Vyas, Amit K This is not available 021535

ISBN 13: 9781243666666

This is not available 021535

 
9781243666666: This is not available 021535
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The performance of a wireless mesh network depends on many factors: the environment, the placer lent of mesh points, the equipment (transmitter and receiver), the set of established links and their physical layer (PHY) parameters (data rate and transmit power), and the operational protocols (media access control and routing). Accounting for these factors makes the design and deployment of mesh networks a challenging problem. In this thesis, we address the key issues of mesh point placement, PHY data rate and transmit power settings, and routing in the context of mesh networks based on the widely used IEEE 802.11 (WiFi) technology. We also present measurement and simulation tools as well as measurement data to allow accurate assessment of the performance of different deployment configurations and operational protocols. We present a measurement and analysis tool (WiSMART) that allows one to characterize environments in terms of signal attenuation, and wireless receivers in terms of correlation between the received signal-to-noise ratio (SNR) and error rate at each stage of packet reception (carrier synchronization, PHY header reception and data reception). We use the tool to characterize two environments---the Gates Building at Stanford University at 5 GHz (802.11a) and the Telecommunications Museum of Pleumeur-Bodou (France) at 2.4 GHz (802.11b/g). In the latter environment, where simple path loss models cannot be applied due to lack of regularity, we propose a methodology to model the environment with a limited number of measurements and suggest a placement of mesh points to provide coverage and connectivity. We also characterize an IEEE 802.11a OFDM-based wireless receiver at the various PHY data rates, and quantify the impact of interference from simultaneous packet transmissions on packet reception. We find that the impact of interference is weaker than noise, with nodes being able to receive packets with a signal-to-interference ratio (SIR) 5 dB lower than the SNR corresponding to the same error probability. We also present a high-fidelity network simulator (Stanford-Enhanced GloMoSim) with enhanced modeling of wireless propagation, receiver performance, PHY and MAC layers. Using the simulator, we find that the end-to-end throughput of flows in a wireless network is highly sensitive to the receiver model, thereby highlighting the importance of the above measurements. In terms of network design, we address the setting of PHY data rates and transmit powers on links, and routing between the mesh points. In the simple scenario of a linear homogeneous network, we illustrate the impact of the PHY settings of links on the throughput of a multihop path, and show how much throughput is lost due to various factors, such as interference, the media access scheme, maximum transmit power limit, and overhead at various networking layers. In the more general scenario of a mesh network, we propose a link metric (RCI) that strikes a balance between the Resources used by a link (blocking of neighbors and channel time used), and the Contention and Interference faced by it, in a traffic independent manner. The metric can be used for both shortest path routing and as a cost function to be minimized for configuring the link data rates and transmit powers. We find that the RCI metric can provide gains of up to 100% in network capacity compared to existing traffic independent methods. The network capacity increases with the density of mesh points when RCI is used, and does not decrease or saturate as it does when some of the simpler metrics are used. We also describe a simple distributed algorithm that can realize the rate, power and route selection...

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