Miltiades Filippou -
Date: - Location: Eurecom
Title: Hybrid Cognitive Radio Systems: Optimally Adapting Secondary Transmissions to Spectrum Sensing Results Cognitive Radio (CR) was proposed as an efficient means of dynamically utilizing the available wireless spectrum. To this end, two of the often investigated CR approaches are: a) interweave (opportunistic) CR systems, in which secondary nodes sense the spectrum and then transmit within time-frequency blocks which are free of primary activity and b) underlay (spectrum sharing) CR systems, where primary and secondary networks coexist, provided that the interference received by primary terminals does not overcome a certain limit. Nevertheless, each of these two approaches is characterized by drawbacks of different nature. Motivated by this, a new, hybrid CR approach has been introduced, where secondary transmissions constantly occur, by adapting to the Spectrum Sensing (SS) results. In this talk, focusing on the hybrid CR approach, we choose to tackle problems of optimizing key system design parameters (SS parameters, power allocation), with the aim of improving secondary communication (e.g., in terms of average rate, Bit Error Rate (BER)), subject to a Quality-of-Service (QoS) constraint on primary communication. In order to solve such problems, closed form expressions (or approximations) of the involved quantities are derived by assuming imperfect Channel State Information (CSI). Significant performance gains of the designed hybrid CR system over the conventional systems are illustrated for a number of scenarios.
