Blind Multi User Detection in DS-CDMA Systems using Natural Gradient based Symbol Recovery Structures

Blind Multi User Detection (BMUD) is the process to simultaneously estimate multiple symbol sequences associated with multiple users in the downlink of a Code Division Multiple Access (CDMA) communication system using only the received data. In this paper, we propose BMUD algorithms based on the Natural Gradient Blind Source Recovery (BSR) techniques in feedback and feedforward structures developed for linear convolutive mixing environments. The quasi-orthogonality of the spreading codes and the inherent independence among the various transmitted user symbol sequences form the basis of the proposed BMUD methods. The application of these algorithms is justified since a slowly fading multipath CDMA environment is conveniently represented as a linear combination of convolved independent symbol sequences. The proposed structures and algorithms demonstrate promising results as compared to (i) the conventional techniques comprising matched filters and MMSE receivers, and (ii) previous BMUD structures and algorithms. This paper also extends the earlier proposed BMUD CDMA models by including effects of the channel symbol memory. Illustrative simulation results compare the BER performance of the various natural gradient algorithms, both in the instantaneous (i.e., on-line) and the batch modes, to the conventional detectors.