Dissertations / Theses on the topic 'Energy network'

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 97-104).
Energy is one of the most important considerations in designing reliable low-power wireless communication networks. We focus on the problem of energy aware network coding. In particular, we investigate practical energy efficient network code design for wireless body area networks (WBAN). We first consider converge-cast in a star-shaped topology, in which a central base station (BS), or hub, manages and communicates directly with a set of nodes. We then consider a wireless-relay channel, in which a relay node assists in the transmission of data from a source to a destination. This wireless relay channel can be seen as a simplified extended star network, where nodes have relay capabilities. The objective is to investigate the use of network coding in these scenarios, with the goal of achieving reliability under low-energy and lower-power constraints. More specifically, in a star network, we propose a simple network layer protocol, study the mean energy to complete uploads of given packets from the nodes to the BS using a Markov chain model, and show through numerical examples that when reception energy is taken into account, the incorporation of network coding offers reductions in energy use. The amount of achievable gains depends on the number of nodes in the network, the degree of asymmetry in channel conditions experienced by different nodes, and the relative difference between transmitting and receiving power at the nodes. We also demonstrate the compatibility of the proposed scheme with the IEEE 802.15.6 WBAN standard by describing ways of incorporating network coding into systems compliant to the standard. For a wireless relay channel, we explore the strategic use of network coding according to both throughput and energy metrics. In the relay channel, a single source communicates to a single sink through the aid of a half-duplex relay. The fluid flow model is used to describe the case where both the source and the relay are coding, and Markov chain models are proposed to describe packet evolution if only the source or only the relay is coding. Although we do not attempt to explicitly categorize the optimal network coding strategies in the relay channel under different system parameters, we provide a framework for deciding whether and where to code, taking into account of throughput maximization and energy depletion constraints.
by Xiaomeng Shi.
Ph.D.

Orientador: Nelson Luis Saldanha da Fonseca
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Computação
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Resumo: A virtualização de redes é uma tecnologia promissora para a Internet do futuro, já que facilita a implementação de novos protocolos e aplicações sem a necessidade de alterar o núcleo da rede. Um passo chave para instanciar redes virtuais é a alocação de recursos físicos para elementos virtuais (roteadores e enlaces). A fim de contribuir para o esforço global de poupança de energia, a escolha de recursos físicos para instanciar uma rede virtual deveria minimizar o consumo de energia rede. No entanto, esta não é uma tarefa trivial, já que requerimentos de QoS devem ser atingidos. A busca da solução ótima deste problema é NP-difícil. O mapeamento de redes virtuais em substratos de rede físicos em cenários de alocaç?o e desalocaç?o de redes virtuais pode não levar a um consumo mínimo de energia devido à dinâmica das atribuições dos elementos virtuais previamente alocados. Tal dinâmica pode levar à subutilização da rede substrato. Para reduzir os efeitos negativos desta dinâmica, técnicas tais como a migração de redes virtuais em tempo real podem ser empregadas para rearranjar as redes virtuais previamente mapeadas para poupar energia. Esta dissertação apresenta um conjunto de novos algoritmos para o mapeamento de redes virtuais em substratos de rede com o objetivo de reduzir o consumo de energia. Além disso, dois novos algoritmos são propostos para a migração dos roteadores e enlaces virtuais para reduzir o número de roteadores e amplificadores ópticos requeridos. Os resultados obtidos por simulação mostram a eficácia dos algoritmos propostos
Abstract: Network virtualization is a promising technology for the Internet of the Future since it facilitates the deployment of new protocols and applications without the need of changing the core of the network. A key step to instantiate virtual networks is the allocation of physical resources to virtual elements (routers and links). In order to contribute to the global effort of saving energy, choice of physical resources to instantiate a virtual network needs to minimize the network energy consumption. However, this is not a trivial task, since the QoS of the application requirements has to be supported. Indeed, the search for the optimal solution of this problem is NP-hard. The mapping of virtual networks on network substrates at the arrival time of requests to the establishment of virtual networks may not lead to a global minimum energy consumption of energy due to the dynamic allocations and deallocations of virtual networks. Actually, such dynamics can lead to the underutilization of the network substrate. To mitigate the negative effect of this dynamics, techniques such as live migration can be employed to rearrange already mapped virtual networks to achieve energy savings. This dissertation presents a set of new algorithms for the mapping of virtual networks on network substrates aiming to reduce energy consumption. Additionally, two new algorithms are proposed for the migration of virtual routers and links to reduce the number of powered routers and optical amplifiers. Results derived by simulation show the efficacy of the proposed algorithms
Mestrado
Ciência da Computação
Mestre em Ciência da Computação

The major difference between wired and wireless networks is their broadcast nature, specifically how transmitted data by one node may reach other nodes and vice-versa. This broadcast nature is a curse for wired networks but a blessing for wireless networks. Network coding is a technique where instead of just forwarding packets arrived at relay nodes, the node will collect several packets and then combine them together using an algebraic algorithm for transmissions. Network coding reduces the energy consumption by decreasing the number of transmissions required to communicate a given amount of information across the network. The aim of this thesis is to enhance network-coding strategy in order to improve energy gain, which in turn increases throughput in ad hoc networks. To that end, this thesis also proposes an even parity scheme that reduces processing time and power of nodes by improving coding opportunities. In addition, an even parity scheme allows for the coding of large numbers of packets at a time instead of coding just two packets using normal XOR operation.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering and Computer Science

In this thesis we propose the use of network coding to improve the energy efficiency in core networks, by reducing the resources required to process traffic flows at intermediate nodes. We study the energy efficiency of the proposed scheme through three approaches: (i) developing a mixed integer linear programme (MILP) to optimise the use of network resources. (ii) developing a heuristic based on minimum hop routing. (iii) deriving an analytical bounds and closed form expressions. The results of the MILP model show that implementing network coding over typical networks can introduce savings up to 33% compared to the conventional architectures. The results of the heuristic show that the energy efficient minimum hop routing in network coding enabled networks achieves power savings approaching those of the MILP model. The analytically calculated power savings also confirm the savings achieved by the model. Furthermore, we study the impact of network topology on the savings obtained by implementing network coding. The results show that the savings increase as the hop count of the network topology increases. Using the derived expressions, we calculated the maximum power savings for regular topologies as the number of nodes grows. The power savings asymptotically approach 45% and 23% for the ring (and line) and star topology, respectively. We also investigate the use of network coding in 1+1 survivable IP over WDM networks. We study the energy efficiency of this scheme through MILP, a heuristic with five operating options, and analytical bounds. We evaluate the MILP and the heuristics on typical and regular network topologies. Implementing network coding can produce savings up to 37% on the ring topology and 23% considering typical topologies. We also study the impact of varying the demand volumes on the network coding performance. We also develop analytical bounds for the conventional 1+1 protection and the 1+1 with network coding to verify the results of the MILP and the heuristics and study the impact of topology, focusing on the full mesh and ring topologies, providing a detailed analysis considering the impact of the network size.

Wireless sensor networks (WSNs) have a wide variety of applications in civilian, medical and military applications. However, the nodes in such a network are limited to one type of action: sensing the environment. With increasing requirements for intelligent interaction with the environment, there is a need to not only perceive but also control the monitored environment. This has led to the emergence of a new class of networks, referred to as wireless sensor and actor networks (WSANs), capable of performing both sensing and acting tasks on the environment. The evolution from WSNs, which can be thought of as performing only read operations, to WSANs, which can perform both read and write operations, introduces unique and new challenges that need to be addressed. In this research, the fundamental challenges required for effective operation of WSANs are analyzed from the following three different perspectives: (i) operation correctness, (ii) resource optimality, and (iii) operation performance. The solutions proposed to address the challenges are evaluated with the optimal solution and other competing approaches through analytical and simulation results. The feasibility of the proposed solutions is demonstrated through a testbed implementation.

