In recent years, many strides have been achieved in the area of Wireless Sensor Networks (WSNs), which is leading to constant innovations in the types of applications that WSNs can support. Much advancement has also been achieved in the area of smart homes, enabling its occupants to manually and easily control their utility expenses. In this thesis, both areas of research will be colluded for a simple, yet critical application: efficient and economical comfort control in smart residential spaces. The goal is to design a central, modular energy consumption control system for residential spaces, which manages energy consumption in all aspects of a typical residence. This thesis is concerned with two facets of energy consumption in residences. The first facet is concerned with controlling when the heating, ventilating, and air conditioning unit (HVAC) operates for each room separately. This is in contrast to a typical HVAC system where comfort is provided across the floor as a whole. The second facet is concerned with controlling the lighting in each room so as to not exceed a certain input value. The communication network that supports the realization of these coveted goals is based on Zigbee interconnected sensor nodes which pour data unto a smart thermostat which does all the required calculations and activates the modules required for comfort control and energy management, if needed. A Java-based discrete event simulator is then written up to simulate a floor of a typical Canadian single-family dwelling. The simulation assumes error-less communication and proceeds to record certain room variables and the ongoing cost of operation periodically. These results from the simulator are compared to the results of the well known simulator, created by DesignBuilder, which describes typical home conditions. The conclusion from this analysis is that the Comfort Control and Energy Management Algorithms (CEMA) are feasible, and that their implementation incurs significant monetary savings.

Sensor network web services have recently emerged as promising tools to provide remote management, data collection and querying capabilities for sensor networks. They can be utilized in a large number of elds among which Demand-Side Energy Management (DSEM) is an important application area that has become possible with the smart electrical power grid. DSEM applications generally aim to reduce the cost and the amount of power consumption. In the traditional power grid, DSEM has not been implemented widely due to the large number of households and lack of ne-grained automation tools. However by employing intelligent devices and implementing communication infrastructure among these devices, the smart grid will renovate the existing power grid and it will enable a wide variety of DSEM applications. In this thesis, we analyze various DSEM scenarios that become available with sensor network web services. We assume a smart home with a Wireless Sensor Network (WSN) where the sensors are mounted on the appliances and they are able to run web services. The web server retrieves data from the appliances via the web services running on the sensor nodes. These data can be stored in a database after processing, where the database can be accessed by the utility, as well as the inhabitants of the smart home. We showthat our implementation is e cient in terms of running time. Moreover, the message sizes and the implementation code is quite small which makes it suitable for the memory-limited sensor nodes. Furthermore, we show the application scenarios introduced in the thesis provide energy saving for the smart home.

Localization and coverage are two important and closely related problems in wireless ad hoc networks. Localization aims to determine the physical locations of devices in a network, while coverage determines if a region of interest is sufficiently monitored by devices. Localization systems require a high degree of coverage for correct functioning, while coverage schemes typically require accurate location information. This thesis investigates the relationship between localization and coverage such that new schemes can be devised which integrate approaches found in each of these well studied problems. This work begins with a thorough review of the current literature on the subjects of localization and coverage. The localization scheduling problem is then introduced with the goal to allow as many devices as possible to enter deep sleep states to conserve energy and reduce message overhead, while maintaining sufficient network coverage for high localization accuracy. Initially this sufficient coverage level for localization is simply a minimum connectivity condition. An analytical method is then proposed to estimate the amount of localization error within a certain probability based on the theoretical lower bounds of location estimation. Error estimates can then be integrated into location dependent schemes to improve on their robustness to localization error. Location error estimation is then used by an improved scheduling scheme to determine the minimum number of reference devices required for accurate localization. Finally, an optimal coverage preserving sleep scheduling scheme is proposed which is robust to localization error, a condition which is ignored by most existing solutions. Simulation results show that with localization scheduling network lifetimes can be increased by several times and message overhead is reduced while maintaining negligible differences in localization error. Furthermore, results show that the proposed coverage preserving sleep scheduling scheme results in fewer active devices and coverage holes under the presence of localization error.

