Partial expansion sphere decoder with reduced branching factor for MIMO systems

Multiple-input multiple-output (MIMO) detection could be modeled to a tree search problem. This paper proposes one sphere decoder algorithm called partial expansion sphere decoder (PESD) by pruning the search tree using a reduced branching factor. The main idea of the proposed PESD is to reduce the detection complexity by decreasing the branching factor for the search tree. The trade-off between the performance and complexity can be easily controlled by the branching factor. In order to further improve the PESD, a hybrid PESD is proposed by combining the full enumeration for the first several layers of the search tree and the proposed PESD. The simulation results demonstrate that the PESD achieves a flexible trade-off depending on the branching factor and shows that the hybrid PESD obtains performance gains than the pure PESD with the same branching factor.