Research On Cooperative Spectrum Sensing Technology For Cognitive Radio Based On Distributed Antenna

With the rapid development of wireless communication technology, more and more communication businesses are competing on the use of wireless access, which makes the shortage of radio spectrum resources and low utilization of the spectrum becoming the bottleneck of future development of broadband wireless communication, so there is an urgent need to find effective ways to solve the problem. The advent of cognitive radio, which is an intelligent spectrum sharing technology, not only solves the shortage problem of wireless spectrum, but also improves the utilization of spectrum resource. Spectrum sensing is the most important technology in cognitive radio, it can rapidly and accurately detect whether the primary users are using the licensed spectrum. Moreover, the distributed antenna technology has been widely used in the communication system with its unique advantages; therefore, this paper applies the distributed antenna technology to cognitive radio network for cooperative spectrum sensing, and to improve the performance of spectrum sensing by diversity and multiplexing technology.In the first chapter, this paper has a sufficient survey of the background, the research status at home and abroad and the development trend; and introduces the significance of the cooperative spectrum detection based on distributed antenna at last. Secondly, this paper analyzes the related knowledge and basic theory of the sensing algorithms with single user and multi-user spectrum. After summarizing and comparing the advantages and disadvantages of those algorithms, this paper also realizes the performance of those algorithms by simulation.How to detect the radio spectrum efficiently and accurately is the key technology of cognitive radio, so this article analyzes the different fractal characteristics of noise and modulation signals in Gauss channel and Rayleigh channel in the third chapter, and realizes the spectrum sensing algorithm based on fractal dimension by simulation. Moreover, this paper assumes the box dimension of gauss noise obeys gamma distribution and puts forward to set the threshold value by the constant false alarm rate. Simulation results prove that the algorithm based on fractal dimension has better performances than traditional algorithms, and to set the threshold value by the constant false alarm rate not only more rigorous, but also can obtain better detection performance than the threshold value is set to a fixed value.Finally, this paper realizes the cooperative spectrum sensing system based on distributed antenna in the forth chapter after giving its structure and principle. Compared with multi-user cooperative spectrum sensing, cooperative spectrum sensing based on distributed antenna has many advantages, such as separated location of each antenna unit can avoid all antenna units in fading environment at the same time, and the ideal fiber feedback channel does not need to consider the error rate and allows the fusion center can either use hard decision rule or soft decision rule. In the distributed antenna cognitive radio network, antenna units cooperatively detect the idle spectrum and orientate the location of primary user to exclude those antenna units which are outside of the coverage of the primary user; this technique not only uses of the airspace resources rationally, but also improves the sensing performance and utilization rate of radio spectrum resources. Simulation results prove that cooperative spectrum sensing based on distributed antenna can gain a better performance than the multi-user cooperative spectrum sensing; combined with positioning of the primary user, cooperative spectrum sensing has a higher detection probability; furthermore, in distributed antenna radio cognitive system, cooperative spectrum sensing based on box dimension has a higher detection performance than energy spectrum sensing algorithm.Based on the distributed antenna cognitive radio system in this paper, future work is going to improve the algorithm to enhance the application of correlation dimension, and discuss the spectrum sensing algorithm based on information dimension; moreover, to restrain the effect of NLOS on the positioning error by distributed multi-antenna, and obtain more accurate position of the primary user by3D orientation technology.