Дисертації з теми "Wireless sensor networks Quality control"

L'objectif de la thèse est d'étudier la variation temporelle de la qualité des liens dans les réseaux de capteurs sans fil à grande échelle, de concevoir des estimateurs permettant la différenciation, à court terme et long terme, entre liens de qualité hétérogène. Tout d'abord, nous étudions les caractéristiques de deux paramètres de la couche physique: RSSI (l'indicateur de puissance du signal reçu) et LQI (l'indicateur de la qualité de liaison) sur SensLab, une plateforme expérimentale de réseau de capteurs à grande échelle situé à l'intérieur de bâtiments. Nous observons que le RSSI et le LQI permettent de discriminer des liens de différentes qualités. Ensuite, pour obtenir un estimateur de PRR, nous avons approximé le diagramme de dispersion de la moyenne et de l'écart-type du LQI et RSSI par une fonction Fermi-Dirac. La fonction nous permet de trouver le PRR à partir d'un niveau donné de LQI. Nous avons évalué l'estimateur en calculant le PRR sur des fenêtres de tailles variables et en le comparant aux valeurs obtenues avec l'estimateur. Par ailleurs, nous montrons en utilisant le modèle de Gilbert-Elliot (chaîne de Markov à deux états) que la corrélation des pertes de paquets dépend de la catégorie de lien. Le modèle permet de distinguer avec précision les différentes qualités des liens, en se basant sur les probabilités de transition dérivées de la moyenne et de l'écart-type du LQI. Enfin, nous proposons un modèle de routage basé sur la qualité de lien déduite de la fonction de Fermi-Dirac approximant le PRR et du modèle Markov Gilbert-Elliot à deux états. Notre modèle est capable de distinguer avec précision les différentes catégories de liens ainsi que les liens fortement variables
The goal of the thesis is to investigate the issues related to the temporal link quality variation in large scale WSN environments, to design energy efficient link quality estimators able to distinguish among links with different quality on a short and a long term. First, we investigate the characteristics of two physical layer metrics: RSSI (Received Signal Strength Indication) and LQI (Link Quality Indication) on SensLAB, an indoor large scale wireless sensor network testbed. We observe that RSSI and LQI have distinct values that can discriminate the quality of links. Second, to obtain an estimator of PRR, we have fitted a Fermi-Dirac function to the scatter diagram of the average and standard variation of LQI and RSSI. The function enables us to find PRR for a given level of LQI. We evaluate the estimator by computing PRR over a varying size window of transmissions and comparing with the estimator. Furthermore, we show using the Gilbert-Elliot two-state Markov model that the correlation of packet losses and successful receptions depend on the link category. The model allows to accurately distinguish among strongly varying intermediate links based on transition probabilities derived from the average and the standard variation of LQI. Finally, we propose a link quality routing model driven from the F-D fitting functions and the Markov model able to discriminate accurately link categories as well as high variable links

High information quality is a paramount requirement for wireless sensor network monitoring applications. However, it is challenging to achieve a cost effective information quality solution due to unpredictable environment noise and events, unreliable wireless channel and network bandwidth, and resource and energy constraints. Specifically, the dynamic and unreliable nature of WSNs make it difficult to pre-determine optimum sensor rates and predict packet loss. To address this problem, we use information quality metrics presented by [26, 11] which characterize information quality based on the sampling frequency of sensor nodes and the packet loss rate during network transmission. These fundamental quality metrics are based on signal-to-noise ratio and are therefore application independent. Based on these metrics, a quality-aware scheduling system (QSS) is developed, which exploits cross-layer control of sensor nodes to effectively schedule data sensing and forwarding. Particularly, we develop and evaluate several QSS scheduling mechanisms: passive, reactive and perceptive. These mechanisms can adapt to environment noise, bandwidth variation and wireless channel collisions by dynamically controlling sensor rates and sensor phase. Our software and hardware experimental results indicate that our QSS is a novel and effective approach to improve information quality for WSNs.

Wireless sensor actuator networks (WSANs) are becoming a solution for the implementation of control applications. Sensors and actuators can be deployed forming a large or dense network to monitor and control physical parameters or systems. However, this comes with challenges. Reliable data transmission and real-time communication constraints are the most significant challenges in WSANs for control applications because wireless networks are characterised by harsh transmission conditions. The use of WSANs for critical control applications has not gained sufficient progress as wireless networks are perceived to be totally unreliable and hence unsuitable. This makes reliable data transmission a priority in this research. Control applications will have a number of quality of service (QoS) requirements, such as requiring a very low packet-loss rate (PLR), minimum delay and guaranteed packet delivery. The overall goal of this research is to develop a framework that ensures reliable and real-time communication within the sensor network. A totally reliable network design involves ensuring reliability in areas such as the medium access control, connectivity, scalability, lifetime, clustering and routing with trade-offs such as energy consumption, system throughput and computational complexity. In this thesis, we introduce a unique method of improving reliability and real-time communication for control applications using a link quality routing mechanism which is tied into the ZigBee addressing scheme. ZigBee routing protocols do not consider link quality when making routing decisions. The results based on common network test conditions give a clear indication of the impact on network performance for various path loss models. The proposed link quality aware routing (LQAR) showed a highly significant 20.5% improvement in network delays against the ZigBee hierarchical tree routing (HTR) protocol. There is also a 17% improvement in the PLR. We also investigate variable sampling to mitigate the effects of delay in WSANs using a neural network delay predictor and observer based control system model. Our focus on variable sampling is to determine the appropriate neural network topology for delay prediction and the impact of additional neural network inputs such as PLR and throughput. The major contribution of this work is the use of typical obtainable delay series for training the neural network. Most studies have used random generated numbers which are not a correct representation of delays actually experienced in a wireless network. In addition, results show that the use of network packet loss information improves the prediction accuracy of delay. Our results show that adequate prediction of the time-delay series using the observer based variable sampling model influences the performance of the control system model under the assumptions and stated conditions.

Wireless sensor networks (WSNs) are becoming widely adopted across multiple industries to implement sensor and non-critical control applications. These networks of smart sensors and actuators require energy efficient and reliable operation to meet application requirements. Regulatory body restrictions, hardware resource constraints and an increasingly crowded network space makes realising these requirements a significant challenge. Transmission power control (TPC) protocols are poised for wide spread adoption in WSNs to address energy constraints and prolong the lifetime of the networked devices. The complex and dynamic nature of the transmission medium; the processing and memory hardware resource constraints and the low channel throughput makes identifying the optimum transmission power a significant challenge. TPC protocols for WSNs are not well developed and previously published works suffer from a number of common deficiencies such as; having poor tuning agility, not being practical to implement on the resource constrained hardware and not accounting for the energy consumed by packet retransmissions. This has resulted in several WSN standards featuring support for TPC but no formal definition being given for its implementation. Addressing the deficiencies associated with current works is required to increase the adoption of TPC protocols in WSNs. In this thesis a novel holistic TPC protocol with the primary objective of increasing the energy efficiency of communication activities in WSNs is proposed, implemented and evaluated. Firstly, the opportunities for TPC protocols in WSN applications were evaluated through developing a mathematical model that compares transmission power against communication reliability and energy consumption. Applying this model to state-of-the-art (SoA) radio hardware and parameter values from current WSN standards, the maximum energy savings were quantified at up to 80% for links that belong to the connected region and up to 66% for links that belong to the transitional and disconnected regions. Applying the results from this study, previous assumptions that protocols and mechanisms, such as TPC, not being able to achieve significant energy savings at short communications distances are contested. This study showed that the greatest energy savings are achieved at short communication distances and under ideal channel conditions. An empirical characterisation of wireless link quality in typical WSN environments was conducted to identify and quantify the spatial and temporal factors which affect radio and link dynamics. The study found that wireless link quality exhibits complex, unique and dynamic tendencies which cannot be captured by simplistic theoretical models. Link quality must therefore be estimated online, in real-time, using resources internal to the network. An empirical characterisation of raw link quality metrics for evaluating channel quality, packet delivery and channel stability properties of a communication link was conducted. Using the recommendations from this study, a novel holistic TPC protocol (HTPC) which operates on a per-packet basis and features a dynamic algorithm is proposed. The optimal TP is estimated through combining channel quality and packet delivery properties to provide a real-time estimation of the minimum channel gain, and using the channel stability properties to implement an adaptive fade margin. Practical evaluations show that HTPC is adaptive to link quality changes and outperforms current TPC protocols by achieving higher energy efficiency without detrimentally affecting the communication reliability. When subjected to several common temporal variations, links implemented with HTPC consumed 38% less than the current practise of using a fixed maximum TP and between 18-39% less than current SoA TPC protocols. Through offline computations, HTPC was found to closely match the performance of the optimal link performance, with links implemented with HTPC only consuming 7.8% more energy than when the optimal TP is considered. On top of this, real-world implementations of HTPC show that it is practical to implement on the resource constrained hardware as a result of implementing simplistic metric evaluation techniques and requiring minimal numbers of samples. Comparing the performance and characteristics of HTPC against previous works, HTPC addresses the common deficiencies associated with current solutions and therefore presents an incremental improvement on SoA TPC protocols.

Energy is the biggest concern for any heterogeneous WSNs and achieving high energy efficiency is of paramount importance for the longevity of a heterogeneous WSNs. Communicating in- formation from the sensing region to the sink is a critical task in the entire operation of a heterogeneous WSNs. Such information needs to be reliably communicated, while avoiding any network congestion, from source to sink in order to ensure that application-specific Quality of Service objectives are met for any given scenario. This thesis developed several transport layer protocols to address the issues of congestion control, reliability assurance, simultaneously supporting heterogeneous traffic environment and energy efficiency for a heterogeneous WSNs.The first aim of the proposed research is to develop a congestion control scheme for a heterogeneous WSNs. The envisaged congestion control scheme has dual functionality. Firstly, it should be capable of handling the traffic heterogeneity and secondly, it intelligently assigns the source transmission rates and channel bandwidth for avoiding congested scenarios within the network, thereby avoiding any unnecessary packet retransmissions, due to packet drops caused by congestion. This produces high network good throughput, effective use of channel bandwidth, minimum E-2-E data packet latency etc. All the proposed transport layer protocol schemes e.g. End-to-End Reliable and Congestion Aware Transport Layer Protocol (ERCTP), Lightweight Congestion Aware Reliable Transport protocol (LCART) and Lightweight Congestion Aware Reliable Transport Protocol-implicit (LCARTi) are designed with this aim in mind.The second aim of the proposed research is to develop an intelligent reliability ensuring scheme capable of handling bidirectional reliability issues associated with data and control information flow within the heterogeneous WSNs. The design takes into account the variable nature of reliability assurance based on the nature of the traffic. For instance, multimedia flow is given a high reliability measure in comparison to scalar and non-event information flow, since the multimedia has a high retransmission cost. All the proposed transport layer protocol schemes such as ERCTP, LCART and LCARTi are designed in order to achieve this objective.The third aim of the proposed research is to develop a scheme that simultaneously handles the heterogeneous traffic flows within the same network. The proposed scheme has the intelligence to determine the nature of traffic and to allocate different bandwidth based on this nature in order to meet the stringent requirements as imposed by the application-specific QoS constraints like E-2-E data packet latency, high good throughput etc. All the proposed transport layer protocol schemes such as ERCTP, LCART and LCARTi are designed with this objective in mind.The fourth and final aim of the proposed research is to create a mechanism that merges the common functionalities of different layers of the WSNs communication stack in order to maximise energy efficiency. This involves finding the relationship between the transport and the lower MAC and wireless-physical layers of the WSNs communication stack. This merging will result in better utilization of network resources such as bandwidth, storage etc. and helps to achieve the objective of energy efficiency. Only the LCART and LCARTi designs achieve this proposed research aim.

