Relay Selection for Secure Successive AF Relaying Networks With Untrusted Nodes

In this paper, the security aspect of an amplify-and-forward relaying network with untrusted relay nodes is considered. The untrusted nodes can help to forward the received signal and they may also try to decode such information, which can be regarded as potential eavesdroppers (Eves). To deal with such a challenging issue, a successive relaying scheme is adopted, where the multi-antenna source transmits to two selected nodes alternately, and the conventional detrimental inter-relay interference is used to jam the untrusted nodes without external helpers. Considering different complexity requirements, several relay selection schemes are proposed, and the closed-form expressions of the lower bound of secrecy outage probability are derived accordingly. To obtain some insights for the network design, an asymptotic analysis is also given, which shows that the maximum secrecy diversity order of N - 1 can be achieved, where N is the number of the untrusted relays. Moreover, the spectral efficiency is improved dramatically with the successive relaying scheme. Simulation results show that the proposed max-min scheme has almost the same performance as that of the optimal one, and the theoretical results match well with the simulation results.