Broadcasting, coverage, duty cycling, and capacity improvement are some of the important areas of interest in Wireless Networks. We address different problems related with broadcasting, duty cycling, and capacity improvement by sensing different network conditions and dynamically adapting to them. We propose two cross layer broadcasting protocols called CASBA and CMAB which dynamically adapt to network conditions of congestion and mobility. We also propose a broadcasting protocol called DASBA which dynamically adapts to local node density. CASBA, CMAB, and DASBA improve the reachability while minimizing the broadcast cost. Duty cycling is an efficient mechanism to conserve energy in Wireless Sensor Networks (WSNs). Existing duty cycling techniques are unable to handle the contention under dynamic traffic loads. Our proposed protocol called SA-RI-MAC handles traffic contention much more efficiently than RI-MAC without sacrificing the energy efficiency. It improves the delivery ratio with a significant reduction in the latency and energy consumption. Due to limited battery life and fault tolerance issues posed by WSNs, efficient methods which ensure reliable coverage are highly desirable. One solution is to use disjoint set covers to cover the targets. We formulate a problem called MDC which addresses the maximum coverage by using disjoint set covers S1 and S2. We prove that MDC is NP-complete and propose a √n-approximation algorithm for the MDC problem to cover n targets. The use of multi-channel MAC protocols improves the capacity of wireless networks. Efficient multi-channel MAC protocols aim to utilize multiple channels effectively. Our proposed multi-channel MAC protocol called LCV-MMAC effectively utilizes the multiple channels by handling the control channel saturation. LCV-MMAC demonstrates significantly better throughput and fairness compared to DCA, MMAC, and AMCP in different network scenarios.

With various new alternatives of low-cost sensor devices, there is a strong demand for large scale wireless sensor networks (WSN). Energy efficiency in routing is crucial for achieving the desired levels of longevity in these networks. Existing routing algorithms that do not combine information on transmission energies on links, residual energies at nodes, and the identity of data itself, cannot reach network capacity. A proof-of-concept routing algorithm that combines data aggregation with the minimum-weight path routing is studied in this thesis work. This new algorithm can achieve much larger network lifetime when there is redundancy in messages to be carried by the network, a practical reality in sensor network applications.

Internet of Things (IoT) is a scenario that theorizes objects and people as potential nodes in an ever-growing wireless network. This idea pushes the development of low-cost wireless technologies that can run on portable power sources for months, or even years. One candidate technique that has shown promising results in this area thru the last years is BluetoothLow Energy (BLE). This thesis studies various techniques to enable and maintain large scale mesh networks over BLE communication. The initial study puts focus on an existing flooding based BLE mesh protocol. The thesis later presents an improved protocol that reduces power consumption with respect to the packet delivery ratio. Other enhancements which are added to the improved protocol are a self-adapting procedure and a packet routing algorithm. Simulations show that the improved protocol can save up to 50 % of the power consumption for a device, compared to the original protocol.
Sakernas Internet (IoT) är ett scenario som skisserar objekt och människor som potentiella noder i ett ständigt växande trådlöst nätverk. Denna vision driver utvecklingen av trådlösa lågkostnadsteknologier som kan köras på portabla strömkällor i flera månader. En kandiderande teknik som har visat goda resultat inom detta område är Bluetooth Low Energy (BLE). Detta uppsatsarbete studerar flera tekniker för att möjliggöra och upprätthålla storskaliga meshnätverk över BLE-kommunikation. Den inledande studien granskar ett existerande översvämningsbaserat meshprotokoll för BLE. Uppsatsarbetet presenterar därefter ett förbättrat protokoll som reducerar strömförbrukningen med avseende på kvoten mellan antalet mottagna paket genom antalet skickade paket. Ytterliggare upprustningar som tillkommer i det förbättrade protokollet är en procedur för självanpassning, samt en algorithm för dirigering av paket. Simuleringar visar att det förbättrade protokollet kan spara upp till 50 % av strömkonsumptionen för en enhet, jämfört med originalprotokollet.

Notre travail s'inscrit dans le cadre des recherches sur le Sleeping mode. Notre contribution est structurée principalement autour deux axes : l'étude et l'évaluation de la performance des processus de mise en veille/réveil des points d'accès et la sélection du nombre minimal des points d'accès dans un milieu urbain dense. Dans un premier temps, nous étudions les processus de mise en veille/réveil des points d'accès dans un scenario classique de réseau domestique. Ce scenario suppose que le point d'accès mis en veille doit détecter la présence d'un utilisateur potentiel dans sa zone de couverture et réagir par conséquence d'une façon autonome pour se mettre en état de fonctionnement normal. Nous avons choisi quatre processus de réveil du point d'accès, et nous avons ensuite étudié chacun de ces processus, et proposé un protocole de communication qui permette à un utilisateur d'envoyer l'ordre au point d'accès de s'éteindre. Lorsque cela était possible, nous avons utilisé le protocole COAP qui est prévu pour établir des sessions de commande pour l'Internet des Objets. Nous avons ensuite mesuré les performances du point de vue de l'économie d'énergie qu'il permet de réaliser et du délai entre le moment où un utilisateur potentiel est détecté et le moment où le point d'accès devient opérationnel. Nous avons aussi étudié un réseau dense dans un milieu urbain (le centre ville de Rennes) où la zone de couverture d'un point d'accès pouvait être partiellement ou totalement couverte par d'autres points d'accès. Pour évaluer la redondance dans le réseau, nous avons collecté des informations réelles sur les points d'accès en utilisant l'application Wi2Me. Le traitement de ces informations nous a permis d'identifier les points d'accès existants dans la zone étudiée et leurs zones de couverture respectives démontrant ainsi la superposition de ces zones de couverture et le potentiel d'élimination d'un certain nombre de points d'accès sans affecter la couverture globale. Nous avons alors proposé un système centralisé qui collecte les données de couverture des points d'accès observée par les utilisateur. Nous avons donc utilisé ce simple fait pour centraliser la vue du réseau de plusieurs utilisateurs, ce qui permet d'avoir une vue assez précise de la disponibilité des points d'accès dans une zone géographie. Nous avons alors proposé une représentation de ces données de couverture à travers des matrices qui traitent les différentes erreurs de capture (coordonnées GPS non précises, réutilisation des noms de réseaux, etc). Enfin, nous avons ensuite proposé deux algorithmes permettant de sélectionner l'ensemble minimal des points d'accès requis fournissant une couverture identique à celle d'origine
The main goal of the thesis is to design an Energy Proportional Network by taking intelligent decisions into the network such as switching on and off network components in order to adapt the energy consumption to the user needs. Our work mainly focuses on reducing the energy consumption by adapting the number of APs that are operating to the actual user need. In fact, traffic load varies a lot during the day. Traffic is high in urban areas and low in the suburb during day work hours, while it is the opposite at night. Often, peak loads during rush hours are lower than capacities of the networks. Thus they remain lightly utilized for long periods of time. Thus keeping all APs active all the time even when the traffic is low causes a huge waste of energy. Our goal is to benefit from low traffic periods by automatically switch off redundant cells, taking into consideration the actual number of users, their traffic and the bandwidth requested to serve them. Ideally we wish to do so while maintaining reliable service coverage for existing and new coming users. First we consider a home networking scenario. In this case only one AP covers a given area. So when this AP is switched off (when no users are present), there will be no other AP to fill the gap of coverage. Moreover, upon the arrival of new users, no controller or other mechanism exists to wake up the AP. Consequently, new arriving users would not be served and would remain out of coverage. The study of the state of the art allowed us to have a clear overview of the existing approaches in this context. As a result, we designed a platform to investigate different methods to wake up an AP using different technologies. We measure two metrics to evaluate the Switching ON/OFF process for the different methods. The first is the energy consumed by the AP during the three phases it goes through. The second is the delay of time for the AP to wake up and be operational to serve the new users. In the second case we consider a dense network such as the ones found in urban cities, where the coverage area of an AP is also covered by several other APs. In other words, the gap resulting from switching off one or several APs can be covered by other neighbouring ones. Thus the first thing to do was to evaluate the potential of switching off APs using real measurements taken in a dense urban area. Based on this collected information, we evaluate how many APs can be switched off while maintaining the same coverage. To this end, we propose two algorithms that select the minimum set of APs needed to provide full coverage. We compute several performance parameters, and evaluate the proposed algorithms in terms of the number of selected APs, and the coverage they provide

