Research On Cognitive Radio Spectrum Sensing Technology Based On Fractal Dimension

With the constant utilization of limited spectrum resources, fewer and fewer bands are available, while the utilization of wireless spectrum resources is not high, but the contradiction is that the utilization of wireless spectrum is very low, many bands is idle because of the inactive primary users, unauthorized users are not entitled to use these bands. Cognitive radio technology is an important technology to make full use of the wireless spectrum resources, and it is the key to solve the shortage of spectrum resource and utilize the wireless spectrum efficiently in the future.The essence of spectrum sensing is to detect existing signals in the spectral environment around the cognitive network. The essence of the communication signal is as a sequence in time domain or frequency domain, and it is very similar to fractal. It can describe the degree of irregularity of communication by fractal description.Cognitive radio spectrum sensing technology based on fractal dimension can transforms irregular signal analysis into quantitative form based on the idea of fractal dimension in fractal theory. Using the fractal characteristics of signal which can be extracted to make decision. The whole procession is simple and easy to be calculated and has high detection rate at low signal-to-noise ratio.Based on the characteristics of several different fractal dimension calculation methods, this paper analyzes the shortcomings of traditional fractal dimension spectrum sensing method, and proposes three new spectrum sensing methods based on fractal dimension. This thesis made a detailed elaboration from the principle of the method to the realization of the process. The new method has the characteristics of high detection rate at low signal-to-noise ratio, and it takes less time to detect the average system than the traditional detection method.This thesis makes the simulation between traditional methods and new methods at different signal-to-noise ratio condition. The average running time of the proposed method is shorter than that of the existing method, and the detection rate is still high when signal-to-noise ratio is low.The simulation results are in agreement with the theoretical expectation,which verifies the superiority and effectiveness of the proposed spectrum sensing method based on fractal dimension.The work of this thesis is the important part of the project of the National Natural Science Foundation of China. During the study period a related paper was posted. The title of the paper is "A Cooperative Sensing Method Using Katz Fractal Dimension in Frequency Domain".