Achievable rate-equivocation regions for relay broadcast channels with confidential messages

In this paper, we investigate the effects of an additional relay node on the secrecy of broadcast channels by considering the model of relay broadcast channels with confidential messages (RBC-CM). More specifically, first, we investigate the discrete memoryless relay broadcast channels with two confidential messages and one common message. Three inner bounds (with respect to decode-forward, generalized noise-forward and compress-forward strategies) on the capacity-equivocation region are provided. Second, we investigate the discrete memoryless relay broadcast channels with one confidential message and one common message. This work generalizes Lai-Gamal's work on the relay-eavesdropper channel by considering an additional common message for both the legitimate receiver and the eavesdropper. Inner bounds on the capacity-equivocation region are provided, and the results are further explained via a Gaussian example. Compared with Csiszár-Körner's work on broadcast channels with confidential messages (BCC), we find that with the help of the relay node, the secrecy capacity region of the Gaussian BCC is enhanced.