| As technology improving constantly, the requirements and applications for the wireless communications in the future will be more and more intensive and diversification, yet the scarce of radio spectrum resources and its poor utilization will be a critical issue which will impede the above trend, in order to solve this problem, the theory and applied research for the cognitive radio will also be more and more urgent. At the same time, the development direction of the mobile communications in the future must be full-service type, including radio access network side and core network side will be grow to a converged integration architecture way, so in the future all voice services and data services will be based on the same bearer network, for this reason meet the content charging and the QoS requirements of different services has become a necessity. Therefore spectrum handoff technology as a key technology which has become the research focus of our article, and that is the origin and meaning of our topic.This paper first describes the research background and significance of our article, also plan the chapter structure of full text, and then do the analysis and summary work of some key technologies in the cognitive radio and the MAC layer, after this based on the existing research we leads to the main contents.Aim at the existing spectrum handoff mechanism shows relatively simple and has a poor outage probability and delay performance, in the third chapter, our paper proposes a spectrum handoff mechanism based on the reservation spectrums. Based on the comparison between two types of the current spectrum handoff mechanism, we propose an improved scheme, namely through establishment of the backup channel list to reserve the backup channels, and how to select the backup channel depend on the availability and the available time length of the spectrum. The simulation results show that the improved strategy not only has a better handoff delay performance, but also effectively reduces the network handoff probability and user call drop rate.Aim at the existing distributed MAC protocol has a poor delay and fairness performance, based on the research results of the third chapter, in the fourth chapter our paper proposes a service classification low latency MAC protocol. First classify the different types of services in the network, mainly divided into the delay sensitive service and the non-delay sensitive service, and based this do the appropriate classification in the data transmission period of the super frame structure, and then extend the RTS/CTS frame format about adding the BCL contents, moreover also design an improved algorithm about the traditional BEB algorithm, namely DAC algorithm, which consider both node fairness and system delay performance. The simulation results show that the improved SCLL-MAC protocol not only has a better delay sensitive service performance, but also can effectively improve system throughput and fairness performance. |