In today's world of ubiquitous Smartphone use, extending the battery life has become an important issue. A significant contributor to battery drain is wireless networking. Common usage patterns expect Smartphones to maintain a constant Internet connection which exacerbates the problem.;Our research entitled A Network Traffic Approach to Smartphone Energy Savings focuses on extending Smartphone battery life by investigating how network traffic impacts power management of wireless devices. We explore 1) Real-time VoIP application energy savings by exploiting silence periods in conversation. WiFi is opportunistically placed into low power mode during Silence periods. 2.) The priority of Smartphone Application network traffic is used to modifiy WiFi radio power management using machine learning assisted prioritization. High priority network traffic is optimized for performance, consuming more energy while low priority network traffic is optimized for energy conservation. 3.) A hybrid multiple PHY, MAC layer approach to saving energy is also utilized. The Bluetooth assisted WiFi approach saves energy by combining high power, high throughput WiFi with low power, lower throughput Bluetooth. The switch between Bluetooth and WiFi is done opportunistically based upon the current data rate and health of the Bluetooth connection.;Our results show that application specific methods for wireless energy savings are very effective. We have demonstrated energy savings exceeding 50% in generic cases. With real-time VoIP applications we have shown upwards of 40% energy savings while maintaining good call quality. The hybrid multiple PHY approach saves more than 25% energy over existing solutions while attaining the capability of quickly adapting to changes in network traffic.

Telecommunications operators are continuously exploring new lternatives to up-grade their networks in order to handle the ever increasing Internet traffic demand. However, increase in bandwidth have been accompanied with the increase in power consumption which is an important subject to be addressed. For the said purpose my research is focused on developing methods of bringing energy efficiency in the core telecommunications networks. The target of this thesis is the improvement of the energy efficiency in wired telecommunication networks. Indeed, several research studies have underlined that the already huge energy consumption is destined to increase in the next years since the traffic in telecommunication networks will continue to grow constantly due to the increasing popularity of new bandwidth-consuming applications, and the increase of population using them. This situation thus urges to find strategies that can mitigate the demand of energy in the networks. The main contributions concern the definition of algorithms and strategies that incorporate and exploit the knowledge of the network topology, the carried traffic and the power behavior of network devices to achieve energy efficiency in the network. In particular, during the three years, research work targeting the energy efficient designing of conventional fixed grid (Wavelength Division Multiplexing) WDM networks and Orthogonal Frequency Division Multiplexing (OFDM) based elastic optical networks is being carried out. The problem is tackled using Mixed Integer Linear Programming (MILP), greedy heuristics and sophisticated meta-heuristics. Results show that an appropriate design can increase energy efficiency in fixed-grid WDM and flexible-grid elastic optical networks. The problem of power-efficient design of IP-over-WDM networks is investigated through explicitly targeting the minimization of power consumption. Results, obtained over an extensive set of scenarios and networks, indicate that both the MILP and heuristics provide solutions for power-efficient networks. Moreover, it was observed that most of the power in an IP-over-WDM network is consumed by routers and line cards, even when high power consumption of OLAs and WDM terminals is assumed. The other topic covered during my research activity is the investigation of energy-efficient design of flexible-grid networks. The activity was mainly focused on the design of the logical layer, which is usually disregarded when dealing with flexible-grid networks. More precisely, the impact of introducing an energy-aware electronic traffic grooming in flexible-grid network design is evaluated. Two greedy heuristics for the network design are proposed, one exploiting traffic grooming, and their energy efficiency is compared. In summary, this thesis makes important contributions to the networking research community providing new methods and approaches for the definition of energy efficient networking techniques.

The rapid expansion of mobile services and the emerging demand for multimedia applications have led to an impressive traffic growth. To this end, Mobile Network Operators (MNOs) seek to extend their infrastructure by installing more Base Stations (BSs), in an effort to increase the network capacity and meet the pressing traffic demands. Furthermore, to fulfill the escalated demands, Heterogeneous Networks (HetNets), which consist of Small Cells (SCs) and the traditional BSs, constitute the new trend of next generation networks. The deployed infrastructure implies a rise in the Capital Expenditures and has a direct impact on the network energy consumption, thus resulting in higher Operational Expenditures. Hence, the investigation of energy efficient solutions will bring down the energy consumption and the network cost. Since the BS is the most power hungry component, the research community has shifted towards the investigation of BS deactivation schemes. These schemes propose that part of the infrastructure can be temporarily switched off, when the traffic is low, while the active BSs extend their coverage to serve the network. Based on a comprehensive review of the state-of-the-art, a set of research opportunities were identified. This thesis provides contributions to the field of BS switching off strategies for wireless macro BSs networks and HetNets of single and multiple MNOs by proposing mechanisms that enhance different aspects of the network performance. The BSs deactivation, the innovative trend of infrastructure sharing and the financially driven collaboration among the involved parties of the current and future networks promise significant improvements in terms of energy and cost savings. The main thesis contributions are divided into three parts, described next. The first part of the thesis introduces innovative BS switching off approaches in single-operator environments, where only macro BSs are deployed. The proposed strategies exploit the inherit characteristics of the traffic load pattern (e.g., distribution of the users, traffic volume, etc.) and the distinctive features of the wireless cellular networks (e.g., BSs position, topology, etc.). Theoretical analysis and computer-based simulations show the performance improvement offered by the switching off strategies with respect to energy efficiency. The second part of the thesis explores a different challenge in network planning. The coexistence of multiple MNOs in the same geographical area has motivated a new business model, known as infrastructure sharing. A roaming-based deactivation scheme is proposed, by taking into account the rationality and the conflicting interests of the MNOs. The proposed game theoretic framework enables the MNOs to take individual switching off decisions, thus bypassing potential complicated agreements. The theoretical and simulation results show that our proposal significantly improves the energy efficiency, guaranteeing at the same time the throughput in realistic scenarios. Moreover, the proposed scheme provides higher cost efficiency and fairness compared to the state-of-the-art algorithms, motivating the MNOs to adopt game theoretic strategies. The third part of the thesis focuses on the exploitation of HetNets and the proposal of energy and cost effective strategies in SC networks with multiple MNOs. We effectively address the cost sharing by proposing accurate cost models for the SCs to share the network cost. Taking into account the impact of the traffic on the cost, we propose novel cost sharing policies that provide a fair outcome. In continuation, innovative auction-based schemes within multiobjective optimization framework are introduced for data offloading from the BSs, owned by the MNOs, to the third-party SC networks. The proposed solution captures the conflicting interests of the MNOs and the third-party companies and the obtained results show that the benefit of proposing switching off approaches for HetNets.
La rápida expansión de los servicios móviles y de la demanda emergente de aplicaciones multimedia han dado lugar a un impresionante crecimiento del tráfico. Operadores de redes móviles (MNOs) tratará de extender su infraestructura mediante la instalación de más estaciones base (BSs), en un esfuerzo por aumentar la capacidad de la red y satisfacer las apremiantes demandas de tráfico. Además, para cumplir con las exigencias escalada, redes heterogéneas (HetNets), constituyen la nueva tendencia de las redes de próxima generación. La infraestructura implica un aumento en los gastos de capital y tiene un impacto directo en el consumo de energía a la red, lo que resulta en un aumento de los gastos operacionales. La investigación de soluciones de eficiencia energética hará bajar el consumo de energía y el coste de la red. La comunidad científica se ha desplazado hacia la investigación de los sistemas de desactivación de BSs. Estos esquemas proponen que parte de la infraestructura se puede cdesectivarse, cuando el tráfico es bajo, mientras que los BSs activas extender su cobertura al servicio de la red. Esta tesis ofrece contribuciones al campo de la BSs desconexión para las redes y HetNets con uno o multiples MNOs, proponiendo mecanismos que mejoran diferentes aspectos del rendimiento de la red. La desactivación de BS,s la tendencia innovadora de compartir infraestructura y la colaboración impulsada financieramente entre las partes implicadas de las redes actuales y futuras prometen mejoras significativas en términos de ahorro energético y económico. Las principales contribuciones de tesis se dividen en tres partes, que se describen a continuación. La primera parte de la tesis introduce innovadora apagar enfoques en entornos de un solo operador, donde se despliegan sólo macro BSs. Las estrategias propuestas explotan las características de tráfico (por ejemplo, la distribución de los usuarios, el volumen de tráfico, etc.) y las características distintivas de las redes (por ejemplo, la posición BS, topología, etc.). Análisis teórico y simulaciones muestran la mejora del rendimiento ofrecido por las estrategias de conmutación con respecto a la eficiencia energética. La segunda parte de la tesis explora un reto diferente en la planificación de la red. La coexistencia de múltiples operadores en la misma zona geográfica ha motivado un nuevo modelo de negocio, conocida como la compartición de infraestructura. Se propone un esquema de desactivación basada en itinerancia, teniendo en cuenta la racionalidad y los intereses en conflicto de los operadores de redes móviles. Los resultados teóricos y de simulación muestran que nuestra propuesta mejora significativamente la eficiencia energética, garantizando al mismo tiempo el rendimiento en escenarios realistas. Por otra parte, el esquema propuesto proporciona una mayor eficiencia de costes y la equidad en comparación con los algoritmos del estado de la técnica, motivar al mnos de adoptar estrategias de teoría de juegos. La tercera parte de la tesis se centra en la explotación de HetNets y la propuesta de estrategias eficaces de energía y costes en las redes con múltiples operadores. Nos dirigimos efectivamente la participación en los costos, proponiendo modelos de costos precisos para para compartir el costo de la red. Teniendo en cuenta el impacto del tráfico en el coste, proponemos políticas costos compartidos novedosas que proporcionan un resultado justo. En la continuación, los esquemas basados en subastas innovadoras dentro de marco de optimización multiobjetivo se introducen los datos que descargan de la BS. La solución propuesta recoge los intereses en conflicto de los operadores de redes móviles y las compañías de terceros y los resultados obtenidos muestran que el beneficio de proponer la desconexión se acerca para HetNets

