Optimal Slot Length Configuration in Cognitive Radio Networks

In cognitive radio networks, a slotted time structure is widely adopted. Accordingly, the slot length is a factor that can largely affect the performance of cognitive radio networks. In this paper, a slot length configuration scheme is proposed. In the proposed scheme, we assume imperfect spectrum sensing. The spectrum sensing result is considered when configuring the slot length. Therefore, slots with different sensing results have different slot lengths. This setting fully takes into account the fact that the sojourn time of channel idle state and busy state are usually different. An optimization problem to find out the optimal slot length configuration is formulated (which maximizes the secondary throughput) and analyzed. In the formulated problem, primary activities are protected by limiting the percentage of time that the primary activities are interfered with, and the energy efficiency of the secondary system is guaranteed by limiting the percentage of time for spectrum sensing. After a theoretical analysis of the problem, an algorithm is proposed to solve it. In the case of perfect spectrum sensing, another algorithm with low complexity is developed to solve the problem. The numerical results demonstrate that, by having different slot lengths with different sensing results, largely improved performance can be achieved. Impacts of system parameters on the secondary system performance are also discussed.