Spectral Efficiency Maximization for Spatial Modulation Aided Layered Division Multiplexing: An Injection Level Optimization Perspective

The layered division multiplexing (LDM) is recently combined with spatial modulation (SM) systems to provide a more efficiency way for broadcasting transmission. In SM aided LDM (SM-LDM) systems, the service of each layer, which is allocated with different power, is transmitted via SM scheme. In this paper, a gradient descent based iterative method is proposed to optimize the injection level, which can enhance the spectral efficiency (SE) in the two-layer SM-LDM systems with maximum ratio combining (MRC). In addition, the concavity analysis of this optimization problem is also conducted. Monte Carlo simulations are also provided to verify the effectiveness of our proposed injection level optimization method.