Maximum-likelihood MIMO detection using adaptive hybrid tree search

A hybrid tree search algorithm is described for maximum-likelihood symbol detection in spatial multiplexing (SM) systems. Essentially, the search tree is iteratively expanded in the breadth-first (BF) manner until the probability that the current most likely path is correct exceeds a specified threshold, at which point the depth-first (DF) stage is initiated to traverse the rest of the tree. In contrast to the sphere decoding (SD) algorithm, the proposed algorithm uses the BF stage to enhance the accuracy of the initial DF search direction, by exploiting the diversity inherent in the SM scheme. Simulation results demonstrate that the proposed algorithm achieves a significantly lower complexity than the SD algorithm in many scenarios of practical interest.