Iterative Soft-In Soft-Out Sphere Detection for MIMO Systems

Soft-input soft-output (SISO) tree search algorithms provide a promising approach for complexity reduced iterative MIMO detection. Realizations based on depth-first search enable near max-log optimal detection at reduced but still high complexity. In this paper we introduce how SISO sphere detectors based on enhancements of single tree search and tuple search algorithms can be efficiently used in iterative detection, outclassing previously proposed decoders or list based iterations. The complexity of the proposed algorithms can be significantly reduced by MMSE preprocessing in combination with a novel unbiased and separated candidate assimilation. Internal clipping of search paths enables further complexity reduction as well as alignment of the tree searches leading to efficient realizations.