Jamming power control for secure communication via untrusted relay with imperfect channel estimation

This paper investigates a secure communication via an untrusted relay with channel estimation error, in which a destination-assisted jamming strategy is adopted to prevent the relay from recovering a source signal. In the presence of channel estimation error in the relay-to-destination link, a destination cannot decode the source signal as well as eliminate a jamming signal perfectly, which causes a serious degradation in secrecy performance. Therefore, it is required to propose an effective strategy to determine jamming power level for maximizing secrecy rate. Under the assumption of high transmit signal-to-noise ratio, we derive the closed-form expression of a suboptimal jamming power ratio and propose an adaptive jamming power allocation which can be operated in practical systems. Numerical results confirm that the proposed scheme outperforms the conventional scheme in terms of secrecy rate.