Artificial-Noise-Aided Secure Multicast Precoding for Directional Modulation Systems

In a multicast scenario, all desired users are divided into <inline-formula><tex-math notation="LaTeX">$K$</tex-math> </inline-formula> groups. Each group receives its own individual confidential message stream. Eavesdropper group aims to intercept <inline-formula><tex-math notation="LaTeX">$K$</tex-math></inline-formula> confidential message streams. To achieve a secure transmission, two secure schemes are proposed: Maximum group receive power plus null-space (NS) projection (Max-GRP plus NSP) and leakage. The former obtains its precoding vector per group by maximizing its own group receive power subject to the orthogonal constraint, and its AN projection matrix consist of all bases of NS of all desired steering vectors from all groups. The latter attains its desired precoding vector per group by driving the current confidential message power to its group steering space and reducing its power leakage to eavesdropper group and other <inline-formula><tex-math notation="LaTeX">$K-1$</tex-math></inline-formula> desired ones by maximizing signal-to-leakage-and-noise ratio. And its AN projection matrix is designed by forcing AN power into the eavesdropper steering space by viewing AN as a useful signal for eavesdropper group and maximizing AN to leakage-and-noise ratio. Simulation results show that the proposed two methods are better than conventional method in terms of both bit-error-rate and secrecy sum-rate per group. Also, the leakage scheme performs better than Max-GRP-NSP, especially in the presence of direction measurement errors. However, the latter requires no channel statistical parameters and, thus, is simpler compared to the former.