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

Abstract: In this paper, we study beamforming in decode-and-forward (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 $R_{0}$ 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 $R_{0}$ 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.