Context: Wireless Mesh Network (WMN) is a form of ad-hoc network with flexible backhaul infrastructure and configuration, provides adaptive wireless internet connectivity to end users with high reliability. WMN is a wireless network consisting of mesh clients, mesh routers and gateways which are organized in a mesh topology with decentralized nature can consume more energy for data transmission. The networking performance of WMNs can be degraded due to the fact of high energy consumption for data transmission. Therefore, energy efficiency is the primary factor for attaining eminent performance. Organizing efficient routing and proper resource allocation can save huge amount of energy. Objectives: The main goal of this thesis is to reduce the energy consumption in WMNs. To do this, a new energy efficient routing algorithm is suggested. Adaptive rates based on rate allocation strategy and end to end delay metric are used mainly for optimal path selection in routing, which may in turn reduces the resource utilization and energy consumption. Method: An energy efficient routing algorithm is implemented by using the Ad hoc OnDemand Distance Vector (AODV) routing protocol. The RREQ packet in AODV is modified by adding a new field known as delay parameter which measures end to end delay between nodes. Adaptive rates obtained from Rate allocation policy are considered in the routing process to reduce energy consumption in the network. Energy measurement of the WMN and its performance is evaluated by measuring the metrics such as Throughput, End-to-End delay, Packet Delivery Ratio (PDR). For performing the simulation process, in this thesis, Network Simulator - 3 (NS-3) which is an open source discrete-event network simulator in which simulation models can be executed in C++ and Python is used. Using NetAnim-3.107 animator in NS-3-25.1, traffic flows between all the nodes are displayed. Results: The results are taken for existing algorithm and proposed algorithm for 25,50,75 and 100 nodes. Comparison of results shows that the total energy consumption is reduced for proposed algorithm for in all four scenarios. Conclusion: Energy efficient routing algorithm is implemented in different scenarios of radio access networks and energy is saved. Due to this algorithm even the performance metrics, Throughput, End-to-End delay, Packet Delivery Ratio (PDR) have shown eminent performance.

L’utilisation des réseaux de capteurs offre de nouvelles perspectives dans de nombreux domaines (médecine, militaire, etc.). Les données récoltées par ces capteurs circulent en clair sur les réseaux de capteurs et peuvent être interceptées par un espion. Selon le domaine d’utilisation, le niveau de sécurité souhaité peut être élevé, ce qui peut provoquer une hausse de la consommation d’énergie sur les nœuds. Ces deux contraintes, sécurité et énergie, sont difficilement conciliables. Il y a donc un compromis à trouver entre l’économie d’énergie qui va conditionner la durée de vie du réseau, et le niveau de sécurité souhaité par l’application. L’objectif de cette thèse est d’étudier les compromis à trouver entre ces deux contraintes, à la fois d’un point de vue théorique et d’un point de vue pratique (par une implémentation des algorithmes et des tests réels sur des réseaux de capteurs par choisissant les algorithmes DES et AES). L’algorithme de cryptographie symétrique DES a ´ et ´e choisi comme objet d’étude. Les résultats obtenus sur la plateforme académique Senslab ont permis de déterminer une relation précise entre la consommation d’énergie et le nombre de rondes de DES et donc le niveau de sécurité. Ces expériences ont été renouvelées avec l’algorithme AES, plus récent et plus sûr, mais aussi plus consommateur en énergie. Puis, à partir des résultats obtenus, un modèle générique de consommation pour les algorithmes cryptographiques a été construit pour un réseau complet. L’utilisation complémentaire de la compression des données a permis de réduire cet impact de manière intéressante. Enfin, l’utilisation de la mémoire et l’évaluation du temps de chiffrement et de compression ont été évalué de manière à rester dans des fourchettes réalistes d’utilisation réaliste
Wireless sensor networks give us opportunities to improve many applications in many fields(medicine, military, etc.). The data collected by sensor node flies as plain text on sensor networkand can be intercepted by a spy. Depending on the importance of data, the wanted level of securitycould be high which may impact the energy consumption of sensor nodes. These two constraints,security and energy are difficult to combine. There is a trade-off between energy savings that willdetermine the lifetime of the network and the level of security desired by the application.The objective of this thesis is to study the trade-off between these two constraints, both from atheoretical perspective and from a practical point of view (with an implementation of algorithms andreal tests on sensor networks). The DES symmetric cryptographic algorithm was chosen as a casestudy. The results obtained on the academic platform Senslab have shown a clear relationshipbetween energy consumption and the number of rounds of DES and therefore the level of security.These experiments were repeated with the AES algorithm, newer and safer, but also more energyconsumer.Then, from the results, a generic model of consumption for cryptographic algorithms has been builtfor a complete network. The complementary use of data compression has reduced this impact ofenergy consumption in an interesting way. Finally, the memory usage and the time of encryption andcompression were evaluated in order to stay within realistic ranges of use

