Researches On Malicious-Node-Against Cooperative Sensing In Cognitive Radio System

With the continuous development of wireless communication, spectrum resource scarcity is getting more and more attention. Cognitive radio can alleviate the inefficient frequency assignment problem and improve the utilization of licensed spectrum bands.Cooperative spectrum sensing for cognitive radio system outperforms single user spectrum sensing in many aspects. However, cooperative spectrum sensing may be attacked by malicious users. In this paper, methods to against malicious attack in cooperative spectrum sensing system are studied.Firstly, the thesis introduces cognitive radio system, in which unlicenced users sense the licenced user and then opportunistically dynamically access the licenced spectrum band when it is not occupied. Spectrum sensing technique which identifies the idle bands is a core issue in cognitive radio system. Performance parameters for spectrum sensing and energy detection technique are presented in detail in the thesis. A model of spectrum sensing in deep fading enviroment is built to analysis disadvanages of single-user sensing and advantages of multiple-user cooperative sensing.Secondly, potential secure problems in cooperative sensing system are studied in the paper. The problem malicious nodes attacking fusion center is considered as a Byzantine attack problem, in which we need to eliminate the effects of malicious nodes and let the fusion center give the proper results using the information from honest nodes. Simulation results in this paper show that potential malicious nodes with different attack modes may significantly decrease the performance of cooperative sensing system. Results show that the higher the malicious nodes ratio is, the worse the sensing performance is.And then, methods which are used to identify malicious nodes and to eliminate the effects of malicious nodes are studied. Methods based on outlier detection and weighting function are applied to solve Byzantine attack problem, which are studied in detail in this paper. We can see the positive effects from simulation results by using methods upon. Methods against Byzantine attacks improve the sensing performance of cooperative sensing system with Byzantine attack.Finally, two method improvements are introduced:one is that each secondary user takes a pre-progress of local detection data; the other one is choosing a bigger quantization bits for control channel. By simulating the cooperative sensing system with Byzantine attack, we can see that method improvements can make further improvement on system performance.Simulation results show malicious nodes’ Byzantine attack will decrease performance of cooperative sensing system and methods against malicious attack present in this paper can improve the performance to a certain degree. Analysis indicates that methods in this paper are robust against malicious attacks and can successfully raise cognitive radio system security.