Multiuser Detector for Multicarrier CDMA Systems

Introduction: In the recent decade, there have been significant efforts in developing multiuser detection technologies to alleviate the effect of multiple access interference (MAI) in codedivision multiple-access (CDMA) systems. Blind multiuser detection is of special interest for MAI mitigation in CDMA systems since it is impractical to assume perfect knowledge of parameters such as spreading codes, time delays and amplitudes of all the users in a rapidly changing mobile environment. In [1], the blind decorrelating detector and the minimum mean square error (MMSE) detector were developed based on subspace estimation and derived in closed forms of the signal subspace components. In order to combat frequency-selective fading, the subspace approach to blind multiuser detection was extended to multi-carrier CDMA (MCCDMA) systems, e.g., in [2]. In this correspondence, we further develop the algorithm presented in [1, 2], and show how the condition of the signal subspace can be improved by using not only the autocorrelation, but also the pseudo-autocorrelation of the received observations, leading to an improved performance in blind multiuser detection. To the best of our knowledge, the development of blind multiuser detectors using condition improved subspace has not been addressed in the existing literature. The notations are summarized as follows: (·)H matrix conjugate transpose, (·)T matrix transpose, (·)∗ matrix conjugate, E[·] expectation operation, C complex filed.