Secrecy Outage Probability of Two-Path Successive Relaying in Physical Layer Security

Relaying is a promising technique to improve wireless physical-layer security. Existing literature shows that a full-duplex relay can further improve the secrecy capacity and secrecy outage probability compared to conventional half-duplex relay, but this comes at a price of sophisticated implementation. For sake of easy implementation, two-path successive relaying has been proposed to emulate the full-duplex relay by scheduling a pair of half-duplex relays to assist the source transmission alternately. However, the performance of two-path successive relaying in secrecy communication remains unexplored. This paper proposes a secrecy two-path successive relaying protocol for a scenario with one source, one destination and two half-duplex relays. The relays operate alternately in a time division mode to forward messages continuously from source to destination in the presence of an eavesdropper. To further confuse the eavesdropper, the source and relay are scheduled to transmit jamming signals at appropriate intervals. Analytical results on the secrecy outage probability reveals that the proposed protocol is able to deliver the target secrecy rate when the SNR of the eavesdropping channels are high. In addition, the secrecy outage probability of the proposed protocol is the joint secrecy outage probability of the relay pair. Numerical simulations show that the proposed protocol achieves the highest ergodic secrecy capacity and lowest secrecy outage probability compared to the existing half duplex relaying, full duplex relaying and full duplex jamming schemes.