This thesis proposes and discusses aspects of a low-cost wireless network called "Hopscotch" as a potential solution to the rural broadband problem. Providing broadband internet access to rural locations is challenging due to the long distances between internet backbone and households, the sparse population density and difficult terrain. Hopscotch uses a network of renewable powered base stations, termed "WindFi", connected by point-to-point links, to deliver internet access to rural communities. A combination of frequency bands are used within Hopscotch. Standard IEEE 802.11 5 GHz WiFi access technology is used for high capacity links, and an ultra high frequency TV "white space" spectrum overlay in the 600-800 MHz band provides long distance coverage. The advantages of "white space" spectrum are demonstrated for a rural wireless scenario; reducing the number of base stations required to cover a community and decreasing the transmit power required to create long distance links over challenging terrain. The use of renewable power allows WindFi base stations to be well placed to serve a community, irrespective of available infrastructure. The power system is the biggest cost component of the base station therefore the system must be carefully sized. The design of the WindFi base station is presented and the specification of the renewable power generation system validated with operational data. To reduce the energy required, and therefore the demand on the renewable power system, aspects of energy use within the base station are considered. Models of the power consumption and data rate selection for radios used in Hopscotch are presented. Hopscotch trials have been running on the Scottish islands of Bute and Tiree. Measurement based models of household distribution, daily network internet traffic and large-scale path loss for a rural community are presented based on trial results, which are useful for simulating rural broadband networks. To minimise the power consumption of the WindFi base station, an energy optimisation is presented for a Hopscotch scenario. Dynamically altering the assignment of users between two overlay radio access networks, based on the instantaneous capacity required, is shown to reduce power consumption. The optimum assignment between the networks to maximise individual user throughput is also presented.

Efficient energy use is primarily for any sensor networks to function for a longer time period. There have been many efficient schemes with various progress levels proposed by many researchers. Yet, there still more improvements are needed. This thesis is an attempt to make wireless sensor networks with further efficient on energy usage in the network with respect to rate of delivery of the messages. In sensor network architecture radio, sensing and actuators have influence over the power consumption in the entire network. While listening as well as transmitting, energy is consumed by the radio. However, if by reducing listening times or by reducing the number of messages transmitting would reduce the energy consumption. But, in real time scenario with critical information sensing network leads to information loss. To overcome this an adaptive routing technique should be considered. So, that it focuses on saving energy in a much more sophisticated way without reducing the performance of the sensing network transmitting and receiving functionalities. This thesis tackles on parts of the energy efficiency problem in a wireless sensor network and improving delivery rate of messages. To achieve this a routing technique is proposed. In this method, switching between two routing paths are considered and the switching decision taken by the server based on messages delivered comparative previous time intervals. The goal is to get maximum network life time without degrading the number of messages at the server. In this work some conventional routing methods are considered for implementing an approach. This approach is by implementing a shortest path, Gradient based energy routing algorithm and an observer component to control switching between paths. Further, controlled switching done by observer compared to normal initial switch rule. Evaluations are done in a simulation environment and results show improvement in network lifetime in a much more balanced way.

Les infrastructures Internet et l'installation d'appareils très gourmands en énergie (en raison de l'explosion du nombre d'internautes et de la concurrence entre les services efficaces offerts par Internet) se développent de manière exponentielle. Cela entraîne une augmentation importante de la consommation d'énergie. La gestion de l'énergie dans les systèmes de distribution de contenus à grande échelle joue un rôle déterminant dans la diminution de l'empreinte énergétique globale de l'industrie des TIC (Technologies de l'information et de la communication). Elle permet également de diminuer les coûts énergétiques d'un produit ou d'un service. Les CDN (Content Delivery Networks) sont parmi les systèmes de distribution à grande échelle les plus populaires, dans lesquels les requêtes des clients sont transférées vers des serveurs et traitées par des serveurs proxy ou le serveur d'origine, selon la disponibilité des contenus et la politique de redirection des CDN. Par conséquent, notre objectif principal est de proposer et de développer des mécanismes basés sur la simulation afin de concevoir des politiques de redirection des CDN. Ces politiques prendront la décision dynamique de réduire la consommation d'énergie des CDN. Enfin, nous analyserons son impact sur l'expérience utilisateur. Nous commencerons par une modélisation de l'utilisation des serveurs proxy et un modèle de consommation d'énergie des serveurs proxy basé sur leur utilisation. Nous ciblerons les politiques de redirection des CDN en proposant et en développant des politiques d'équilibre et de déséquilibre des charges (en utilisant la loi de Zipf) pour rediriger les requêtes des clients vers les serveurs. Nous avons pris en compte deux techniques de réduction de la consommation d'énergie : le DVFS (Dynamic Voltage Frequency Scaling) et la consolidation de serveurs. Nous avons appliqué ces techniques de réduction de la consommation d'énergie au contexte d'un CDN (au niveau d'un serveur proxy), mais aussi aux politiques d'équilibre et de déséquilibre des charges afin d'économiser l'énergie. Afin d'évaluer les politiques et les mécanismes que nous proposons, nous avons mis l'accent sur la manière de rendre l'utilisation des ressources des CDN plus efficace, mais nous nous sommes également intéressés à leur coût en énergie, à leur impact sur l'expérience utilisateur et sur la qualité de la gestion des infrastructures. Dans ce but, nous avons défini comme métriques d'évaluation l'utilisation des serveurs proxy, d'échec des requêtes comme les paramètres les plus importants. Nous avons transformé un simulateur d'événements discrets CDNsim en Green CDNsim, et évalué notre travail selon différents scénarios de CDN en modifiant : les infrastructures proxy des CDN (nombre de serveurs proxy), le trafic (nombre de requêtes clients) et l'intensité du trafic (fréquence des requêtes client) en prenant d'abord en compte les métriques d'évaluation mentionnées précédemment. Nous sommes les premiers à proposer un DVFS et la combinaison d'un DVFS avec la consolidation d'un environnement de simulation de CDN en prenant en compte les politiques d'équilibre et de déséquilibre des charges. Nous avons conclu que les techniques d'économie d'énergie permettent de réduire considérablement la consommation d'énergie mais dégradent l'expérience utilisateur. Nous avons montré que la technique de consolidation des serveurs est plus efficace dans la réduction d'énergie lorsque les serveurs proxy ne sont pas beaucoup chargés. Dans le même temps, il apparaît que l'impact du DVFS sur l'économie d'énergie est plus important lorsque les serveurs proxy sont bien chargés. La combinaison des deux (DVFS et consolidation des serveurs) permet de consommer moins d'énergie mais dégrade davantage l'expérience utilisateur que lorsque ces deux techniques sont utilisées séparément
Explosive increase in Internet infrastructure and installation of energy hungry devices because of huge increase in Internet users and competition of efficient Internet services causing a great increase in energy consumption. Energy management in large scale distributed systems has an important role to minimize the contribution of Information and Communication Technology (ICT) industry in global CO2 (Carbon Dioxide) footprint and to decrease the energy cost of a product or service. Content distribution Networks (CDNs) are one of the popular large scale distributed systems, in which client requests are forwarded towards servers and are fulfilled either by surrogate servers or by origin server, depending on contents availability and CDN redirection policy. Our main goal is therefore, to propose and to develop simulation-based principled mechanisms for the design of CDN redirection policies which will do and carry out dynamic decisions to reduce CDN energy consumption and then to analyze its impact on user experience constraints to provide services. We started from modeling surrogate server utilization and derived surrogate server energy consumption model based on its utilization. We targeted CDN redirection policies by proposing and developing load-balance and load-unbalance policies using Zipfian distribution, to redirect client requests to servers. We took into account two energy reduction techniques, Dynamic Voltage Frequency Scaling (DVFS) and server consolidation. We applied these energy reduction techniques in the context of a CDN at surrogate server level and injected them in load-balance and load-unbalance policies to have energy savings. In order to evaluate our proposed policies and mechanisms, we have emphasized, how efficiently the CDN resources are utilized, at what energy cost, its impact on user experience and on quality of infrastructure management. For that purpose, we have considered surrogate server's utilization, energy consumption, energy per request, mean response time, hit ratio and failed requests as evaluation metrics. In order to analyze energy reduction and its impact on user experience, energy consumption, mean response time and failed requests are considered more important parameters. We have transformed a discrete event simulator CDNsim into Green CDNsim and evaluated our proposed work in different scenarios of a CDN by changing: CDN surrogate infrastructure (number of surrogate servers), traffic load (number of client requests) and traffic intensity (client requests frequency) by taking into account previously discussed evaluation metrics. We are the first who proposed DVFS and the combination of DVFS and consolidation in a CDN simulation environment, considering load-balance and loadunbalance policies. We have concluded that energy reduction techniques offer considerable energy savings while user experience is degraded. We have exhibited that server consolidation technique performs better in energy reduction while surrogate servers are lightly loaded. While, DVFS impact is more considerable for energy gains when surrogate servers are well loaded. Impact of DVFS on user experience is lesser than that of server consolidation. Combination of both (DVFS and server consolidation) presents more energy savings at higher cost of user experience degradation in comparison when both are used individually

