28-08-2013, 02:47 PM
Multiple Access Techniques for Wireless Communication
[attachment=57525]
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
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
Wideband systems
Transmission b/w of a single channel is much larger than the coherence b/w of the channel.
large number of transmitters on one channel
TDMA -time slots to many tx’s on one channel and only one channel is allowed to acces channel.
CDMA –allows all tx’s to access channel at same time
FDD or TDD multiplexing techniques
TDMA/FDD and TDMA/TDD
CDMA/FDD and CDMA/TDD
FDMA compared to TDMA
fewer bits for synchronization
fewer bits for framing
higher cell site system costs
higher costs for duplexer used in base station and subscriber units
FDMA requires RF filtering to minimize adjacent channel interference
Features of TDMA
a single carrier frequency for several users
transmission in bursts
low battery consumption
handoff process much simpler for subscriber unit
FDD : switch instead of duplexer as tx and rx are done on different time slots
very high transmission rate
high synchronization overhead
guard slots necessary
Solution by SDMA systems
adaptive antennas promise to mitigate reverse link problems
limiting case of infinitely fast track ability
thereby unique channel that is free from interference
all user communicate at same time using the same channel
[attachment=57525]
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
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
Wideband systems
Transmission b/w of a single channel is much larger than the coherence b/w of the channel.
large number of transmitters on one channel
TDMA -time slots to many tx’s on one channel and only one channel is allowed to acces channel.
CDMA –allows all tx’s to access channel at same time
FDD or TDD multiplexing techniques
TDMA/FDD and TDMA/TDD
CDMA/FDD and CDMA/TDD
FDMA compared to TDMA
fewer bits for synchronization
fewer bits for framing
higher cell site system costs
higher costs for duplexer used in base station and subscriber units
FDMA requires RF filtering to minimize adjacent channel interference
Features of TDMA
a single carrier frequency for several users
transmission in bursts
low battery consumption
handoff process much simpler for subscriber unit
FDD : switch instead of duplexer as tx and rx are done on different time slots
very high transmission rate
high synchronization overhead
guard slots necessary
Solution by SDMA systems
adaptive antennas promise to mitigate reverse link problems
limiting case of infinitely fast track ability
thereby unique channel that is free from interference
all user communicate at same time using the same channel