Achievable rate regions for broadcast channels with cognitive relays

We investigate the fundamental limits of broadcast channels with cognitive relays. Specifically, we develop a new coding strategy and the associated achievable rate regions for the broadcast channel with two receivers and two additional cognitive relays. The new achievable rate regions exhibit potentially higher rates than existing schemes. We also consider a simplified model where there is only one cognitive relay. In this scenario we develop a general coding strategy that includes most existing schemes over the cognitive radio channel. We demonstrate the advantages associated with our generalized coding scheme for a broadcast channel with a single cognitive relay in Gaussian noise.