Vacate on demand algorithm in cognitive radio networks

Cognitive radio networks (CRNs) have been recognized as an advanced and promising paradigm to address the spectrum under-utilization problem. Cognitive Radio (CR) users improve spectrum efficiency by opportunistic spectrum access when the licensed spectrum is not occupied by the primary users (PUs). CR users also need to sense the spectrum and vacate the channel upon the detection of the PU´s presence to protect PUs from harmful interference. To achieve these fundamental CR functions, CR users usually coordinate with each other by using a common medium for control message exchange ensuring a priority of PUs over CR users. This paper presents the Vacate on Demand (VD) algorithm which enables dynamic spectrum access and ensures to vacate the assigned channel in case of PU activity and move the CR user to some other vacant channel to make spectrum available to PUs as well as to CR users. The basic idea is to use a ranking table of the available channels based on the PU activity detected on each channel. The VD algorithm is characterized by two features: (a) vacate the assigned channel in case of PU activity, (b) move the CR user to some other vacant channel in minimum possible time. We evaluate the performance of our algorithm through analysis and MATLAB simulations.