Multiuser demodulation for DS-CDMA systems in fading channels.
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Date
2000
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Abstract
The problems of optimal as well as suboptimal detection for CDMA
transmissions over an additive white Gaussian noise (AWGN) channel, have
been the focus of study in the recent past. However, CDMA transmissions
are frequently made over channels which exhibit fading and/or dispersion;
hence receivers need to be designed which take into account this behaviour.
In spite of the major research effort invested in multiuser demodulation
techniques, several practical as well as theoretical open problems still exist.
Some of them are considered in more detail in this thesis. The aim of the
thesis is to develop multiuser demodulation algorithms for mobile
communication systems in frequency-selective fading channels, and to
analyze their implementation complexity. The emphasis is restricted to the
uplink of an asynchronous DS-CDMA system where the users transmit in an
uncoordinated manner and are received by one centralized receiver.
The original work that is undertaken for the MScEng study is the evaluation
of a multiuser receiver structure for a frequency-selective fading channel,
where there exists a steady specular path and two fading paths.
Furthermore, the effect of using selection diversity is investigated by
examining the bit error rate, asymptotic multi user efficiency and near-far
resistance of the proposed detector structure. These results are confirmed
both analytically and by simulation in the thesis. An investigation is also
conducted into the application of neural networks to the problem of
multiuser detection in code division multiple access systems. The neural
network will be used as a classifier in an adaptive receiver which
incorporates an extended Kalman filter for joint amplitude and delay
estimation. Finally, some open problems for future research will be pointed
out in the thesis.
Keywords: AWGN channel , DS-CDMA system, frequency-selective,
multi user demodulation, asymptotic multiuser efficiency, near-far resistance,
neural network, Kalman filter.
Description
Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.
Keywords
Code division multiple access., Mobile communication systems., Kalman filtering., Random noise theory., Radio--Transmitters and transmission--Fading., Demodulation (Electronics), Theses--Electronic engineering.