Feedback enhances the security of degraded broadcast channels with confidential messages and causal channel state information

In this paper, we investigate the degraded broadcast channels with confidential messages (DBC-CM), causal channel state information (CSI), and with or without noiseless feedback. The inner and outer bounds on the capacity-equivocation region are given for the non-feedback mode, and the capacity-equivocation region is determined for the feedback model. We find that by using this noiseless feedback, the achievable rate-equivocation region (inner bound on the capacity-equivocation region) of the DBC-CM with causal CSI is enhanced.