Relay selection and scaling law in destination assisted physical layer secrecy systems

A distributed wireless network with one source, one destination, one eavesdropper and multiple Decode-and-Forward (DF) relays is investigated. A two-slot cooperative relaying scheme is considered, in which relays help the source transmit to the destination while keeping the message as secret as possible from the eavesdropper. To prevent the system becoming interference limited, a destination assisted jamming scheme is used, i.e., the destination transmits a jamming signal rather than listening to the source. Several relay selection methods are proposed to let the system benefit from increase of the number of relays. With the proposed transmission scheme, the system secrecy rate is shown to outperform the methods in literature and maintain a scaling law of the achievable secrecy rate of log₂(1 + P₀/8 log K) -1.6252, where K is the number of relays and P₀ is the total transmit power.