A DECISION FEEDBACK EQUALIZER WITH TIME-REVERSAL STRUCTURE

This paper describes the use of a receiver with time-reversal structure for low-complexity decision feedback equalization of slowly fading dispersive indoor radio channels. Time-reversal operation is done by storing each block of received signal samples in a buffer and reversing the sequential order of these signal samples in time prior to equalization. As a result, the equivalent channel impulse response as seen by the equalizer is a time-reverse of the actual channel impulse response. Selective time-reversal operation, therefore, allows a decision feedback equalizer (DFE) with a small number of forward filter taps to perform equally well for both minimum-phase and maximum-phase channel characteristics. We evaluate the theoretical performance bounds for such a receiver and quantify the possible performance improvement relative to an implementation without time reversal on discrete multipath channels with Rayleigh fading statistics. Two extreme cases of DFE examples are considered: 1) an infinite-length DFE; and 2) a DFE with a single forward filter tap. Optimum burst and symbol timing recovery is addressed and several practical schemes are suggested. We then present simulation results for a proposed receiver implementation that incorporates the time reversal concept. The combined use of equalization and diversity reception is considered. The result of this study indicates that a DFE with a very short forward filter can be effectively used in eliminating the effects of multipath lasting up to several symbols in duration.