Detecting Primary Users For Cognitive Radio

With the penetration of wireless communications technology, the number of wireless subscribers has increased dramatically. As a result, wireless bandwidth resources are becoming more and more limited over time. How to improve the efficiency of radio resources is a pressing problem. The cognitive radio technology brings a new idea for solving this problem, it is a radio that's aware of and can sense its environment and location; learn from the environment and alter its power, frequency, modulation and other parameters so as to dynamically reuse available spectrum. It is a smart spectrum sharing technology to effectively improve the utilization of radio resources.Its basic idea of cognitive radio is to make wireless terminals have the abilities of detecting "spectrum holes" and making full use of them. Most of the "spectrum holes" are spectrum somebody own, for this reason, the CR users should use them with ensure not affect the private users. So, a cognitive radio must detect the presence of primary users to avoid interfering with them. However, it has been assumed that many devices in primary networks such as televisions and cellular phones are passive, i.e. the cognitive radio cannot find their locations. There for, we have to try to know the condition of the receiver.Network-establishing of Cognitive radio has intimate relationship with detection of original users. This dissertation compares the three different kinds of network establishing of cognitive radio, and chooses one of those as an example to present the working mode and the principle of collaborative detection among the users of the network.Then basing on the two main types of the signal characteristics of the original users in the network, the dissertation present the detection based on spectral correlation density. According to lots of matlab simulation, the dissertation analyzes whether the way of detection is feasible or efficient. Then the dissertation shows the three dimension figure of cyclic spectrum and contour line of TV signal and wireless microphone signal with different signal-to-noise ratio.Moreover, this dissertation introduces some new methods of detecting primary receiver in cognitive radio briefly, for example, cooperative spectrum sensing, local oscillator leakage detecting, etc. Furthermore it also gives the feasibility of these new methods, brings convenience for future research.