Variable bandwidth spectrum access for secondary user in cognitive radio networks

In cognitive radio networks (CRNs), how to efficiently take advantage of vacant frequency bands for secondary users (SUs) has become a key to improve quality of service (QoS). Detection error has certain impacts on spectrum access, leading to overlook vacant frequency bands or occur the collision between primary users(PUs) and SUs. Since sensing mistake is inevitable, an optimal dynamic access scheme should be based on imperfect detection outcome. Therefore we propose a variable bandwidth spectrum access scheme with imperfect spectrum sensing. In this scheme, SUs can access different amount of frequency bands by detecting spectrum resources. As soon as PUs reclaim the frequency bands, SUs adjust own frequency bands according to the state of spectrum resources, meanwhile renewing their service quality level. Considering the impact of detection error on CRNs performance, this scheme is based on imperfect sensing and modeled by three-dimension Continuous-Time Markov Chain (3D-CTMC). We give the expression of performance metrics evaluating QoS of CRNs and use QBD theory to gain the solution of steady state probability. Theory analysis and simulation experiments show that the proposed scheme efficiently improves QoS of CRNs with an acceptable degradation of SUs´service quality level, the degradation has no influence on the normal transmission of SUs.