Frequency Domain Realization of Space-Time Receivers in Dispersive Wireless Channels

In this paper, we present a class of low complexity space-time receivers for frequency-selective channels in multiple input and multiple output (MIMO) systems. The main idea is that under certain conditions the matrices involved in the implementation of linear and nonlinear equalizers for MIMO systems can be approximated with block circulant matrices which can be inverted via block DFT operations. As result, the computational complexity of the receiver implementation is drastically reduced. First, we extend to MIMO systems two linear approaches originally derived in the framework of joint detection techniques for code division multiple access. Next, we develop a hybrid zero-forcing block decision feedback equalizer (DFE) and a minimum mean square error block DFE for MIMO systems, by performing in the frequency domain the feedback processing as in Benvenuto and Sostrato and the block linear equalizer as in Vollmer et al., while interference cancellation is performed in the time domain. Last, we extend to the frequency domain the fully connected ordered successive interference cancellation DFE. We show that these receivers yield almost the same performance as the original space-time receivers implemented in the time domain, and their computational complexity is lower, even against state of the art fast "time-domain" realizations.