Admission control and resource optimization for multiple-user OFDMA Cognitive Radio systems

In Cognitive Radio (CR) systems, the fluctuating nature of the available frequency resource due to Primary Users (PUs) activity necessitates the introduction of admission and eviction measures at the CR system if a guaranteed Quality of Service (QoS) is required by Real Time (RT) Secondary Users (SUs). This problem has been recently addressed in the literature with simplified assumptions that might become unrealistic in practical system setups. In this paper, we tackle the problem of admission and eviction control of RT SUs in multiple-user Orthogonal Frequency Division Multiple Access (OFDMA) CR systems and propose new solutions that are practical and efficient at the same time. In particular, we propose three different ways to install a Resource Buffer Zone (RBZ) at the time of admission to limit future call drops resulting from fluctuating PU activity. We also study the effect of PU activity on the feasibility of the resource allocation problem and propose three different methods to resolve system outages once they occur. Numerical results obtained through Monte Carlo simulations demonstrate the efficacy of the proposed techniques.