Research On Congestion Control Algorithms In Internet And The Cognitive Radio MAC Schemes

For the effiencient utility of networks resources, the research on some models and key schemes in the networks are very important. The End-to-End network including two parts:radio acess network and core network. With the rapid development of Internet, the problem of network congestions and resources allocation become much worse. The network congestions are unavoidable phenomena, because TCP and UDP users want to obtain available bandwidths as high as possible, while the network capacity is limited. Therefore, to prevent and control network congestions has been a hot area of research in recent years.And with the development of wireless communication technology and widely used laptop computers,the advantages of mobile wireless reflected,such as simple installation,strong mobility.But the spectrum resources are limited in the current wireless communication system, even so we can not make full use of them and have extremely low spectrum utilization. Cognitive radio is an effective way fro the confliction of the low usage of spectrum resources and the exiguity of spectrum resources. It can dynamically adjust to the changing of the wireless radio resources within change its spectrum frequency and transmission mode. Hence, this thesis focuses on the research of models and schemes from the following two topics:(1) research on the congestion control mechanism in Internet, including the research of Acitve Queue management mechanism in routers. (2) Research on the MAC (Medium Access Control) layer of IEEE 802.22 in Cognitive Radio network.In this thesis, the contributions on the models research in Internet and CR MAC scheme are:1. Study on the model of Active Queue Management mechanism (AQM) of routers in Internet. Firstly, we analyze the fluid model of TCP/AQM/RED system, and give a sufficient condition for system stability. Furthermore, we extend the TCP/AQM/RED time-delay system model for the system of TCP and UDP combined flows and multi-queues router, and propose a TCP-UDP/AQM/RED model. Based on this model, we can analyze the performance of TCP/AQM system with UDP flows existing. At last we introduce an AQM scheme that support flows with different priorities,it can guarantee the QoS of high priority user.2.While the cognitive radio network Media Access Control (MAC) layer is required not only to provide traditional services but also to perform an entirely new function for effective using the available bandwidths for the unlicensed users called Secondary Users (SU). To solve the problem, this paper develops a new MAC scheme that allows unlicensed users adaptively select spectrum, and it supports the QoS of high priority unlicensed users.