Les réseaux de capteurs sans fil (RCSF) sont largement utilisés dans les applications environnementales où l’objectif est de détecter un phénomène physique tel que la température, l’humidité, la pollution de l’air, etc. Dans ce contexte d’application, l’utilisation de RCSF permet de comprendre les variations du phénomène et donc être en mesure de prendre des décisions appropriées concernant son impact. En raison des limitations de ses méthodes de suivi traditionnelles et de sa grande variabilité spatiale et temporelle, la pollution de l'air est considérée comme l'un des principaux phénomènes physiques qui restent à étudier et à caractériser. Dans cette thèse, nous considérons trois applications concernant l’utilisation de RCSF pour le suivi de la pollution de l’air : la cartographie en temps réel de la qualité de l’air, la détection de dépassements de seuils des polluants et la correction de modèles physiques qui simulent le phénomène de dispersion de la pollution. Toutes ces applications nécessitent de déployer et d’ordonnancer minutieusement les capteurs afin de mieux comprendre la pollution atmosphérique tout en garantissant un coût de déploiement minimal et en maximisant la durée de vie du réseau. Notre objectif est de résoudre les problèmes de déploiement et d'ordonnancement tout en tenant compte des caractéristiques spécifiques du phénomène de la pollution de l’air. Nous proposons pour chaque cas d'application une approche efficace pour le déploiement de noeuds capteurs et puits. Nous proposons également une approche d’ordonnancement adaptée au cas de la correction de modèles physiques. Nos approches d'optimisation prennent en compte la nature physique de la pollution atmosphérique et intègrent les données réelles fournies par les plateformes existantes de suivi de la qualité de l’air. Dans chacune de nos approches d’optimisation, nous utilisons la programmation linéaire en nombres entiers pour concevoir des modèles d’optimisation adaptés à la résolution de petites et moyennes instances. Pour traiter les grandes instances, nous proposons des heuristiques en utilisant des techniques de relaxation linéaire. Outre nos travaux théoriques sur le suivi de la pollution atmosphérique, nous avons conçu et déployé dans la ville de Lyon un réseau de capteurs de pollution économe en énergie. Sur la base des caractéristiques de notre système et des jeux de données de la pollution atmosphérique, nous avons évalué l’efficacité de nos approches de déploiement et d’ordonnancement. Nous présentons et discutons dans cette thèse les résultats d'évaluation de performances ainsi que des lignes directrices pour la conception de systèmes de suivi de la pollution de l’air. Parmi nos principales conclusions, nous soulignons le fait que la taille optimale du réseau de capteurs dépend du degré de variation des concentrations de pollution dans la région de déploiement
Wireless sensor networks (WSN) are widely used in environmental applications where the aim is to sense a physical phenomenon such as temperature, humidity, air pollution, etc. In this context of application, the use of WSN allows to understand the variations of the phenomenon over the monitoring region and therefore be able to take adequate decisions regarding the impact of the phenomenon. Due to the limitations of its traditional costly monitoring methods in addition to its high spatial and temporal variability, air pollution is considered as one of the main physical phenomena that still need to be studied and characterized. In this thesis, we consider three main applications regarding the use of WSN for air pollution monitoring: 1) the construction of real time air quality maps using sensor measurements; 2) the detection of pollution threshold crossings; and 3) the correction of physical models that simulate the pollution dispersion phenomenon. All these applications need careful deployment and scheduling of sensors in order to get a better knowledge of air pollution while ensuring a minimal deployment cost and a maximal lifetime of the deployed sensor network. Our aim is to tackle the problems of WSN deployment and scheduling while considering the specific characteristics of the air pollution phenomenon. We propose for each application case a new efficient approach for the deployment of sensor and sink nodes. We also propose a WSN scheduling approach that is adapted to the case of physical models’ correction. Our optimization approaches take into account the physical nature of air pollution dispersion and incorporate real data provided by the existing pollution sensing platforms. As part of each approach, we use integer linear programming to derive optimization models that are well adapted to solving small and medium instances. To deal with large instances, we propose heuristic algorithms while using linear relaxation techniques. Besides our theoretical works on air pollution monitoring, we design from scratch and deploy in the Lyon city a cost-effective energy-efficient air pollution sensor network. Based on the characteristics of our monitoring system in addition to real world air pollution datasets, we evaluate the effectiveness of our deployment and scheduling approaches and provide engineering insights for the design of WSN-based air pollution monitoring systems. Among our conclusions, we highlight the fact that the size of the optimal sensor network depends on the degree of the variations of pollution concentrations within the monitoring region

Data sensing and retrieval in WSNs have a great applicability in military, environmental, medical, home and commercial applications. In query-based WSNs, a user would issue a query with QoS requirements in terms of reliability and timeliness, and expect a correct response to be returned within the deadline. Satisfying these QoS requirements requires that fault tolerance mechanisms through redundancy be used, which may cause the energy of the system to deplete quickly. This dissertation presents the design and validation of adaptive fault tolerant QoS control algorithms with the objective to achieve the desired quality of service (QoS) requirements and maximize the system lifetime in query-based WSNs. We analyze the effect of redundancy on the mean time to failure (MTTF) of query-based cluster-structured WSNs and show that an optimal redundancy level exists such that the MTTF of the system is maximized. We develop a hop-by-hop data delivery (HHDD) mechanism and an Adaptive Fault Tolerant Quality of Service Control (AFTQC) algorithm in which we utilize "source" and "path" redundancy with the goal to satisfy application QoS requirements while maximizing the lifetime of WSNs. To deal with network dynamics, we investigate proactive and reactive methods to dynamically collect channel and delay conditions to determine the optimal redundancy level at runtime. AFTQC can adapt to network dynamics that cause changes to the node density, residual energy, sensor failure probability, and radio range due to energy consumption, node failures, and change of node connectivity. Further, AFTQC can deal with software faults, concurrent query processing with distinct QoS requirements, and data aggregation. We compare our design with a baseline design without redundancy based on acknowledgement for data transmission and geographical routing for relaying packets to demonstrate the feasibility. We validate analytical results with extensive simulation studies. When given QoS requirements of queries in terms of reliability and timeliness, our AFTQC design allows optimal â sourceâ and â pathâ redundancies to be identified and applied dynamically in response to network dynamics such that not only query QoS requirements are satisfied, as long as adequate resources are available, but also the lifetime of the system is prolonged.
Ph. D.

Several applications have been proposed for wireless sensor networks, including habitat monitoring, structural health monitoring, pipeline monitoring, and precision agriculture. Among the desirable features of wireless sensor networks, one is the ease of deployment. Since the nodes are capable of self-organization, they can be placed easily in areas that are otherwise inaccessible to or impractical for other types of sensing systems. In fact, some have proposed the deployment of wireless sensor networks by dropping nodes from a plane, delivering them in an artillery shell, or launching them via a catapult from onboard a ship. There are also reports of actual aerial deployments, for example the one carried out using an unmanned aerial vehicle (UAV) at a Marine Corps combat centre in California -- the nodes were able to establish a time-synchronized, multi-hop communication network for tracking vehicles that passed along a dirt road. While this has a practical relevance for some civil applications (such as rescue operations), a more realistic deployment involves the careful planning and placement of sensors. Even then, nodes may not be placed optimally to ensure that the network is fully connected and high-quality data pertaining to the phenomena being monitored can be extracted from the network. This work aims to address the problem of random deployment through two complementary approaches: The first approach aims to address the problem of random deployment from a communication perspective. It begins by establishing a comprehensive mathematical model to quantify the energy cost of various concerns of a fully operational wireless sensor network. Based on the analytic model, an energy-efficient topology control protocol is developed. The protocol sets eligibility metric to establish and maintain a multi-hop communication path and to ensure that all nodes exhaust their energy in a uniform manner. The second approach focuses on addressing the problem of imperfect sensing from a signal processing perspective. It investigates the impact of deployment errors (calibration, placement, and orientation errors) on the quality of the sensed data and attempts to identify robust and error-agnostic features. If random placement is unavoidable and dense deployment cannot be supported, robust and error-agnostic features enable one to recognize interesting events from erroneous or imperfect data.

L'apparition récente de petits capteurs peu couteux fonctionnant sur batteries, capables de traiter les données acquises et de les transmettre par ondes radio ont le potentiel de révolutionner les applications de surveillance traditionnelles. Les réseaux sans fils composés de nœuds capteurs autonomes proches de la cible à surveiller permettent des tâches de surveillance précises allant du contrôle de la température dans des bâtiments jusqu'a la détection de feux de forêt. Récemment, de nouvelles applications de réseaux de capteurs sans fil telles que des applications multimédia ou dans le domaine de la santé ont émergé. Les réseaux sous-jacents déployés pour ces applications sont souvent compos'es de nœuds hétérogènes comportant différents capteurs et doivent fournir un niveau de service conforme aux exigences des différents types de trafic en s'adaptant à la charge variable. Cependant, concevoir des protocoles efficaces adaptés à ces applications tout en s'accommodant des ressources limitées des réseaux de capteurs est une tâche difficile. Dans cette thèse, nous nous focalisons sur le support de la qualité de service au niveau de la couche MAC, car cette couche conditionne et détermine largement les performances du réseau étant donné qu'elle est responsable de l'organisation de l'accès au canal. Dans un premier temps, nous étudions les contraintes spécifiques des applications ayant des exigences fortes ainsi que des applications hétérogènes et nous examinons les travaux proposés dans la littérature. Etant donné l'inadéquation des solutions existantes en présence d'un trafic important, nous proposons AMPH, un protocole MAC adaptatif avec qualité de service pour les réseaux de capteurs sans fil hétérogènes. Notre solution consiste en une méthode d'accès au canal hybride basée sur le multiplexage temporel, dans laquelle tous les nœuds peuvent accéder au canal à chaque division de temps en utilisant un nouveau mécanisme de compétition qui favorise le trafic prioritaire. Grâce à ces techniques, AMPH utilise efficacement le canal quelque soit la charge de trafic et assure une latence faible au trafic temps réel. Nous vérifions les performances d'AMPH à l'aide de simulations et d'un modèle mathématique.

La quinta generación de redes móviles (5G) se encuentra a la vuelta de la esquina. Se espera provea de beneficios extraordinarios a la población y que resuelva la mayoría de los problemas de las redes 4G actuales. El éxito de 5G, cuya primera fase de estandarización ha sido completada, depende de tres pilares: comunicaciones tipo-máquina masivas, banda ancha móvil mejorada y comunicaciones ultra fiables y de baja latencia (mMTC, eMBB y URLLC, respectivamente). En esta tesis nos enfocamos en el primer pilar de 5G, mMTC, pero también proveemos una solución para lograr eMBB en escenarios de distribución masiva de contenidos. Específicamente, las principales contribuciones son en las áreas de: 1) soporte eficiente de mMTC en redes celulares; 2) acceso aleatorio para el reporte de eventos en redes inalámbricas de sensores (WSNs); y 3) cooperación para la distribución masiva de contenidos en redes celulares. En el apartado de mMTC en redes celulares, esta tesis provee un análisis profundo del desempeño del procedimiento de acceso aleatorio, que es la forma mediante la cual los dispositivos móviles acceden a la red. Estos análisis fueron inicialmente llevados a cabo por simulaciones y, posteriormente, por medio de un modelo analítico. Ambos modelos fueron desarrollados específicamente para este propósito e incluyen uno de los esquemas de control de acceso más prometedores: access class barring (ACB). Nuestro modelo es uno de los más precisos que se pueden encontrar en la literatura y el único que incorpora el esquema de ACB. Los resultados obtenidos por medio de este modelo y por simulación son claros: los accesos altamente sincronizados que ocurren en aplicaciones de mMTC pueden causar congestión severa en el canal de acceso. Por otro lado, también son claros en que esta congestión se puede prevenir con una adecuada configuración del ACB. Sin embargo, los parámetros de configuración del ACB deben ser continuamente adaptados a la intensidad de accesos para poder obtener un desempeño óptimo. En la tesis se propone una solución práctica a este problema en la forma de un esquema de configuración automática para el ACB; lo llamamos ACBC. Los resultados muestran que nuestro esquema puede lograr un desempeño muy cercano al óptimo sin importar la intensidad de los accesos. Asimismo, puede ser directamente implementado en redes celulares para soportar el tráfico mMTC, ya que ha sido diseñado teniendo en cuenta los estándares del 3GPP. Además de los análisis descritos anteriormente para redes celulares, se realiza un análisis general para aplicaciones de contadores inteligentes. Es decir, estudiamos un escenario de mMTC desde la perspectiva de las WSNs. Específicamente, desarrollamos un modelo híbrido para el análisis de desempeño y la optimización de protocolos de WSNs de acceso aleatorio y basados en cluster. Los resultados muestran la utilidad de escuchar el medio inalámbrico para minimizar el número de transmisiones y también de modificar las probabilidades de transmisión después de una colisión. En lo que respecta a eMBB, nos enfocamos en un escenario de distribución masiva de contenidos, en el que un mismo contenido es enviado de forma simultánea a un gran número de usuarios móviles. Este escenario es problemático, ya que las estaciones base de la red celular no cuentan con mecanismos eficientes de multicast o broadcast. Por lo tanto, la solución que se adopta comúnmente es la de replicar e contenido para cada uno de los usuarios que lo soliciten; está claro que esto es altamente ineficiente. Para resolver este problema, proponemos el uso de esquemas de network coding y de arquitecturas cooperativas llamadas nubes móviles. En concreto, desarrollamos un protocolo para la distribución masiva de contenidos, junto con un modelo analítico para su optimización. Los resultados demuestran que el modelo propuesto es simple y preciso, y que el protocolo puede reducir el con
La cinquena generació de xarxes mòbils (5G) es troba molt a la vora. S'espera que proveïsca de beneficis extraordinaris a la població i que resolga la majoria dels problemes de les xarxes 4G actuals. L'èxit de 5G, per a la qual ja ha sigut completada la primera fase del qual d'estandardització, depén de tres pilars: comunicacions tipus-màquina massives, banda ampla mòbil millorada, i comunicacions ultra fiables i de baixa latència (mMTC, eMBB i URLLC, respectivament, per les seues sigles en anglés). En aquesta tesi ens enfoquem en el primer pilar de 5G, mMTC, però també proveïm una solució per a aconseguir eMBB en escenaris de distribució massiva de continguts. Específicament, les principals contribucions són en les àrees de: 1) suport eficient de mMTC en xarxes cel·lulars; 2) accés aleatori per al report d'esdeveniments en xarxes sense fils de sensors (WSNs); i 3) cooperació per a la distribució massiva de continguts en xarxes cel·lulars. En l'apartat de mMTC en xarxes cel·lulars, aquesta tesi realitza una anàlisi profunda de l'acompliment del procediment d'accés aleatori, que és la forma mitjançant la qual els dispositius mòbils accedeixen a la xarxa. Aquestes anàlisis van ser inicialment dutes per mitjà de simulacions i, posteriorment, per mitjà d'un model analític. Els models van ser desenvolupats específicament per a aquest propòsit i inclouen un dels esquemes de control d'accés més prometedors: el access class barring (ACB). El nostre model és un dels més precisos que es poden trobar i l'únic que incorpora l'esquema d'ACB. Els resultats obtinguts per mitjà d'aquest model i per simulació són clars: els accessos altament sincronitzats que ocorren en aplicacions de mMTC poden causar congestió severa en el canal d'accés. D'altra banda, també són clars en què aquesta congestió es pot previndre amb una adequada configuració de l'ACB. No obstant això, els paràmetres de configuració de l'ACB han de ser contínuament adaptats a la intensitat d'accessos per a poder obtindre unes prestacions òptimes. En la tesi es proposa una solució pràctica a aquest problema en la forma d'un esquema de configuració automàtica per a l'ACB; l'anomenem ACBC. Els resultats mostren que el nostre esquema pot aconseguir un acompliment molt proper a l'òptim sense importar la intensitat dels accessos. Així mateix, pot ser directament implementat en xarxes cel·lulars per a suportar el trànsit mMTC, ja que ha sigut dissenyat tenint en compte els estàndards del 3GPP. A més de les anàlisis descrites anteriorment per a xarxes cel·lulars, es realitza una anàlisi general per a aplicacions de comptadors intel·ligents. És a dir, estudiem un escenari de mMTC des de la perspectiva de les WSNs. Específicament, desenvolupem un model híbrid per a l'anàlisi de prestacions i l'optimització de protocols de WSNs d'accés aleatori i basats en clúster. Els resultats mostren la utilitat d'escoltar el mitjà sense fil per a minimitzar el nombre de transmissions i també de modificar les probabilitats de transmissió després d'una col·lisió. Pel que fa a eMBB, ens enfoquem en un escenari de distribució massiva de continguts, en el qual un mateix contingut és enviat de forma simultània a un gran nombre d'usuaris mòbils. Aquest escenari és problemàtic, ja que les estacions base de la xarxa cel·lular no compten amb mecanismes eficients de multicast o broadcast. Per tant, la solució que s'adopta comunament és la de replicar el contingut per a cadascun dels usuaris que ho sol·liciten; és clar que això és altament ineficient. Per a resoldre aquest problema, proposem l'ús d'esquemes de network coding i d'arquitectures cooperatives anomenades núvols mòbils. En concret, desenvolupem un protocol per a realitzar la distribució massiva de continguts de forma eficient, juntament amb un model analític per a la seua optimització. Els resultats demostren que el model proposat és simple i precís
The 5th generation (5G) of mobile networks is just around the corner. It is expected to bring extraordinary benefits to the population and to solve the majority of the problems of current 4th generation (4G) systems. The success of 5G, whose first phase of standardization has concluded, relies in three pillars that correspond to its main use cases: massive machine-type communication (mMTC), enhanced mobile broadband (eMBB), and ultra-reliable low latency communication (URLLC). This thesis mainly focuses on the first pillar of 5G: mMTC, but also provides a solution for the eMBB in massive content delivery scenarios. Specifically, its main contributions are in the areas of: 1) efficient support of mMTC in cellular networks; 2) random access (RA) event-reporting in wireless sensor networks (WSNs); and 3) cooperative massive content delivery in cellular networks. Regarding mMTC in cellular networks, this thesis provides a thorough performance analysis of the RA procedure (RAP), used by the mobile devices to switch from idle to connected mode. These analyses were first conducted by simulation and then by an analytical model; both of these were developed with this specific purpose and include one of the most promising access control schemes: the access class barring (ACB). To the best of our knowledge, this is one of the most accurate analytical models reported in the literature and the only one that incorporates the ACB scheme. Our results clearly show that the highly-synchronized accesses that occur in mMTC applications can lead to severe congestion. On the other hand, it is also clear that congestion can be prevented with an adequate configuration of the ACB scheme. However, the configuration parameters of the ACB scheme must be continuously adapted to the intensity of access attempts if an optimal performance is to be obtained. We developed a practical solution to this problem in the form of a scheme to automatically configure the ACB; we call it access class barring configuration (ACBC) scheme. The results show that our ACBC scheme leads to a near-optimal performance regardless of the intensity of access attempts. Furthermore, it can be directly implemented in 3rd Generation Partnership Project (3GPP) cellular systems to efficiently handle mMTC because it has been designed to comply with the 3GPP standards. In addition to the analyses described above for cellular networks, a general analysis for smart metering applications is performed. That is, we study an mMTC scenario from the perspective of event detection and reporting WSNs. Specifically, we provide a hybrid model for the performance analysis and optimization of cluster-based RA WSN protocols. Results showcase the utility of overhearing to minimize the number of packet transmissions, but also of the adaptation of transmission parameters after a collision occurs. Building on this, we are able to provide some guidelines that can drastically increase the performance of a wide range of RA protocols and systems in event reporting applications. Regarding eMBB, we focus on a massive content delivery scenario in which the exact same content is transmitted to a large number of mobile users simultaneously. Such a scenario may arise, for example, with video streaming services that offer a particularly popular content. This is a problematic scenario because cellular base stations have no efficient multicast or broadcast mechanisms. Hence, the traditional solution is to replicate the content for each requesting user, which is highly inefficient. To solve this problem, we propose the use of network coding (NC) schemes in combination with cooperative architectures named mobile clouds (MCs). Specifically, we develop a protocol for efficient massive content delivery, along with the analytical model for its optimization. Results show the proposed model is simple and accurate, and the protocol can lead to energy savings of up to 37 percent when compared to the traditional approach.
Leyva Mayorga, I. (2018). On reliable and energy efficient massive wireless communications: the road to 5G [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/115484
TESIS

