Capacity region and optimum power allocation strategies for fading cognitive relay multiple access channels

We consider a fading Gaussian cognitive relay multiple-access channel (CR-MAC), consisting of K sources and an active cognitive relay that wish to simultaneously communicate with a single destination. We assume that the relay has its own message to communicate and is aware of the messages of the other K sources non-causally. Furthermore, the message of the relay and the messages of the other K sources are independent. Assuming that all the sources, the cognitive relay and the destination are aware of the instantaneous channel state information (CSI) we characterize the ergodic capacity region. For the case where the cognitive relay does not have its own message to transmit, we derive the optimal power allocation strategies that achieve any arbitrary point on the boundary surface of the capacity region.