Opportunistic Selection of Threshold in Cognitive Radio Networks

In a cognitive radio (CR) system based on energy detection spectrum sensing scheme, the threshold is mainly selected, either under a given detection probability of \(\overline{{P_{d} }}\) known as the constant detection rate (CDR) principle, or under the given false alarm probability of \(\overline{{P_{fa} }}\), known as the constant false alarm rate (CFAR) principle. In order to promise sufficient quality of service (QoS) to the licensed users, the threshold selection under the CDR principle is most favorable. However, this undesirably degrades throughput of the cognitive users, mainly under the most suitable conditions of spectrum reuse when the licensed user is located far away from the sensing node where chances of interference are negligible. To improve the licensed spectrum utilization, this paper proposes a technique for the selection of threshold based on the opportunistic use of CDR and CFAR principles depending upon the distance d of licensed user from the unlicensed one. Under the proposed approach, when the distance d is less than or equal to a formulated critical distance d _c (d ≤ d _c ), then, to promise sufficient QoS to the licensed users, the CDR principle is used. But for the reverse case d > d _c , to maximum exploit the spectrum reuse conditions, the advantages of CFAR principle are relished. The CR system under the proposed approach obtains a significant gain in its throughput compared to the case where CDR principle is used blindly.