On the detection of a class of fast frequency-hopped multiple access signals

The capacity of a fast frequency-hopped multiple access (FHMA) system is di ctated by two major related design concerns: the hopping pattern and the re ceiver structure. This paper studies the impact of these two factors. We pr esent a maximum likelihood (ML) diversity combiner for detecting asynchrono us FHMA multilevel FSK (MFSK) signals in Rician fading channels and analyze the performance of a close approximation of the ML receiver. We compare sy stems using random hopping patterns and those using optimal hopping pattern s of Einarsson [8]. Performance comparisons between chip-synchronous and ch ip-asynchronous systems are made as well. We propose and examine the effect iveness of a two-stage multiuser detector, in which the first stage makes a n initial decision while the second stage tries to reduce multiple access i nterference (MAI) and resolve the ambiguity left by the first stage detecto r. The MAI caused by undesired users is constituted by a cochannel interfer ence (CCI) contribution and an interchannel interference (ICI) contribution . This detector is of modest complexity and is capable of removing most of the CCI and part of the ICI. Two methods for mitigating MAI are also examin ed.