The Application Of Quickest Detection For Spectrum Sensing In Cognitive Radio

Recently the scarce of radio spectrum resource severely limits the development of wireless communication. CR (Cognitive Radio) is a promising technique that can solve this problem. As a key technique of CR, spectrum sensing draws enormous attention. This paper investigates the spectrum sensing technique and models it as a quickest detection problem, which opens up a new direction in the research of spectrum sensing. The topic of this paper is one of the key technologies in the National Natrual Science Foundation Funds, which is of high theretical and practical values.Traditional spectrum sensing methods are generally'block-based'methods. This kind of methods assumes that the signal would stay in the same state, i.e. "present" or "absent", throughout the same sensing period. However, in practical, this is not always true, and hence these methods become ineffective. At the same time, since the sampling number is fixed in the traditional'block-based'methods, it cannot react quickly to the change of stat(?) of the primary user.To improve the traditional methods, this paper model the spectrum sensing problem as a change detection problem, to detect the change of state of the primary signal, this is, "appearance" or "disappearance". We assign costs to the detection delay and detection error respectively, in order to formulate a comprehensive cost function as our optimization objective. Specifically, we use quickest detection method in the energy detection, to solve the problem of detecting the "appearance" and "disappearance" of the primary signal, in the cases of when the power of the primary signal is known or unknown. By theoretical analyze and computer simulation, we verified that quickest detection is optimal in minimizing the detection delay while maintaining a certain error probability, which improve the effectiveness of the detection method significantly. The result of this paper also points out a new direction for research in spectrum sensing.This paper has five chapters, which as follows:Chapter one is the overview of the development of cognitive development.Chapter two mainly introduces the sequential detection, which is the basis of quickest detection.Chapter three mainly introduces Bayesian quickest detection and Non-Bayesian quickest detection.Chapter four is about how to apply quickest detection approach in the energy detection of primary user's signal.Chapter five is for the conclusion and research prospect.