Wireless Sensor Network routing protocols rely on the estimation of the quality of the links between nodes to determine a suitable path from the data source nodes to a data-collecting node. Several link estimators have been proposed, but most of these use only one link property. Fuzzy logic based link quality estimators have been recently proposed which consider a number of link quality metrics. The fuzzification of crisp values to fuzzy values is done through membership functions. The shape of the fuzzy link quality estimator membership functions is primarily performed leveraging qualitative knowledge and an improper assignment of fuzzy membership functions can lead to poor route selection and hence to unacceptable packet losses. This thesis evaluated the Channel Quality membership function of, an existing fuzzy link quality estimator and it was seen that this membership function didn???t perform as well as expected. This thesis presents an experimental approach to determine a suitable Channel Quality fuzzy membership function based on varying the shape of the fuzzy set for a multipath wireless sensor network scenario and choosing an optimum shape that maximizes the Packet Delivery Ratio of the network. The computed fuzzy set membership functions were evaluated against an existing fuzzy link quality estimator under more complex scenarios and it is shown the performance of the experimental refined membership function was better in terms of packet reception ratio and end to end delay.The fuzzy link quality estimator was applied in WiseRoute (a simple converge cast based routing protocol) and shown that this SNR based fuzzy link estimator performed better than the original implemented RSSI based link quality used in WiseRoute.

Wireless sensor networks suffer from limited power resources. Therefore, managing the energy constraints and exploring new ways to minimize the power consumption during the operation of the nodes are critical issues. Conventional MAC protocols deal with this problem without considering the internal properties of the sensor nodes’ batteries. However, recent studies about battery modeling and behaviour showed that the pulsed discharge mechanism and the charge recovery effect may have a significant impact on wireless communication in terms of power saving. In this thesis we propose two battery-aware MAC protocols that take benefit of these factors to save more energy and to prolong the lifetime of the nodes/network without affecting the throughput. In both protocols we measure the remaining battery capacity of the node and use that measurement in the back-off scheme. The first protocol gives the nodes with higher remaining battery capacity more priority to access the medium, while the other one provides more medium access priority to the nodes with lower remaining battery capacity. The objective is to investigate, through simulations, which protocol reduces the power consumption of the nodes, improve the lifetime of the network, and compare the results with the CSMA-CA protocol.

