An Optimized-Hierarchy-Aided Maximum Likelihood Detector for MIMO-OFDM

In this paper we propose a novel low-complexity maximum likelihood (ML) 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 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 achieves the optimum performance of the ML detector even in heavily over-loaded scenarios, while the associated computational complexity is only moderately increased