A signicant growth was witnessed in the led of Wireless Sensor Networks (WSNs), the previous decade. Advances in hardware miniaturization coupled with increased processing capabilities and memory capacity have extended the application domains of WSNs. In light of this, standardization organizations led by academia and industries initiated activities for the design of protocols such as IEEE 802.15.4 and IETF RPL (Routing Protocol for Low power and Lossy Networks). IEEE 802.15.4 denes physical and media access layers for WSNs while IETF RPL denes the functionality of the routing layer. This thesis investigates research issues in wireless sensor networks and network controlled systems that control micro-biological processes for water treatment plants. By choosing a process model that can relate to an industrial process, feasibility of control over IEEE 802.15.4 and RPL protocols is evaluated for stability with regards to network delay and packet loss. Settling time and overshoot are measured to indicate control performance. Control messages related to routing and routing table lengths are measured to indicate network stability and scalability. The system model used is a centralized discrete controller controlling a thermal processes running on the sensors. This model is chosen for representing wide industrial networked control systems while adding a WSN dimension based on IEEE 802.15.4 and RPL. The main contribution of this thesis is an experimental study where both the network and controller performance is validated while utilizing commercial o-theshelf sensor platforms. The results from this experimental work include rst the use of established theorems for analyzing control using WSNs. Moreover, the ability of IEEE 802.15.4 and RPL to provide stable communication that is reliable enough for actual industrial control implementation is validated.

Wireless sensor networks are receiving a considerable degree of research interest due to their deployment in an increasing number and variety of applications. However, the efficient management of the limited energy resources of such networks in a way that maximises the information value of the data collected is a significant research challenge. To date, most of these systems have adopted a centralised control mechanism, but from a system's perspective this raises concerns associated with scalability, robustness, and the ability to cope with dynamism. Given this, decentralised approaches are appealing. But, the design of efficient decentralised regimes is challenging as it introduces an additional control issue related to the dynamic interactions between the network's interconnected nodes in the absence of a central coordinator. Within this context, this thesis first concentrates on decentralised approaches to adaptive sampling as a means of focusing a node's energy consumption on obtaining the most important data. Specifically, we develop a principled information metric based upon Fisher information and Gaussian process regression that allows the information content of a node's observations to be expressed. We then use this metric to derive three novel decentralised control algorithms for information-based adaptive sampling which represent a trade-off in computational cost and optimality. These algorithms are evaluated in the context of a deployed sensor network in the domain of flood monitoring. The most computationally efficient of the three is shown to increase the value of information gathered by approximately 83%, 27%, and 8% per day compared to benchmarks that sample in a naive non-adaptive manner, in a uniform non-adaptive manner, and using a state-of-the-art adaptive sampling heuristic (USAC) correspondingly. Moreover, our algorithm collects information whose total value is approximately 75% of the optimal solution (which requires an exponential, and thus impractical, amount of time to compute). The second major line of work then focuses on the adaptive sampling, transmitting, forwarding, and routing actions of each node in order to maximise the information value of the data collected in resource-constrained networks. This adds additional complexity because these actions are inter-related, since each node's energy consumption must be optimally allocated between sampling and transmitting its own data, receiving and forwarding the data of other nodes, and routing any data. Thus, in this setting we develop two optimal decentralised algorithms to solve this distributed constraint optimization problem. The first assumes that the route by which data is forwarded to the base station is fixed (either because the underlying communication network is a tree, or because an arbitrary choice of route has been made) and then calculates the optimal integration of actions that each node should perform. The second deals with flexible routing, and makes optimal decisions regarding both the sampling, transmitting, and forwarding actions that each node should perform, and also the route by which this data should be forwarded to the base station. The two algorithms represent a trade-off in optimality, communication cost, and processing time. In an empirical evaluation on sensor networks (whose underlying communication networks exhibit loops), we show that the algorithm with flexible routing delivers approximately twice the quantity of information to the base station compared to the algorithm with fixed routing. However, this gain comes at a considerable communication and computational cost (increasing both by a factor of 100 times). Thus, while the algorithm with flexible routing is suitable for networks with a small numbers of nodes, it scales poorly, and as the size of the network increases, the algorithm with fixed routing should be favoured.

Wireless Sensor Networks (WSN) offer a flexible low-cost solution to the problem of event monitoring, especially in places with limited accessibility or that represent danger to humans. WSNs are made of resource-constrained wireless devices, which require energy efficient mechanisms, algorithms and protocols. One of these mechanisms is Topology Control (TC) composed of two mechanisms, Topology Construction and Topology Maintenance. This dissertation expands the knowledge of TC in many ways. First, it introduces a comprehensive taxonomy for topology construction and maintenance algorithms for the first time. Second, it includes four new topology construction protocols: A3, A3Lite, A3Cov and A3LiteCov. These protocols reduce the number of active nodes by building a Connected Dominating Set (CDS) and then turning off unnecessary nodes. The A3 and A3-Lite protocols guarantee a connected reduced structure in a very energy efficient manner. The A3Cov and A3LiteCov protocols are extensions of their predecessors that increase the sensing coverage of the network. All these protocols are distributed -they do not require localization information, and present low message and computational complexity. Third, this dissertation also includes and evaluates the performance of four topology maintenance protocols: Recreation (DGTRec), Rotation (SGTRot), Rotation and Recreation (HGTRotRec), and Dynamic Local-DSR (DLDSR). Finally, an event-driven simulation tool named Atarraya was developed for teaching, researching and evaluating topology control protocols, which fills a need in the area of topology control that other simulators cannot. Atarraya was used to implement all the topology construction and maintenance cited, and to evaluate their performance. The results show that A3Lite produces a similar number of active nodes when compared to A3, while spending less energy due to its lower message complexity. A3Cov and A3CovLite show better or similar coverage than the other distributed protocols discussed here, while preserving the connectivity and energy efficiency from A3 and A3Lite. In terms of network lifetime, depending on the scenarios, it is shown that there can be a substantial increase in the network lifetime of 450% when a topology construction method is applied, and of 3200% when both topology construction and maintenance are applied, compared to the case where no topology control is used.

Recent advances in wireless communication and micro-electro-mechanical systems (MEMS) have led to the development of implementation of low-cost, low power, multifunctional sensor nodes. These sensor node are small in size and communicate untethered in short distances. The nodes in sensor networks have limited battery power and it is not feasible or possible to recharge or replace the batteries, therefore power consumption should be minimized so that overall network lifetime will be increased. In order to minimize power consumed during idle listening, some nodes, which can be considered redundant, can be put to sleep. In this thesis study, basic routing algorithms and duty cycle control algorithms for WSNs in the literature are studied. One of the duty cycle control algorithms, Role Alternating, Coverage Preserving, and Coordinated Sleep algorithm (RACP) is examined and simulated using the ns2 simulation environment. A novel duty cycle control algorithm, Sink Initiated Path Formation (SIPF) is proposed and compared to RACP in terms of sleep sensor ratio and time averaged coverage.

Sensor nodes within networks are often grouped to participate to a common processing task. Cooperative diversity is a technique that exploits groups of sensor node randomly placed to cooperatively relay a common received signal toward a destination with the goal to combat severe attenuation or disconnections of the signal strength. In recent years, cooperative diversity has received attention for cellular radio systems and ad-hoc wireless networks. Such systems, however, are usually equipped with high processing capability. On the contrary, the nodes of a WSNs have limited memory and power capabilities and are usually deployed in unfriendly environment, where recharging and maintenance is not possible. In this thesis, we investigate the problem of power control of nodes performing cooperative diversity. Specifically, we study the problem of minimizing the power consumption of the sensor nodes transmitters while guaranteeing a minimum quality of the signal at the data collector. After studying the most relevant algorithms existent in literature for had-hoc networks, we propose an sub-optimal algorithm suitable for nodes equipped with low computational capabilities. We implement a WSNs performing cooperative diversity with Omnet++, where the network simulator includes the sub-optimal solution. Numerical results show that for the set of parameters of practical interest, our solution exhibits good performance for low correlated channel links, while the increase of relaying nodes ensures a decreasing of total power consumption.

Wireless Sensor Networks have received significant attention due to their capability for distributed sensing at relatively low cost, in applications which range from environmental to industrial monitoring. More recently, wireless underground sensor networks have been proposed for applications such as personnel tracking in underground mines and moisture monitoring for precision agriculture. Wireless underground sensor networks are typically categorised into wireless sensor networks for mines and tunnels (which communicate overthe- air) and Subsoil Wireless underground sensor networks (which communicate wirelessly through soil). For Subsoil wireless underground sensor networks specifically, it is well known that the soil medium introduces a number of challenges. Firstly, the path loss in soil is very high. Secondly, propagation characteristics are dependent on soil conditions and properties, which can change due to irrigation or rain. Thirdly, communication in Subsoil Wireless underground sensor networks takes place over three different types of channels: underground-to-underground, aboveground-to-underground and underground-toaboveground. Therefore, communication protocols developed for over-the-air wireless sensor networks are not suitable for wireless underground sensor networks. Although some studies on wireless underground sensor networks have focussed on channel characterization, many aspects related to link characteristics have not been thoroughly investigated. Understanding the link behaviour in wireless underground sensor networks is a fundamental building block for protocol development for medium access, topology management and routing. The aim of this research is to gain insight into the link quality in wireless underground sensor networks which can aid in the development of efficient and reliable communication protocols. To this end, the link quality in the three wireless underground sensor network communication channels is characterized empirically for dry and wet soil conditions. This characterization is performed using the received signal strength, link quality indicator and packet reception rate. The results show that links in the underground-to-underground channel are very stable (in terms of received signal strength) and exhibit high symmetry and high packet reception rate, even for received signal strength values near the receiver sensitivity, but the communication ranges are limited due to the very high attenuation. On the other hand, links in the aboveground-to-underground /underground-to-aboveground channels are typically asymmetric and have longer communication ranges. For most links in all three channels, it is observed that the link quality indicator is highly variant and is not correlated with received signal strength and packet reception ratio. Furthermore, an increase in the soil moisture also affects the link asymmetry and the width of the transitional windows in the aboveground-to-underground/underground-to-aboveground channels. The results show that efficient communication protocols for wireless underground sensor networks will have to be highly adaptive/reactive to soil conditions, and link quality estimation has to be robust to the asymmetry present in most links.
Dissertation (MEng)--University of Pretoria, 2014.
tm2015
Electrical, Electronic and Computer Engineering
MEng
Unrestricted

