Retrasmission Algorithm Optimization Of TCP Over LTE Network

The development and popularization of smart terminals have led to a revolution in the Internet.A new form of data services,mobile Internet,takes charge of more and more transmission tasks.Meanwhile,the core of the mobile Internet service is transferring into photographs and multimedia from basic text files.In order to ensure the efficiency of mobile network,LTE(Long Term Evolution)network has become the main carrier of mobile data transmission.Subject to many uncontrollable quality-affecting factors,including environmental disturbance and frequent handoff,LTE network exhibits much higher BER(Bit Error Rate)and more frequently bandwidth fluctuation than wired network.Because of this,TCP(Transmission Control Protocol),which was first designed for reliable data transmission in traditional wired network,has some incompatibility issues with LTE network.According to statistics,there are much many TCP flows recovered from packet losses by retransmission timeout rather than fast recovery.These undesirable timeouts are spurious timeouts.This paper first analyses the traditional TCP protocol mechanism and takes lots of experiments for analysis.The performance and side effects of spurious timeout are summarized,and the possible reasons of spurious timeout are also exposited in this paper.For the abnormal congestion window updating,a feedback control model of TCP transmission process is established based on shadow price,taking advantage of the feedback information to monitor the network situation.Synthesizing the above results,a new method termed as TCP-SR(TCP-Shadow Retransmission)is proposed.TCP-SR can both avoid spurious timeout by retransmission packet detection,and alleviate the side effect by using feedback control theory to modify the congestion window updating algorithm.Several simulations,including a point-to-point and a LTE scenario,are carried out with NS-3 to verify the performance of TCP-SR.The results indicate that the frequency of occurrence of RTOs are significantly reduced using the proposed algorithm.Compared with other common version of TCP,TCP-SR gains better throughput in both high BER and bandwidth fluctuation network environment.Furthermore,it tends to yield better performance than TCP-Westwood with a 23%-28%throughput improvement in the LTE scenario.