Iterative multiuser detection for turbo-coded FHMA communications

摘要

An iterative receiver structure Is proposed for turbo-codednfrequency-hop multiple access (FHMA) systems. In FHMA systems, thenadjacent channel interference (ACI) is the major contributor of multiplenaccess interference (MAI) if orthogonal hopping patterns are used. ThenACI is a function of the tone spacings of the adjacent subchannels andnthe rolloff factor of the pulse-shaping filter. The calculation of thenACI for a square-root raised-cosine pulse-shaping filter in an FHMAnsystem is presented in this paper. In addition, a low complexityniterative multiuser detector is developed to mitigate the degradationncaused by ACI in the FHMA systems. The iterative receiver structure isnbased on a modified turbo decoding algorithm which makes use of the anposteriori log-likelihood ratio (LLR) information of the systematic bitsnto obtain the a posteriori information of the turbo-encoded parity bits.nIterations of the receiver/decoder are used as the mechanism to estimatenand mitigate the MAI in the FHMA system. The properties of both soft andnhard interference suppressors based on the modified turbo decodingnalgorithm are examined and an efficient recursive implementation isnderived. Compared to maximum-likelihood multiuser detection, thenproposed system is more practical and its complexity is only a linearnfunction of the number of users. Simulation results show that thenproposed iterative receiver structure offers significant performancengain in bandwidth efficiency and the required signal-to-noise ration(SNR) for a target bit-error rate (BER) over the noniterative receivernstructure. Moreover, the single user performance can be achieved whennimperfect power control exists