Thesis (M.S.)--University of Texas at Dallas, 2007. / Includes vita. Includes bibliographical references (leaves 163-166)

Thesis (M. App. Sc.)--Carleton University, 2004. / Includes bibliographical references (p. 93-97). Also available in electronic format on the Internet.

Dissertation (Ph.D.)--Auburn University, 2006. / Abstract. Includes bibliographic references (p.93-99).

Thesis (M.E.)--University of Canterbury, 2008. / Typescript (photocopy). "April 2008." Includes bibliographical references (leaves [93]-96). Also available via the World Wide Web.

Master thesis deals with the design of network topologies with multiple redundant links for investor’s local area network. The objective of the thesis is to design more topology proposals according to investor’s requirements and applied technologies. Design is based on an analysis of the current state, which describes current topology of investor’s network. The main part of the thesis proposes a solution based on currently available network redundancy protocols. The functionality of the proposed solutions is tested in laboratory conditions. Finally, the individual variants are compared and their individual benefits evaluated.

Vehicular Ad hoc Networks (VANETs) have the potential to enable various kinds of applications aiming at improving road safety and transportation efficiency. These applications require uni-cast routing, which remains a significant challenge due to VANETs characteristics. Given VANET dynamic topology, geographic routing protocols are considered the most suitable for such network due to their scalability and low overhead. However, the optimal selection of next-hop nodes in geographic routing is a challenging problem where the routing performance is highly affected by the variable link quality and bandwidth availability. In this dissertation, a number of enhancements to improve geographic routing reliability in VANETs are proposed. To minimize packet losses, the direction and link quality of next-hop nodes using the Expected Transmission Count (ETX) are considered to select links with low loss ratios. To consider the available bandwidth, a cross-layer enchantment of geographic routing, which can select more reliable links and quickly react to varying nodes load and channel conditions, is proposed. We present a novel model of the dynamic behavior of a wireless link. It considers the loss ratio on a link, in addition to transmission and queuing delays, and it takes into account the physical interference e ect on the link. Then, a novel geographic routing protocol based on fuzzy logic systems, which help in coordinating di erent contradicting metrics, is proposed. Multiple metrics related to vehicles' position, direction, link quality and achievable throughput are combined using fuzzy rules in order to select the more reliable next-hop nodes for packet forwarding. Finally, we propose a novel link utility aware geographic routing protocol, which extends the local view of the network topology using two-hop neighbor information. We present our model of link utility, which measures the usefulness of a two-hop neighbor link by considering its minimum residual bandwidth and packet loss rate. The proposed protocol can react appropriately to increased network tra c and to frequent topology dis-connectivity in VANETs. To evaluate the performance of the proposed protocols, extensive simulation experiments are performed using network and urban mobility simulation tools. Results confirm the advantages of the proposed schemes in increased traffic loads and network density. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

Motivated by the fact that the contention graph associated with ICN is a Markov random field (MRF) with respect to the probability distribution of its system states, and that the belief propagation algorithm (BP) is an efficient way to solve "inference" problems in graphical models such as MRF, we study how to apply BP algorithms to the analysis and control of CSMA wireless networks. We investigate three applications: (1) computation of link throughputs given link access intensities; (2) computation of link access intensities required to meet target link throughputs; and (3) optimization of network utility via the control of link access intensities. We show that BP solves the three problems with exact results in tree networks and has manageable computation errors in a network with loopy contention graph. In particular, we show how a generalized version of BP, GBP, can be designed to solve the three problems above with higher accuracy. Importantly, we show how the BP and GBP algorithms can be implemented in a distributed manner, making them useful in practical CSMA network operation. / The above studies focus on computation and control of "equilibrium" link throughputs. Besides throughputs, an important performance measure in CSMA networks is the propensity for starvation. In this thesis, we show that links in CSMA wireless networks are particularly susceptible to "temporal" starvation. Specifically, certain links may have good equilibrium throughputs, yet they can still receive no throughput for extended periods from time to time. We develop a "trap theory" to analyze temporal throughput fluctuations. The trap theory serves two functions. First, it allows us to derive new mathematical results that shed light on the transient behavior of CSMA networks. Second, we can develop automated analytical tools for computing the "degrees of starvation" for CSMA networks to aid network design. We believe that the ability to identify and characterize temporal starvation as established in this thesis will serve as an important first step toward the design of effective remedies for it. / This thesis investigates the performance and control of CSMA wireless networks. To this end, an analytical model of CSMA wireless networks that captures the essence of their operation is important. We propose an Ideal CSMA Network (ICN) model to characterize the dynamic of the interactions and dependency of links in CSMA wireless networks. This model allows us to address various issues related to performance and control of CSMA networks. / We show that the throughput distributions of links in ICN can be computed from a continuous-time Markov chain and are insensitive to the distributions of the transmission time (packet duration) and the backoff countdown time in the CSMA MAC protocol given the ratio of their means rho, referred to as the access intensity. An outcome of the ICN model is a Back-of-the-Envelope (BoE) approximate computation method that allows us to bypass complicated stochastic analysis to compute link throughputs in many network configurations quickly. The BoE computation method emerges from ICN in the limit rho → infinity. Our results indicate that BoE is a good approximation technique for modest-size networks such as those typically seen in 802.11 deployments. Beyond serving as the foundation for BoE, the theoretical framework of ICN is also a foundation for understanding and optimization of large CSMA networks. / Kai, Caihong. / Adviser: Soung Chang Liew. / Source: Dissertation Abstracts International, Volume: 73-03, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 180-183). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

