Statistical Analysis and Minimization of Security Vulnerability Region in Amplify-and-Forward Cooperative Systems

Abstract

Secrecy rate achievability in three-node amplify-and-forward cooperative systems at the presence of passive eavesdroppers without location information is statistically analyzed and optimized. First, the effective vulnerability area, the area in which no secrecy rate is achievable when an eavesdropper resides in that area, is introduced as the performance metric to measure the security of the cooperative system. Then, it is shown analytically that the best location of the relay to minimize the effective vulnerability region is on the source–destination crossing line. In addition, it is proved that the optimum relay with the best location and power allocation is located on the line segment bounded by the source and destination. Exact and some special closed-form expressions for the probability of secrecy rate achievability are obtained for the Rayleigh fading environment. Using this, the impact of the location and the relay power on the effective vulnerability area are analyzed and the best cases minimizing this area are numerically computed. It is shown that the effective vulnerability area can be reduced more than 50% in comparison with the case where no relay is used if the optimum relay location and the optimum relay power allocation are adopted.