Space-frequency linear precoding with optimal detection for MIMO-OFDM systems

This paper considers the use of precoding in MIMO-OFDM systems based on deterministic channel state information at the transmitter (CSIT). The proposed technique combats subcarrier fading using a linear spreading of the source information in the spatial and frequency domains. Unlike previous works, it is assumed that the receiver does not necessarily has to rely on linear processing, allowing in this way more powerful receiver strategies. In particular, it is shown that a detector based on the maximum likelihood (ML) criterion brings along important performance benefits. Different spreading strategies are evaluated in terms of their performance and ML detection complexity. It can be observed that spreading the information and optimising the system over a group of subcarriers (rather than on a per subcarrier-basis or all subcarriers together) extracts virtually all the diversity the wireless channel can provide while remaining computationally feasible. Simulation results are presented within the context of the new WLAN standard IEEE 802.11n in order to illustrate the practicality of the proposed technique.