Distributed Transmit Power Allocation for Relay-Assisted Cognitive-Radio Systems

We address the issue of optimal transmit power allocation in relay-assisted cognitive-radio (CR) systems. In particular, we assume that the frequency band chosen for unlicensed spectrum usage is not completely unoccupied, but contains one or more licensed narrowband users. For such a setting, we develop distributed transmit power allocation schemes, which optimize the performance of the CR system, while at the same time the interference experienced by the licensed users is limited. Numerical performance results illustrate that notable improvements compared to non-cooperative transmission are achieved by our proposed schemes.