A New Communication Paradigm in Wiretap Channels: Simultaneous Information Transmission and Cooperative Jamming

This paper considers a Gaussian vector wiretap channel with two users, where user $1$ is secrecy-sensitive and transmits both secret and open (non-confidential) messages, and user $2$ is secrecy non-sensitive and transmits only open messages. We provide an achievable rate region and show that by introducing `garbage' messages and applying random coding, simultaneous information transmission and cooperative jamming (SIT-CJ) can be achieved, i.e., user $2$ can transmit useful information to the legitimate receiver and at the same time act as a friendly jammer for user $1$. To evaluate the performance of SIT-CJ, we maximize the secrecy rate and compare with the No-jamming case, where there is only user $1$, and also the Gaussian noise (GN) jamming scheme, where user $2$ jams by transmitting Gaussian noise. For the SIMO case, we prove that though non-convex, the power control problems for all jamming schemes can be optimally solved. Things are much more complicated in the MIMO case. However, we show that by using matrix simultaneous diagonalization, all precoder design problems can be efficiently solved with a low complexity. Simulation results show that the proposed SIT-CJ scheme can help greatly enhance the secrecy of user $1$, and outperforms the GN-jamming scheme in secrecy improvement. Moreover, since besides confidential information, all users transmit open messages, the system's spectral efficiency can be dramatically increased by SIT-CJ compared with the GN-jamming scheme and also the case where only secret messages of user $1$ are considered.