Compress-and-forward strategy for Causal Cognitive Interference Channel

In this paper, we consider Causal Cognitive Interference Channel (CC-IFC), wherein the cognitive user overhears the channel and exploits knowledge of the primary user's message from the causally received signals. We propose a coding scheme which combines Compress-and-Forward (CF) strategy with Marton coding with common information at the cognitive user. Rate splitting for messages at both transmitters is used to have a collaborative strategy. Moreover, the cognitive user compresses its channel observation using Wyner-Ziv coding and splits the index of its compressed signal. Then, the cognitive user having common information to both receivers and private information to each of them, jointly maps its split message and split index to codewords, using Marton coding with common information. Besides the fact that, this strategy allows users to cooperate, cognitive user mitigates part of the interference by binning its codewords against each other. We utilize the sliding-window and simultaneous joint decoding techniques at the receivers. Using this scheme, we establish a new inner bound on the capacity region (achievable rate region) for CC-IFC. Further, we extend our achievable rate region to the Gaussian case and compare it with the previously obtained results which are based on Decode-and-Forward (DF) strategy, via numerical examples.