Adaptive Jamming Power Control for Untrusted Relay Networks with Imperfect Channel Reciprocity

In an untrusted relay network where a destination transmits a jamming signal to prevent an untrusted relay from recovering the data sent by a source, we consider imperfect channel reciprocity (ICR) between the relay and the destination. This ICR prevents the destination from removing jamming interference perfectly, meaning that transmit power of the jamming signal has a significant impact on the secrecy rate. In this article, we present a system model of an untrusted relay network with ICR, and verify that the secrecy rate is concave with respect to the jamming power. We derive an asymptotic optimal jamming power to maximize the secrecy rate in closed-form and propose an adaptive scheme for jamming power control (JPC). Numerical results show that the proposed JPC scheme achieves a near-optimal secrecy rate, as well as outperforming conventional schemes by controlling the jamming power adaptively. In particular, we note that to improve the secrecy rate, it is advantageous to reduce the jamming power to decrease the residual jamming interference as the reciprocity error increases or the channel between the relay and the destination improves.