Opportunistic Interference Cancellation in Cognitive Radio Systems

In this paper we investigate the problem of spectrally efficient operation of a cognitive radio (CR), also called secondary system (SS), under an interference from the primary system (PS). A cognitive receiver (CRX) observes a multiple (MA) access channel of two users, the secondary and the primary transmitter, respectively. We advocate that the SS should apply opportunistic interference cancellation (OIC) and decode the PS signal when such an opportunity is created by the rate selected in the PS and the power received from the PS. We derive the achievable data rate in the SS when OIC is applied. When the PS is decodable, we devise a method applied by the SS to achieve the maximal possible secondary rate. This method has a practical significance, since it enables rate adaptation without requiring any action from the PS. We investigate the power allocation in the SS when OIC is applied over multiple channels. We show that the optimal power allocation can be achieved with intercepted water-filling instead of the conventional water-filling. The results show a significant gain for the rate achieved by OIC.