A comparative study of scheduling schemes for cognitive radio networks: A quality of service perspective

Quality of Service (QoS) based scheduling in Cognitive radio networks (CRN) is a pressing research problem. The objective of this work is to study the feasibility of using CRN for delay sensitive applications in the presence of primary users with random ON/OFF periods. The first contribution of this work is the modeling of a cognitive node as a Queuing system and characterization of the average delay encountered by a packet on a cognitive node for various scheduling disciplines. This delay characterization gives the application/user the decision power to choose whether to transmit using a particular node depending upon the delay and rate requirements. It also gives the designer of higher layer the ability to make more informed decisions for routing in a multiple node scenario. The second contribution of this work is a comparative study of various scheduling disciplines in a cognitive radio environment. We have considered First Come First Serve (FCFS), strict priority and a proposed Queue Proportional Batch Scheduling (QPBS). QPBS maintains a balance between priority and fairness as opposed to the strict priority scheduling where the fairness is sacrificed at the cost of priority and FCFS where there is no notion of priority. This comparative study clearly brings out the relative pros and cons of aforementioned scheduling schemes in a cognitive radio environment. A discrete event based simulation study has been performed to verify the efficacy of mathematical modeling and validate the results.