Efficient near-ML detection for MIMO channels: the sphere-projection algorithm

It is well known that suboptimal detection schemes for MIMO spatial multiplexing systems (equalization-based as well as nulling-and-cancelling detectors) cannot exploit all of the available diversity. We show that this inferior performance is primarily caused by poorly conditioned channel realizations. We then present the novel sphere-projection algorithm (SPA) that is robust to poorly conditioned channels. The SPA is a computationally efficient add-on to standard suboptimal detectors. Simulation results show that the SPA is able to achieve near-ML performance and significantly increased diversity gains. The SPA's computational complexity is comparable to that of nulling-and-cancelling detectors and only a fraction of that of the Fincke-Phost sphere-decoding algorithm for ML detection (Fincke, U. and Phost, M., Math. of Comp., vol.44, p.463-71, 1985).