Transmit diversity and spatial multiplexing in four-transmit-antenna OFDM

This paper studies a practical design for achieving both spatial diversity and spatial multiplexing in an OFDM system with four transmit antennas. In a certain range of spectral efficiency, the proposed hybrid space-time block coding/multiple-input multiple-output (STBC/MIMO) design is found to be a good design choice based on performance and receiver complexity, when compared with MIMO-only or diversity-only STBC designs. For the hybrid design, we propose a simple receive algorithm that requires no matrix inversion. Outage capacity evaluated with a Monte Carlo approach is used to provide insight into the simulation-based comparison of the different designs. The robustness to channels that lack spatial separability is also studied in the simulations.