Research On Wideband Spectrum Sensing And Fusion Algorithms For Cognitive Radio

As one of the key technologies and primary basis for realization of cognitive radio system, spectrum sensing technology is taken extensive attention by researchers. This paper has deeply studied in single-user wideband spectrum sensing and fusion algorithms of multi-user cooperative spectrum sensing. The main work includes the following aspects.Firstly, this thesis briefly presents the concept, background and research status at home and abroad of cognitive radio. On the basis of it, spectrum sensing technology is described in detail through the research status, system model and classical methods. Then, aiming to improve the performance of single-user energy sensing and achieve wideband sensing, a wideband energy sensing method based on polyphase filter bank is analyzed and simulated detailedly and the simulation results prove its effectiveness. Secondly, in order to deal with the limitation of single-user spectrum sensing, this thesis introduces the concept and model of multi-user cooperative spectrum sensing and analyzes deeply the sensing performance of various classical fusion algorithms by simulation.For soft combination algorithms of cooperative spectrum sensing, a new cooperative spectrum sensing algorithm based on exponential weighted soft combination is proposed aiming to improve the sensing accuracy, with the goal is to reach better approximation of weights-SNR curve and probability of detection-SNR curve so as to better use SNR information to assign more reasonable weights for cognitive users. By simulating and comparing the new algorithm and traditional soft combination algorithms in AWGN, Rayleigh and Nakagami channel to verify its validity and then to obtain the optimal threshold of it. Finally, this paper has studied and simulated the scheme that applies the new algorithm to cluster-based cooperative spectrum sensing. The results indicate that the proposed algorithm can effectively improve cluster-based cooperative spectrum sensing performance.Considering the defects of soft combination algorithms about transfering large amount of information and being not suitable for bandwidth-limited system, a new double threshold cooperative spectrum sensing algorithm is proposed based on softened two-bit hard combination. The algorithm firstly implements local sensing of secondary users whose received energy are outside of double threshold region by using traditional double threshold energy sensing. Then when sensing failure is occurred, softened two-bit hard combination is carried out by all cognitive users whose received energy are between double threshold region as local sensing. The simulation results in AWGN and Rayleigh channel indicate that the new algorithm can apply to bandwidth-limited cognitive radio systems. Meanwhile, compared to traditional double threshold cooperative spectrum sensing algorithms, the new algorithm not only eliminates the sensing failure, but also achieves a good compromise between transmission overhead and sensing accuracy.