Researches On Spectrum Sensing In Cognitive Radio Vehicular Ad Hoc Networks

While the increasing number of vehicles brings much convenience to people’s lives, it also creates a lot of problems. In order to solve the traffic congestion and emerging issues such as driving safety, intelligent transportation systems(ITS) came into being. As an effective traffic control system, it has been obtained wide attention.Vehicular Ad hoc Nertworks(VANET) is an important part of ITS that can improve the safety of traveling on the road and therefore exert great impact on society. It has received a lot of study in recent years and still faces many challenges, one of which is the inadequate frequency spectrum used for communications in VANETs. To solve the problem, cognitive radio is proposed to apply to exploit licensed but unused frequency bands, which can solve the problem of shortage of spectrum resources effectively.Firstly, the thesis introduces the background of CR-VANETs. As a special case of mobile ad hoc networks(MANETs), the VANET serves as a promising application to change the lifestyle of human beings. As an intelligent cognitive radio technology, it enables the secondary user access the spectrum opportunity so as to improve the efficiency of spectrum utilization. In addition to a great remedy to the spectrum starvation problem, CR is suitable in VANETs due to its highly mobile and dynamic networking environment. Based on the introduction to the spectrum sensing techniques in the thesis, a model of spectrum sensing in deep fading environment is built to analyze the disadvantages of single- and multiple-user cooperative sensing.Secondly, on the basis of the aforementioned works, the thesis researches the spectrum sensing algorithm in the CR-VANETs. Focusing on the special VANET scenario, we firstly take into account the effect of correlation in mobile environment. The thesis studies the performance of spectrum sensing under correlate Rayleigh fading channel firstly, with the focusing on the performance analysis of the effect of speed for different fusion algorithm. The simulation results show that the accuracy of sensing increases with vehicle speed due to the increased spatiotemporal diversity. Meanwhile, MRC algorithm performs better than the EGC algorithm. Then the composite channel model for shadow fading is built to analyze the effect of various parameters.Finally, a trusted sensing techniques for CR-VANETs is studied in this thesis with the focus on the problem of security and the influence of environment factors such as fading. Several commonly used malicious nodes and attacking modes are considered. This thesis discusses the effect of malicious nodes on the performance of spectrum sensing. In order to eliminate the influence of malicious nodes and uncertain factors such as fading, in view of the real road environment, we study the Location Reliability(LR) and credibility of a malicious user detection based algorithm. The results of simulation show that the proposed algorithm can effectively improve the performance of the system.