Nonblind and Semiblind Space-Frequency Multiuser Detection for Multirate MC-CDMA Systems

Multicarrier code-division multiple access (MC-CDMA) is a promising candidate for the air interface of future wireless communication systems. After the development of a unified signal model that applies to the different multirate MC-CDMA schemes studied in this paper, a novel space-frequency multiuser detection scheme for multirate uplink MC-CDMA systems with multiple receive antennas is proposed. In particular, a space-frequency minimum mean-squared error (MMSE)-based hybrid serial/parallel interference cancellation receiver (SF-MMSE/HIC) is developed which produces the SF-MMSE combiner as a byproduct. The signal processing of this new detector is jointly carried out in space and frequency domains which leads to the advantage of combating the interference resulting from different sources simultaneously. Based on subspace estimation, a semiblind implementation of the receiver is introduced for slow fading channels. Furthermore, the impact of subcarrier interleaving is investigated for variable spreading factor (VSF) MC-CDMA systems. Based on the characteristic function (CF) of a complex Gaussian random vector (CGRV), a method for analyzing the bit error probability (BEP) performance is presented. Several representative simulation examples of the detector are provided to demonstrate the performance of the proposed receiver. In a fully loaded system, the proposed receiver can offer performance close to the single-user bound. Moreover, the results indicate that multicode and VSF MC-CDMA schemes give very similar performance