Beamforming and Transmit Power Design for Intelligent Reconfigurable Surface-Aided Secure Spatial Modulation

Intelligent reflecting surface (IRS) is a promising solution to build programmable wireless environment for future communication systems, in which the reflector elements steer incident signal fully customizable ways by passive beamforming. In this paper, an IRS-aided secure spatial modulation (SM) proposed, where IRS perform beamforming and information transfer simultaneously adjusting on-off states of elements. We formulate optimization problem maximize average secrecy rate (SR) jointly optimizing at transmit power transmitter under consideration that direct pathes channels from receivers are obstructed obstacles. As expression SR complex, we derive newly fitting (NASR) traditional approximate (TASR), has simpler closed-form more convenient subsequent optimization. Based on above two expressions, three methods, called maximizing NASR via successive convex approximation (Max-NASR-SCA), dual ascent (Max-NASR-DA) TASR semi-definite relaxation (Max-TASR-SDR) proposed improve performance. Additionally, design (TPD) methods based Max-NASR-TPD Max-TASR-TPD. Simulation results show Max-NASR-DA Max-NASR-SCA beamformers harvest substantial performance gains over Max-TASR-SDR. For TPD, performs better than Particularly, solution.