The Performance Improvement Research Of TCP Protocol Based On Transport Layer In Cognitive Wireless Network

Today radio spectrum resources can't meet the increasing demand from people, which has limited the rapid development of wireless technology in the future. The relevant technology of Cognitive Radio (CR) can dynamically detect the unused spectrum resources in network and we can make full use of them to alleviate the shortage of resources. So Cognitive Radio has become a widely popular topic in the modern radio field. At the same time, cognitive radio network which is based on cognitive radio technology gradually catches a lot of attention from scholars. However, the studies to improve the TCP protocol in cognitive radio network are few. The environment of cognitive radio network changes a lot. If the traditional TCP protocol cannot adapt to the network, it will only reduce the TCP transmission performance and the end to end throughput.Tn order to solve these problems, this paper has introduced Cross-Layer structure and Layer-Preserved structure, and analyses the factors which have affected the performance of TCP protocol, and improve the traditional TCP protocol. Specific research and improvement is as follows:First, this paper introduces the knowledge of the TCP protocol, such as TCP packet format, transportation connection management, and some involved mechanisms to achieve reliable transmission. It focuses on four kinds of congestion control principles and related algorithms. This paper analyses relevant factors which influence the TCP transport in cognitive radio networks, such as the authorized user activities, cognitive users'spectrum detection and switch, etc.Then, this paper introduces the relevant principles and theories of the Cross-Layer structure. The cognitive user has special detection function which can sense idle spectrums and the authorize users'access. If the authorized user arrival and there are idle spectrums, the cognitive user switches spectrum in order to not interrupt authorized users. But the cognitive user's detection and spectrum switch will produce delay, leading to the retransmission timer over the set value. The cognitive user will be forced into the slow start stage, which reduces the end to end transmission performance. In order to improve the above problems, this paper adopts TCP-MAC cross-layer and put forward an improved TCP-CR protocol based on cognitive radio network. And we use the NS2 simulation tool in different network environment, to compare the transmission performance between TCP-CR protocol and traditional TCP protocol. The results can be drawn that TCP-CR can alleviate delay problems which are brought by cognitive user's spectrum detection and switch, and it can effectively improve the transmission throughput of the network.Finally, this paper introduces Layer-Preserved structural model. There are two modules:(?)dge module and cognitive module. The KM module collect and store related information (?) is needed to realize cognitive functions, such as link round trip time RTT, timeout retransmission timer RTO, and so on. The CM module store some related algorithms and set the corresponding rules to achieve the improvement of the existing TCP protocol by using the collected information in KM module. Based on the NS2 simulation platform, and compared the transmission performance between the improved protocol and the traditional ones in the same scene. Simulation proves that under the same packet loss rate, the improved protocol can improve the end to end throughput and TCP transmit performance.