Renewable energy generation is becoming a major part of energy supply, often in the form of distributed generation (DG) connected to distribution networks. While growth has been rapid, there is awareness that limitations on spare capacity within distribution (and transmission) networks is holding back development. Developments are being shelved until new network reinforcements can be built, which may make some projects non-viable. Reinforcements are costly and often underutilised, typically only loaded to their limits for a few occasions during the year. In order to accommodate new DG without the high costs or delays, active network management (ANM) is being promoted in which generation and other network assets are controlled within the limits of the existing network. There is a great deal of complexity and uncertainty associated with developing ANM and devising coherent plans to accommodate new DG is challenging for Distribution Network Operators (DNOs). As such, there is a need for robust network planning tools that can explicitly handle ANM and which can be trusted and implemented easily. This thesis describes the need for and the development of a new distribution expansion planning framework that provides DNOs with a better understanding of the impacts created by renewable DG and the value of ANM. This revolves around a heuristic planning framework which schedules necessary upgrades in power lines and transformers associated with changes in demand as well as those driven by the connection of DG. Within this framework a form of decentralised, adaptive control of DG output has been introduced to allow estimation of the impact of managing voltage and power flow constraints on the timing and need for network upgrades. The framework is initially deployed using simple scenarios but a further advance is the explicit use of time series to provide substantially improved estimates of the levels of curtailment implied by ANM. In addition, a simplified approach to incorporating demand side management has been deployed to facilitate understanding of the scope and role this may play in facilitating DG connections.

Building portfolio management on campus and metropolitan scale involves decisions about energy retrofits, energy resource pooling, and investments in shared energy systems, such as district cooling, community PV and wind power, CHP systems, geothermal systems etc. There are currently no tools that help a portfolio/campus manager make these decisions by rapid comparison of variants. The research has developed an energy supply network management tool at the campus scale. The underlying network energy performance (NEP) model uses (1) an existing energy performance toolkit to quantify the energy performance of building energy consumers on hourly basis, and (2) added modules to calculate hourly average energy generation from a wide variety of energy supply systems. The NEP model supports macro decisions at the generation side (decisions about adding or retrofitting campus wide systems) and consumption side (planning of new building design and retrofit measures). It allows testing different supply topologies by inspecting which consumer nodes should connect to which local suppliers and to which global suppliers, i.e. the electricity and gas utility grids. A prototype software implementation allows a portfolio or campus manager to define the demand and supply nodes on campus scale and manipulate the connections between them through a graphical interface. The NEP model maintains the network topology which is represented by a directed graph with the supply and demand nodes as vertices and their connections as arcs. Every change in the graph automatically triggers an update of the energy generation and consumption pattern, the results of which are shown on campus wide energy performance dashboards. The dissertation shows how the NEP model supports decision making with respect to large-scale building energy system design with a case study of the Georgia Tech campus evaluating the following three assertions: 1. The normative calculations at the individual building scale are accurate enough to support the network energy performance analysis 2. The NEP model supports the study of the tradeoffs between local building retrofits and campus wide energy interventions in renewable systems, under different circumstances 3. The NEP approach is a viable basis for routine campus asset management policies.

This thesis investigates the emergence, functioning and evolution of voluntary, informal networks of regulators. Via a combination of inductive and deductive reasoning, qualitative and quantitative methods, this research sheds light on thus far unexplored mechanisms of networked regulatory collaboration. These are: the conditions leading to spontaneous network emergence and consolidation into an institutional structure; the factors determining network members’ ties to each other; the strategies that network members deploy to ensure network survival; the conditions facilitating network entrepreneurship; and the role of informal networks in the implementation of foreign policy agendas. Through six empirical chapters, divided in three parts, this thesis explains why regulators network. The core argument is that regulators use networks as levers: they leverage their collective collaboration in order to obtain goals that are both individually and collectively desirable. The first part shows that they network for control: regulators form networks whenever they face concrete threats to the scope of their authority and the extent of their autonomy. The second part shows that regulators network for resources: similarity in the political economy and expertise explain the structure of regulators’ relationships together with resources, as regulators rely on their peers to compensate for their scarce staff numbers. The third part shows that regulators network for survival, and that the institutional integration of networks facilitates regulators’ network entrepreneurship. Further, it shows that international organisations and regulators deem informal networks capable of fostering policy change; hence, they export regulatory networks to target jurisdictions in the explicit attempt of replicating their success formula. The thesis accomplishes this ambitious research agenda by focusing on four empirical cases of transnational/trans-jurisdictional networks of energy regulators: the Council of European Energy Regulators (CEER), the National Association of Regulatory Utility Commissioners (NARUC) of the USA, and their respective progeny, i.e. the Association of Mediterranean Energy Regulators (MedReg) and the Energy Regional Regulatory Association (ERRA) of Central and Eastern Europe.

This thesis focuses on the design of network coding schemes and radio frequency (RF) energy transfer in wireless communication networks. During the past few years, network coding has attracted significant attention because of its capability to transmit maximum possible information in a network from multiple sources to multiple destinations via a relay. Normally, the destinations are only able to decode the information with sufficient prior knowledge. To enable the destinations to decode the information in the cases with less/no prior knowledge, a pattern of nested codes with multiple interpretations using binary convolutional codes is constructed in a multi-source multi-destination wireless relay network. Then, I reconstruct nested codes with convolutional codes and lattice codes in multi-way relay channels to improve the spectrum efficiency. Moreover, to reduce the high decoding complexity caused by the adopted convolutional codes, a network coded non-binary low-density generator matrix (LDGM) code structure is proposed for a multi-access relay system. Another focus of this thesis is on the design of RF-enabled wireless energy transfer (WET) schemes. Much attention has been attracted by RF-enabled WET technology because of its capability enabling wireless devices to harvest energy from wireless signals for their intended applications. I first configure a power beacon (PB)-assisted wireless-powered communication network (PB-WPCN), which consists of a set of hybrid access point (AP)-source pairs and a PB. Both cooperative and non-cooperative scenarios are considered, based on whether the PB is cooperative with the APs or not. Besides, I develop a new distributed power control scheme for a power splitting-based interference channel (IFC) with simultaneous wireless information and power transfer (SWIPT), where the considered IFC consists of multiple source-destination pairs.

