Research And Implementation Of Multipath Transmission Performance Optimization In Wireless Network

In recent years,one of significant changes in network is that the wired network turns to the wireless network gradually.TCP protocol is designed mainly for the wired network originally.However,random packet losses caused by signal fading and interference in wireless network make the traditional TCP congestion control scheme not applicable.As a result,the transmission performance declines dramatically.The second significant change in network is that the structure turns from single-path to multi-path gradually.IETF proposed MPTCP,which is the extension of TCP in multi-path.However,the difference of performance between heterogeneous networks brings'bottleneck link' problem to MPTCP.In addition,MPTCP requires a big receiving buffer space.In order to solve those problems mentioned above,the existing research attempts to combine Network Coding and MPTCP.This paper also draws on the idea of using the redundant coded packet for packet recovering instead of retransmission to improve MPTCP.Under the guidance of the structure of MPTCP,this paper designed a multipath transmission protocol based on Systematic Fountain codes,which named SF-MPTCP(Systematic Fountain code-based Multipath TCP).How much of the data block size should be chosen?This article models this problem as a constrained optimization problem.Minimize redundancy is the optimization goal in this model,one of restricted conditions is end to end delay,and the other restricted condition is probability threshold of successful decoding.We consider the process of transmission in a block as a 'multi-round' model,and just append enough redundancy packages in the 'final round' for block redundancy control algorithm.Which encode algorithm should we choose?This paper compares the advantages and disadvantages of fixed-rate and non-rate code as well as the advantages and disadvantages of systematic and non-systematic code.When combined with subsequent multi-path scheduling algorithm,we use 'fountain code system' as the encoding scheme.Finally,this paper designs a multi-path scheduling algorithm based on path quality assessment.The typical metrics of path performance are packet loss rate,delay,the size of send window and so on,which just indicate partial performance of a sub-path.This paper use'Expected Response Time' as a unified measure for the performance of multiple heterogeneous paths,in order to quantify the performance of all sub-paths.Then we propose a multi-path scheduling algorithm based on'Expected Arriving Time' to make better use of multiple paths and improve the efficiency of multi-path transmission.Finally we demonstrate the effectiveness of SF-MPTCP through simulation.