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Tdma, Cdma, Fdma & Sdma

This document discusses multiple access techniques for wireless communication including FDMA, TDMA, CDMA, and SDMA. It describes how these techniques work in both narrowband and wideband systems using concepts like frequency division duplexing, time division duplexing, code division multiple access, and how different cellular systems employ various techniques like GSM using TDMA/FDD and IS-95 using CDMA/FDD.

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350 views15 pages

Tdma, Cdma, Fdma & Sdma

This document discusses multiple access techniques for wireless communication including FDMA, TDMA, CDMA, and SDMA. It describes how these techniques work in both narrowband and wideband systems using concepts like frequency division duplexing, time division duplexing, code division multiple access, and how different cellular systems employ various techniques like GSM using TDMA/FDD and IS-95 using CDMA/FDD.

Uploaded by

MegB
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PPT, PDF, TXT or read online on Scribd
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Multiple Access Techniques for

Wireless Communication

FDMA
TDMA
SDMA
PDMA
Introduction
• many users at same time
• share a finite amount of radio spectrum
• high performance
• duplexing generally required
• frequency domain
• time domain
Frequency division duplexing (FDD)
• two bands of frequencies for every user
• forward band
• reverse band
• duplexer needed
• frequency seperation between forward band
and reverse band is constant
reverse channel forward channel
frequency seperation f
Time division duplexing (TDD)

• uses time for forward and reverse link


• multiple users share a single radio channel
• forward time slot
• reverse time slot
• no duplexer is required

reverse channel forward channel


t
time seperation
Multiple Access Techniques

• Frequency division multiple access (FDMA)


• Time division multiple access (TDMA)
• Code division multiple access (CDMA)
• Space division multiple access (SDMA)
• grouped as:
• narrowband systems
• wideband systems
Narrowband systems

• large number of narrowband channels


• usually FDD
• Narrowband FDMA
• Narrowband TDMA
• FDMA/FDD
• FDMA/TDD
• TDMA/FDD
• TDMA/TDD
Logical separation FDMA/FDD

forward channel
user 1
reverse channel

... f

forward channel
user n
reverse channel

t
Logical separation FDMA/TDD

user 1
forward channel reverse channel

... f

user n
forward channel reverse channel

t
Logical separation TDMA/FDD

forward forward
channel channel
user 1 ... user n f
reverse reverse

channel channel

t
Logical separation TDMA/TDD

user 1 user n

...
forward reverse forward reverse f
channel channel channel channel

t
Wideband systems
• large number of transmitters on one channel
• TDMA techniques
• CDMA techniques
• FDD or TDD multiplexing techniques
• TDMA/FDD
• TDMA/TDD
• CDMA/FDD
• CDMA/TDD
Logical separation CDMA/FDD

user 1
forward channel reverse channel

... code

user n
forward channel reverse channel

f
Logical separation CDMA/TDD

user 1
forward channel reverse channel

... code

user n
forward channel reverse channel

t
Multiple Access Techniques in use

Multiple Access
Cellular System
Technique
Advanced Mobile Phone System (AMPS) FDMA/FDD
Global System for Mobile (GSM) TDMA/FDD
US Digital Cellular (USDC) TDMA/FDD
Digital European Cordless Telephone (DECT) FDMA/TDD
US Narrowband Spread Spectrum (IS-95) CDMA/FDD
Frequency division multiple access FDMA

• one phone circuit per channel


• idle time causes wasting of resources
• simultaneously and continuously
transmitting
• usually implemented in narrowband systems
• for example: in AMPS is a FDMA
bandwidth of 30 kHz implemented

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