| The Transmission Control Protocol (TCP) performs very well in the Internet. However, the performance of TCP suffers from significant throughput degradation when it applies to wireless network. How to improve the performance of TCP over wireless networks has become one of the important research subjects. This thesis mainly studies TCP improvement algorithms over cellular wireless networks and mobile ad hoc networks.This thesis first analyzes TCP performance both over cellular wireless network and ad hoc network. For cellular wireless network, the transmission feature of wireless link is analyzed, and performance of variant TCP over wireless link is compared with each other. Also, TCP performance over three kinds of topologies is analyzed for ad hoc wireless network. By theory and experiment analysis, this thesis summarizes some factors that affect TCP performance over wireless network.Then a new TCP congestion control algorithm based on bandwidth estimation is proposed. The algorithm estimates the bandwidth through the packet arrival time carried by acknowledgement packet and uses the estimated bandwidth to update congestion window. The experiment results show that the new algorithm has higher performance compared with traditional TCP protocols such as TCP Newreno and TCP Sack if the links have high bit error rate. So it is more suitable for wireless networks.In addition, this thesis proposes a new end-to-end protocol named TCP-Probe. TCP-Probe uses selecting acknowledgement mechanism to decrease network load and probability of collision, so the utilization of bandwidth is improved. The simulation results show that TCP-Probe can improve the performance of TCP over mobile ad hoc network.Finally, this thesis implements a graphics user interface network simulator. The simulator can generate simulation script, analyze simulation results and generate tables and figures automatically. By using the simulator, researchers can evaluate and analyze network protocols conveniently.
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