Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, March 2003. / Thesis advisor(s): Tri T. Ha, Jan E. Tighe. Includes bibliographical references (p. 105). Also available online.

Includes bibliographical references (p. 113-119).

Thesis (Ph.D.)--University of Central Florida, 2008. / Adviser: Wasfy B. Mikhael. Includes bibliographical references (p. 152-166).

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Xiaoping Yun, Fotis Papoulias. Includes bibliographical references (p. 81-82). Also available online.

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 111-118). Also available in electronic version. Access restricted to campus users.

Advances in micro-embedded computing systems, coupled with developments in wireless technology have enabled the deployment of large scale wireless and sensor networks for many important applications. These networks are characterized by local geographic connectivity among nodes and by very little computational and storage capabilities at each node. Moreover, data transfer is mainly through packet forwarding by intermediary nodes. Due to the nature of their connectivity, nodes may have extremely limited information about their network, possibly only of their one-hop neighbors. In such a scenario where the nodes may have limited/erroneous network state information, we study the two basic network primitives: (i) point-to-point routing and (ii) broadcasting. First, we study the problem of point-to-point routing in a network of nodes where each node has a corresponding destination to send/receive data. We consider geographic routing (routing based on the position of the nodes), as this routing scheme is scalable and of low complexity and well suited to operate over sensor networks. We study the effect of imperfect routing information on the path lengths of the individual routes. We provide error models for the routing errors and demonstrate routing strategies that achieve order-wise optimal delays even when only a small fraction of the nodes have any (possibly imperfect) geographic information. We characterize the throughput capacity of the network and show that for a class of progressive routing strategies with limited routing data, the throughput capacity is order-wise optimal. While much of the current research focuses on greedy routing in uniform sensor networks, we study routing in imperfect (anisotropic) networks where greedy geographic forwarding fails due to holes (nodes without any neighbors that are closer to the destination). We develop routing strategies in such networks that operate with geographic location at the nodes to achieve order-wise optimal delays while maximizing the network throughput capacity. These algorithms inherit the beneficial properties of geographic routing algorithms such as scalability and low complexity while providing near-optimal throughput and delay in a robust manner. We also study routing strategies in networks where the traffic demand may be non-uniform. Routing schemes such as geographic routing that minimize some metric of routing distance cause local points of congestion as they do not consider the traffic demands across different parts of the network and may concentrate traffic along some paths that lie across regions of higher demand. We design randomized routing schemes based on geographic routing that are shown to be able to support any traffic demand that is achievable (i.e. achievable by any other scheme). Second, we study the issue of broadcasting in networks with limited local information. We analyze broadcast schemes where nodes have little geographic information or state information (memory of transmitted packets). We demonstrate randomized broadcast algorithms that utilize the limited information and perform broadcasting with minimal transmission overheads. Further, we also study branching random walks in R[superscript d], in the context of broadcasting a message over a spatial network to understand the asymptotic distribution of the broadcast. We derive analytic results on the density of these branching processes / text

Wireless communication continues to make a profound impact upon our daily lives. The oft-touted benefits of high data rates and improved reliability via wireless communication are limited by its inherent drawbacks, including path loss, fading and interference. One promising strategy for overcoming these problems is to deploy nodes in the region between a transmitter and its intended receiver. These intermediate nodes can improve communication for this transmitter-receiver pair by receiving a transmitted message, processing it and relaying the processed output to the receiver. This transmission strategy, known as relay-assisted communication, can be especially beneficial when the transmitter-receiver pair are either separated by a large distance or when a large obstruction blocks the path between them. In a reasonably dense network, several relays may be available to assist a particular transmitter-receiver pair. Deciding which relays should forward the transmitted message is actually quite difficult. For example, the relay with the best physical-layer channel gain to the destination may also be running low on battery power. Another relay may have a good physical-layer channel gain to the destination and a reasonable amount of remaining battery power, but its queue may be full of messages from other transmitters, so it cannot forward a newly arrived message within a given delay constraint. Thus, optimal relay selection entails carefully balancing all system parameters, which is prohibitively complex in current wireless systems. This dissertation provides novel results for dealing with the relay selection problem in two distinct types of wireless systems. First, several selection algorithms are designed for single-antenna wireless networks, including a decentralized random access-based strategy and centralized methods that are based on throughput maximization and downlink user scheduling. Second, selection algorithms based on transmission hop length are designed for multipleantenna wireless networks. The presented strategies for both single-antenna and multiple-antenna relaying are highly intuitive, as they allow for concise descriptions, making them amenable to practical implementation. Also, the presented strategies illustrate the importance of application-specific design, since each of them yields good performance by focusing on a small set of system parameters. For example, observed latency is of paramount importance for wireless networks that support a significant level of video traffic. / text

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy