Dynamic Queuing Model for the Secondary Users in a Cognitive Radio Network for Improvement of QoS

The advent of various bandwidth-hungry applications now-a-days has increased the spectrum demand, thereby resulting in spectrum scarcity. Cognitive Radio Networks (CRN), proposed by the researchers, is a probable solution to the problem. CRN allows licensed Primary Users (PUs) to partly lease their unutilized spectrum to the opportunistic Secondary Users (SU) for effective Channel Utilization (CU) and enhanced Quality of Service (QoS). Now, use of buffers is a common approach to provide improved QoS to the SUs. However, if the waiting time of the SUs in the buffers exceed their time-out interval, the QoS degrades instead of improving. Thus, in this work, firstly, a CRN has been modeled using two buffers, namely, the New Queue (NQ) and the Pre-empted Queue (PQ). The NQ holds the newly requesting SUs while the PQ holds the SUs pre-empted by the PUs. Next, a model to determine the dynamic length of buffers has been proposed. It works based on the prior activity of the end-users and the requesting SU's waiting threshold. The model ensures service to user if it is admitted in the network. Otherwise, it is blocked or dropped. Blocking or dropping of the calls in this case provides a chance to the SUs to transmit via other base stations. The system is modeled using a multidimensional Continuous Time Markov Chain (CTMC) model. The dynamic queue helps to restrict the Level of Impatience (LOI) to 19.90% for the New Queue SUs and 14.93% for Preempted Queue SUs while achieving 99.33% CU.