Evaluation and Enhancement of TCP with Network Coding in Wireless Multihop Networks

Abstract: Network coding is a very promising technology to efficiently utilize resources of both wired and wireless networks, and has received much attention from both academia and industry recently. Since wireless channel is inherently broadcast and suitable for application of network coding. However, the performance of legacy TCP over wireless ad hoc network is not satisfactory due to the special features of wireless networks, such as hidden terminal and exposed terminal problems, transmission errors, topology variations and routing instability, etc. As we know, the performance degradation of TCP may be caused by the rate control mechanism of TCP itself and routing protocol, while no research on this issue has been found until now. Thus, in this paper, we implement the COPE based on NS-2, and evaluate the performance of COPE with other TCP protocols adapted for wireless ad hoc network, such as TCP-FeW and TCP-AP. The simulation results show that COPE can greatly improve the network throughput and is reasonable framework to wireless network coding. However, COPE does not work for every network topology with each TCP protocol, or even worse than the traditional transmission mode. To overcome this problem, I propose two schemes to improve the performance of TCP over wireless network coding. One is called Encode Once, which ensures the packet being encoded at most one time and improves the performance of COPE. Another one is called Network Coding Aware TCP, which adapts sending rate of TCP based on TCP-AP protocol and increases the network throughput.