Performance Analysis of Secret Precoding-Aided Spatial Modulation With Finite-Alphabet Signaling

The precoding-aided spatial modulation (PSM) is first characterized with respect to its secrecy performance, which shows that the PSM is a secrecy embedded communication scheme when operated in the time-division duplex mode, but experiences security risk under frequency-division duplex mode. Therefore, we extend the PSM to a secret PSM (SPSM) that is suitable for operation in any communications scenarios experiencing passive eavesdropping. In the proposed SPSM, the secrecy performance is enhanced by using a part of transmit power to interfere the eavesdropper's reception. In this paper, the secrecy performance of SPSM with discrete inputs is comprehensively investigated in terms of both bit error rate and secrecy rate and by both analysis and simulations. Relying on the asymptotic analysis, we also derive the upper and lower bounds for the error performance and secrecy rate of SPSM. Furthermore, we study the power allocation between information and interference transmission in order to maximize SPSM's secrecy performance. Our studies result in a range of expressions, which are validated by Monte Carlo simulations. Furthermore, our studies demonstrate that the analytical formulas are beneficial to the optimization of SPSM systems for maximizing its security performance.