Improving Physical Layer Security Via Random Precoding

Existing secure strategies based on precoding-aided spatial modulation (PSM) ensure the secrecy communication by introducing time-varying interference with extra power towards the eavesdropper, which, however, reduces the energy efficiency. In this paper, we propose two novel schemes to enhance the secrecy performance based on PSM. The first scheme utilizes the random antenna selection (RAS) technique, namely RAS-PSM, to generate zero-forcing (ZF) precoding matrices with randomly activated transmit antennas. It ensures efficient transmission to the legitimate user, while confusing the eavesdropper via the turbulence of RAS without extra power consumption. The second scheme, called hybrid secret PSM (HS-PSM), is an enhanced version of RAS-PSM by introducing the time-varying artificial noise into RAS-PSM. The resulting secrecy rates by the two proposed schemes are theoretically analyzed and evaluated via Monte Carlo simulations as well, whose results demonstrate that RAS-PSM achieves a higher secrecy rate than the existing schemes and HS-PSM is capable of further improving the secrecy performance especially at high signal-to-noise ratio (SNR).