MULTIPLE ACCESS COMMUNICATION

CONTENTS TO DISCUSSED

• INTRODUCTION

• HISTORY

• MULTIPLE ACCESS TECHNIQUES

• FDMA

• TDMA

• CDMA

• SDMA

• COMPARISON OF MULTIPLE ACCESS COMMUNICATION

INTRODUCTION

Multiple access schemes allow many users to share a finite amount of radio

spectrum in efficient manner

As the spectrum is limited, so the sharing

is required to increase the capacity of cell

or over a geographical area by allowing the

available bandwidth to be used at the same

time by different users.

Multiple Access communication

HISTORYWIRELESS COMMUNICATION :

Wireless communications is a type of

data communication that is performed and

delivered wirelessly

In 1894 Guglielmo Marconi began developing a wireless telegraph (first transatlantic wireless messages) system using radio waves

Later wireless applications, including broadcasting

(both audio and video), radar, and mobile telephony

came into existence

Alexander Graham Bell Made a first Wireless

Phone That Ran on Sunshine

Marconi wireless telegraph

MULTIPLE ACCESS TECHNIQUES

KINDS OF MULTIPLE ACCESS TECHNIQUES

FREQUENDY DIVISON MULTIPLE ACCESS

This was the initial multiple-access technique for cellular systems in

which each individual user is assigned a pair of frequencies while

making or receiving a call

Applications of FDMA

FDMA is used variety of applications such as telephone systems,

radio systems, TV

Advantages of FDMA

1.Simple to implement

2.Efficient with small base population

Disadvantages of FDMA

1.Network and spectrum planning are time consuming

2.Channels are dedicated to single user

TIME DIVISON MULTIPLE ACCESS

In digital systems, continuous transmission is not required because users do not use the allotted

bandwidth all the time. In such cases, TDMA is a complimentary access technique to FDMA.

Global Systems for Mobile communications (GSM) uses the TDMA technique. In TDMA, the

entire bandwidth is available to the user but only for a finite period of time. In most cases the

available bandwidth is divided into fewer channels compared to FDMA and the users are allotted

time slots during which they have the entire channel bandwidth at their disposal

Applications of TDMATDMA is used variety of applications such as 2G cellular

system,GSM

Advantages of TDMA1. TDMA can easily adapt to transmission of data as well as

voice communication2.Ability to carry 64 kbps to 120 Mbps of data rates

3.Most cost effective technology to convert an analog

system to digital.

Disadvantages of TDMA1.Dropped calls are possible

2.Higher costs due greater equipment

CODE DIVISON MULTIPLE ACCESS

CDMA is a form of multiplexing, which allows numerous signals to occupy a single

transmission channel, optimizing the use of available bandwidth. The technology is

used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and

1.9-GHz bands.

Applications of CDMACDMA is used variety of applications such as 3G cellular

system,LTE,Satellite communication, Data security, GPS

Advantages of CDMA1.Better signal quality

2.High data rates

3.Impossible for hackers to decipher the code sent.

Disadvantages of CDMA1. Self-jamming(if sync not done b/w users)

2. As the number of users increases, the overall quality of

service decreases

SPACE/BEAM DIVISON MULTIPLE ACCESS

SDMA serves different users by using spot beam (A spot

beam, in telecommunications parlance, is a satellite

signal that is specially concentrated in power (i.e. sent by

a high-gain antenna) so that it will cover only a limited

geographic area on Earth) antenna,sectorized antennas

can be thought as SDMA

Applications of SDMAOPTOELECTRONICS, Satellite communication

Advantages of SDMA1.Increses channel capacity and transmission quality

2.High data rates Tb/sec throughput

3.Purely optical signal path

Disadvantages of SDMA1. Interfacing problem

REFERENCES

1. T. S. Rappaport, Wireless Communications: Principles and Practice, 2nd ed. Singapore:

Pearson Education, Inc., 2002.

2. K. Feher, Wireless Digital Communications: Modulation and Spread Spectrum

Applications. Upper Saddle River, NJ: Prentice Hall, 1995.

3. J. G. Proakis, Digital Communications, 4th ed. NY: McGraw Hill, 2000.

4. G. R. Cooper and C. D. McGillem, Modern Communications and Spread Spectrum, NY:

McGraw Hill, 1986

Presented byMADUGULA SAIKUMAR3rd year, ECE-’B’ Sec.

15A51A0495