In wireless sensor networks (WSN), nodes have very limited power due to hardware constraints. Packet losses and retransmissions resulting from congestion cost precious energy and shorten the lifetime of sensor nodes. This problem motivates the need for congestion control mechanisms in WSN. In this thesis, an observation of multiple non-empty queues in sensor networks is first reported. Other aspects affected by congestion like queue length, delay and packet loss are also studied. The simulation results show that the number of occupied queues along a path can be used to detect congestion. Based on the above result, a congestion control scheme for the transport layer is proposed in this thesis. It is composed of three parts: (i) congestion detection by tracking the number of non-empty queues; (ii) On-demand midway non-binary explicit congestion notification (CN) feedback; and (iii) Adaptive rate control based on additive increase and multiplicative decrease (AIMD). This scheme has been implemented in ns2. Extensive simulations have been conducted to evaluate it. Results show that it works well in mitigating and avoiding congestion and achieves good performance in terms of energy dissipation, latency and transmission effciency.

As the trends towards decentralization, miniaturization, and longevity of deployment continue in many domains, power management has become increasingly important. In this work, we develop power-aware control strategies for wireless sensor networks to improve the lifetime of the network and to ensure that the desired performance is guaranteed. For the case of static networks (networks of agents with no mobility), we identify the problem of the effects of power variations on the performance of an individual sensing device and on the entire network. To address this problem in a randomly deployed sensor network comprising of sensing devices whose sensing range is a function of transmitted power, we propose power-aware controllers to compensate for the variations in available power and maintain desired performance. We also propose a novel energy-efficient sleep-scheduling scheme that is random in nature and allows limited coordination among neighboring sensors for making switching decisions. This scheme is based on the concept of a hard-core point process from stochastic geometry, in which neighboring points are allowed to interact with each other through some predefined interaction laws. For the case of mobile networks (networks of agents with mobility), we propose a solid framework for distributed power-aware mobility strategies that can achieve any desired global objective while minimizing total energy consumption. This goal is achieved by first exploring fundamental trade-offs among various modes of operations of mobile devices and then exploiting these trade-offs for minimizing energy consumption. Through this framework, a whole class of decentralized power-aware controllers emerge for solving canonical problems in multi-agent systems like connectivity maintenance, rendezvous, and coverage control.

Wireless personal area networks have emerged as an important communication infrastructure in areas such as at-home healthcare and home automation, independent living and assistive technology, as well as sports and wellness. Wireless personal area networks, including body sensor networks, are becoming more mature and are considered to be a realistic alternative as communication infrastructure for demanding services. However, to transmit data from e.g., an ECG in wireless networks is also a challenge, especially if multiple sensors compete for access. Contention-based networks offer simplicity and utilization advantages, but the drawback is lack of predictable performance. Recipients of data sent in wireless sensor networks need to know whether they can trust the information or not. Performance measurements, monitoring and control is of crucial importance for medical and healthcare applications in wireless sensor networks. This thesis focuses on development, prototype implementation and evaluation of a performance management system with performance and admission control for wireless sensor networks. Furthermore, an implementation of a new method to compensate for clock drift between multiple wireless sensor nodes is also shown. Errors in time synchronization between nodes in Bluetooth networks, resulting in inadequate data fusion, are also analysed.

QC 20120529

The use of wireless technology in the process industry is becoming increasingly important to obtain fast deployment at low cost. However, poor channel quality often leads to retransmissions, which are governed by Automatic Repeat Request (ARQ) schemes. While ARQ is a simple and useful tool to alleviate packet errors, it has considerable disadvantages: retransmissions lead to an increase in energy expenditure and latency. The use of Forward Error Correction (FEC) however offers several advantages. We consider a Hybrid-ARQ-Adaptive-FEC scheme (HAF) based on BCH codes and Channel State Information. This scheme is evaluated on AWGN and fading channels. It is shown that HAF offers significantly improved performance both in terms of energy efficiency and latency, as compared to ARQ.

Security and quality of service (QoS) issues in cluster-based wireless sensor networks are investigated. The QoS perspective is mostly at application level consisting of four attributes, which are spatial resolution, coverage, system lifetime and packet loss due to collisions. The addressed security aspects are message integrity and authentication. Under this scope, the interactions between security and service quality are analyzed with particular emphasis on the tradeoff between security and spatial resolution for channel capacity. The optimal security and spatial resolution levels which yield the best tradeoff are determined. In addition, a control strategy is proposed to achieve the desired quality of service and security levels during the entire operation of a cluster-based sensor network. Compared to the existing studies, the proposed method is simpler and has superior performance.

Intelligence is the power which makes the owner capable of making a decision defined by reasoning. When traditional solutions and approaches, such as First Principal Modelling or Statistical Modelling, are not feasible or able to effectively address complex real- world problems, then Computational Intelligence with some nature-inspired computational techniques and methodologies is employed. For transferring data between two non-directly connected devices when some other devices are in-between, a set of rules are used by routers which are devices between sender and receiver, to determine the most appropriate paths into which routers should forward data toward the intended destination. This set of rules is called routing protocol. Researchers use some computational itelligence techniques to design network routing protocols. Wireless Sensor Networks (WSNs) play an important role in today's data communication systems and researchers are expected to proliferate in the field of wireless communication in the near future. The deployment of wireless sensor networks offer several advantages in comparison to traditional infrastructure-based networks, such as fully distributed mobile operation, the easy discovery of joining wireless devices, and instant and low cost network setup. Designing an effective routing protocol is one of the main challenges in the ad-hoc networking paradigm and the utilisation of an adequate link-cost metric is essential. WSN researchers address issues such as low throughput and high latency in wireless sensor data communication. Routing Protocols in WSNs play a key role in data communication and the main parameter in all routing protocols is data communications link-cost. This research delivers two surveys on existing routing protocols and link-quality metrocs for wireless sensor networks. Most of the routing protocols in this area are considered in different groups. The majority of link-quality metrics in WSNs are studied in different categories. Link-quality and traffic-aware metrics account for most of the metrics, as well as metrics in multi-channel networks and cognitive radio systems, which are also considered in detail. Metrics are reviewed in detail in terms of their performance; summary and comparison tables of link-quality metrics are provided to enable better comparison and show a brief overview of their appearance to get a clearer picture. Routing-metrics are important is determining paths and maintaining quality of service in routing protocols. The most efficient metrics need to send packets to maintain link-quality measurement by using the Radi Frequency (RF) module. In this study, a set of statistical analyses is done on some link-quality metrics to select the best metric for energy-aware scenarios. Two prominent link-quality metrics; Received Signal Strength Indication (RSSI) and Link-Quality Indication (LQI), are described in detail. The symmetry of RSSI and LQI in two directions is studied, and relations with the Expected Transmission Count (ETX), RSSI, and LQI as link-quality metrics are analysed. The evaluation in this research is based on a series of WSN test-beds in real scenarios. Due to implementation of routing protocols in limited power supply devices in WSNs, one novel link-quality metric and also some routing protocols for wireless sensor networks are proposed in this research to obtain better performance in different scenarios. Rainbow Collection Tree Protocol (RCTP) is presented and evaluated as an enhanced version of Collection Tree Protocol (CTP). It uses the Trickle algorithm to optimise overhead cost and the algorithm also makes RCTP quickly adaptable to changes in topology. The Rainbow mechanism is used in RCTP to detect and route around connectivity nodes and avoid routes through dead-end paths. Energy-efficient Rainbow Collection Tree Routing Protocol (ERCRP) is presented and evaluated as a novel, real-time, position-based and energy-efficient routing protocol in this research. ERCRP is a lightweight protocol that reduced the number of nodes which receive the RF signal using a novel Parent Forwarding Region (PFR) algorithm. ERCRP as a Geographical Routing Protocol (GRP) reduced the number of forwarding nodes and thus decreases traffic and packet collision in the network. WSNs are used in three-dimension (3D) scenarios such as sea or land surfaces with different levels of height. Three-Dimension Position-Based Adaptive Real-Time Routing Protocol (3DPBARP) is presented and evaluated as a novel, real-time, position-based and energy-efficient routing protocol for WSNs in this research. 3DPBARP is a lightweight protocol that reduces the number of nodes which received the RF signal using a novel PFR algorithm. 3DPBARP as a GRP decreases the number of nodes which participate in packet forwarding and thus shrink the traffic and collision in the network.

Given the potential benefits offered by wireless sensor networks(WSNs), they are becoming an appealing technology for process,manufacturing, and industrial control applications. In thisthesis, we propose a novel approach to WSN protocol design forcontrol applications. The protocols are designed to minimize theenergy consumption of the network, while meeting reliability andpacket delay requirements. The parameters of the protocol areselected by solving a constrained optimization problem, where theobjective is to minimize the energy consumption and theconstraints are the probability of successful packet reception andthe communication delay. The proposed design methodology allowsone to perform a systematic tradeoff between the controlrequirements of the application and the network energyconsumption. An important step in the design process is thedevelopment of analytical expressions of the performanceindicators. We apply the proposed approach to optimize the networkfor various communication protocols.

In Paper A, we present an adaptive IEEE 802.15.4 for energyefficient, reliable, and low latency packet transmission. Thebackoff mechanisms and retry limits of the standard are adapted tothe estimated channel conditions. Numerical results show that theproposed protocol enhancement is efficient and ensures a longerlifetime of the network under different conditions. Furthermore,we investigate the robustness and sensitivity of the protocol topossible errors during the estimation process.

 

In Paper B, we investigate the design and optimization ofduty-cycled WSNs with preamble sampling over IEEE 802.15.4. Theanalytical expressions of performance indicators are developed andused to optimize the duty-cycle of the nodes to minimize energyconsumption while ensuring low latency and reliable packettransmissions. The optimization results in a significant reductionof the energy consumption compared to existing solutions.

