Matched filtering with rate back-off for low complexity communications in very large delay spread channels

Abstract

We study the possibility to transmit data over channels with large delay spreads under the constraint of a very simple receiver which has only one tap. Such a scheme is of interest when a cost-efficient way to transmit potentially high data rates are sought after. We investigate the performance of the optimal prefilter for this scheme and compare it to a simplified, so-called time-reversal (TR) prefilter which has very low complexity. At low SNRs, the TR prefilter and the optimal prefilter are equivalent. At high SNRs, the TR prefilter achieves a performance that is independent from the delay spread of the channel and hence its performance is the same for any bandwidth. In applications where bandwidth is abundant, such as ultra-wide band (UWB) communications, any required performance can be obtained by TR prefilters with a rate back-off transmission (i.e. transmission rate lower than the allowable bandwidth). Similar performance can also be obtained with full-rate transmission using several transmit antennas. This performance is guaranteed, since the high diversity of the large delay spread channel effectively eliminates any fading.