Research On Dynamic Spectrum Management Of Cognitive Radios

Cognitive radio can sense the external radio environment intelligently, discover and rationally use "spectrum holes" in order to improve the spectrum utilization and thus relieve the contradiction between resource demands and scarcities. It is the hot spot of study in wireless communication field. Dynamic spectrum management is the key technology of cognitive radio, which includes spectrum sensing, spectrum decision and sharing, and spectrum mobility management, etc.The dynamic spectrum management of cognitive radios is mainly studied in this thesis.At first, the research background and significance are introduced, besides, the key technologies of dynamic spectrum management of cognitive radios and their currently studies are discussed in detail.Next, a wideband spectrum sensing approach based on multiband signal sampling and wavelet transform is presented. With modulated wideband converter (MWC), sub-bands signals are obtained by low rate sampling. An estimation method for noise power and threshold is proposed, such that the spectrum sensing for signal sub-bands can be carried out by energy detection. And then the edge detection for signal sub-bands by using wavelet transform is used to obtain the exact locations of spectrum which are occupied by primary users. Simulation results show that the proposed wideband spectrum sensing approach can complete the sampling process with several low-rate ADCs (Analog to Digital Converter), detecte the "spectrum holes" and obtain its exact locations in wideband region. It makes the practical implementation of wideband spectrum sensing possible.Then, the spectrum sharing methods based on channel performance and user demands are discussed respectively. Because the performance of each available channel varies widely in cognitive radio network, an ON-OFF model of usage case is constructed and the statistical parameters are given. And the handoff probability of secondary user is derived and a measurement using the changing rate of channel state is presented. On that basis, a spectrum allocation algorithm combined with channel performance is proposed. Simulation results show that the handoff probability is reduced and actual total benefit is improved by using the proposed algorithm. In order to use the surplus assignment obtained by secondary users in spectrum allocation, an allocation model based on demand is constructed and the objective function is set, and then a spectrum allocation algorithm with short-time handoff based on demand is proposed. Simulation results show that the proposed algorithm can make effective use of the surplus assignment, improve the profit of actual use and have the superior performance of anti-interference. At last, the spectrum handoff methods based on channel reservation mechanism are researched. Three basic types of spectrum handoff scheme are described by using channel reservation mechanism, which is proposed by draft standard of IEEE 802.22. To reduce the new-call blocking probability, a buffering method for the new call is proposed. Simulation results show that the proposed method can greatly reduce the blocking probability of new call and the value of GoA (Grade of Annoyance) with the switching performance guaranteed. Due to the time-varying characteristics of available spectrum in cognitive radio networks, a dynamic selection scheme for channel reservation based on exact potential game is proposed. It considers cognitive radio as a kind of interference reducing network and achieves adjustments of dynamic parameters according to the interactive game theory. Simulation results show that the channel can be dynamic reserved with a slight increase in network interference, and the reserved channel is not subject to the environment and thus can be applied to all of the network coverage.