Secrecy Performance Analysis of Artificial-Noise-Aided Spatial Modulation in the Presence of Imperfect CSI

The security of information over wireless channels has always been an important aspect of wireless communication research. In this paper, the secrecy performance of a spatial modulated system with an artificial noise is investigated over the Rayleigh channel, and the corresponding secrecy rate is analyzed in the presence of imperfect channel state information (CSI). Based on the secrecy performance analysis, the ergodic rates and the corresponding lower bounds of the legitimate receiver and eavesdropper are, respectively, derived. As a result, the closed-form lower bound of ergodic rate of the legitimate receiver is obtained, and the lower bound of ergodic rate of the eavesdropper and the corresponding ergodic secrecy rate (ESR) can be achieved by calculating the mean values. To avoid the mean operation and reduce the complexity, the closed-form approximated expression of ESR is also derived. This theoretical ESR can include the one under perfect CSI as a special case and has the value close to the corresponding simulation. Thus, it can provide good performance evaluation for the artificial-noise-aided spatial modulation system with imperfect CSI. Simulation results verify the effectiveness of the theoretical analysis. The system with imperfect CSI is found to have low ESR as compared to the one with perfect CSI due to the estimation error. Moreover, initially, the ESR increases with increasing power of artificial noise, but then, due to the total power constraint, it starts decreasing.