An improved sphere decoding scheme for MIMO systems using an adaptive statistical threshold

The fixed-complexity sphere decoder (FSD) has been previously proposed for multiple input-multiple output (MIMO) detection to overcome the two main drawbacks of the original sphere decoder (SD), namely the variable complexity and sequential structure. However, one issue for the FSD is that many redundant computations are introduced resulting in high power consumption, which will become more evident when many antennas are involved and/or higher-order constellations are utilised. In this paper, a statistical threshold based scheme (ST-FSD) is proposed in order to speedup the algorithm by eliminating its unnecessary search paths. The optimum threshold of the proposed scheme has been derived through analysis of the statistical distributions of the correct and erroneous estimate. Further, a tight lower bound on the threshold has been obtained by using the singular value decomposition (SVD) method and applied to the FSD. From simulation results, the proposed scheme is shown to be able to achieve a significant reduction in computational complexity with almost no performance degradation compared to the original FSD algorithm.