Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

stds-802-16: Multiple access techniques



Multiple access techniques which allow us to share a communication medium 
between different users represent one of the most challenging topics in 
digital communications. In terms of the number of users that can be 
accommodated on a given channel, there are two distinct classes of multiple 
access techniques: The first class includes the well-known 
frequency-division multiple access (FDMA), time-division multiple access 
(TDMA), and orthogonal code-division multiple access (OCDMA). On a channel 
whose bandwidth is N times the bandwidth of the individual user signals, 
these techniques can accommodate N users without any mutual interference, 
but not a single additional user can be supported beyond this limiting 
number. The second class includes code-division multiple access with 
pseudo-noise spreading sequences (which we refer to as PN-CDMA) and some 
other related schemes. PN-CDMA does not have a hard limit on the number of 
users that can be accommodated, but is subject to multiuser interference, 
which grows linearly with the number of users. In this paper, after 
reviewing the capacity limits of existing multiple access techniques, we 
describe some newly introduced concepts which allow to accommodate N users 
without any interference while also accommodating additional users at the 
expense of some signal-to-noise ratio (SNR) penalty.

_________________________________________________________________
It's fast, it's easy and it's free. Get MSN Messenger today! 
http://www.msn.co.uk/messenger