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.
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