Adaptive Equalization and Reed–Solomon Coding in High-Data-Rate Frequency-Hop Spread-Spectrum Communications

Abstract

There is an increasing need for mobile packet radio networks that support link data rates of hundreds of kilobits per second to several megabits per second. If a radio network employing slow-frequency-hop (SFH) spread-spectrum modulation operates at these high data rates, however, the channel is likely to exhibit frequency-selective fading within each frequency slot of the SFH system. The frequency selectivity manifests itself as intersymbol interference at the receiver, and adaptive equalization must be employed in the receiver for each dwell interval in order to compensate for the intersymbol interference. In this paper, we examine the performance of a SFH spread-spectrum system with Reed–Solomon coding in a channel that exhibits time-selective and frequency-selective fading within each frequency slot. The performance is evaluated for systems in which the receiver employs maximum-likelihood sequence estimation in an equalizer that is retrained on a hop-by-hop basis. The performance of a receiver that uses errors-only decoding of Reed–Solomon codewords is considered. The use of the parity-bit method for erasure insertion and errors-and-erasures decoding is also investigated. The performance of a receiver that employs erasures of individual symbols only is compared with the performance of a receiver that also employs threshold-based erasures of entire dwell intervals. The effect of the system bandwidth and the Doppler spread on the comparison is also examined.