Hardware-Aware Quadrature Spatial Modulation

Spatial modulation (SM) is a simple multi-input multi-output (MIMO) communication technique in which a single transmit antenna is active for each symbol period. Quadrature spatial modulation (QSM), on the other hand, is a form of SM in which independent transmit antenna selection is made for the real and imaginary parts of the symbols. In these techniques, the spectral efficiency (SE) can be increased logarithmically by increasing the number of antennas used on the transmitter-side. Besides, in classical SM and QSM schemes, the number of antennas must be the power of two. In this paper, a flexible QSM scheme is proposed, which eliminates the necessity of antenna number and increases SE value linearly with the number of antennas for RF systems. This scheme, called hardware-aware quadrature spatial modulation (HAQSM), uses optimized constellations for the desired SE value. Optimal constellations are obtained using convex optimization under a constraint aimed at keeping the distance between neighboring symbols above the desired value. The bit error rate (BER) performances of the HAQSM scheme were obtained by Monte Carlo simulations and compared with the existing schemes in the literature.