Interference supression for quasi-orthogonal space-frequency MIMO OFDM systems

In this paper, we use quasi-orthogonal STBC (QO-STBC) instead of the conventional O-STBC as the inner code for OFDM MIMO systems, resulting in a quasi-orthogonal space-frequency STBC (QO-SFBC). Due to the effects of multi-path, the conventional pair-wise signal detector will introduce severe interference and hence cause an irreducible error floor in the high signal-to-noise ratio (SNR) region for the new QO-SF-OFDM systems. This paper addresses this issue by employing iterative interference cancellation to reduce the error floor. While the computational complexity of the IC detector is a little higher than that of the conventional pair-wise detector, the new IC detector provides much better performance by subtracting the interference resulting from variations between the adjacent OFDM sub-carriers (SCs).