An asymptotic secrecy rate analysis of a cooperative jamming strategy for physical-layer security

In this paper, we investigate a cooperative jamming strategy combined with a null-steering beamforming technique (CJ-NB strategy) for physical-layer security. To evaluate the achievable secrecy rate, the source input distribution is assumed to be Gaussian, and the achievable secrecy rate can be formulated as an optimization problem for power allocation (PA). By solving the problem, an asymptotically optimal PA is obtained with an exactly closed-form expression. In addition, we provide an asymptotic analysis of the achievable secrecy rate. The asymptotic result shows that the achievable secrecy rate is linearly proportional to the signal-to-noise ratio, but it will become saturated when the number of jammers is high enough. Therefore, we then develop a simple and efficient jammer selection algorithm to find an appropriate jamming set to achieve almost the same performance, but significantly reduce the number of jammers used compared with all the jammers performing the CJ-NB strategy. Finally, we provide simulation results to support our analyses.