The low efficiency of the current license-based usage model for the radioelectric spectrum has motivated fresher approaches to the problem, generally referred to as Cognitive Radio or Dynamic Spectrum Access, in order to better exploit this scarce and precious resource. This new paradigm, which allows operation of wireless licenseless systems in frequency bands assigned to primary users, poses many different technical challenges. Our group has been addressing several aspects of this problem, often via collaboration with other groups such as the Cognitive Radio Group (University of New Mexico), the Advanced Signal Processing Group (University of Cantabria), and the Signal Processing and Communications Group (Universitat Politècnica de Catalunya).
The preservation of the quality of the primary service is the major concern when inserting new signals in the wireless medium. The development of very accurate spectrum sensing tools is a critical requirement in order to detect unused portions of spectrum and then exploit transmission opportunities. Another possibility is to use occupied frequency slots for transmission (the so-called underlay paradigm), an approach that requires careful signal design and interference management, possibly having to allocate some power to the reinforcement of the primary signal. Statistical detection, optimization, and game theory are some of the mathematical tools that prove key to the developments and results we have obtained in this area.