A Study Of Spectrum Detection Technology Based On Cognitive Radio Network

With the increasing of wireless communication services,the spectrum resources are becoming more and more sparse.Cognitive radio is considered as the best solution to this problem.Cognitive radio is an intelligent wireless communication system which can learn intelligently and make corresponding changes of modulation, encoding,protocol and bandwidth by sensing the spectrum environment.Cognitive radio is designed to achieve the reuse of spectrum,and significantly improve the spectrum utilization.Spectrum detection is one of the key technologies for a cognitive radio system and the fast and accurate detection of an authorized user is very important for the application of cognitive radio.This work introduces the researching background,significance and key technologies of cognitive radio system, and analyzes both the advantages and disadvantages of existing spectrum detection algorithms.In practical communication environment,appropriate detection algorithm should be selected intentionally. Then the energy detection algorithm is analyzed detailedly in the AWGN channel and fading channel and related simulation is done.At the same time,the impact of noise uncertainty on energy detection has also been researched relatively.In a communication environment which is characterized by shadow fading, multipath fading and noise uncertainty, in order to improve the detection performance of a cognitive radio user, the detection of distributed multi-user cooperation can be used to improve the limitation. On the basis of existing multi-user cooperative detection algorithm,this paper proposes a cooperative detection method which adjusts decision threshold dynamically. Simulation results show that, compared to conventional cooperative detection methods,this method can further improve detection probability and avoid interference on the authorized user.This paper also proposes a spectrum detection method based on Dempster-Shafer evidence theory. According to the different environment in which each cognitive user is operating,a trust coefficient is assigned to the test results of every cognitive user to measure the reliability of test results.Test results and their credibility are transmitted to the fusion center via the control channel.The fusion center adopts D-S evidence theory rule to combine and obtain the final judgment.Monte Carlo simulation results show, combining with D-S evidence theory can further improve the detection probability and overcome the impact of fading channel on the detection performance than that with or logical rule.