Physical layer security in two-path successive relaying

This paper proposes a bandwidth-efficient transmission protocol with one source, one destination and two assisting half-duplex relays. The two relays operate alternately in a time-division-duplex mode to forward messages from source to destination in the presence of an eavesdropper. Therefore, the source transmits new information continuously and the bandwidth efficiency of ideal full-duplex relay network can be achieved. The two relays provide higher diversity gain compared to the existing schemes assisted by one relay. By considering the achievable secrecy rate as the minimum between the secrecy rate of the S-R and R-D links, the achievable secrecy capacity can be improved. We investigate the performance of the protocol in terms of ergodic secrecy capacity and secrecy outage probability and compared to the existing half-duplex relaying, full-duplex relaying and full-duplex jamming schemes. The proposed protocol achieves the highest ergodic secrecy capacity and the lowest probability of secrecy outage compared to the existing schemes.