Receiver design for spatially layered downlink MC-CDMA system

One of the most promising candidates for the air interface of the upcoming multiuser broadband communication systems is multicarrier code-division multiple-access (MC-CDMA). In the pursuit for higher data rates and reliability of communication in fading environments, a vast amount of spatial multiplexing and transmit diversity techniques have been recently proposed for the multi-antenna systems. In this paper, we study the receiver design for downlink (base station to mobile) multi-antenna MC-CDMA when layered space-time (LST) architectures and space-time coding techniques are utilized. Due to the inevitable complexity restrictions, sub-optimal chip and symbol-level minimum mean squared error (MMSE) based receiver front-ends are derived. For further improvements in performance, an iterative MMSE based detector with soft co-antenna interference cancellation is designed. Performance of the different algorithms is evaluated in spatially correlated and uncorrelated fading channels. The results demonstrated that the proposed multi-antenna schemes combining recently discovered space-time turbo coded modulation and group-wise LST architectures are able to provide significant improvements both in error rate performance and spectral efficiency over the conventional single-antenna system also in spatially correlated environments. By utilizing iterative processing at the receiver, the considered 4×4 system was found to perform within 1.5 dB from the channel outage capacity in a spatially uncorrelated frequency-selective fading channel.