Thesis (Ph.D.)--George Mason University, 2008. / Vita: p. 152. Thesis director: Robert Simon. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Computer Science. Title from PDF t.p. (viewed Jan. 8, 2009). Includes bibliographical references (p. 144-151). Also issued in print.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2010. / Title from title screen (site viewed July 8, 2010). PDF text: 179 p. : col. ill. ; 13 Mb. UMI publication number: AAT 3397143. Includes bibliographical references. Also available in microfilm and microfiche formats.

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

Philosophiae Doctor - PhD / Wireless sensor networks (WSNs) have become a popular research area that is widely gaining the attraction from both the research and the practitioner communities due to their wide area of applications. These applications include real-time sensing for audio delivery, imaging, video streaming, and remote monitoring with positive impact in many fields such as precision agriculture, ubiquitous healthcare, environment protection, smart cities and many other fields. While WSNs are aimed to constantly handle more intricate functions such as intelligent computation, automatic transmissions, and in-network processing, such capabilities are constrained by their limited processing capability and memory footprint as well as the need for the sensor batteries to be cautiously consumed in order to extend their lifetime. This thesis revisits the issue of the energy efficiency in sensor networks by proposing a novel clustering approach for routing the sensor readings in wireless sensor networks. The main contribution of this dissertation is to 1) propose corrective measures to the traditional energy model adopted in current sensor networks simulations that erroneously discount both the role played by each node, the sensor node capability and fabric and 2) apply these measures to a novel hierarchical routing architecture aiming at maximizing sensor networks lifetime. We propose three energy models for sensor network: a) a service-aware model that account for the specific role played by each node in a sensor network b) a sensor-aware model and c) load-balancing energy model that accounts for the sensor node fabric and its energy footprint. These two models are complemented by a load balancing model structured to balance energy consumption on the network of cluster heads that forms the backbone for any cluster-based hierarchical sensor network. We present two novel approaches for clustering the nodes of a hierarchical sensor network: a) a distanceaware clustering where nodes are clustered based on their distance and the residual energy and b) a service-aware clustering where the nodes of a sensor network are clustered according to their service offered to the network and their residual energy. These approaches are implemented into a family of routing protocols referred to as EOCIT (Energy Optimization using Clustering Techniques) which combines sensor node energy location and service awareness to achieve good network performance. Finally, building upon the Ant Colony Optimization System (ACS), Multipath Routing protocol based on Ant Colony Optimization approach for Wireless Sensor Networks (MRACO) is proposed as a novel multipath routing protocol that finds energy efficient routing paths for sensor readings dissemination from the cluster heads to the sink/base station of a hierarchical sensor network. Our simulation results reveal the relative efficiency of the newly proposed approaches compared to selected related routing protocols in terms of sensor network lifetime maximization.

<p>In the recent past, wireless sensor networks have been introduced to use in many applications. To </p><p>design the networks, the factors needed to be considered are the coverage area, mobility, power </p><p>consumption, communication capabilities etc. The challenging goal of our project is to create a </p><p>simulator to support the wireless sensor network simulation. The network simulator (NS-2) which </p><p>supports both wire and wireless networks is implemented to be used with the wireless sensor </p><p>network. This implementation adds the sensor network classes which are environment, sensor </p><p>agent and sensor application classes and modifies the existing classes of wireless network in NS- </p><p>2. This NS-2 based simulator is used to test routing protocols – Destination-Sequenced Distance </p><p>Vector (DSDV), and Ad-Hoc On-Demand Distance Vector (AODV) as one part of simulations. </p><p>Finally, the sensor network application models and the extension methods of this NS-2 based </p><p>simulator for simulations in specific wireless sensor network applications are proposed.</p>

A wireless sensor network (WSN) is comprised of a few hundred or thousand au-tonomous sensor nodes spatially distributed over a particular region. Each sensornode is equipped with a wireless communication device, a small microprocessor, anda battery-powered energy source. Typically, the applications of WSNs such as habitatmonitoring, re detection, and military surveillance, require data collection, process-ing, and transmission among the sensor nodes. Due to their energy constraints andhostile environments, the main challenge in the research of WSN lies in prolongingthe lifetime of WSNs.In this dissertation, we present four dierent topology management protocols forK-coverage and load balancing to prolong the lifetime of WSNs.First, we present a Randomly Ordered Activation and Layering (ROAL) protocolfor K-coverage in a stationary WSN. The ROAL suggests a new model of layer cov-erage that can construct a K-covered WSN using the layer information received fromits previously activated nodes in the sensing distance. Second, we enhance the faulttolerance of layer coverage through a Circulation-ROAL (C-ROAL) protocol. Us-ing the layer number, the C-ROAL can activate each node in a round-robin fashionduring a predened period while conserving reconguration energy. Next, MobilityResilient Coverage Control (MRCC) is presented to assure K-coverage in the presence of mobility, in which a more practical and reliable model for K-coverage with nodalmobility is introduced. Finally, we present a Multiple-Connected Dominating Set(MCDS) protocol that can balance the network trac using an on-demand routingprotocol. The MCDS protocol constructs and manages multiple backbone networks,each of which is constructed with a connected dominating set (CDS) to ensure a con-nected backbone network. We describe each protocol, and compare the performanceof our protocols with Dynamic Source Routing (DSR) and/or existing K-coveragealgorithms through extensive simulations.The simulation results obtained by the ROAL protocol show that K-coverage canbe guaranteed with more than 95% coverage ratio, and signicantly extend networklifetime against a given WSN. We also observe that the C-ROAL protocol provides abetter reconguration method, which consumes only less than 1% of the recongura-tion energy in the ROAL protocol, with a greatly reduced packet latency. The MRCCprotocol, considering the mobility, achieves better coverage by 1.4% with 22% feweractive sensors than that of an existing coverage protocol for the mobility. The resultson the MCDS protocol show that the energy depletion ratio of nodes is decreasedconsequently, while the network throughput is improved by 35%.

