Special issue on 10 years of cognitive radio: state-of-the-art and perspectives

Cognitive radio (CR) is a technology that is of growing interest internationally. Currently, there is a highly active worldwide community of academic and industrial researchers working in this field. Significant efforts have been made and focused on the many technical questions as well as on the economic and political challenges in order to move this new technology from research concept to reality. A CR is a radio that is able to behave somehow as a cognitive system, having at least the capabilities of observing, making decisions and adapting, i.e., the three main functions of the simplified cognitive cycle. CR technologies, such as Dynamic Spectrum Access (DSA), create huge opportunities for interesting research and development in a wide range of applications. Since 1999, CR received a lot of attention especially in spectrum optimization. Currently, technical efforts and standardization are focused on UHF spectrum and TV bands. TV signals are easy to detect and are quasi-static in the sense that transmitters’ locations and frequencies are fixed. Furthermore, due to the allocation and frequency reuse in order to protect against interferences, typically there is a lot of unused spectrum at a specific location. This free spectrum is known as “White Spectrum” or “White Space”. CR has been often reduced to the use of white space by DSA, but CR could be envisaged in a much wider sense, depending on which types of sensors are considered. At a larger scale, CR gives equipments smartness that can be exploited at every level of the equipment, in order to make it more efficient for the network and more helpful to the user. A CR system may manage its power resources, anticipate its environment changes, make networks vertical handover, etc. Cognitive networks aim at improving system capacity, thanks to CR devices providing enhanced spectrum sharing capabilities, a better quality of service and performance.