Adaptive power allocation (PA) algorithms based on optimization of the minimum distance dmin between signal points at the receiver side are investigated in spatial modulation (SM) systems. Firstly, a closed-form solution of the optimal maximum-dmin aided PA algorithm is derived in the case of two transmit antennas. Moreover, for a higher number of transmit antennas (TA), we propose a numerical approach, which appropriately splits the power between the specific TA-pair associated with dmin, so as to increase this distance. Furthermore, our PA-aided SM systems may be readily combined with adaptive modulation (AM) for further improving the system’s performance. Our numerical results show that the proposed algorithms provide beneficial system performance improvements compared to both the equal-gain PA based SM and the identical-throughput PA-aided spatial multiplexing systems.
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