Doubly ordered sphere decoding for spatial modulation

In this study, novel ordering algorithms of sphere decoding (SD) for spatial modulation (SM) are proposed to reduce the computational complexity. In the receive-ordering (Rx-ordering) scheme, the signals encountered at receive antennas are ordered to increase the probability of early termination during the search process. In contrast, the transmit-antenna indices and the constellation points in the transmit-ordering (Tx-ordering) scheme are ordered on the basis of a suboptimal solution, which is obtained from a subset of the received signals. To further reduce the computational complexity, the combined scheme of Rx-ordering and Tx-ordering is also presented. Simulation results show that SD aided by the proposed ordering schemes provides a substantial reduction in the computational complexity compared to existing SD algorithms in various environments while achieving near-optimal decoding performance.