Research On Resources Scheduling Scheme For Cognitive Radio Nerworks

Low utilization efficiency of spectrum, which is caused by fixed spectrum allocation scheme, is the bottleneck of wireless communication systems. The Cognitive Radio (CR) technology is proposed by Joseph Mitola and refers to a smart radio that has the ability to sense the external environment, learn from the history and make intelligent decisions to adjust its transmission parameters according to the current state of the environment. It receives much attention for two reasons:flexibility and potential gains in spectrum efficiency.CR offers the potential to dramatically change the way spectrum is used in systems and increase the amount of spectrum available for wireless communications. It can utilize unused spectrum in an intelligent, coordinated and opportunistic way based on no or acceptable harm to existing services so that it becomes a promising technology to improve the utilization of the existing radio spectrum.One of the key technologies for CR is the scheduling between the available spectrum and user data. After sensing for a period of time, each secondary user obtains some information about available spectrum, such as the number, the stability and so on. Based on such information, secondary users can dynamically use the idle spectrum bands to transmit their information. However, they must make sure their service will not cause harmful interference when primary users want to use the spectrum again. In other words, if primary users reclaim the spectrum, the secondary users must vacate it as soon as possible, which makes their service delayed or lost. In order to ensure the QoS for secondary users and use spectrum resource more efficiently, we need to choose better resource scheduling scheme based on the available spectrum.In general, the contents of this thesis include following aspects:Firstly, based on the development trend of future wireless communications, the CR technology is introduced, including the origins, present status, standardization, challenge and future development.For ensuring QoS of secondary users and spectrum efficiency, a layered spectrum scheduling scheme with spectrum stability for cognitive radio networks is proposed. Based on Layered Coding (LC), the scheme assigns the base layer to the most stable spectrum and the enhancement layers to less stable ones. If primary users use the spectrum again, only one or several enhancement layers are destroyed instead of losing the whole data. So users can still acquire basic service experiences rather than be destroyed by networks. For better data and resource scheduling, we also do some improvements on the proposed scheduling scheme. The improvements are based on the combination of the LC scheme, the single channel scheme and diversity scheme. The expectation-utility theory is used to evaluate the performance of the proposed scheme according to the supposed spectrum occupation states.Moreover, base on the LC scheme above, an improved opportunistic scheduling scheme for cognitive radio networks is developed, aiming at maximizing the reward of the secondary users. Different from the traditional scheduling scheme which only aims to maximal throughput in CR networks, the proposed scheme schedules data packets with different priority by taking the channel stability information of CR networks, data rate, time delay and data dependencies into account and can realize better QoS experiences for secondary users.Finally, a summary is given, where the future research trend related to this thesis is also pointed out.