The cross-layer protocol called Breath is proposed in Paper C. Theprotocol is suitable for control applications by using theconstrained optimization framework proposed in the thesis. It isbased on randomized routing, CSMA/CA MAC, and duty-cycling. Theprotocol is implemented and experimentally evaluated on a testbed,and it is compared with a standard IEEE 802.15.4 solution. Breathexhibits a good distribution of the work load among the networknodes, and ensures a long network lifetime.

 

 

In a wireless network, the medium is a shared resource. The nodes in the network negotiate access of the shared resource using the Medium Access Control (MAC) protocol. The design of a MAC protocol for a sensor node is not the same as that for a wireless transceiver. Due to the transceiver characteristics, the MAC protocol design is limited in terms of medium access methods. However, in most cases, the protocols rely on simple access methods i.e. Time Division Multiple Access (TDMA) or Carrier Sense Multiple Access / Collision Avoidance (CSMA / CA). Control and monitoring applications, running over a wireless network, are typical examples of Wireless Sensor Actuator Network (WSAN) application in industries. In an industrial network, the message deliveries must be time-bounded otherwise, they are of no use. This report aims to present the thesis work carried out at ABB AB, Västerås. The purpose of this thesis was to compare the performance of WLAN and WirelessHART when it comes to control applications. For the purpose of WLAN, the media access schemes are analyzed in terms of deadline misses. There are other metrices for the performance evaluation but our focus was on the latency, since it is very important in the field of industrial automation. NS-2 was used for the purpose of MAC layer analysis and it is also shown that PCF gives better performance as compared to DCF, in terms of deadline misses. Finally, WLAN is proven to accommodate more control loops as compared to WirelessHART for a given scenario.

Abstract Wireless sensor networks (WSNs) offer us a potential for greater awareness of our surroundings, collecting, measuring, and aggregating parameters beyond our current abilities, and provide an opportunity to enrich our experience through context-awareness. As a typical sensor node is small with limited processing power, memory, and energy resources, in particular, these WSNs must be very energy-efficient for practical deployment. Medium access control (MAC) protocols are central to the energy-efficiency objective of WSNs, as they directly control the most energy consuming part of a sensor node: communications over the shared medium. This thesis focuses on evaluating MAC protocols within the WSN domain by, firstly, surveying a representative number of MAC protocols and their features. Secondly, three novel MAC protocols are proposed, one for layered contention-based access, one for layered scheduled access, and one for cross-layer contention-based access. Thirdly, a novel energy consumption model is proposed, and fourthly, a holistic MAC protocol evaluation model is proposed that takes into account application emphasis on performance metrics. The MAC protocols are evaluated analytically. In addition, the layered contention-based MAC protocol has been implemented and measured, and the cross-layer contention-based protocol operating over an impulse radio-ultra wideband (IR-UWB) physical layer has been verified by simulations with relevant physical layer characteristics. The energy consumption evaluation model proposed is straightforward to modify for evaluating delay, and it can reuse state transition probabilities derived from throughput analysis. The holistic application-driven MAC protocol evaluation model uses a novel single compound metric that represents a MAC protocol's relative performance in a given application scenario. The evaluations have revealed several significant flaws in sensor MAC protocols that are adapted to sensor networking from ad hoc networks. Furthermore, it has been shown that, when taking sufficient details into account, single hop communications can outperform multi-hop communications in the energy perspective within the feasible transmission ranges provided by sensor nodes. The impulse radio physical layer introduces characteristics to MAC protocols that invalidate traditional techniques which model the physical layer in terms of simple collisions. Hence, these physical layer characteristics have been modelled and included in the analysis, which improves the level of agreements with simulated results.

The main contribution of this thesis is to present the design and evaluation of intelligent MAC protocols for Wireless Sensor Networks (WSNs). The objective of this research is to improve the channel utilisation of WSNs while providing flexibility and simplicity in channel access. As WSNs become an efficient tool for recognising and collecting various types of information from the physical world, sensor nodes are expected to be deployed in diverse geographical environments including volcanoes, jungles, and even rivers. Consequently, the requirements for the flexibility of deployment, the simplicity of maintenance, and system self-organisation are put into a higher level. A recently developed reinforcement learning-based MAC scheme referred as ALOHA-Q is adopted as the baseline MAC scheme in this thesis due to its intelligent collision avoidance feature, on-demand transmission strategy and relatively simple operation mechanism. Previous studies have shown that the reinforcement learning technique can considerably improve the system throughput and significantly reduce the probability of packet collisions. However, the implementation of reinforcement learning is based on assumptions about a number of critical network parameters. That impedes the usability of ALOHA-Q. To overcome the challenges in realistic scenarios, this thesis proposes numerous novel schemes and techniques. Two types of frame size evaluation schemes are designed to deal with the uncertainty of node population in single-hop systems, and the unpredictability of radio interference and node distribution in multi-hop systems. A slot swapping techniques is developed to solve the hidden node issue of multi-hop networks. Moreover, an intelligent frame adaptation scheme is introduced to assist sensor nodes to achieve collision-free scheduling in cross chain networks. The combination of these individual contributions forms state of the art MAC protocols, which offers a simple, intelligent and distributed solution to improving the channel utilisation and extend the lifetime of WSNs.

This thesis studies the applications of biologically inspired algorithms and behaviours to the Medium Access Control (MAC) layer of Wireless Sensor Networks (WSNs). By exploring the similarity between a general communications channel and control engineering theory, we propose a simple method to control transmissions that we refer to as transmission delay. We use this concept and create a protocol inspired by Particle Swarm Optimisation (PSO) to optimise the communications. The lessons learned from this protocol inspires us to move closer to behaviours found in nature and the Emergence MAC (E-MAC) protocol is presented. The E-MAC protocol shows emergent behaviours arising from simple interactions and provides great throughput, low end-to-end delay and high fairness. Enhancements to this protocol are later proposed. We empirically evaluate these protocols and provide relevant parameter sweeps to show their performance. We also provide a theoretical approach to proving the settling properties of E-MAC. The presented protocols and methods provide a different approach towards MAC in WSNs.

Our work in this thesis have provided two distinctive contributions to WSNs in the areas of data handling and topology control. In the area of data handling, we have demonstrated a solution to improve the power efficiency whilst preserving the important data features by data compression and the use of an adaptive sampling strategy, which are applicable to the specific application for oceanography monitoring required by the SECOAS project. Our work on oceanographic data analysis is important for the understanding of the data we are dealing with, such that suitable strategies can be deployed and system performance can be analysed. The Basic Adaptive Sampling Scheduler (BASS) algorithm uses the statistics of the data to adjust the sampling behaviour in a sensor node according to the environment in order to conserve energy and minimise detection delay. The motivation of topology control (TC) is to maintain the connectivity of the network, to reduce node degree to ease congestion in a collision-based medium access scheme; and to reduce power consumption in the sensor nodes. We have developed an algorithm Subgraph Topology Control (STC) that is distributed and does not require additional equipment to be implemented on the SECOAS nodes. STC uses a metric called subgraph number, which measures the 2-hops connectivity in the neighbourhood of a node. It is found that STC consistently forms topologies that have lower node degrees and higher probabilities of connectivity, as compared to k-Neighbours, an alternative algorithm that does not rely on special hardware on sensor node. Moreover, STC also gives better results in terms of the minimum degree in the network, which implies that the network structure is more robust to a single point of failure. As STC is an iterative algorithm, it is very scalable and adaptive and is well suited for the SECOAS applications.

Thesis (M.S.)--Villanova University, 2008.
"This research work is funded in part by National Science Foundation (NSF), Computing and Communication Foundation (CCF) award 0728909"--P. iii. Computer Science Dept. Includes bibliographical references.

Sensor network congestion avoidance and control primarily aims to reduce packet drops while maintaining fair bandwidth allocation to existing network flows. The design of a congestion control algorithm suited for all types of applications in sensor networks is a challenging task due to the application-specific nature of these networks. With numerous sensors transmitting data simultaneously to one or more base stations (also called sinks), sensor nodes located near the base station will most likely experience congestion and packet loss. In this thesis, we propose a novel distributed congestion avoidance algorithm which calculates the ratio of the number of downstream and upstream nodes. This ratio value (named Characteristic ratio) is used to take a routing decision and incorporate load balancing while also serving as a pointer to the congestion state of the network. Available queue sizes of the downstream nodes are used to detect incipient congestion. Queue characteristics of candidate downstream nodes are used collectively to implement both congestion avoidance and fairness by adjusting the node's forwarding rate and next hop destination. Such an approach helps to minimize packet drops, improve energy efficiency and load balancing. In cases of severe congestion, the source is signaled to reduce its sending rate and enable the network recovery process. This is essentially a transport layer algorithm and would work best with a multi-path routing protocol and almost any MAC layer standard. We present the design and implementation of the proposed protocol and compare it with the existing avoidance protocols like Global rate control and Lightweight buffering. Our simulation results show a higher packet delivery ratio with greater node buffer utilization for our protocol in comparison with the conventional mechanisms.
M.S.Cp.E.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Computer Engineering MSCpE

Efficient energy use is paramount if sensor networks are to function for long periods.Already, researchers have delivered many efficiency schemes with various levels ofsuccesses; however, there is still need for improvements. This thesis is an attempt tomake further improvements on energy efficiency within wireless sensor networks.

Radio, sensing and light emitting diodes have dominated the power consumption oncurrent sensor network architectures. The radio consumes nearly as much energywhile it is listening as it does while transmitting. Naturally, if we reduce listening timesor if we reduce the number of messages transmitted then we would have reduced theenergy consumption. Some early successes in this area include power saving mediaaccess control protocols such as X-MAC that reduces the radio listening times bycycling through sleep and wake states and adaptive sampling techniques that havehelped to reduce the sensing and transmission numbers. This work is similar to theadaptive sampling techniques in that it focuses on saving energy by reducing thetransmission numbers.

This thesis tackles the problem of energy efficiency from a Quality of Information(QoI) perspective. Data is delivered with the quality of information at the forefront ofdelivery decisions, thus, samples are taken at a rate so that important events are notmissed, then a decision is taken whether to transmit the packet or not. Further tothis, we implement a routing protocol that is information aware, allowing it to providea better quality of service to important packets. Our goal is to lower the number ofmessages without degrading the quality of information.

This work is an improvement over static sampling methods because important eventscan be missed if the sampling rate is too low. We investigate our approach byimplementing a QoI aware routing algorithm based on the SPEED protocol and doevaluations using simulations and on a sensor network testbed with data from realdeployments.

