On the secrecy mutual information of spatial modulation with finite alphabet

In this paper, the spatial modulation (SM) is considered as a novel physical layer technique to improve the physical layer security of wireless networks. Exploiting the index of antenna as an additional dimension to convey part of source information bits, SM helps to achieve multiplexing gain and realize higher data rates. Moreover, by properly designing the transmission signal, SM can also improve physical layer security. The secrecy mutual information of SM with finite alphabet input is derived in this work, and a preceding scheme is proposed to improve the physical layer security performance of SM. Analysis and numerical results verify the validity and effectiveness of the proposed scheme, and it also shows that the maximum achievable secrecy mutual information is the logarithm of the number of transmit antennas.