The causal cognitive interference channel

The (non-causal) cognitive interference channel, studied recently by Liang et. al., is a model for a classical twouser discrete memoryless interference channel, over which two transmitters send a pair of independent messages. It is assumed that the first message is shared by both encoders, whereas the second message in known only to Encoder 2 – the cognitive transmitter. Receiver 2 needs to decode both messages, and Receiver 1 should decode only the first message while Message 2 should be kept as secret as possible from Receiver 1. The level of secrecy is measured by the equivocation rate. For this model the capacity-equivocation region has been derived by Liang et. al.. In this work we dispense of the assumption that Message 1 is shared a-priori by both encoders. Instead, we study the case in which Encoder 2 cribs causally from Encoder 1. We derive an achievable rate-equivocation region for this model and establish the capacity-equivocation region for a degraded interference channel.