Low-Complexity Sphere Search-Based Adaptive Spatial Modulation

This correspondence paper proposes a low-complexity adaptive spatial modulation (ASM) scheme, which is based on sphere search (SS). To find the optimal ASM mode, the existing ASM schemes examine each error vector in the search space. By contrast, in the proposed SS-aided strategy, the search space is reduced to the error vectors inside a sphere, which results in significant complexity reduction. By exploiting a similar structure between the error vectors in ASM and symbol vectors in generalized spatial modulation (GSM), we modify the sphere decoder for GSM to develop an efficient two-step SS scheme for ASM. In addition, an early termination scheme is employed to further reduce the computational load of the SS process for each ASM mode. Simulation results show that SS-aided ASM provides a significant reduction in computational complexity compared to the existing ASM schemes.