Decode-and-Forward Relay Beamforming with Secret and Non-Secret Messages

In this paper, we study beamforming in decode-andforward (DF) relaying using multiple relays, where the source node sends a secret message as well as a non-secret message to the destination node in the presence of multiple non-colluding eavesdroppers. The non-secret message is transmitted at a fixed rate R0 and requires no protection from the eavesdroppers, whereas the secret message needs to be protected from the eavesdroppers. The source and relays operate under a total power constraint. We find the optimum source powers and weights of the relays for both secret and non-secret messages which maximize the worst case secrecy rate for the secret message as well as meet the information rate constraint R0 for the non-secret message. We solve this problem for the cases when (i) perfect channel state information (CSI) of all links is known, and (ii) only the statistical CSI of the eavesdroppers links and perfect CSI of other links are known. keywords: Cooperative relaying, physical layer security, secret and nonsecret messages, secrecy rate, multiple eavesdroppers.