Supporting Real Time Traffic in Cognitive Radio Networks

Abstract

Data rates of mobile users have been increasing multiple times year- after- year. Number of mobile users is also increasing continuously. Providing wireless bandwidths in order to support these increasing data rate requirements and users has become a challenge, as almost all the frequencies that can be used by cellular systems are already allotted by the governments for various purposes. So the option left is to move to higher frequencies like the millimetre waves, but these higher frequencies have their own problems like propagation challenges and coverage distance issues. In this context, it is contemplated to use the available spectrum of sub- 6 gigahertz frequencies in efficient manner. newlineResearch studies have revealed that some of the users allotted with spectrum are not using the whole bandwidth allotted to them, while some others are using the allotted frequencies at selected geographical locations only though the license has been obtained to use the allotted frequencies in the entire country. It was also found that some licensed users were using spectrum intermittently only and not for all the times of the day. In addition to the above, some frequencies that were allotted for terrestrial TV transmissions have become vacant after they have got converted from analog to digital modes which need less bandwidth. In this backdrop, researchers have explored to make use of these underutilized licensed frequencies of the spectrum for the transmissions of unlicensed users when the licensed users are not using them. This has given rise to the concept of a dynamic spectrum access or opportunistic spectrum access by the unlicensed users, who are called as secondary users in this context. Devices of these users have to observe the spectrum-usage on continuous basis and should use the frequencies, only when their licensed users (who are called as primary users) are not using them.