10,594 research outputs found
Enhancing TCP delivery over wireless networks
No full textWireless communication has become a significant life style in the daily use. The wireless communication can be used to extend the service of wired communication. Based on the idea
of simplicity, Transmission Control Protocol (TCP) has been used widely over wired network. When network applications take place using wireless link, TCP is still useful because partial
wired connection might be necessary. Although wired and wireless communication do share something in common, they have distinct features. Therefore, TCP needs to be adjusted to
fit in the wireless environment.This research aims to enhance wireless TCP performance. In order to study network protocols and behaviours, network simulators are often used for researchers to configure and
monitor the network factors and system states. Unfortunately, most network simulators cannot demonstrate what the real network does. They are applications. In this research, a network simulator based on the real Linux TCP/IP stacks is proposed. This simulator is able to not only simulate the wired network, but also allow users to extend its structure for live wireless emulation. By means of simulator and emulator, researchers can understand and configure detail factors for further experiments. Eventually, a new wireless TCP enhancement is proposed.In this research, some contributions are delivered. Firstly, a network simulator based on Linux TCP stacks is implemented. Secondly, a wireless emulator and test environment are built, so the wireless factors can be configured and performance can be monitored. Thirdly, a wireless TCP mechanism, TCP NewZag, is proposed. Finally, several experiments to show the value of NewZag are reported in the thesis
Two-stage winner designs for non-inferiority trials with two to three experimental treatments and an active control
No full textIn drug development, two-stage winner design can be cost-effective when the best treatment is to be determined from multiple experimental treatments. In this design, an interim analysis is devised to select the best treatment to avoid high cost, long-term trial conduction, and exposure to ineffective treatments. When an existing effective treatment is available, but new experimental treatments have advantages such as less cost, easier delivery, less invasive and fewer side effects, etc., including placebo in the trial may be considered unethical. It is desirable to conduct a non-inferiority trial that directly compares new treatments with the existing treatment (active control), and show that the new treatments are not less effective than the active control by a certain amount (so called non-inferiority margin). In this dissertation, we extended the framework of the two-stage winner design of Shun et al. (2008) to conduct non-inferiority tests. Specifically, we considered designs of trials with two or three experimental treatments and an active control. Our methods include superiority hypotheses as a special case, but the hypothesis setting is more general than that studied by Shun et al.. We studied the distribution of test statistics, cut-off values, sample size and power calculations using exact distribution of the test statistics as well as using normal approximations. Theoretical justifications and extensive numerical assessments were conducted to calculate the design parameters and evaluate the performance of our methods.Ph. D.Includes bibliographical referencesIncludes vitaby Pin-wen Wan
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