Quasi‐orthogonal space–frequency and space–time–frequency block codes with modified performance and simplified decoder

Abstract

Due to their superior performance and moderate computational complexity, quasi-orthogonal space–frequency block codes (QOSFBCs) and quasi-orthogonal space–time–frequency block codes (QOSTFBCs) are among prime candidates for implementation in multiple-input multiple-output communications systems. Originally, these codes were introduced for two transmit antennas and it is proved that they are full-diversity within channels with equal-power profile and integer delays. In this study, first, the authors generalise the construction of QOSFBCs and QOSTFBCs for arbitrary number of transmit antennas. Then, they provide the theoretical proof that these codes are full-diversity for any arbitrary number of transmit antennas and any arbitrary delay and power profiles. Furthermore, they prove that the coding advantage of these codes is decomposed into two distinct parts, one of which represents the effect of the channel and the other represents the effect of the precoder. By optimising these two parts, they propose a modified version of QOSFBCs and QOSTFBCs which outperforms the latest space–frequency block codes and space–time–frequency block codes in the literature according to the analytical results and support of simulation results. Finally, they propose a new suboptimum linear decoder for the QOSFBCs and the QOSTFBCs which could achieve almost the same performance as the maximum-likelihood decoder for large number of subcarriers.