting
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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
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FUNDAMENTAL OF CELLULAR SYSTEM
channel characteristics
- Multipath fading
t1 t
2
t3
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FUNDAMENTAL OF CELLULAR SYSTEM
-It gives a Rayleigh fading distribution
- Rayleigh fading is frequency
selective
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FUNDAMENTAL OF CELLULAR SYSTEM
• To overcome multipath fading we use :
- Microscopic diversity and combining techniques - Frequency hopping - Error correction - Interleaving technique - adaptive power control
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FUNDAMENTAL OF CELLULAR SYSTEM
-Microscopic diversity techniques :
1-Time diversity technique
2-Frequency diversity technique
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FUNDAMENTAL OF CELLULAR SYSTEM
3-Space diversity technique
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FUNDAMENTAL OF CELLULAR SYSTEM
-Space diversity technique
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FUNDAMENTAL OF CELLULAR SYSTEM
- Combining techniques : 1-Selective technique - used in mobile due to simplicity 2-Maximal ratio technique - Best fading reduction 3-Equal gain technique
Receiver
comparator
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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.
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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 .
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FUNDAMENTAL OF CELLULAR SYSTEM
- Co-channel interference
D
c
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FUNDAMENTAL OF CELLULAR SYSTEM
- Adjacent channel interference
Frequency
Signal level (dB)
Filter
Required ch.
Adjacent channel interference
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FUNDAMENTAL OF CELLULAR SYSTEM
- 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
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FUNDAMENTAL OF CELLULAR SYSTEM
- Delay Spread (Time dispersion)
- Due to multipath fading - To overcome this we use delay equalizer
1 2 3 4 6 5
1 2 3 4 6 5
Path 1
Path 2
t1 t
2
t3
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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
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FUNDAMENTAL OF CELLULAR SYSTEM
- Path loss Pr α Pt Rβ
β = 3 ~ 4
Signal level (dB)
Distance
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FUNDAMENTAL OF CELLULAR SYSTEM
- Combined signal loss
Path loss
Rayleigh fading
Shadowing
Signal level (dB)
Log d