An optimal OSA approach based on channel-usage estimate under collision probability constraint in cognitive radio systems

Opportunistic spectrum access system allows the secondary user to access spectrum holes not being utilized by the primary user. Traditional opportunistic spectrum access approaches only sense and utilize current spectrum holes. This can result in uncontrollable collision probability, which exceed the maximum collision probability allowed by the primary user network. In this paper, we consider a cognitive radio system with one primary channel and one secondary user, and then, we introduce a channel-usage pattern model and a fundamental access scheme in this system. Based on the fundamental access scheme, we adopt fixed detection duration and transmission duration ratio approach to analyze what and how to determine spectrum holes utilization and collision probability in this model. On the basis of this model and fundamental access scheme, we study optimal opportunistic spectrum access problem and formulate it as an optimization problem that the secondary user maximizes spectrum holes utilization under the constraint of collision tolerable level, and then we solve this optimization problem in two cases: one is that the idle period is exponential distribution, the other is that the idle period is Pareto distribution. According to the solution of the optimization problem, we respectively propose an optimal opportunistic spectrum access algorithm in each case. Theoretical analysis and simulation results both show that the optimal opportunistic spectrum access algorithms can maximize spectrum holes utilization under the constraint that the collision probability is bounded below collision tolerable level.