Research On TCP Performance Based On Network Coding In Wireless Ad Hoc Networks

Face to the problem of TCP protocol performance decline in wireless Ad hoc networks, the researchers proposed many improved schemes such as end to end scheme, single-layer improved scheme, cross-layer improved scheme and so on. But these schemes all have their own disadvantages; especially they can't effectively resolve the problem of TCP performance caused by high packet loss rate. In recent years, network coding provides a new idea to solve the problem. Sundararajan and others proposed a new TCP protocol based network coding technique which named TCP/NC. With the aid of network coding technique, TCP/NC makes the missing link show no missing. So, in the case of high packet loss rate this scheme can significantly improve TCP performance in wireless networks. However, the TCP/NC is a framework which made use of network coding to solve the TCP performance issues, some implementation details need to be improved. Furthermore, it does not take into account the synchronous problem of decoding operation and the data transmission in network coding layer.On the basis of the research of Sundararajan and others, we study the TCP/NC in-depth and propose the improved protocol TCP/NCW using the optimal decoding window. Firstly, the TCP/NC's network coding layer is re-designed, and the buffer management, coding and decoding window management, coding and decoding algorithm implement details, complete the new ACK mechanism are given. Secondly, we analysis the problem that decoding operation synchronized with the data transmission existing in TCP/NC, verified the existence of optimal decoding window by experiment and given the chose strategy of optimal decoding window. Finally, on the basis of the TCP/NC, the improved protocol TCP/NCW is proposed.The TCP/NC and TCP/NCW is implemented in NS2, and tested in many scenarios. The simulation results show that TCP/NC and TCP/NCW can significantly improve the throughput compared to the traditional TCP-Vegas. In addition, the performance of TCP/NCW is superior to TCP/NC.