This paper investigates power control and relay selection in Full DuplexCognitive Relay Networks (FDCRNs), where the secondary-user (SU) relays cansimultaneously receive and forward the signal from the SU source. We study bothnon-coherent and coherent scenarios. In the non-coherent case, the SU relayforwards the signal from the SU source without regulating the phase, while inthe coherent scenario, the SU relay regulates the phase when forwarding thesignal to minimize the interference at the primary-user (PU) receiver. Weconsider the problem of maximizing the transmission rate from the SU source tothe SU destination subject to the interference constraint at the PU receiverand power constraints at both the SU source and SU relay. We developlow-complexity and high-performance joint power control and relay selectionalgorithms. The superior performance of the proposed algorithms are confirmedusing extensive numerical evaluation. In particular, we demonstrate thesignificant gain of phase regulation at the SU relay (i.e., the gain of thecoherent mechanism over the noncoherent mechanism).
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