Reduced-complexity sphere decoding with dimension-dependent sphere radius design

A modified sphere decoding (SD) scheme is proposed for multiple-input multiple-output (MIMO) communication systems in this paper. The conventional SD goes from the lower dimension to the higher dimension to examine whether a lattice point lies inside the sphere of some radius, which remains fixed for all dimensions. Since the sphere radius directly affects the search range and thus the complexity, it is an important parameter to design. The proposed scheme employs a set of dimension-dependent sphere radii, which performs more aggressive search-space reduction in low dimensions. The proposed method is shown by computer simulation to offer substantial complexity benefits with little symbol error rate (SER) performance loss (0.5 dB), compared to the optimal maximum likelihood (ML) decoding. The contribution of this paper includes the complexity advantage yielded by the proposed scheme as well as the introduction of a systematic approach to sphere radius design and control.