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Wireless networks have been widely adopted in homes, offices and public hot spots. Two problems with wireless networks are the limited range and unavoidable packet loss. Much effort has been investigated in these problems, such as packet relaying based on node cooperation and diagnosing the cause of a packet loss; these existing solutions require modifications either to both the packet transmitter and receiver or to the physical layer. We revisit the problems and propose ubiquitously compatible solutions in medium access control layer - L2Relay and Locora. L2Relay is a layer 2 packet relay protocol that can improve the performance and extend the range of the network. A L2Relay device overhears the packet transmissions and may retransmit a packet on behalf of the access point or the node if no ACK is overheard and if it is in a better position to retransmit the packet than the original sender. L2Relay exploits many layer 2 functionalities such as carrier sense. L2Relay encompasses unique solutions to link quality measurement, rate adaptation, relayer selection, while maintaining low overhead. One important feature of L2Relay is its ubiquitous compatibility, i.e., it is compatible with any Wi-Fi devices, such that one or multiple relayers can be installed in any network easily without any modifications to the AP or nodes. Locora, which stands for Loss Cause Oracle, is a system that can help a Wi-Fi device achieve higher performance by diagnosing the actual cause of the packet loss and taking correct response upon packet loss with only local information observable by the packet sender. Locora uses novel methods to estimate the collision level, the channel change, and the hidden terminal activities, such that it can react to packet loss with suitable responses to improve the efficiency. One notable feature of Locora is its single-point upgradability. By making the decisions with only local observation, Locora enables the users to enjoy the performance gain by modifying only one end of the wireless link, i.e., upgrading only one device, which makes the deployment much simpler. L2Relay and Locora are solutions of low complexity that are implementable in firmware level. We implemented both solutions in the OpenFWWF platform. Our experiments show that L2Relay and Locora can lead to higher performance.
A Dissertation submitted to the Department of Computer Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Includes bibliographical references.
Zhenghao Zhang, Professor Directing Dissertation; Ming Yu, University Representative; Sudhir Aggarwal, Committee Member; Xin Yuan, Committee Member.
Florida State University
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