An improved achievable secrecy rate for the relay-eavesdropper channel

This paper study information-theoretic security for a four-node relay-eavesdropper channel. We propose a new achievable scheme whose key idea is to combine noisy network coding for relay channels and the interference assisted strategy for wiretap channel with a helping interferer. The corresponding achievable secrecy rate is characterized for both discrete memoryless and Gaussian channels. The previous interference assisted schemes such as noise-forwarding and cooperative jamming are shown to be special cases of the proposed scheme. Moreover, in some very strong eavesdropping case where these interference assisted schemes can only achieve zero secrecy rate, the proposed secrecy scheme can still achieve a positive secrecy rate.