Non-orthogonal rate-2 space-frequency block code on MIMO-OFDM systems

Space-time block coding is one of the widely used schemes to increase robustness and performance of wireless physical layer links. However, code orthogonality limits its data throughput thus reducing spectral efficiency. In this paper, non-orthogonal rate-2 space-time and space-frequency block codes are implemented in MIMO-OFDM systems in order to increase spectral efficiency while compromising orthogonal full diversity gains. A computationally efficient soft QRD-M MIMO symbol detection algorithm is used for both space-time and space-frequency block coding approaches. A 4×2 MIMO system was simulated to verify the implementation concept and demonstrate its performance. The simulation results shows that the performance gap between space-time and space-frequency approach is minimal as long as the bandwidth of the space-frequency block coding depth is within the coherence bandwidth of the channel.