Signal detection and channel estimation in multipath channels

The main goal for designing a wireless communication system is to achieve efficient and robust transmission through a radio propagation channel that imposes many physical impairments. This dissertation deals with certain problems on signal detection and channel estimation in wireless communication systems when the channel is subject to multipath fading. Specifically, four topics are investigated: multipath interference analysis in FM subcarrier digital systems, analysis and equalization techniques for FM discriminator based non-coherent detection of Gaussian Minimum Shift Keying (GMSK) signals in multipath channels, semi-blind block channel estimation and signal detection algorithms based on maximum likelihood (ML) methods, and iterative ML channel estimation and signal detection algorithms for orthogonal frequency division multiplexing (OFDM) and coded OFDM systems.; The work on FM subcarrier digital systems presents analytical techniques to study the effects of multipath interference on FM subcarrier data signals. A closed form expression for the signal received from a discriminator is obtained for a general multipath channel model. The power spectral density under weak multipath interference is derived. The conditions for observing linear interference at the receiver is determined.; The multipath interference analysis is then extended to FM discriminator based non-coherent reception of GMSK signals. A click phenomenon resulting from multipath interference is studied. An analytical expression is obtained for evaluating the error floor of discriminator detection in multipath fading channels. A Viterbi equalizer is proposed to overcome the error floor problem.; To cope with an unknown channel, channel estimation in a multipath environment is investigated. Based on joint ML estimation and the Baum-Welch algorithm for hidden Markov models, two semiblind block channel estimation and signal detection algorithms are proposed. The effects of block length on the performance of the algorithms are studied.; Applying joint ML estimation to OFDM systems, a very simple structure to iteratively estimate the multipath channel and the transmitted data sequence is obtained. The scheme is then extended to coded OFDM systems, and an algorithm that uses reliability information is developed. A modified expectation-maximization (EM) algorithm is proposed for ML channel estimation for coded OFDM systems.