IB-DFE-based receivers for MC-CDMA systems with interference alignment

In this paper we design two multi-user receivers based on the iterative block decision feedback equalization (IB-DFE) concept for MC-CDMA systems with closed-form interference alignment (IA). The receivers are designed in two steps: first a linear equalizer is used to mitigate the inter-user aligned interference; then iterative frequency-domain receivers are designed to efficiently separate the spatial streams, in the presence of both residual inter-user and inter-carrier interferences at the output of the first equalizer. Two strategies are considered: in the first one the matrices are obtained by minimizing the mean square error (MSE) of each individual data stream at each subcarrier, while in the second approach the matrices are computed by minimizing the overall MSE of all data streams at each subcarrier. Our schemes achieve the maximum degrees of freedom provided by the IA precoding, while allowing a close-to-optimum space-diversity gain, with performance approaching the matched filter bound (MFB).