Research On Spectrum Aggregation Technology And Fairness Resource Scheduling In Cognitive Radio

With the rapid development of wireless communication technology, the limited spectrum resource becomes the bottleneck. As an intelligent radio technology, cognitive radio(CR) breaks the bottleneck and becomes the key technology for alleviating spectrum shortage. The working group of IEEE802.22 makes CR technology as the standard of air interface for WRAN physical layer and MAC layer. Spectrum aggregation(SA) technology is proposed for the first time in 2006. And it’s attracted much attention in the world. SA makes rational use of idle spectrum fragments to provide necessary service for users. As broadband wireless communication rising sharply, it is difficult to satisfy 100 MHz bandwidth of contiguous spectrum required by IMT-A in existing spectrum resource. Therefore, a special SA technology, which is carrier aggregation(CA), is researched in LTE-A system. By utilizing multiple component carriers, CA technology solved the problem of requirements for broadband spectrum resource in LTE-A system. The interval of different frequency bands may be large enough for other communication systems existence in the background of SA. Thus, the signal after aggregation needs to guarantee no interference for other existing communication systems. Secondary users(SUs) can opportunistic occupy the channels of primary users(PUs) without interfering the communications of PUs in CR system. The characteristic requirements of no interference are identical for SA and CR. This thesis focuses on combining the two technologies and utilizes the cognitive ability of CR to coexist with TV and broadcasting services in WRAN so as to ensure the broadband demand of SUs in order to maximize the utilization of spectrum.Firstly, a static spectrum aggregation(SSA) algorithm is proposed for fixed working frequency band of PUs within a short time based on CR system. The SSA is on the basis of two types of SA algorithms. One makes the number of SU who can access to idle band as an optimization goal and the other makes the utilization of spectrum as an optimization goal. SSA considers both optimization goals above and permits more SUs access to idle band with high spectrum utilization. Simulation results show that SSA algorithm can maximize spectrum utilization and SUs’ number comparing with the other two algorithms under the influence of span, idle band number and subcarriers number.Secondly, spectrum handoff of SUs should be considered by SA algorithm for unfixed working frequency band of PUs when they appear randomly. Therefore, a hybrid handoff strategy of SA is presented to deal with a complicated condition which is the working frequency band changing of PUs in WRAN. The hybrid handoff strategy extracts the advantages from proactive handoff and reactive handoff. Combined with the demand of spectrum resources for SA, a basic model of hybrid handoff strategy is established as well as specific steps for operation. Compared with proactive and reactive handoff, hybrid handoff strategy compromises latency and the handoff number. In addition, backup channels are provided for SUs to look for a target channel immediately if handoff events happen. According to the probabilities of handoff, the backup channels are sorted for SUs. When handoff occurs, SU will choose the backup channel with the minimum probability of handoff as target channel in order to reduce occurrence of next handoff. This hybrid handoff strategy and mechanisms are significance for the research on performance characteristics of SA in a complex scenario.Lastly, a positional proportional fairness scheduling algorithm(PPF-SA) is proposed based on SA. The unfairness problem of resource allocation among SUs caused by position factors can be solved by PPF-SA. Resource scheduling fairly leads to the fairness of SUs in SA. Spectrum resource allocation for SUs will be different due to changing of geographical positions under a single base station. Spectrum resource for aggregation is plenty if the SU is close to the base station. Spectrum resource for aggregation is scarce if the SU is at the edge of the base station. A proportional fairness scheduling criterion is established based on the system model of resource scheduling in SA. Through the phenomenon of unfairness caused by position factors, positional weighied factor is brought in. SUs’ priorities become closer attributed to the weighted factor regulation so that resource scheduling will be relatively fair. The simulation results present that PPF-SA algorithm can improve priorities for SUs in the restrained region of resource aggregation so as to solve the problem of unfairness in SA.