On optimal detection for linearly precoded MIMO-OFDM systems with imperfect CSIT

Optimum detection based on maximum likelihood (ML) has been recently explored within the context of linearly precoded subcarrier cooperative MIMO-OFDM systems, showing that large performance gains can be obtained in comparison to an all-linear setup (i.e., linear transmitter/receiver) at the cost of increased computational complexity. Nonetheless, low complexity alternatives, yet retaining optimality, have been also proposed. Most of these previous works have assumed the availability of perfect channel state information at the transmitter (CSIT) despite this is rarely the case since feedback delay and/or quantisation effects will usually render imperfect CSIT. This paper studies how these imperfections affect the performance of the ML-based receiver. Particularly, it focuses on fully loaded setups, that is, those configurations where the number of independent streams transmitted equals the number of available spatial modes. Remarkably, for these configurations, an interesting interplay arises between the presence of CSIT imperfections, the spreading of the information symbols in the frequency and spatial domains and the diversity order achieved.