Queueing Analysis of Opportunistic Access in Cognitive Radios

This paper presents queueing analysis of opportunistic access in cognitive radios. The primary (licensed user) has priority over the secondary user and it does not need to care about the secondary user transmissions. A time slotted system is assumed, so that the secondary user can perform spectrum sensing at the beginning of the slot to know if it is occupied by primary or not. If the slot is free, it can be utilized for secondary transmissions. This leads to no interference with primary user communication, assuming perfect sensing. Finding waiting time and queue length of this type of system has not, according to our best knowledge, been performed before. We perform theoretical analysis by applying M/D/1 priority queueing scheme. The results were used to evaluate the performance of the cognitive network. Simulation are used to validate the results, and simulation results demonstrate a high degree of accuracy for the derived expressions. Results indicate that the performance of the secondary user depends on the data traffic characteristics of the primary user, and under high arrival rate for the primary, the average waiting and average queueing length of the secondary user grow especially when the combined arrival rate approach the queue utilization factor.