Sensing-delay tradeoff for a relay-assisted cognitive link

We consider a cognitive setting in which a secondary user tries to opportunistically access a primary channel. Due to the large distance between the secondary source and its destination, the cognitive link involves a relay to forward the secondary data packets to the destination. Since the secondary relay is assumed to be half-duplex, the source and relay operate at exclusive time slots. We obtain the optimal scheduling of the source-relay and relay-destination links in addition to the optimal spectrum sensing parameters. The objective is to minimize the end-to-end secondary queueing delay subject to a constraint on the detection probability of the primary signal and such that the queues at both the source and the relay are stable. We present numerical results that show the system´s performance and how it depends on the various parameters.