Abstract—Cognitive radio network (CRN) is an established approach for solving the challenge of spectrum underutilization and scarcity respectively. This can be achieved through a dynamic spectrum access (DSA) policy. The incumbent user (Primary User), being the licensed owner/user, has higher priority to utilize the channel while the unlicensed user (secondary users) can access the primary channel opportunistically anytime when the channel is not occupied by Primary User (PUs). Whenever the Primary User (PU) arrives and the unlicensed user is still occupying (utilizing) channel, the secondary users (SU) either coexist if the interference/power threshold is minimal or it is forced to terminate/queue in a buffer if the interference is destructive. However, if the PU arrives and enough channel/resources is available, how does this transaction affect the SU performance in an overlay scenario. This paper investigates and evaluates the effect of the incumbent user on unlicensed user channels in terms of throughput, average service time, delay and packet blocking. The occupancy of the primary channel is modelled as a discrete-time two state Markovian chain. An analytical model is presented to evaluate the performance of opportunistic spectrum access policy using a Discrete Time Markov Chain (DTMC) model which is validated by extensive simulations. 


Index Terms—Cognitive radio networks, discrete-time, markov chain, overlay, primary user, secondary users.