A Two-Stage Memetic Algorithm for Blind Equalization in DS/CDMA Systems

Abstract

This study proposes a novel memetic algorithm (MA) for the blind equalisation of digital multiuser channels with direct-sequence/code-division multiple-access sharing scheme. Equalisation involves two different tasks, the estimation of (i) channel response and (ii) transmitted data. The corresponding channel model is first analysed and then the MA is developed for this specific communication system. Convergence, population diversity and near–far resistance have been analysed. Numerical experiments include comparative results with traditional multiuser detectors as well as with other nature-inspired approaches. The proposed receiver is proved to allow higher transmission rates over existing channels while supporting stronger interferences as well as fading and time-variant effects. Required computation requisites are kept moderate in most of the cases. The proposed MA saves ∼80% of computation time with respect to a standard genetic algorithm and about 15% with respect to a similar two-stage MA, while keeping a statistically significant higher performance. Besides, complexity increases only by a factor of 5, when the number of active users doubles, instead of 32 × found for the optimum maximum likelihood algorithm. The proposed method also exhibits high near–far resistance and achieves accurate channel response estimates, becoming an interesting and viable alternative to so far proposed methods.