Cognitive Radio Networks: How Much Spectrum Sharing Is Optimal?

The authors explore the performance tradeoff between opportunistic and regulated access inherent in the design of multi-user cognitive radio networks. They consider a cognitive radio system with sensing limits at the secondary users and interference tolerance limits at the primary and secondary users. Their objective is to determine the optimal amount of spectrum sharing, i.e., the number of secondary users that maximizes the total deliverable throughput in the system. They begin with the case of perfect primary user detection and zero interference tolerance at each of the primary and secondary nodes. They find that the optimal fraction of licensed users lies between the two extremes of fully opportunistic and fully licensed operation and is equal to the traffic duty cycle.