Contatto di riferimento: Prof. Roberto Verdone
Abstract
Cognitive radio (CR) is considered as an intelligent technology and an important part of the next fifth generation wireless systems. It promises a great utilization of the radio spectrum, and it enables more subscribers to access the network and exchange data. CR is a communication system that has the ability to make self-decisions in order to connect its subscribers (secondary users (SUs)) to the network whenever there is a particular section of the spectrum that is unoccupied by primary users (PUs) to use it for data exchange. In addition, it has to be capable of predicting whenever a PU is going to utilize the spectrum band (spectrum sensing), which means the SU should leave the band, for the purpose of not disturbing the PU.
Alternatively, the CR must maintain a good quality of service (QoS) level for its users by finding other opportunities for them to continue their activities. The SUs of the cognitive radio are named as such because they, unlike the PUs, do not have the right for spectrum band access at any given time, since the PU paid for the right of accessing the band at any given time in the first place. Therefore, the SU gains access to the band if the PU is not occupying it, or when the PU itself allows the SU to share the band, given that the SU will not disturb the activity of the PU in any sort of way.
Spectrum sensing is almost a continuous process during the life cycle of cognitive radio communications. Sensing must be done initially to find an idle channel, and then it must be done periodically to protect the PU when he decides to use his licensed channel again. In this case, sensing is invoked again to find a different idle channel. Therefore, reducing sensing time increases the room left for transmission and consequently achieves the main goal of CR in increasing the utilization of the wireless spectrum. In fact, sensing does not only allow CR nodes to use the idle licensed channels, but also plays an important role in protecting the PU from interference. Thus, sensing has received a lot of attention in CR in the research community.
Technically, the sensing process implies detecting the existence of a primary transmitter on a specific channel. The CR nodes are allowed to use the PU’s channels if they can identify the channel as idle. Otherwise, the CR nodes back off to allow the PU to use its channel with no interference.