Our results show that it is possible to reduce the number of messages transmittedand to reconstruct the missing data at the Sink with high fidelity. We were able toachieve in some instances up to 75% message reduction in our temperaturemeasuring application with 94% of all errors falling below 0.5 degrees Celsius.

Wireless Sensor Networks (WSNs) are based on innovative technologies that had revolutionized the methods in which we interact with the environment; i.e., through sensing the physical (e.g., fire motion, contact) and chemical (e.g., molecular concentration) properties of the natural surroundings. The hardware in which utilized by WSNs is rapidly evolving into sophisticated platforms that seamlessly integrate with different vendors and protocols (plug-n-play). In this thesis, we propose a WSN framework which provides assistance with monitoring environmental conditions; we focus on three main applications which include: a. Air-quality monitoring, b. Gas-leak detection, and c. Fire sensing. The framework involves four specifications: 1. Over the air programming (OTAP), 2. Network interconnections, 3. Sensors manageability, and 4. Alarm signaling. Their aim is to enhance the internetwork relations between the WSNs and the outside-world (i.e., main users, clients, or audience); by creating a medium in which devices efficiently communicate, independent of location or infrastructure (e.g., Internet), in order to exchange data among networked-objects and their users. Therefore, we propose a WSN-over-IP architecture which provides several renowned services of the Internet; the major functionalities include: live-data streaming (real-time), e-mailing, cloud storage (external servers), and network technologies (e.g., LAN or WLAN). WSNs themselves operate independently of the Internet; i.e., their operation involve unique protocols and specific hardware requirements which are incompatible with common network platforms (e.g., within home network infrastructure). Hybrid technologies are those which support multiple data-communication protocols within a single device; their main capabilities involve seamless integration and interoperability of different hardware vendors. We propose an overall architecture based on hybrid communication technology in which data is transmitted using three types of protocols: 802.11 (Wi-Fi), 802.15.4 and Digimesh (WSN).

Many domains, such as geographical and biological sciences, can benefit from the ability of wireless sensor networks to provide long term, high temporal and spatial resolution sensing. Such networks must be able to trade off various requirements against each other to extend network lifetime while still providing useful, good quality data. The challenges faced by equipment in the field can very unpredictable and therefore a wireless sensor network should be able to cope with these challenges and return to a balanced state. Using readily available, low-cost components, this work was inspired by the human endocrine systems ability to maintain homeostasis, or balance, in a large number of parameters simultaneously. This work developed a number of endocrine inspired methods. These were aimed both at improving the power usage of nodes in a wireless sensor network and improving the quality of the data collected. Methods for improving power consumption and data quality were achieved. These methods were successfully deployed, for the purposes of environmental monitoring on a mesh network consisting of 20 nodes, for a period of almost 6 months. Analysis showed that the use of power by individual nodes was improved and that the endocrine inspired methods, aimed at improving data quality, were successful. Node lifetimes were extended, duplicate data reduced and the quality of data improved. The use of low-cost, readily available components was largely successful, and challenges and changes to these components were discussed.

A new class of Wireless Sensor Networks (WSNs) is emerging within the Internet of Things (IoT) that features extremely high node density, low data rates per node, and high network dependability. Applications such as industrial IoT, factory automation, vehicular networks, aviation, spacecraft and others will soon feature hundreds of low power, low data rate (1-15 kbps) wireless sensor nodes within a limited spatial environment. Existing Medium Access Control (MAC) layer protocols, namely IEEE 802.15.4, may not be suitable for highly dense, low rate networks. A new MAC protocol has been proposed that supports a Receiver-Assigned Code Division Multiple Access (RA-CDMA) physical (PHY) layer multiple access technique, which may enable higher network scalability while maintaining performance and contributing additional robustness. This thesis presents a comparison of the contention mechanisms of IEEE 802.15.4 non- beacon enabled mode and RA-CDMA along with a Matlab simulation framework used for end-to-end simulations of the protocols. Simulations suggest that IEEE 802.15.4 networks begin to break down in terms of throughput, latency, and delivery ratio at a relatively low overall traffic rate compared to RA-CDMA networks. Results show that networks using the proposed RA-CDMA multiple access can support node densities on the order of two to three times higher than IEEE 802.15.4 within the same bandwidth. Furthermore, features of a new MAC layer protocol are proposed that is optimized for RA-CDMA, which could further improve network performance over IEEE 802.15.4. The protocol's simple and lightweight design eliminates significant overhead compared to other protocols while meeting performance requirements, and could further enable the deployment of RA-CDMA WSNs.
Master of Science

Create our own simulator much more oriented to Bluetooth networks, we will program the simulator in Java language and a graphical environment through Java. Fully modular and open so it can be expanded with more tools that we could develop. Initially the simulator will not work with all the specifications of Bluetooth, we will focus on the Bluetooth 2.0+EDR version. It will be only a demo version with several features working properly.

Un réseau de capteurs sans fil (Wireless Sensor Network, WSN) consiste en une distribution spatiale d'équipements embarqués autonomes, qui coopèrent de manière à surveiller l'environnement de manière non-intrusive. Les données collectées par chaque capteur (tels que la température, des vibrations, des sons, des mouvements etc.) sont remontées de proche en proche vers un puits de collecte en utilisant des technologies de communication sans fil. Voilà une décennie que les contraintes inhérentes à ces réseaux attirent l'attention de la communauté scientifique. Ainsi, de nombreuses améliorations à différents niveaux de la pile de communication ont été proposées afin de relever les défis en termes d'économie d'énergie, de capacité de calcul et de contrainte mémoire imposés par l'utilisation d'équipements embarqués. Plusieurs déploiements couronnés de succès démontrent l'intérêt grandissant pour cette technologie. Les récentes avancées en termes d'intégration d'équipements et de protocoles de communication ont permis d'élaborer de nouveaux scénarios plus complexes. Ils mettent en scène des réseaux denses et dynamiques par l'utilisation de capteurs mobiles ou de différentes méthodes de collection de données. Par exemple, l'intérêt de la mobilité dans les WSN est multiple dans la mesure où les capteurs mobiles peuvent notamment permettre d'étendre la couverture d'un réseau, d'améliorer ses performances de routage ou sa connexité globale. Toutefois, ces scénarios apportent de nouveaux défis dans la conception de protocoles de communication. Ces travaux de thèse s'intéressent donc à la problématique de la dynamique des WSN, et plus particulièrement à ce que cela implique au niveau du contrôle de l'accès au médium (Medium Access Control, MAC). Nous avons tout d'abord étudié l'impact de la mobilité et défini deux nouvelles méthodes d'accès au médium (Machiavel et X-Machiavel) qui permettent d'améliorer les conditions d'accès au canal pour les capteurs mobiles dans les réseaux denses. Notre deuxième contribution est un algorithme d'auto-adaptation destiné aux protocoles par échantillonnage. Il vise à minimiser la consommation énergétique globale dans les réseaux caractérisés par des modèles de trafic antagonistes, en obtenant une configuration optimale sur chaque capteur. Ce mécanisme est particulièrement efficace en énergie pendant les transmissions par rafales qui peuvent survenir dans de tels réseaux dynamiques.

Wireless Sensor Networks (WSNs) are dense clusters of sensor nodes, made up of small, intelligent, resource-constrained wireless devices that are deployed to monitor a specific phenomenon in a certain field. The sensor nodes can be constrained by limited power supply, memory capacity and/or processing capabilities, which means that the design of WSNs requires all algorithms and protocols to be lightweight and efficient, and use as little power as possible. The Medium Access Control (MAC) protocol in WSNs, defined by the IEEE 802.15.4 standard, employs the Carrier Sense Multiple Access with Collision Avoidance (CSMA-CA) algorithm to control the nodes contending for access to the communication medium. Though the performance of this protocol has been studied extensively, and several improvements to its backoff counter, superframe format and contention-free period (CFP) features have been proposed, very few studies have addressed improving the Clear Channel Assessment (CCA) feature. In this thesis, we study the impact of increasing the value of the contention window beyond the standard value of 2, on the performance of the MAC protocol. We propose a semi-persistent MAC protocol that is a hybrid form of 802.11 and 802.15.4, to achieve a favorable performance that can serve a broad range of applications over the IEEE 802.15.4-based WSNs. We build an analytical model of the proposed protocol based on Markov chain modelling and derive the analytical expressions of the performance metrics, which we then validate against the simulation result sets generated by our in-house built simulation framework. We prove analytically that the probability of collision of the semi-persistent MAC is lower than that of the standard protocol. Based on our theoretical and simulated models, we show that incorporating the semi-persistent feature into existing MAC protocols leads to significant improvement of the performance metrics, including the probability of collision, throughput, energy consumption, transmission delay and reliability, particularly for networks with a large number of sensor nodes.

Wireless Sensor Networks (WSNs) are now widely used for monitoring and controlling of systems where human intervention is not desirable or possible. Connected Dominating Sets (CDSs) based topology control in WSNs is one kind of hierarchical method to ensure sufficient coverage while reducing redundant connections in a relatively crowded network. Moreover, Minimum-sized Connected Dominating Set (MCDS) has become a well-known approach for constructing a Virtual Backbone (VB) to alleviate the broadcasting storm for efficient routing in WSNs extensively. However, no work considers the load-balance factor of CDSsin WSNs. In this dissertation, we first propose a new concept — the Load-Balanced CDS (LBCDS) and a new problem — the Load-Balanced Allocate Dominatee (LBAD) problem. Consequently, we propose a two-phase method to solve LBCDS and LBAD one by one and a one-phase Genetic Algorithm (GA) to solve the problems simultaneously. Secondly, since there is no performance ratio analysis in previously mentioned work, three problems are investigated and analyzed later. To be specific, the MinMax Degree Maximal Independent Set (MDMIS) problem, the Load-Balanced Virtual Backbone (LBVB) problem, and the MinMax Valid-Degree non Backbone node Allocation (MVBA) problem. Approximation algorithms and comprehensive theoretical analysis of the approximation factors are presented in the dissertation. On the other hand, in the current related literature, networks are deterministic where two nodes are assumed either connected or disconnected. In most real applications, however, there are many intermittently connected wireless links called lossy links, which only provide probabilistic connectivity. For WSNs with lossy links, we propose a Stochastic Network Model (SNM). Under this model, we measure the quality of CDSs using CDS reliability. In this dissertation, we construct an MCDS while its reliability is above a preset applicationspecified threshold, called Reliable MCDS (RMCDS). We propose a novel Genetic Algorithm (GA) with immigrant schemes called RMCDS-GA to solve the RMCDS problem. Finally, we apply the constructed LBCDS to a practical application under the realistic SNM model, namely data aggregation. To be specific, a new problem, Load-Balanced Data Aggregation Tree (LBDAT), is introduced finally. Our simulation results show that the proposed algorithms outperform the existing state-of-the-art approaches significantly.

