Abstract-The capacity of a fast frequency-hopped multiple access (FHMA) system is dictated by two major related design concerns: the hopping pattern and the receiver structure. This paper studies the impact of these two factors. We present a maximum likelihood (ML) diversity combiner for detecting asynchronous FHMA multilevel FSK (MFSK) signals in Rician fading channels and analyze the performance of a close approximation of the ML receiver. We compare systems using random hopping patterns and those using optimal hopping patterns of Einarsson [8]. Performance comparisons between chip-synchronous and chip-asynchronous systems are made as well. We propose and examine the effectiveness of a two-stage multiuser detector, in which the first stage makes an initial decision while the second stage tries to reduce multiple access interference (MAI) and resolve the ambiguity left by the first stage detector. The MAI caused by undesired users is constituted by a cochannel interference (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 examined.
The capacity of a multilevel FSh' (MFSK), frequency-hopped multiple access (FHMA) system is dictated b y two major design concerns: the hopping pattern and the receiver structure. This paper studies the i:mpacts of both factors. W e present a maximum likelihood (ML) diversity combiner for asynchronous FHMA systems in Rayleigh fading and compare systems using random hopping patterns and those that use a set of optimal hopping patterns. On the other hand, a multiuser detector for an FHMA/MFSK system usually consists of two stages. The first stage makes an initial decision while the second stage tries to resolve the ambiguity and reduce the cochannel interference (CCI) left b y the first stage detector. After analyze the performance of the first stage detector thlat uses appropriate diversity combining, we then examine the effectiveness of a second stage detector which is a modification of an earlier structure developed b y Timor. This receiver is of modest complexity and is capable of removing most of the CCI. Moreover, we also find that it is insensitive t o power variations of the system users.
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