Analysis And Enhancement Of TCP Performance In Wireless Ad Hoc Networks

Wireless ad hoc network is a special peer-to-peer network without fixed infrastructure such as base stations. Mobile nodes are connected by wireless links and each node acts as a router in the network. Traditional Transmission Control Protocol (TCP) works well in wired network but suffers from performance degradation in wireless ad hoc networks due to the fact that it cannot distinguish packet losses due to congestion from packet losses due to link breakage, channel error and route changes. Due to the prevalence of TCP application, the research on TCP performance improvement in wireless ad hoc networks becomes a hot issue. This thesis analyzes the possible reasons of TCP's poor performance in ad hoc networks and proposes enhancements.At first the thesis introduces briefly the characteristics of wireless ad hoc networks and the TCP protocol. Afterwards, the thesis investigates the TCP performance problem in mobile ad hoc networks and proposes an enhancement of TCP named TCP Freeze-Probing to effectively improve the TCP throughput.Based on TCP Reno throughput model, the thesis introduces a new throughput model for TCP Freeze-Probing. The model is validated then through simulation.Analysis and computer simulation in Network Simulator 2 have proved the correctness and the effectiveness of the TCP Freeze-Probing protocol by using throughput as a main performance metric. By analyzing the simulation results in various mobile topology environments, TCP Freeze-Probing has been proved to outperform traditional TCP protocol. Compared with other improved schemes, TCP Freeze-Probing is much easier to implement in real systems because it uses simple yet effective algorithms in end nodes and does not require the cooperation of intermediate nodes.TCP instability in wireless ad hoc network is also a well-known problem. The thesis investigates the Teasons of TCP instability in static wireless ad hoc networks and proposes schemes combing MAC layer and route layer enhancements to solve this problem. Simulation results show that the proposed schemes are correct and efficient.Finally, the thesis concludes by summarizing the main contributions of the research and presenting directions for future work.