Cooperative Jamming Power Allocation With Frequency Offset in Physical Layer Security

This paper considers a point-to-point communication system which is protected by a cooperative jammer from being eavesdropped. Previous works in this field always assume that the cooperative jamming is cancelled perfectly at the receiver, without considering any imperfections in the jamming cancellation of practical systems. In this paper, by taking into account the residual jamming caused by frequency offset at the receiver, a power allocation scheme is proposed to maximize the secrecy capacity over the additive white Gaussian noise (AWGN) channel, which is derived as an exact closed-form solution. In addition, the relationship between the optimal jamming power and the relative channel quality is analyzed under imperfect jamming cancellation. Simulation results confirm that the proposed power allocation scheme outperforms the power allocation scheme without considering any imperfections in the jamming cancellation, and illustrate that the frequency offset significantly degrade the security performance. Specially. for small frequency offset, the total power consumption increases with the frequency offset, which means the frequency offset consumes extra power to achieve the secrecy capacity target. However, for large frequency offset, the secrecy capacity may fail to meet its preset goal no matter how sufficient the power budget is. More seriously, when the frequency offset is remarkable, the secrecy capacity may drop to 0, which implies that the eavesdropper can always overhear the confidential information.