Wireless networks are a popular means of communications in daily social and business activities of many users nowadays. However, current estimates indicate that wireless networks are expected to significantly contribute to the rapidly increasing energy consumption and carbon emissions of the Information and Communication Technologies (ICT) sector. Crucial factors leading to this trend are the continuous growth of wireless network infrastructure coupled with the increased number of user wireless devices equipped with various radio interfaces and batteries of extremely limited capacity (e.g., smartphones). The serious problem of energy consumption in wireless networks is mainly related to the current standard designs of wireless technologies. These approaches are based on a stack of protocol layers aiming to maximize performance-related metrics, such as throughput or Quality of Service (QoS), while paying less attention to energy efficiency. Although the focus has shifted to energy efficiency recently, most of the existing wireless solutions achieve energy savings at the cost of some performance degradation.This thesis aims at contributing to the evolution of green wireless networks by exploring new approaches for energy saving at the Medium Access Control (MAC) protocol layer and the combination of these with the integration of the Network Coding (NC) paradigm into the wireless network protocol stack for further energy savings. The main contributions of the thesis are divided into two main parts. The first part of the thesis is focused on the design and performance analysis and evaluation of novel energy-efficient distributed and centralized MAC protocols for Wireless Local Area Networks (WLANs). The second part of the thesis turns the focus to the design and performance analysis and evaluation of new NC-aware energy- efficient MAC protocols for wireless ad hoc networks. The key idea of the proposed mechanisms is to enable multiple data exchanges (with or without NC data) among wireless devices and allow them to dynamically turn on and off their radio transceivers (i.e., duty cycling) during periods of no transmission and reception (i.e., when they are listening or overhearing). Validation through analysis, computer-based simulation, and experimentation in real hardware shows that the proposed MAC solutions can significantly improve both the throughput and energy efficiency of wireless networks, compared to the existing mechanisms of the IEEE 802.11 Standard when alone or combined with the NC approach. Furthermore, the results presented in this dissertation help understand the impact of the on/off transitions of radio transceivers on the energy efficiency of MAC protocols based on duty cycling. These radio transitions are shown to be critical when the available time for sleeping is comparable to the duration of the on/off radio transitions.

Wireless networks are a popular means of communications in daily social and business activities of many users nowadays. However, current estimates indicate that wireless networks are expected to significantly contribute to the rapidly increasing energy consumption and carbon emissions of the Information and Communication Technologies (ICT) sector. Crucial factors leading to this trend are the continuous growth of wireless network infrastructure coupled with the increased number of user wireless devices equipped with various radio interfaces and batteries of extremely limited capacity (e.g., smartphones). The serious problem of energy consumption in wireless networks is mainly related to the current standard designs of wireless technologies. These approaches are based on a stack of protocol layers aiming to maximize performance-related metrics, such as throughput or Quality of Service (QoS), while paying less attention to energy efficiency. Although the focus has shifted to energy efficiency recently, most of the existing wireless solutions achieve energy savings at the cost of some performance degradation.This thesis aims at contributing to the evolution of green wireless networks by exploring new approaches for energy saving at the Medium Access Control (MAC) protocol layer and the combination of these with the integration of the Network Coding (NC) paradigm into the wireless network protocol stack for further energy savings. The main contributions of the thesis are divided into two main parts. The first part of the thesis is focused on the design and performance analysis and evaluation of novel energy-efficient distributed and centralized MAC protocols for Wireless Local Area Networks (WLANs). The second part of the thesis turns the focus to the design and performance analysis and evaluation of new NC-aware energy- efficient MAC protocols for wireless ad hoc networks. The key idea of the proposed mechanisms is to enable multiple data exchanges (with or without NC data) among wireless devices and allow them to dynamically turn on and off their radio transceivers (i.e., duty cycling) during periods of no transmission and reception (i.e., when they are listening or overhearing). Validation through analysis, computer-based simulation, and experimentation in real hardware shows that the proposed MAC solutions can significantly improve both the throughput and energy efficiency of wireless networks, compared to the existing mechanisms of the IEEE 802.11 Standard when alone or combined with the NC approach. Furthermore, the results presented in this dissertation help understand the impact of the on/off transitions of radio transceivers on the energy efficiency of MAC protocols based on duty cycling. These radio transitions are shown to be critical when the available time for sleeping is comparable to the duration of the on/off radio transitions.

Depuis quelques années, les réseaux optiques sur puce (ONoC) sont devenus une solution intéressante pour surpasser les limitations des interconnexions électriques, compte tenu de leurs caractéristiques attractives concernant la consommation d’énergie, le délai de transfert et la bande passante. Cependant, les éléments optiques nécessaires pour définir un tel réseau souffrent d’imperfections qui introduisent des pertes durant les communications. De plus, l'utilisation de la technique de multiplexage en longueurs d'ondes (WDM) permet d'augmenter les performances, mais introduit de nouvelles pertes et de la diaphonie entre les longueurs d'ondes, ce qui a pour effet de réduire le rapport signal sur bruit et donc la qualité de la communication. Les contributions présentées dans ce manuscrit adressent cette problématique d’amélioration de performance des liens optiques dans un ONoC. Pour cela, nous proposons tout d’abord un modèle analytique des pertes et de la diaphonie dans un réseau optique sur puce WDM. Nous proposons ensuite une méthodologie pour améliorer les performances globales du système s'appuyant sur l'utilisation de codes correcteurs d'erreurs. Nous présentons deux types de codes, le premier(Hamming) est d'une complexité d'implémentation faible alors que le second(Reed-Solomon) est plus complexe, mais offre un meilleur taux de correction. Nous avons implémenté des blocs matériels supportant ces corrections d'erreurs avec une technologie 28nm FDSOI. Finalement, nous proposons la définition d'une interface complète entre le domaine électrique et le domaine optique permettant d'allouer les longueurs d'ondes, de coder l'information, de sérialiser le flux de données et de contrôler le driver du laser pour obtenir la modulation à la puissance optique souhaitée
Electrical Network-on-Chip (ENoC) has long been considered as the de facto technology for interconnects in multiprocessor systems-on-chip (MPSoCs). However, with the increase of the number of cores integrated on a single chip, ENoCs are less and less suitable to adapt the bandwidth and latency requirements of nowadays complex and highly-parallel applications. In recent years, due to power consumption constraint, low latency, and high data bandwidth requirements, optical interconnects became an interesting solution to overcome these limitations. Indeed, Optical Networks on Chip (ONoC) are based on waveguides which drive optical signals from source to destination with very low latency. Unfortunately, the optical devices used to built ONoCs suffer from some imperfections which introduce losses during communications. These losses (crosstalk noises and optical losses) are very important factors which impact the energy efficiency and the performance of the system. Furthermore, Wavelength Division Multiplexing (WDM) technology can help the designer to improve ONoC performance, especially the bandwidth and the latency. However, using the WDM technology leads to introduce new losses and crosstalk noises which negatively impact the Signal to Noise Ratio (SNR) and Bit Error Rate (BER). In detail, this results in higher BER and increases power consumption, which therefore reduces the energy efficiency of the optical interconnects. The contributions presented in this manuscript address these issues. For that, we first model and analyze the optical losses and crosstalk in WDM based ONoC. The model can provide an analytical evaluation of the worst case of loss and crosstalk with different parameters for optical ring network-on-chip. Based on this model, we propose a methodology to improve the performance and then to reduce the power consumption of optical interconnects relying on the use of forward error correction (FEC). We present two case studies of lightweight FEC with low implementation complexity and high error-correction performance under 28nm Fully-Depleted Silicon-On-Insulator (FDSOI) technology. The results demonstrate the advantages of using FEC on the optical interconnect in the context of the CHAMELEON ONoC. Secondly, we propose a complete design of Optical Network Interface (ONI) which is composed of data flow allocation, integrated FECs, data serialization/deserialization, and control of the laser driver. The details of these different elements are presented in this manuscript. Relying on this network interface, an allocation management to improve energy efficiency can be supported at runtime depending on the application demands. This runtime management of energy vs. performance can be integrated into the ONI manager through configuration manager located in each ONI. Finally, the design of an ONoC configuration sequencer (OCS), located at the center of the optical layer, is presented. By using the ONI manager, the OCS can configure ONoC at runtime according to the application performance and energy requirements

