Low complexity approximate log-MAP detection for MIMO systems

In this paper we propose a novel low-complexity log-MAP space-time detection method, which can be regarded as an advanced extension of the complex sphere decoder (CSD). We demonstrate that as opposed to the previously published variants of the soft-output CSD, the proposed technique may be employed in the so-called "over-loaded" scenario, where the number of transmit antennas exceeds that of the receive antennas. The proposed method closely approaches the optimum performance of the Log-MAP detector even in heavily over-loaded scenarios, while the associated computational complexity is only moderately increased