An Enhanced Multi-Stream Spatial Modulation Scheme for High-Rate MIMO Systems

Abstract

This paper proposes an Enhanced Multi-Stream Spatial Modulation (En-MSM) system employing Nt transmit antennas, where two antennas are activated simultaneously, for high-rate MIMO systems. En-MSM conveys information bits through both the spatial domain, i.e., the indexes of the active antennas, and PAM/QAM symbols. Each transmit signal vector, or transmit codeword, includes one M-PAM and one conventional N-QAM symbol, with the M-PAM symbols generated as even multiples. To further improve spectral efficiency, the M-PAM symbols are combined to form new M-APSK symbols, which replace the PAM symbols in the transmit vector. This design expands the available transmit codeword set and increases the minimum distance in the signal space. A sub-optimal detector is also proposed for signal recovery in the En-MSM scheme to support scenarios requiring low detection complexity, at the expense of some performance degradation. Simulation results demonstrate that En-MSM achieves noticeable performance gains compared with conventional MSM, ESM, and GSM-MIM across various scenarios, while maintaining comparable hardware complexity. Moreover, compared with SM, En-MSM not only achieves significant performance gains but also requires substantially fewer transmit antennas.