Multiuser detection for MFSK frequency-hopped multiple access systems

The capacity of a multilevel FSK (MFSK), frequency-hopped multiple access (FHMA) system is dictated by two major design concerns: the hopping pattern and the receiver structure. This paper studies the impacts of both factors. We 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 by the first stage detector. After analyze the performance of the first stage detector that uses appropriate diversity combining, we then examine the effectiveness of a second stage detector which is a modification of an earlier structure developed by Timor. This receiver is of modest complexity and is capable of removing most of the CCI. Moreover, we also find that it is insensitive to power variations of the system users.