OFDM space-time trellis coded MIMO systems with experimental results

Multi-input multi-output (MIMO) systems have been shown to provide extremely high capacity in non-line-of-sight channels, and are thus well suited for mobile tactical communications. Using space-time trellis coded vector transmission, the paper shows that maximum likelihood joint detection (MLJD) receivers provide substantial improvements over layered space time (LST) approaches. It is shown that in full-rank channels, the MLJD approach provides significant SNR improvement over LST techniques. It is also shown that an MLJD receiver is much more robust in reduced rank channels. Unfortunately, these improvements come at the cost of high computational complexity at the receiver. One way to reduce the computational complexity is to employ a hybrid approach, in which the MLJD receiver is applied to groups of transmit antennas at a time, combined with an outer group-wise LST approach. Methods of performing this grouping based on channel conditions is presented and shown to provide a means of smoothly trading complexity for performance. Simulations and over-the-air measurements are presented that compare various MIMO receiver techniques.