Equalization of Doubly Selective Channels Using Iterative and Recursive Methods

All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. 2 DECLARATION This work has not previously been accepted in substance for any degree and is not being concurrently subm itted in candidature for any degree. Signed > (candidate) Date STATEMENT 1 This thesis is the result of my own investigation, except where otherwise stated. Other sources are acknowledged by footnotes giving explicit reference. A bibliography is ap­ pended. I hereby give consent for my thesis, if accepted, to be available for photocopying and for inter-library loan, and for the title and summary to be made available to out side organizations. 3 T o m y parents for their prayers and assistance, my brothers and sisters for their encouragement and my wife for her continuous moral support. Novel iterative and recursive schemes for the equalization of time-varying fre­ quency selective channels are proposed. Such doubly selective channels are shown to be common place in mobile communication systems, for example in second generation systems based on time division multiple access (TDMA) and so-called beyond third generation systems most probably utilizing orthogonal frequency division multiplex­ ing (OFDM). A new maximum likelihood approach for the estimation of the complex multipath gains (MGs) and the real Doppler spreads (DSs) of a parametrically modelled doubly selective single input single output (SISO) channel is derived. Considerable com­ plexity reduction is achieved by exploiting the statistical properties of the training sequence in a TDMA system. The Cramer-Rao lower bound for the resulting estima­ tor is derived and simulation studies are employed to confirm the statistical efficiency of the scheme. A similar estimation scheme is derived for the MGs and DSs in the context of a multiple input multiple output (MIMO) TDMA system. A computationally efficient recursive equalization scheme for both a SISO and MIMO TDMA system which ex­ ploits the estimated MGs and DSs is derived on the basis of repeated application of the m atrix inversion lemma. Bit error rate (BER) simulations confirm the advantage of this scheme over equalizers which have limited knowledge of such parameters. For OFDM transmission over a general random doubly selective SISO channel, the time …