Optimal sensing interval considering per-primary transmission protection in cognitive radio networks

Sufficient protection of primary user is a challenging issues in cognitive radio networks. Previous works have considered either the probability of detection higher than a required one given a priori or the interference ratio (probability of collision) below a certain threshold as the constraint for sufficient protection of primary users. However, satisfying these constraints does not guarantee that an individual transmission period of a primary user (referred to a busy period) is sufficiently protected. Obviously, if a large fraction of a busy period is interfered, the busy period may be subject to a useless transmission potentially degrading the quality of service (QoS) of primary users. We suggest that the busy period impaired more than a certain ratio of so-called required per-transmission interference ratio (required PTIR) is subject to a primary transmission failure (PTF), which has not been considered at all in the literature. As the first attempt, while assuming perfect sensing, the effect of sensing interval on the PTIR and PTF is investigated in this paper. The PTF probability is derived as the function of a sensing interval given the required PTIR Then, for the case where both the required PTIR and required PTF probability are given, the optimal sensing interval that maximizes the achievable throughput for secondary users is derived. Performance evaluation shows the efficiency of the proposed metric in protecting primary users compared to the other considered in the literature.