The cognitive radio channel: From spectrum sensing to message cribbing

Cognitive radios have been considered as an enabling technology toward resolving the spectrum scarcity through spectrum reuse facilitated by the cognitive capability of secondary users. Recent studies, however, have gone beyond spectrum sensing at the medium access control layer; it was conceived to have cognitive radios that are capable of extract information pertaining to the physical layer from the primary users to enable coexistence of multiple users. We take upon this newly proposed approach but refrain from imposing the unrealistic assumption of non-causal cooperation. Specifically, we study the so-called cognitive radio channels from the message cribbing perspective where the term 'cognitive' capability is strictly causal. Information theoretic performance bounds are obtained which shed lights on the impact of such causal cognitive capability.