In this thesis the channel capacity of the noncoherent multiple-access
Rician fading channel is investigated. In this channel, the
transmitted signal is sub ject to additive Gaussian noise and Rician
fading, i.e., the fading process is Gaussian in addition to a
line-of-sight component. On the transmitter side the cooperation
between users is not allowed, i.e., the users are assumed to be
statistically independent.

Based on the known result of the asymptotic capacity of a single-user
fading channel, our work is to generalize it to the multiple-user
sum-rate capacity. We study the single-antenna case only: all
transmitters and the receiver use one antenna. We get a natural upper
bound on the capacity if the constraint of independence between the
users is relaxed, in which case the channel becomes a multiple-input
single-output (MISO) channel. Also, a lower bound can be obtained if
all users apart from one are switched off, which corresponds to a
single-input single-output (SISO) channel. We improve these bounds and
get an exact formula of the asymptotic capacity.

The main concept we use in this thesis is escaping to infinity of
input distributions, which means that when the available power tends
to infinity, the input must use symbols that also tend to infinity. We
propose that in the multiple-access fading channel, at least one
user’s distribution must escape to infinity. Based on this we obtain
the result that the asymptotic sum-rate capacity is identical to the
previously mentioned lower bound: the single-user SISO capacity. We
conclude that in order to achieve the best sum-rate capacity in the
multiple-access system, we have to switch off the users with bad
channels and only allow those with the best channel to transmit.

-||-   _|_ _|_     /    __|__   Stefan M. Moser
[-]     --__|__   /__\    /__   Senior Researcher & Lecturer, ETH Zurich, Switzerland
_|_     -- --|-    _     /  /   Adj. Professor, National Chiao Tung University (NCTU), Taiwan
/ \     []  \|    |_|   / \/    Web: http://moser-isi.ethz.ch/

Last modified: Fri Sep 11 06:46:00 UTC+8 2009