A Low Complexity Soft-Input Soft-Output Fixed-Complexity Sphere Decoding Algorithm

By exchanging soft information between the detector and the channel decoder, an iterative receiver can significantly improve the performance compared to the non-iterative receiver. In this paper, a low complexity soft-input soft-output (SISO) fixed-complexity sphere decoding (FSD) algorithm is proposed for iterative MIMO receiver. The algorithm introduces a simplified parallel candidate adding (SPCA) scheme to provide more accurate soft information. Furthermore, by employing our proposed improved hybrid-enumeration method, the SISO-FSD can reduce the computational complexity substantially. Simulation results show that the algorithm can achieve a near Max-Log optimal maximum a posteriori (MAP) detection performance under flat fading Rayleigh channels. Compared to the SISO K-Best algorithm (K=50), the proposed algorithm saves about 60% computations and provides almost the same performance for detecting 4×4 64-QAM MIMO signal, making it a promising scheme for real-life hardware implementation.