Un réseau de capteurs sans fil (Wireless Sensor Network, WSN) consiste en une distribution spatiale d'équipements embarqués autonomes, qui coopèrent de manière à surveiller l'environnement de manière non-intrusive. Les données collectées par chaque capteur (tels que la température, des vibrations, des sons, des mouvements etc. ) sont remontées de proche en proche vers un puits de collecte en utilisant des technologies de communication sans fil. Voilà une décennie que les contraintes inhérentes à ces réseaux attirent l'attention de la communauté scientifique. Ainsi, de nombreuses améliorations à différents niveaux de la pile de communication ont été proposées afin de relever les défis en termes d'économie d'énergie, de capacité de calcul et de contrainte mémoire imposés par l'utilisation d'équipements embarqués. Plusieurs déploiements couronnés de succès démontrent l'intérêt grandissant pour cette technologie. Les récentes avancées en termes d'intégration d'équipements et de protocoles de communication ont permis d'élaborer de nouveaux scénarios plus complexes. Ils mettent en scène des réseaux denses et différentes méthodes de collection de données. Par exemple, l'intérêt de la mobilité dans les WSNs est multiple dans la mesure ou les capteurs mobiles peuvent notamment permettre d'étendre la couverture d'un réseau, d'améliorer ses performances de routage ou sa connexité globale. Toutefois, ces scénarios apportent de nouveaux défis dans la conception de protocoles de communication. Ces travaux de thèse s'intéressent donc à la problématique de la dynamique des WSNs, et plus particulièrement à ce que cela implique au niveau du contrôle de l'accès au médium (Medium Access Control, MAC). Nous avons tout d'abord étudié l'impact de la mobilité et défini deux nouvelles méthodes d'accès au médium (Machiavel et X-Machiavel) qui permettent d'améliorer les conditions d'accès au canal pour les capteurs mobiles dans les réseaux denses. Notre deuxième contribution est un algorithme d'auto-adaptation destiné aux protocoles par échantillonnage. Il vise à minimiser la consommation énergétique globale dans les réseaux caractérisés par des modèles de trafic antagonistes, en obtenant une configuration optimale sur chaque capteur. Ce mécanisme est particulièrement efficace en énergie pendant les transmissions par rafales qui peuvent survenir dans de tels réseaux dynamiques
A WSN consists in spatially distributed autonomous and embedded devices that cooperatively monitor physical or environmental conditions in a less intrusive fashion. The data collected by each sensor node (such as temperature, vibrations, sounds, movements etc. ) are reported to a sink station in a hop-by-hop fashion using wireless transmissions. In the last decade, the challenges raised by WSN have naturally attracted the interest of the research community. Especially, signicant improvements to the communication stack of the sensor node have been proposed in order to tackle the energy, computation and memory constraints induced by the use of embedded devices. A number of successful deployments already denotes the growing interest in this technology. Recent advances in embedded systems and communication protocols have stimulated the elaboration of more complex use cases. They target dense and dynamic networks with the use of mobile sensors or multiple data collection schemes. For example, mobility in WSN can be employed to extend the network coverage and connectivity, as well as improve the routing performances. However, these new scenarios raise novel challenges when designing communication protocols. The work presented in this thesis focuses on the issues raised at the MAC layer when confronted to dynamic WSN. We have rst studied the impact of mobility and dened two new MAC protocols (Machiavel and X-Machiavel) which improve the medium access of mobile sensor nodes in dense networks. Our second contribution is an auto-adaptive algorithm for preamble sampling protocols. It aims at minimizing the global energy consumption in networks with antagonist trafic patterns by obtaining an optimal configuration on each node. This mechanism is especially energy-efficient during burst transmissions that could occur in such dynamic networks

Monitoring and controlling smart grid assets in a timely and reliable manner is highly desired for emerging smart grid applications. Wireless Sensor Networks (WSNs) are anticipated to be widely utilized in a broad range of smart grid applications due to their numerous advantages along with their successful adoption in various critical areas including military and health care. Despite these advantages, the use of WSNs in such critical applications has brought forward a new challenge of ful lling the Quality of Service (QoS) requirements of these applications. Providing QoS support is a challenging issue due to highly resource constrained nature of sensor nodes, unreliable wireless links and harsh operation environments. In this thesis we critically investigate the problem of QoS provisioning in WSNs. We identify challenges, limitations and requirements for applying QoS provisioning for WSNs in smart grid applications. We nd that the topic of data prioritization techniques at the MAC layer to provide delay bounds in condition monitoring applications is not well developed. We develop six novel QoS schemes that provide data di erentiation and reduce the latency of high priority tra c in a smart grid context. These schemes are namely; Delay-Responsive Cross layer (DRX), Fair and Delay-aware Cross layer (FDRX), Delay-Responsive Cross layer with Linear backo (LDRX), Adaptive Realistic and Stable Model (ARSM), Adaptive Inter-cluster head Delay Control (AIDC) and QoS-aware GTS Allocation (QGA). Furthermore, we propose a new Markov-based model for IEEE 802.15.4 MAC namely, Realistic and Stable Markovbased (RSM). RSM considers actual network conditions and enhances the stability of the WSNs. We show through analytical and simulation results that all of the presented schemes reduce the end-to-end delay while maintaining good energy consumption and data delivery values.

Wireless sensor networks have been a key driver of innovation and societal progressover the last three decades. They allow for simplicity because they eliminate ca-bling complexity while increasing the flexibility of extending or adjusting networksto changing demands. Wireless sensor networks are a powerful means of fillingthe technological gap for ever-larger industrial sites of growing interconnection andbroader integration. Nonetheless, the management of wireless networks is difficultin situations wherein communication requires application-specific, network-widequality of service guarantees. A minimum end-to-end reliability for packet arrivalclose to 100% in combination with latency bounds in the millisecond range must befulfilled in many mission-critical applications.The problem addressed in this thesis is the demand for algorithmic support forend-to-end quality of service guarantees in mission-critical wireless sensor networks.Wireless sensors have traditionally been used to collect non-critical periodic read-ings; however, the intriguing advantages of wireless technologies in terms of theirflexibility and cost effectiveness justify the exploration of their potential for controland mission-critical applications, subject to the requirements of ultra-reliable com-munication, in harsh and dynamically changing environments such as manufactur-ing factories, oil rigs, and power plants.This thesis provides three main contributions in the scope of wireless sensor net-works. First, it presents a scalable algorithm that guarantees end-to-end reliabilitythrough scheduling. Second, it presents a cross-layer optimization/configurationframework that can be customized to meet multiple end-to-end quality of servicecriteria simultaneously. Third, it proposes an extension of the framework used toenable service differentiation and priority handling. Adaptive, scalable, and fast al-gorithms are proposed. The cross-layer framework is based on a genetic algorithmthat assesses the quality of service of the network as a whole and integrates the phys-ical layer, medium access control layer, network layer, and transport layer.Algorithm performance and scalability are verified through numerous simula-tions on hundreds of convergecast topologies by comparing the proposed algorithmswith other recently proposed algorithms for ensuring reliable packet delivery. Theresults show that the proposed SchedEx scheduling algorithm is both significantlymore scalable and better performing than are the competing slot-based schedulingalgorithms. The integrated solving of routing and scheduling using a genetic al-vvigorithm further improves on the original results by more than 30% in terms of la-tency. The proposed framework provides live graphical feedback about potentialbottlenecks and may be used for analysis and debugging as well as the planning ofgreen-field networks.SchedEx is found to be an adaptive, scalable, and fast algorithm that is capa-ble of ensuring the end-to-end reliability of packet arrival throughout the network.SchedEx-GA successfully identifies network configurations, thus integrating the rout-ing and scheduling decisions for networks with diverse traffic priority levels. Fur-ther, directions for future research are presented, including the extension of simula-tions to experimental work and the consideration of alternative network topologies.

Vid tidpunkten för disputationen var följande delarbeten opublicerade: delarbete 4 (manuskript inskickat för granskning), delarbete 5 (manuskript inskickat för granskning)

At the time of the doctoral defence the following papers were unpublished: paper 4 (manuscript under review), paper 5 (manuscript under review)

A Wireless Sensor Network (WSN) is a collection of tiny devices called sensor nodes which are deployed in an area to be monitored. Each node has one or more sensors with which they can measure the characteristics of their surroundings. In a typical WSN, the data gathered by each node is sent wirelessly through the network from one node to the next towards a central base station. Each node typically has a very limited energy supply. Therefore, in order for WSNs to have acceptable lifetimes, energy efficiency is a design goal that is of utmost importance and must be kept in mind at all levels of a WSN system. The main consumer of energy on a node is the wireless transceiver and therefore, the communications that occur between nodes should be carefully controlled so as not to waste energy. The Medium Access Control (MAC) protocol is directly in charge of managing the transceiver of a node. It determines when the transceiver is on/off and synchronizes the data exchanges among neighbouring nodes so as to prevent collisions etc., enabling useful communications to occur. The MAC protocol thus has a big impact on the overall energy efficiency of a node. Many WSN MAC protocols have been proposed in the literature but it was found that most were not optimized for the group of WSNs displaying very low volumes of traffic in the network. In low traffic WSNs, a major problem faced in the communications process is clock drift, which causes nodes to become unsynchronized. The MAC protocol must overcome this and other problems while expending as little energy as possible. Many useful WSN applications show low traffic characteristics and thus a new MAC protocol was developed which is aimed at this category of WSNs. The new protocol, Dynamic Preamble Sampling MAC (DPS-MAC) builds on the family of preamble sampling protocols which were found to be most suitable for low traffic WSNs. In contrast to the most energy efficient existing preamble sampling protocols, DPS-MAC does not cater for the worst case clock drift that can occur between two nodes. Rather, it dynamically learns the actual clock drift experienced between any two nodes and then adjusts its operation accordingly. By simulation it was shown that DPS-MAC requires less protocol overhead during the communication process and thus performs more energy efficiently than its predecessors under various network operating conditions. Furthermore, DPS-MAC is less prone to become overloaded or unstable in conditions of high traffic load and high contention levels respectively. These improvements cause the use of DPS-MAC to lead to longer node and network lifetimes, thus making low traffic WSNs more feasible.
Dissertation (MEng)--University of Pretoria, 2008.
Electrical, Electronic and Computer Engineering
MEng
Unrestricted