07-02-2012, 04:05 PM
Code Division Multiple Access (CDMA)
[attachment=17259]
What is CDMA
CDMA used extensively in radio frequency communication systems, especially in 2G and 3G cellular telephone networks.
Basic Advantage is the way it handles a finite BW among a large number of users (more users can transmit the same data over the same Bandwidth)
Architecture
.Two frequency channels
One control channel
One data channel
.Spreading code
A common spreading code is used by all nodes over the control channel
Several terminal-specific codes can be used over the data channel
.Signal over the control channel is completely orthogonal to any signal over the data channel
How does CDMA work
The principle is the same as in wireless application. Each user is assigned a unique code (spreading length -L-) which is multiplied by each bit. This code is only known to the receiver in order to demodulate the data.
The most important part for correct detection is the code. This code must be uncorrelated from other user’s codes and be orthogonal.
Advantage Of CDMA
Many users of CDMA use the same frequency, TDD or FDD may be used
Multipath fading may be substantially reduced because of large signal bandwidth
No absolute limit on the number of users
Easy addition of more users
Impossible for hackers to decipher the code sent
Better signal quality
[attachment=17259]
What is CDMA
CDMA used extensively in radio frequency communication systems, especially in 2G and 3G cellular telephone networks.
Basic Advantage is the way it handles a finite BW among a large number of users (more users can transmit the same data over the same Bandwidth)
Architecture
.Two frequency channels
One control channel
One data channel
.Spreading code
A common spreading code is used by all nodes over the control channel
Several terminal-specific codes can be used over the data channel
.Signal over the control channel is completely orthogonal to any signal over the data channel
How does CDMA work
The principle is the same as in wireless application. Each user is assigned a unique code (spreading length -L-) which is multiplied by each bit. This code is only known to the receiver in order to demodulate the data.
The most important part for correct detection is the code. This code must be uncorrelated from other user’s codes and be orthogonal.
Advantage Of CDMA
Many users of CDMA use the same frequency, TDD or FDD may be used
Multipath fading may be substantially reduced because of large signal bandwidth
No absolute limit on the number of users
Easy addition of more users
Impossible for hackers to decipher the code sent
Better signal quality
