Digitally modulated signals are known to be cyclostationay and as such they have spectral redundancy. In multiple access wireless systems, the signals cyclostationarity can be exploited to improve the performance of multi-user receivers. This thesis develops adaptive equalizer receiver structures that takes full advantages of the received signals spectral redundancy.

A complete analysis of the Decision Feedback Equalizer (DFE) in a cyclostationary environment is presented. The analysis is based on minimum time averaged mean square error (MTAMSE) criterion. It is shown that the conventional DFE is not optimum for Binary Phase Shift Keying (BPSK) or the Offset-keyed Quadrature Phase Shift Keying (OQPSK) structure but is optimum for Quadrature Phase Shift Keying (QPSK) if and only if all users transmit at equal symbol rate.

Two different DFE structures are suggested. The first structure is based on the Harmonic Series Representation of cyclostationary signals. This structure is called Frequency-Shifted DFE (FRESH-DFE). The second structure is based on the Time Series Representation of the signals and is called the Generalized DFE (GDFE). The analysis shows that the performance of both structures are identical, and in the case of a single data rate of all users, the actual realization of both systems are identical. The analysis also shows that in an interference-dominant environment, the new structures are superior to conventional DFE. An optimum multi-antenna receiver is also considered, and it is shown that the bit error rate can be reduced by increasing the number of antennas