Security-aware routing for artificial-noise-aided multi-hop secondary communications

Physical layer security (PLS) has emerged as a promising technique to guarantee the secrecy of wireless communication against eavesdroppers. Although extensive studies have been devoted to the PLS-based transmission design, the combination of this physical layer technique and network layer mechanisms such as routing still remains an open problem. This paper concentrates on the security issue for the cognitive radio networks. Specifically, we focus on the routing protocol design for the artificial-noise-aided multi-hop multi-antenna secondary communication against randomly distributed eavesdroppers. We first derive the closed-form expression of secure connection probability (SCP) for a single hop link. We optimize the power allocation between the information signal and artificial noise to obtain the maximum SCP of each link. Then a secure routing problem is formulated whose objective is to find the multi-hop path having the highest secrecy throughput. An optimal routing strategy based on a revised Bellman-Ford algorithm is proposed. We also propose a suboptimal strategy based on the Dijkstra algorithm with lower complexity. From numerical results we find that the selected route always makes a detour around the primary user to enhance the secrecy throughput.