Performance Analysis, Comparison, and Optimization of Interweave and Underlay Spectrum Access in Cognitive Radio Networks

Cognitive radio networks (CRNs) have been proposed to exploit licensed bands opportunistically, with secondary users’ (SU) activity being subordinated to primary users (PU). The two most popular types of spectrum access in the CRN are interweave and underlay. There is no clear consensus which one provides better results, for different metrics, despite the fact that there has been a lot of research dedicated to each mode. In this paper, we analyze this problem theoretically, providing formulas that are in closed form. These expressions allow the performance comparison of interweave and underlay modes under a unified network setup. Our focus are two metrics, throughput and delay, which we analyze relying on the renewal-reward theory and queueing theory, respectively. These results enable an SU to decide what mode to use depending on what the optimization objective is, given the key network parameters. Furthermore, relying on the results of our analysis, we propose hybrid policies, which are dynamic, and allow the SU to switch between the two modes at any point. These policies offer an additional performance improvement of up to 50%. We validate our results with extensive realistic simulations.