2. 11/23/201
6
2 Introduction
Multiple access schemes are used to allow many
users to share simultaneously a finite amount
of radio spectrum resources
The channels won’t interfere with each other
3. 11/23/201
6
3
basic technology in the analog Advanced Mobile
Phone System (AMPS), the most widely-installed
cellular phone system in North America
based on Frequency Division Multiplexing technique
4. 11/23/201
6
4
Properties of FDMA
in FDMA system, each user has its own frequency
channel
simultaneously and continuously transmitting
usually implemented in narrowband systems
e.g. 30k Hz
does not need synchronization
need guard bands to alleviate the interference
6. 11/23/201
6
6
Numbers of Channels in FDMA
𝑁 =
𝐵 𝑇 − 2𝐵 𝐺
𝐵𝑐
Where,
𝑁 = no. of channels
𝐵 𝑇 = total bandwidth
𝐵 𝐺 =guard band
𝐵 𝐶 = channel bandwidth
7. 11/23/201
6
7
Application
early cellular telephony mostly used FDMA analogue
transmission
walkie talkies
mobile networks for closed user groups e.g. wi-fi
AM or FM radio broadcasting, where each station
has its own channel etc.
9. 11/23/201
6
9
Advantages of FDMA
channel operations are simple and robust
no need for base control station
having different frequencies & guard bands, no
interference arise
in data transmission, negligible delay distortion effect
continuous transmission & no need for synchronization
10. 11/23/201
6
10
Disadvantages of FDMA
impossible to receive data from more than one
transmission source at a time
expensive and complicated bandpass filters required
strict linearity requirement of the medium
requirement for special filters to avoid interference
between the narrow channels
