The current paper takes into consideration a cognitive radio network with impatient customers, by the help of finite-source retrial queueing system. We consider two different types of customers (Primary and Secondary) assigned to two interconnected frequency bands. A first frequency band with a priority queue and a second one with an orbit, both are respectively dedicated for the Primary Users (PUs) and Secondary Users (SUs). In case the servers are busy, both customers (Licensed and Unlicensed) join either the queue or the orbit. Before joining the orbit, secondary customers receive a random retrial time according to Exponential distribution, which is the holding time before the next retry. Unlicensed users (impatient) are obliged to leave the system once their total waiting time exceeds a given maximum waiting time.The novelty of this work is the investigation of the abandonment and its impact on several performance measures of the system such as the mean response time and waiting time of users, probability of abandonment of SU, etc. Several figures illustrate the problem in question by the help of simulation.

This paper deals with a Cognitive Radio Network (CRN) which is modeled using a retrial queuing system with two finite-sources. This network includes two non-independent service units treating two types of users: Primary Users (PU) and Secondary Users (SU). The primary unit has priority queue (FIFO) and a second service unit contains an orbit both units are dedicated for the Primary Users and Secondary Users, respectively.The current work highlights the unreliability of the servers as we are assuming that both servers of this network are subject to random breakdowns and repairs. All the inter-event times in this CRN are either exponentially or non-exponentially distributed. The novelty of our investigation is to analyze the effect of several distributions (Gamma, Pareto, Log-normal, Hypo-Exponential and Hyper-Exponential) of the failure and repair times on the main performance measure of the system. By the help of simulation we show some interesting results concerning to sensitivity problems.

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The current paper presents a Cognitive Radio Network with impatient customers and unreliable servers by the help of a finite-source retrial queueing system. We consider two types of customers (primary and secondary) assigned to two interconnected frequency bands. A first frequency band with a priority queue and a second frequency band with an orbit are reserved for Primary Users (PUs) and Secondary Users (SUs), respectively. If the servers are busy, both customers (licensed and unlicensed) enter either the queue or orbit. Before they enter orbit, the secondary customers receive a random retrial time according to the exponential distribution, i.e. the waiting time before the next retry. Unlicensed users (impatient) are obliged to leave the system as soon as their total waiting time exceeds a random maximum waiting time. It should be noted, that the secondary service unit of our system is subject to random breakdowns and repairs. The novelty of this work consists in the investigation of the abandonment and secondary server unreliability impact on various performance measures of the system (Cognitive Radio Network), such as the mean response and waiting time of users, the probability of abandonment of SU, etc. Several figures illustrate the problem in question through simulation.

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