Variation of the fixed-complexity sphere decoder

The fixed-complexity sphere decoder is a near-optimum tree search detector for the spatial multiplexing scheme. The search tree is statically divided into a full expansion stage and a single expansion stage. To enable the power-saving design and to achieve a lower average complexity with little performance loss, we propose an algorithm that adapts, based on the channel conditions, the switching point between the two stages. The algorithm preserves the capability of parallel processing and pipelining in tree search, and yields predictable complexities.