Les xarxes de sensors sense fils (WSNs) han esdevingut un dels sistemes de comunicació amb més projecció d'aquesta dècada. Abasten una àmplia varietat d’aplicacions tals com la monitorització del medi ambient, la predicció de desastres naturals, en medicina, en transport, posicionament en interiors, i tasques militars. Els nodes que composen la xarxa, són típicament de baix cost, cosa que atorga una sèrie de limitacions en termes d’energia, velocitat de càlcul i d’ample de banda. Amb els avenços de les comunicacions sense fils i la creixent demanda de noves i més complexes aplicacions, les WSNs s’han d’optimitzar per tal de minimitzar aquestes limitacions. Aquesta tesi proposa un conjunt de tècniques que proporcionen a una WSN les següents característiques: 1. Implementació distribuïda sense necessitat de senyalització entre nodes sensors. 2. Comunicacions energèticament eficients. 3. Poca complexitat als nodes sensors. 4. Empra pocs recursos (temps, ample de banda, etc.) 5. Presenta un error quadràtic mig baix en reconstrucció al receptor. 6. Comunicacions secretes a capa física. Primer, s’estudia la transmissió seqüencial de mostreig reduït. Aquesta tècnica permet la disminució del nombre de transmissions i, per tant, reduir la despesa energètica associada a la comunicació a la xarxa. En particular, s’estudia el rendiment dels codificadors determinístics, probabilístics i condicionals de mostreig reduït per senyals autoregressius. S’obtenen expressions tancades de l’error quadràtic mig pel cas de mostreig reduït determinístic i probabilístic, mentre que pel cas condicional es deriven aproximacions ajustades. A continuació, s’analitza la compressió de la informació per WSNs grans. Pel cas on els paràmetres de correlació del senyal són desconeguts a priori, es proposen dos estimadors millorats: i) un per la predicció emprant el filtre de Wiener i ii) un per l’error quadràtic mig obtingut. Ambdós estimadors s’empren pels dos passos claus de l’algorisme de codificació distribuïda de canal. Aquests estimadors milloren notablement el rendiment de l’algorisme en comparació amb els estimadors de mostres clàssics, especialment quan la dimensió del vector d’observacions és comparable en magnitud amb el nombre de mostres usades a la fase d’entrenament de l’algorisme. Posteriorment, es proposa un esquema de comunicació distribuïda i energèticament eficient anomenat Amplify-and-Forward Compressed Sensing. Aquest esquema es basa en la tècnica de sensat comprimit i aprofita la correlació existent al senyal rebut per tal de reduir tant el nombre de recursos emprats com les despeses energètiques del sistema. Específicament, el sistema es dissenya seguint una funció de cost que controla el compromís existent entre error quadràtic i consum energètic de la xarxa. Per aconseguir aquest disseny, es deriva un model simple que aproxima el rendiment de l’esquema proposat en termes d’error quadràtic mig. A més, es contribueix a la teoria de sensat comprimit amb una nova i més ajustada relació entre el mínim nombre de mesures necessàries donades unes determinades propietats del senyal. Finalment, s’estudia l’esquema proposat Amplify-and-Forward Compressed Sensing des d’un punt de vista de secretisme a capa física. Es demostra que aquest esquema assoleix secretisme perfecte sota la presència d’un o d’un grup reduït d’espies, mentre que per un nombre més gran, és possible deteriorar notablement les seves capacitats d’espionatge gràcies a una tècnica proposta especialment dissenyada per introduir un extra d’incertesa solament a l’estimació dels espies. / Wireless Sensor Networks (WSNs) have emerged as one of the most promising wireless communication systems in the last decade. They can be used in a wide variety of applications such as environmental monitoring, natural disaster prediction, healthcare, transportation, indoor positioning, and military tasks. The cost and the complexity of the nodes within a WSN are typically low, which results in constraints such as energy limitation, low computational speed, and reduced communication bandwidth. With the advances in wireless communications and the growing demand of new and more complex applications, WSNs must be optimized in order to overcome their intrinsic limitations in terms of complexity and power. In this dissertation, and according to these constraints, we propose a set of techniques that provide to a WSN the following interesting features: 1. Distributed operation without the need of signaling among sensing nodes. 2. Energy-efficient communications. 3. Low complexity at the sensing nodes. 4. Low resource (i.e., bandwidth, time, etc.) utilization. 5. Low distortion level at the receiver. 6. Secret communications at the physical layer. First, we study the zero-delay downsampling transmission. This technique allows the system to reduce the number of transmissions and hence decrease the total energy spent. In particular, we study the performance of deterministic, probabilistic and conditional downsampling encoding-decoding pairs for the case of the autoregressive signal model. We obtain closed form expressions for the quadratic error of the deterministic and probabilistic encoder-decoders, while accurate approximations are derived for the quadratic error of the conditional downsampling schemes. Second, we analyze data compression applied to large WSNs. For the realistic case where the correlation parameters are not known a priori, we obtain two enhanced correlation estimators: i) one for the linear Wiener filter vector and ii) one for the achieved mean square error. Both estimators are employed in the two key steps of the distributed source coding algorithm. These estimators notably improve the performance of the algorithm in comparison to the application of classical sample estimators, specially when the dimension of the observation vector is comparable in magnitude to the number of samples used in the training phase. Then, we propose a distributed and energy-efficient communication scheme named Amplify-and-Forward Compressed Sensing. This scheme is based on compressed sensing and exploits the correlation present in the signal in order to reduce both the resource utilization and the energy consumption. More specifically, the system is designed according to a cost function that controls the trade-off between the quadratic error in the reconstruction and the energy consumption of the network. In order to aid the system design, a simple model that accurately approximates the performance of the proposed scheme in terms of the quadratic error has been derived. Furthermore, we contribute to the compressed sensing theory with a tighter relationship between the minimum number of measurements that are required for a given network dimension and the sparsity level of the transmitted signal. Finally, the proposed Amplify-and-Forward Compressed Sensing scheme is also studied in terms of secrecy and wiretap distortion at the physical layer. It is shown that the proposed scheme is perfectly secret in the presence of one or even a small group of eavesdroppers whereas for a larger eavesdropping set, it is still possible to notably deteriorate its espionage capabilities thanks to a proposed technique specifically designed to introduce extra uncertainty only in the channel estimation of the eavesdroppers.