The importance of monitoring physical and environmental conditions increases day by day and, therefore, so is the necessity of having a reliable wireless sensor network (WSN). The need to overcome challenges in WSN deployment and operation arises due to WSN's nature and characteristics such as possible nodes' mobility, limited radio and processing power, available storage and physical effects of the environment (particularly harsh environments) and balancing energy consumption has motivated us to investigate solutions to those problems. By studying related work, it was possible to observe that techniques such as the use of a good link estimator and the deployment of a suitable topology are essential features for a WSN. The core idea is to capture link connectivity dynamically and use it on routing decisions to gain reliability and estimate the whole network connectivity. The three main steps for deployment of a reliable WSN are the following: -         Link estimator -         Routing and neighbor information -         Suitable routing algorithms In addition, self-organization is an important capability that WSNs need to present. They should be reliable, scalable and energy efficient during the network lifetime and self-organization plays a key role in this context. Summing up all these aspects, it comes to the point that reliable connectivity is an important characteristic of a WSN. The goal of this work is to contribute with the research in the subject by means of implementing a suitable topology management and evaluating the network connectivity by the means of quantitative metric for the network as whole. Practical experiments results are presented and discussed.

In the recent past, wireless sensor networks have been introduced to use in many applications. To design the networks, the factors needed to be considered are the coverage area, mobility, power consumption, communication capabilities etc. The challenging goal of our project is to create a simulator to support the wireless sensor network simulation. The network simulator (NS-2) which supports both wire and wireless networks is implemented to be used with the wireless sensor network. This implementation adds the sensor network classes which are environment, sensor agent and sensor application classes and modifies the existing classes of wireless network in NS- 2. This NS-2 based simulator is used to test routing protocols – Destination-Sequenced Distance Vector (DSDV), and Ad-Hoc On-Demand Distance Vector (AODV) as one part of simulations. Finally, the sensor network application models and the extension methods of this NS-2 based simulator for simulations in specific wireless sensor network applications are proposed.

A wireless sensor network (WSN) is comprised of a few hundred or thousand au-tonomous sensor nodes spatially distributed over a particular region. Each sensornode is equipped with a wireless communication device, a small microprocessor, anda battery-powered energy source. Typically, the applications of WSNs such as habitatmonitoring, re detection, and military surveillance, require data collection, process-ing, and transmission among the sensor nodes. Due to their energy constraints andhostile environments, the main challenge in the research of WSN lies in prolongingthe lifetime of WSNs.In this dissertation, we present four dierent topology management protocols forK-coverage and load balancing to prolong the lifetime of WSNs.First, we present a Randomly Ordered Activation and Layering (ROAL) protocolfor K-coverage in a stationary WSN. The ROAL suggests a new model of layer cov-erage that can construct a K-covered WSN using the layer information received fromits previously activated nodes in the sensing distance. Second, we enhance the faulttolerance of layer coverage through a Circulation-ROAL (C-ROAL) protocol. Us-ing the layer number, the C-ROAL can activate each node in a round-robin fashionduring a predened period while conserving reconguration energy. Next, MobilityResilient Coverage Control (MRCC) is presented to assure K-coverage in the presence of mobility, in which a more practical and reliable model for K-coverage with nodalmobility is introduced. Finally, we present a Multiple-Connected Dominating Set(MCDS) protocol that can balance the network trac using an on-demand routingprotocol. The MCDS protocol constructs and manages multiple backbone networks,each of which is constructed with a connected dominating set (CDS) to ensure a con-nected backbone network. We describe each protocol, and compare the performanceof our protocols with Dynamic Source Routing (DSR) and/or existing K-coveragealgorithms through extensive simulations.The simulation results obtained by the ROAL protocol show that K-coverage canbe guaranteed with more than 95% coverage ratio, and signicantly extend networklifetime against a given WSN. We also observe that the C-ROAL protocol provides abetter reconguration method, which consumes only less than 1% of the recongura-tion energy in the ROAL protocol, with a greatly reduced packet latency. The MRCCprotocol, considering the mobility, achieves better coverage by 1.4% with 22% feweractive sensors than that of an existing coverage protocol for the mobility. The resultson the MCDS protocol show that the energy depletion ratio of nodes is decreasedconsequently, while the network throughput is improved by 35%.

In wireless sensor networks (WSNs), flooding is usually adopted by broadcast services to disseminate broadcast messages. However, flooding produces an excessive number of unnecessary control packets, markedly increasing overhead. This work proposes a new gossip-based scheme, in which nodes forward broadcast messages with dynamic probability to decrease the number of redundant messages and thereby improve energy efficiency. By using the novel probability table and adjustment mechanism based on neighbor conditions, nodes can obtain a suitable gossip probability. Furthermore, this work considers some special cases of uneven sensor deployment such as that contains nodes with a low degree. An efficient algorithm was also developed to maintain the stability of the proposed protocol. Hence, the proposed approach can deal with various topologies and node failure. Simulations demonstrate that applying the proposed scheme to control messages forwarding improves performance compared with that of existing gossip-based broadcasting schemes.