At last, we focus on the detection problem in the protocol sequence design. The objective is to construct user-detectable sequences that allow any active user be detected by the receiver via some algorithm within some bounded delay if and only if it has become active. / First of all, in order to minimize variation of throughput due to delay offsets, we investigate protocol sequences whose pairwise Hamming cross-correlation is a constant for all possible relative offsets. It can be viewed as a generalization of completely shift-invariant sequences, which can achieve the zero-variation in throughput over a slot-synchronized channel. / Provided that the number of active users is smaller than the number of potential users, strongly conflict-avoiding codes are introduced with the non-blocking property in the asynchronous channel. It can be viewed as an extension of completely irrepressible sequences. / The second one is a non-blocking property which ensures that each active user can successfully transmit information at least once in its each active period. With the assumption that all potential users may be active simultaneously, user-irrepressible sequences and completely irrepressible sequences are studied respectively for different level of synchronization, to support the non-blocking property. / This thesis is based on Massey's model on collision channels without feedback, in which collided packets are considered unrecoverable. A collision occurs if two or more packets are partially or totally overlapped. Each potential user is assigned a deterministic zero-one pattern, called the protocol sequence, and sends a packet if and only if it is active and the value of the sequence is equal to one. Due to lack of feedback, the beginning of the protocol sequences cannot be synchronized and variation in relative offsets is inevitable. It further yields variation in throughput. / We study the design of protocol sequences from three different perspectives. / Zhang, Yijin. / Adviser: Wing Shing Wong. / Source: Dissertation Abstracts International, Volume: 73-03, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 1116). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

In this research work we propose a 3D node deployment strategy by carefully considering the unique characteristics of underwater acoustic communication as well as 3D dynamic nature of UWSN. This strategy targets 3D UWSN and not only improves the routing protocol performance significantly in terms of end to end delay and energy consumption but also provides reliability in data transmission. This strategy has been developed step by step from a single line of vertical communication to an effective 3D node deployment for UWSN. Several simulation experiments were carried out after adding different features to the final design to observe their impact on the overall routing performance. Finally, it is verified that this design strategy improves the routing performance, provides reliability to the network and increases network lifetime. Furthermore, we compared our results to the random node deployment in 3D, which is commonly used for analysing the performance of UWSN routing protocols. The comparison results verified our effective deployment design and showed that it provides almost 150% less end-to-end delay and almost 25% less energy consumption to the random deployment. It also revealed that by increasing the data traffic, our 3D node deployment strategy has no loss of data due to several back-up paths available, which is in contrast to random node deployment, where the packet loss occurs by increasing the data traffic. Improving the routing performance by carefully analysing the impact of 3D node deployment strategy and ensuring full sensing, transmission and back-up coverage in a highly unpredictable underwater environment, is a novel approach. Embedding this strategy with any networking protocol will improve its performance significantly.

The focus of this thesis is on the resource allocation problems in wireless sensor and cooperative networks. Typically, wireless sensor networks operate with limited energy and bandwidth are often required to meet some specified Quality-of-Service (QoS) constraints. The ultimate objective for the majority of the problems considered in this thesis is to save battery energy and maximize the network lifetime. / In the first part of this thesis, we employ complex mathematical models to emulate a variety of power drains in wireless sensor nodes. In the first instance, we address a lifetime optimization problem of a wireless TDMA/CDMA sensor network for joint transmit power and rate allocations. The effect of fast fading is captured by including rate outage and link outage constraints on each link. After that, a single-hop wireless sensor network is deployed for a certain application - to estimate a Gaussian source within a pre-specified distortion threshold. In this part, we consider lifetime maximization, in different multiple access protocols such as TDMA, an interference limited non-orthogonal multiple access (NOMA) and an idealized Gaussian multiple access channel. This problem is further studied in a multi-hop scenario where sensing and receiving powers are also included in addition to transmission power. Finally, we investigate a balancing problem between the source coding and transmission power for video wireless sensor systems where the sensor node is required to send the collected video clips, through wireless media, to a base station within a corresponding distortion threshold. All these energy saving and lifetime optimization problems in sensor networks can be formulated via nonlinear nonconvex optimization problems, which are generally hard to solve. However, with favourable variable substitution and reasonable approximation, most of these problems are shown to be convex. The only exception is the Gaussian source esitmation problem in NOMA scenario for which we provide a simple successive convex approximation based algorithm for the NOMA case that converges fast to a suboptimal solution. / In the second part of the thesis, we propose an optimal power allocation scheme with a K-block coding delay constraint on data transmission using a three node cooperative relay network assuming a block fading channel model. Channel information is fed back to the transmitter only in a causal fashion, so that the optimal power allocation strategy is only based on the current and past channel gains. We consider the two simplest schemes for information transmission using a three node (a source, a relay and a destination) relay network, namely the amplify and forward (AF) and decode and forward (DF) protocols. We use the dynamic programming methodology to solve the (K-block delay constrained) expected capacity maximization problem and the outage probability minimization problem with a short term sum power (total transmission power of the source and the relay) constraint. / The main contribution of the thesis is a comprehensive suite of power minimization and lifetime maximization methods that can be used in wireless sensor networks. We present several such applications and extensive numerical examples at the end of each chapter.