Efficient node enumeration for soft-input soft-output sphere decoding

Soft-input soft-output (SISO) sphere decoding is applied to multiple-input multi-output (MIMO) systems to offer good bit error rate (BER) performance but at high complexity. To reduce this computational complexity, we propose a novel hybrid enumeration strategy for such decoding that dynamically determines the candidate list; moreover, this strategy uses a new node enumeration based on concentric circles. Specifically, points in an MQAM constellation diagram are divided into several subsets; and the visiting order among subsets is predefined by the concentric circle locations. Simulation results demonstrate that the proposed enumeration strategy outperform previous approach, while keeping a low complexity.