This thesis contributes toward the design of a reliable and energy-efficient transport system for Wireless Sensor Networks. Wireless Sensor Networks have emerged as a vital new area in networking research. In many Wireless Sensor Network systems, a common task of sensor nodes is to sense the environment and send the sensed data to a sink node. Thus, the effectiveness of a Wireless Sensor Network depends on how reliably the sensor nodes can deliver their sensed data to the sink. However, the sensor nodes are susceptible to loss for various reasons when there are dynamics in wireless transmission medium, environmental interference, battery depletion, or accidentally damage, etc. Therefore, assuring reliable data delivery between the sensor nodes and the sink in Wireless Sensor Networks is a challenging task. The primary contributions of this thesis include four parts. First, we design, implement, and evaluate a cross-layer communication protocol for reliable data transfer for data streaming applications in Wireless Sensor Networks. We employ reliable algorithms in each layer of the communication stack. At the MAC layer, a CSMA MAC protocol with an explicit hop-by-hop Acknowledgment loss recovery is employed. To ensure the end-to-end reliability, the maximum number of retransmissions are estimated and used at each sensor node. At the transport layer, an end-to-end Negative Acknowledgment with an aggregated positive Acknowledgment mechanism is used. By inspecting the sequence numbers on the packets, the sink can detect which packets were lost. In addition, to increase the robustness of the system, a watchdog process is implemented at both base station and sensor nodes, which enable them to power cycle when an unexpected fault occurs. We present extensive evaluations, including theoretical analysis, simulations, and experiments in the field based on Fleck-3 platform and the TinyOS operating system. The designed network system has been working in the field for over a year. The results show that our system is a promising solution to a sustainable irrigation system. Second, we present the design of a policy-based Sensor Reliability Management framework for Wireless Sensor Networks called SRM. SRM is based on hierarchical management architecture and on the policy-based network management paradigm. SRM allows the network administrators to interact with the Wireless Sensor Network via the management policies. SRM also provides a self-control capability to the network. This thesis restricts SRM to reliability management, but the same framework is also applicable for other management services by providing the management policies. Our experimental results show that SRM can offer sufficient reliability to the application users while reducing energy consumption by more than 50% compared to other approaches. Third, we propose an Energy-efficient and Reliable Transport Protocol called ERTP, which is designed for data streaming applications in Wireless Sensor Networks. ERTP is an adaptive transport protocol based on statistical reliability that ensures the number of data packets delivered to the sink exceeds the defined threshold while reducing the energy consumption. Using a statistical reliability metric when designing a reliable transport protocol guarantees the delivery of adequate information to the users, and reduces energy consumption when compared to the absolute reliability. ERTP uses hop-by-hop Implicit Acknowledgment with a dynamically updated retransmission timeout for packet loss recovery. In multihop wireless networks, the transmitter can overhear a forwarding transmission and interpret it as an Implicit Acknowledgment. By combining the statistical reliability and the hop-by-hop Implicit Acknowledgment loss recovery, ERTP can offer sufficient reliability to the application users with minimal energy expense. Our extensive simulations and experimental evaluations show that ERTP can reduce energy consumption by more than 45% when compared to the state-of- the-art protocol. Consequently, sensor nodes are more energy-efficient and the lifespan of the unattended Wireless Sensor Network is increased. In Wireless Sensor Networks, sensor node failures can create network partitions or coverage loss which can not be solved by providing reliability at higher layers of the protocol stack. In the final part of this thesis, we investigate the problem of maintaining the network connectivity and coverage when the sensor nodes are failed. We consider a hybrid Wireless Sensor Network where a subset of the nodes has the ability to move at a high energy expense. When a node has low remaining energy (dying node) but it is a critical node which constitutes the network such as a cluster head, it will seek a replacement. If a redundant node is located in the transmission range of the dying node and can fulfill the network connectivity and coverage requirement, it can be used for substitution. Otherwise, a protocol should be in place to relocate the redundant sensor node for replacement. We propose a distributed protocol for Mobile Sensor Relocation problem called Moser. Moser works in three phases. In the first phase, the dying node determines if network partition occurs, finds an available mobile node, and asks for replacement by using flooding algorithm. The dying node also decides the movement schedule of the available mobile node based on certain criteria. The second phase of the Moser protocol involves the actual movement of the mobile nodes to approach the location of the dying node. Finally, when the mobile node has reached the transmission of the dying node, it communicates to the dying nodes and moves to a desired location, where the network connectivity and coverage to the neighbors of the dying nodes are preserved.

Medium access control (MAC) plays a vital role in satisfying the varied quality of service (QoS) requirements in wireless networks. Many MAC solutions have been proposed for these networks, and performance evaluation, optimization and enhancement of these MAC protocols is needed. In this thesis, we focus on the analysis and optimization of MAC protocols for some recently emerged wireless technologies targeted at low-rate and multimedia applications.

Thesis--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 39-43).

Thesis (Ph. D.)--Auburn University. / Abstract. Vita. Includes bibliographical references (p. 118-124).