Performance evaluation of secondary users in Dynamic Spectrum Access system

Cognitive Radio/Dynamic Spectrum Access, which intelligently and opportunistically uses underutilized portions of licensed wireless spectrum such as broadcast bands, has been proposed to effectively address spectrum scarcity problem. However, the dynamics of spectrum usage in licensed bands influences the performances of cognitive radio system because the licensed system takes priority over the cognitive radio system. In this paper, a cognitive radio system is analyzed with the primary users and the secondary users sharing different bandwidth and a scheme is proposed in which a finite buffer is used to store the preempted secondary users to avoid forced termination of the secondary user´s services. A delay-loss multi-channel preemptive priority queuing model is developed and mathematical analysis was presented to study the secondary system performance in terms of forced termination probability, blocking probability, preempted probability and waiting time. Numerical results show that the forced termination is totally eliminated at the price of increasing the delay of the system.