Optimal Sensing Interval Considering Per-primary Transmission Protection in Cognitive Radio Networks

Abstract

Sufficient protection of primary user is a challenging issue in cognitive radio networks. The probability of detection and the interference ratio (probability of collision) have been considered as the main constraints for primary protection in the literature. Based on the sensing parameters designed to comply with these constraints, secondary users are often considered to be able to use licensed bands without giving harmful interference to primary users. However, satisfying these constraints might not guarantee that each primary transmission (i.e., each busy period) is sufficiently protected. Obviously, if a large fraction of a busy period is interfered, the busy period may be subject to the useless transmission potentially degrading the quality of service of primary users. We suggest that the busy period impaired more than a certain ratio of so-called required per-transmission interference ratio (PTIR) is subject to the primary transmission failure (PTF), which has not been considered in the literature. As the first attempt, with the assumption of perfect sensing, the effect of sensing interval on the PTIR and PTF is investigated. The probability of PTF is derived as a function of sensing interval given the required PTIR. Then, given the required PTIR and probability of PTF, the optimal sensing interval that maximizes the throughput for secondary users is derived. Performance evaluation shows that primary users can be more protected with the optimal sensing interval obtained by using the proposed constraint.