Adaptive Long-and-short Sliding Window Based Enhanced TCP Network Coding Technique

As a mechanism to ensure reliable end-to-end transmission,the TCP has become the most commonly used transport layer protocol in the Internet.However,when the packet loss occurs,the TCP will trigger congestion control mechanism and slow down the transmission speed.The congestion control mechanism has little effect on the overall transmission performance due to the low bit error rate(BER)and the small loss of packets in the wired network or the wireless network with good link quality.But in the harsh wireless network environment,such as the high-speed railway wireless network transmission environment,due to the fast time-varying link change,notable doppler effect,frequent handoff,network signal instability and other factors,there is non-negligible increase of the residual BER in the link layer transmission.In this case,the TCP needs to trigger congestion control mechanism frequently,such that the throughput performance of end-to-end transmission is greatly reduced.Therefore,it is necessary to study and improve the TCP in the harsh wireless network environment.This thesis first analyzes the shortcomings of the TCP in the presence of high packet loss,and then reviews several typical methods in order to improve the TCP.Then we focus on the analysis of the TCP based on network coding(TCP/NC),in which the idea and basic principle of network coding was cleverly integrated in the TCP design.On this basis,the problems when applying the TCP/NC in the harsh wireless environment(like high-speed railway vehicle-to-ground wireless network)are highlighted to show the deficiency of the TCP/NC in terms of inaccurate redundancy setting,performance degradation in the presence of burst packet loss,large decoding delay,and so on.In order to further improve TCP/NC transmission throughput and to reduce its processing latency,in this thesis,an enhanced the TCP network coding scheme based on adaptive long-short sliding window(LSSW-TCP/NC)is proposed.In the LSSW-TCP/NC,both the long sliding window and short sliding window mechanism are utilized to estimate packet loss rate more reliably.And the recovery probability based probability is used to set the network coding redundancy.In addition,innovative techniques such as feedback retransmission algorithm is recommended to help the TCP system quicky restore when there are a large number of burst packet losses.In this thesis,the LSSW-TCP/NC is developed and implemented as an embedded kernal module of the Linux operating system.The applicability of the LSSW-TCP/NC is verified with some simulated packet loss environment at first.And then,in the real high-speed rail-to-ground wireless network scenario,a preliminary verification test was carried out.And our analysis results show that,compared with the TCP Reno and the standard TCP/NC,the LSSW-TCP/NC technology can effectively deal with the adverse effects of burst packet loss on TCP/NC transmission performance,shorten the network jamming and pause time in adverse burst packet loss environment.Namely,the LSSW-TCP/NC is helpful to improve the end-to-end throughput performance of the TCP and reduce processing latency,as we expected.The related work of this thesis provides feasible research ideas and technical route for further optimization and research of high-performance the TCP/NC technology suitable for harsh wireless network environment.Moreover,this study provides useful insights for the future research and related appliactions for the following work in this area.