Cognitive Radio System

With the dramatic advance in wireless communication technology, the contradiction between traditional static spectrum allocation mechanism and growth in dependence on radio spectrum resource has become more and more unavoidable. A major bottleneck in wireless communication is now emerging with the spectrum utilization. As a revolutionary smart spectrum sharing technology, Cognitive Radio (CR) addresses the problem of poor spectrum utilization which has drawn increasingly concern within these years. Provided spectrum sensing function, the CR users have the ability of dynamic access and sharing unoccupied licensed spectrum bands. Spectrum sensing which characterizes awareness spirit of CR has been identified as a key enabling functionality for Cognitive Radio Networks (CRN). Therefore, the principal research work of this dissertation is specific to spectrum sensing algorithms in Physical Layer of CRN, the subject selection of which is motivated from National High Technology Research and Development Program (863 Major Project).Under the foundation of Cognitive Radio outline and evolution of relevant standards, the main contributions to the theory and its applications of Physical Layer spectrum sensing algorithms in the dissertation include:Based on deep analysis of CR spectrum sensing principles, focused on research of spectrum sensing algorithms, having learnt the classical statistic signal detection theory, cyclostationary spectrum sensing algorithms with high reliability in detecting weak signals are emphasized. Through MATLAB simulation results and performance comparison of two cyclostationary detectors, the general requirement for spectrum sensing is briefly induced, that the detector can be more effective accounting for the characteristics of target signals.Aiming at spectrum sensing application in primary users with OFDM modulation, a practical sensing technique is provided in Digital TV spectrum band. According to the OFDM signal property, a more robust algorithm improved upon traditional OFDM detector based on Cyclic Prefix (CP) is proposed in this paper. The detector instances are implemented in detecting CMMB and DMB-T digital TV signals in MATLAB platform with expected results. Moreover, the detector with fusion cooperative decision of logic OR-rule after local sensing is also tested and verified to be able to cancel some deleterious impact of fading in Rayleigh channels.