Research On Spectrum Access And Spectrum Handover In Cognitive Radio

As an emerging technology that significantly improves the utilization of licensed frequency bands, cognitive radio exchanges information with its operational environment in order to utilize the spare licensed spectrum and can restrict its interference to guarantee the communication of licensed users. Among the key technologies in cognitive radio, spectrum access and spectrum handover have received extensive concern from both academia and industry.This dissertation focuses on two topics:the effects of spectrum holes'differences on spectrum access and spectrum handover, and the control channel access algorithms. A secondary user's utilization of a spectrum hole is influenced by the frequency of the spectrum hole being used, the wireless environment where the secondary user stays, the interference from primary users and the service requirement of this secondary user. This research studies the differences of spectrum holes, and proposes new algorithms of spectrum access and spectrum handover to utilize these differences enhancing the performance of the secondary system. Based on the research of spectrum access and spectrum handover, the fast control channel selection algorithm is proposed to increase the reliability of control channel and the efficiency of control information exchange. The main contributions and innovations of this dissertation are as follows:1. The influence of the diversity of spectrum holes on spectrum access/spectrum handover is analyzed. According to the analysis, the spectrum access algorithm based on the diversity of spectrum holes is proposed which matches the service requirements of secondary users with the capacities of spectrum holes. The proposed scheme takes the capacity obtained by secondary users as the optimization target. Both the simulations and the evaluations prove that the proposed scheme can guarantee the communication of primary users, reduce the drop ratio of secondary users and increase spectrum utilization.2. Based on the research of time domain diversity of spectrum holes, the active spectrum handover scheme and the spectrum-hole reservation scheme are proposed to increase the reliability of spectrum handover. In active spectrum handover scheme, secondary users predict the duration of spectrum-hole availability according to the statistics of primary users'activity. The duration of spectrum-hole availability is used to trigger a spectrum handover. Secondary users perform the handover when the duration of spectrum-hole availability is too short, and choose the spectrum hole with long duration of availability as the target spectrum hole. The frequency of spectrum handover is reduced in active spectrum handover scheme. In the spectrum-hole reservation scheme, secondary users reserve spectrum holes for handovers to enhance the reliability of handovers. Simulations and evaluations prove that the two schemes can reduce the drop ratio effectively.3. The reliability of control channel is researched based on the analysis of the diversity of spectrum holes. The fast control channel selection algorithm is proposed to enhance the efficiency and the reliability of control channels. Secondary users use the spectrum holes alternitaively to transmit control information in the proposed algorithm. The dwelling time on each spectrum hole is shortened in the algorithm, and the delay of control information transmission is reduced. Secondary users can temporarily borrow the spectrum holes assigned for traffic channel to decrease the probability of control channel failure due to primary user's reappearance. The algorithm optimizes the resource used for control channel, making more spectrum holes available for traffic channels. According to the simulations, the proposed algorithm can reduce the delay of the control channel build-up time and the delay of the control information transmission, and the algorithm can decrease the control channel failure probability.The research of this dissertation enhances the relation between theoretical study and potential engineering application, by introducing the diversity of spectrum holes into the research of spectrum access and spectrum handover. Firstly, the spectrum access algorithm matching secondary users' service requirements and the capacities of spectrum holes is proposed, by quantizing and utilizing the diversity of spectrum holes in frequency domain and spatial domain. Secondly, the active spectrum handover scheme and the spectrum-hole reservation scheme are proposed to increase the reliability of spectrum handover. Thirdly, the fast control channel selection algorithm is proposed to enhance the efficiency and the reliability of control channels, increasing the reliability of both spectrum access and spectrum handover.