Power Allocation-Aided Spatial Modulation for Limited-Feedback MIMO Systems

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