Physical Layer Security for Two-Way Untrusted Relaying with Friendly Jammers

In this paper, we consider a two-way relay network where two sources can communicate only through an untrusted intermediate relay, and investigate the physical layer security issue of this two-way relay scenario. Specifically, we treat the intermediate relay as an eavesdropper from which the information transmitted by the sources needs to be kept secret, despite the fact that its cooperation in relaying this information is essential. We indicate that a non-zero secrecy rate is indeed achievable in this two-way relay network even without external friendly jammers. As for the system with friendly jammers, after further analysis, we can obtain that the secrecy rate of the sources can be effectively improved by utilizing proper jamming power from the friendly jammers. Then, we formulate a Stackelberg game model between the sources and the friendly jammers as a power control scheme to achieve the optimized secrecy rate of the sources, in which the sources are treated as the sole buyer and the friendly jammers are the sellers. In addition, the optimal solutions of the jamming power and the asking prices are given and a distributed updating algorithm to obtain the Stakelberg equilibrium is provided for the proposed game. Finally, the simulations results verify the properties and the efficiency of the proposed Stackelberg game based scheme.