WIRELESS NETWORKING

EC3501 WIRELESS COMMUNICATION UNIT IV: MULTIPLE ACCESS TECHNIQUES




UNIT- IV

MULTIPLE ACCESS TECHNIQUES

Introduction: Introduction To Multiple Access- Frequency Division Multiple Access (FDMA)- Time
Division Multiple Access(TDMA)- Spread Spectrum Multiple Access-Code Division Multiple
Access(CDMA)- Space Division Multiple Access(SDMA)- Capacity Of Cellular Systems: Capacity Of
Cellular CDMA, Capacity Of CDMA With Multiple Cells.



4.1 Introduction To Multiple Access

4.2 Frequency Division Multiple Access (FDMA)

4.3 Time Division Multiple Access (TDMA)

4.4 Spread Spectrum Multiple Access

4.4.1 Frequency Hopped Multiple Access (FHMA)

4.4.2 Code Division Multiple Access (CDMA)

4.5 Space Division Multiple Access (SDMA)

4.6 Capacity Of Cellular Systems:

4.6.1 Capacity Of Cellular CDMA

4.6.2 Capacity Of CDMA With Multiple Cells




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, EC3501 WIRELESS COMMUNICATION UNIT IV: MULTIPLE ACCESS TECHNIQUES




4.1 INTRODUCTION TO MULTIPLE ACCESS



1. Summarize the features of various multiple access techniques used in wireless mobile
communication. State the advantages and disadvantages of each technique. (16m-May
2016)[April/May 2023]


✓ Multiple access techniques are used to allow a more number of mobile users to share the allocated
spectrum in the most efficient manner.
✓ As the spectrum is limited, the sharing is required to increase the capacity of cell or over a geographical
area.It done by allowing the available bandwidth to be used at the same time by different users.
✓ Multiple access or channel access method is based on a multiplexing method.
✓ It allows several data streams or signals to share the same communication channel or physical medium.


Applications of multiple access techniques:
✓ The first generation wireless systems used FDMA
✓ In second generation TDMA and CDMA are used.
✓ CDMA is the targeted multiple access technology for the third generation wireless communication
systems.
✓ This Multiple access technique can be grouped as narrowband and wideband systems, depending upon
how the available bandwidth is allotted to the user.


Types of multiple access techniques:




Multiple Access Techniques



Frequency Division Time Division Code Division
Multiple Access Multiple Access Multiple Access
(FDMA) (TDMA) (CDMA)



Figure: Types of multiple access techniques


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, EC3501 WIRELESS COMMUNICATION UNIT IV: MULTIPLE ACCESS TECHNIQUES



4.2 FREQUENCY DIVISION MULTIPLE ACCESS (FDMA)


1. Explain any one type of multiple access schemes. (6M-May 2012)
FDMA (Frequency division multiple access): The total bandwidth is divided into non-overlapping frequency
sub bands.
✓ It is a basic technology in the Analog Mobile Phone Service (AMPS).
✓ It assigns individual channels to individual users.
✓ Each user is allocated a unique frequency band or channel.
✓ These channels are assigned on demand to users who request service.
✓ During the period of the call, no other user can share the same frequency band.
✓ FDM (frequency division multiplexing) is the division of frequency band allocated for the wireless
telephone communication.




Figure:FDMA where different channels are assigned different frequency bands.


Features of FDMA
(Advantages)
✓ The FDMA channel carries only one phone circuit at a time.
✓ After the assignment of a voice channel, the base station and the mobile transmit simultaneously and
continuously.
✓ The bandwidths of FDMA channels are relatively narrow (30 kHz), because each channel supports only
one circuit per carrier. That is, FDMA is usually implemented in narrowband systems.

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