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P & M C
Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
1/16
Pervasive and Mobile Computing
Dr. Atiq [email protected]
Department of Computer Science & Information TechnologyUniversity of Balochistan
Lecture 06
P & M C
Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
2/16
Outline
1 Wireless and Mobile ComputingCellular Concept
P & M C
Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
3/16
Outline
1 Wireless and Mobile ComputingCellular Concept
P & M C
Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
4/16
Cellular Network Basics
Cellular network/telephony is a radio-based technology;radio waves are electromagnetic waves that antennaspropagate
Most signals are in the 850 MHz, 900 MHz, 1800 MHz,and 1900 MHz frequency bands
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Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
5/16
Cellular Network Basics
Base stations (BS) transmitto and receive from mobilesat the assigned spectrum
Multiple BSs use thesame spectrum (spectralreuse)
Service area of each BS iscalled a cell
Each mobile terminal (MT)is typically served by the‘closest’ BSs
P & M C
Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
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Evolution of Cellular Networks
IS: Interim Services DO: Data Optimized EDGE: Enhanced Data for GSM Evolution
P & M C
Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
7/16
Multiple Access Problem
BSs need to serve many MTs at the same time (bothdownlink and uplink)
All mobiles in the cell need to transmit to the BS
Interference among different senders and receivers
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Dr. AtiqAhmed
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Multiple Access Schemes
Frequency Division Multiple Access (FDMA)
Time Division Multiple Access (TDMA)
Code Division Multiple Access (CDMA)
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Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
9/16
Frequency Division Multiple Access
Each mobile is assigned a separate frequency channel for the duration ofthe call
Sufficient guard band is required to prevent adjacent channel interference
Usually, MTs will have one downlink frequency band and one uplinkfrequency band
Different cellular network protocols use different frequencies
Frequency is a precious and scare resource. We are running out of it
P & M C
Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
10/16
Time Division Multiple Access
Time is divided into slots and only one mobile terminal transmits duringeach slot
Like during the lecture, only one can talk, but others may take thefloor in turn
Each user is given a specific slot. No competition in cellular networkUnlike Carrier Sensing Multiple Access (CSMA) in WiFi
P & M C
Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
11/16
Code Division Multiple Access
Use of orthogonal codes to separate different transmissions
Each symbol of bit is transmitted as a larger number of bits using the userspecific code - Spreading
Bandwidth occupied by the signal is much larger than the informationtransmission rate but all users use the same frequency band together
P & M C
Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
12/16
Code Division Multiple Access
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Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
13/16
Code Division Multiple Access
P & M C
Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
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Code Division Multiple Access
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Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
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Code Division Multiple Access
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Dr. AtiqAhmed
Wireless andMobileComputingCellular Concept
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Multiple Access Schemes
