Multiple relay selection with security constraints for a N-relay diamond network

In this paper we investigate relay selection schemes under physical layer secrecy constrains for a N-relay diamond wireless network. We generalize a single-relay selection scheme by allowing multiple relays to cooperate with the objective to maximize the secrecy capacity. The basic relay selection criterion is based on the instantaneous channel conditions and can be complemented by exhaustive search. We propose two suboptimal schemes to reduce the computation complexity. The system performance in terms of probability of non-zero secrecy capacity, secrecy outage probability and secrecy capacity of the proposed schemes are analyzed and verified by simulations. Numerical results show that our proposed schemes perform better than the corresponding single relay selection method.