Combined MMSE interference suppression and turbo coding for acoherent DS-CDMA system

摘要

The performance of a turbo-coded code division multiaccess systemnwith a minimum mean-square error (MMSE) receiver for interferencensuppression is analyzed on a Rayleigh fading channel. In order tonaccurately estimate the performance of the turbo coding, twonimprovements are proposed on the conventional union bounds: theninformation of the minimum distance of a particular turbo interleaver isnused to modify the average weight spectra, and the tangential bound isnextended to the Rayleigh fading channel. Theoretical results are derivednbased on the optimum tap weights of the MMSE receiver andnmaximum-likelihood decoding. Simulation results incorporating iterativendecoding, RLS adaptation, and the effects of finite interleaving arenalso presented. The results show that in the majority of the scenariosnthat we are concerned with, the MMSE receiver with a rate-1/2 turbo codenwill outperform a rate-1/4 turbo code. They also show that, for a bitnerror rate lower than 10-3, the capacity of the system isnincreased by using turbo codes over convolutional codes, even with smallnblock sizes