Interconnection networks represent the backbone of large-scale parallel systems. In order to build ultra-scale supercomputers larger interconnection networks are being designed and deployed. As compute nodes become more energy-efficient, the interconnect is accounting for an increasing proportion of the total system energy consumption. The interconnect's energy consumption is, however, only starting to receive serious attention. Most of this power consumption is due to the interconnection links. The problem, in terms of power, of an interconnect link is that its power consumption is almost constant, whether or not it is actively exchanging data, since both ends stay active to mantain synchronization. This thesis complements ongoing efforts related to power reduction and energy proportionality of the interconnection network. The thesis contemplates two directions for power savings in the interconnection network; one is the possibility to use lower bandwidth links during the communication phases and thus save energy, while the second one addresses shifting links to low-power mode during computation phases when they are unused. To address the first one we investigate the potential benefits from MPI data compression. When compression of MPI data is possible, the reduction in link bandwidth is enabled without incurring any performance penalty. Consecutively, lower bandwidth leads to lower link energy consumption. In the past, several compression techniques have been proposed as a way to improve the performance and scalability of parallel applications. Those works have shown significant speed-ups when applying compressors to the MPI transfers of certain algorithmic kernels. However, these techniques have not seen widespread adoptation in current supercomputers. In this thesis we will show that although data compression naturally leads to improved performance, the benefit is small, for modern high-performance networks, and it varies greatly between applications. In contrast, combining data compression with switching to low-power mode preserves performance while delivering effective and consistent energy savings, in proportion with the reduction in data rate. In general, application developers view time spent in a communication as an overhead, and therefore strive to keep it at minimum. This leads to high peak bandwidth demand and latency sensitivity, but low average utilization, which provides significant opportunities for energy savings. It is therefore possible to save energy using low-power modes, but link wake-up latencies must not lead to a loss in performance. Thus, we propose a mechanism that can accurately predict when links are idle, allowing them to be switched to more power efficient mode. Our runtime system called the Pattern Prediction System (PPS) can accurately predict not only when a link will become unused but also when it will become active again, allowing links to be switched off during the idle periods and switched back on again in time to avoid incurring a significant performance degradation. Many HPC application benefit from prediction, since they have repetitive computation and communication phases. By implementing the energy-saving mechanisms inside the MPI library, existing MPI programs do not need to be modified. We also develop more advanced version of the prediction system, Self-Tuned Pattern Prediction System (SPPS) which is capable of automatically tuning to the current application communication characteristic and shaping the switching on/off of the links in the most appropriate way. The proposed compression and prediction techniques are evaluated using an event-driven simulator, which is able to replay the traces from real execution of MPI applications. Experimental results show significant energy savings in the IB links while the performance overhead due to wake-up latencies and additional computation time have negligible effects on the final application performance.
En los últimos años, el consumo de energia en la red de interconexión se esta considerando como uno de los factores que pueden condicionar la carrera hacia los sistemas Exascale. En la red de interconexion, la mayor parte de este consumo de energía se debe a los enlaces de red, cuyo consumo permanece constante independientemente de si los datos se intercambian de forma activa, dado que ambos extremos deben de permanecer activos para poder mantener la sincronización. Esta tesis complementa los esfuerzos de investigación que actualmente se estan llevando a cabo a nivel internacional con el objetivo de reducir la potencia y conseguir una proporcionalidad de consumo de energía con respecto al ancho de banda requerido en las comunicaciones. En esta tesis se contemplan dos direcciones complementarias para conseguir dichos objetivos: por un lado, la posibilidad de usar sólo el ancho de banda necesario durante las fases de comunicación; y por lo tanto usar el modo de bajo consumo durante las fases de computación en las que no se requiere de la red de interconexión. Para abordar la primera de ellas se investiga los posibles beneficios de usar compresión en los datos que se transfieren en los mensajes MPI. Cuando ello es posible, se puede realizar la comunicación con una menor necesidad de ancho de banda de los enlaces sin que necesariamente se produzca una penalizacion en el rendimiento de la aplicación. Varias técnicas de compresión han sido propuestas en la literatura con el objetivo de reducir el tiempo de comunicación y la escalabilidad de las aplicaciones paralelas. Aunque estas técnicas han mostrado un potencial importante en ciertos nucleos computacionales, su adopción en sistemas reales no se ha llevado a cabo. En esta tesis, se muestra como el uso de la compresión de datos en los mensajes MPI puede permitir una reducción en el consumo de energia, reduciendo el número de enlaces activos que son requeridos para realizar la comunicación, en proporción a la reducción de los bytes que deben de ser transferidos. En general, los desarrolladores de aplicaciones consideran el tiempo pasado en la comunicación como un gasto innecesario, y por lo tanto se esfuerzan en mantenerlo al mínimo. Esto lleva a una demanda de un ancho de banda que puede afrontar el pico de alto trafico y de una sensibilidad a la latencía, pero con una utilización mediana baja, lo que ofrece unas oportunidades significativas para el ahorro de energía. Por lo tanto, es posible ahorrar la energía apoyándose en los modos de bajo consumo, pero las latencias de reactivación de los enlaces no deben producir una pérdida en el rendimiento. En esta tesis doctoral se propone un mecanismo que permite predecir con exactitud los periodos de inactividad de los enlaces, lo que permitirá pasarlos al modo más eficiente de energía que disponga la infraestructura de red. La propuesta en esta tesis doctoral actua en tiempo de ejecución y se denomina Sistema de Predicción de Patrones (SPP). SPP permite predecir con exactitud no sólo cuando un enlace llega a ser no usado, sino también cuando se requiere de nuevo su reactivación, permitiendo que los enlaces entren en modo de bajo consumo durante los periodos de inactividad y se vuelven de nuevo activos a tiempo evitando provocar una degradación significativa en el rendimiento. Muchas aplicaciones de HPC (High-Performance Computing) pueden beneficiarse de esta predicción, ya que tienen fases de computación y de comunicación repetitivas. Mediante la implementación de los mecanismos de ahorro de energía dentro de la libreria MPI, los programas MPI existentes no requiren ninguna modificación. En la tesis, tambien desarrollamos una version más avanzada del sistema de predicción que dominamos como el Sistema de Prediccion de Patrones con Ajustes Automáticos (SPPA) que además permite ajustar de forma autónoma uno de los parámetros importantes de SPP que determina el grado de agregación de mensajes en el algoritmo de predicción

During the last decades, mobile network operators have witnessed an exponential increase in the traffic demand, mainly due to the high request of services from a huge amount of users. The trend is of a further increase in both the traffic demand and the number of connected devices over the next years. The traffic load is expected to have an annual growth rate of 53% for the mobile network alone, and the upcoming industrial era, which will connect different types of devices to the mobile infrastructure including human and machine type communications, will definitely exacerbate such an increasing trend. The current directions anticipate that future mobile networks will be composed of ultra dense deployments of heterogeneous Base Stations (BSs), where BSs using different transmission powers coexist. Accordingly, the traditional Macro BSs layer will be complemented or replaced with multiple overlapping tiers of small BSs (SBSs), which will allow extending the system capacity. However, the massive use of Information and Communication Technology (ICT) and the dense deployment of network elements is going to increase the level of energy consumed by the telecommunication infrastructure and its carbon footprint on the environment. Current estimations indicates that 10% of the worldwide electricity generation is due to the ICT industry and this value is forecasted to reach 51% by 2030, which imply that 23% of the carbon footprint by human activity will be due to ICT. Environmental sustainability is thus a key requirement for designing next generation mobile networks. Recently, the use of Renewable Energy Sources (RESs) for supplying network elements has attracted the attention of the research community, where the interest is driven by the increased efficiency and the reduced costs of energy harvesters and storage devices, specially when installed to supply SBSs. Such a solution has been demonstrated to be environmentally and economically sustainable in both rural and urban areas. However, RESs will entail a higher management complexity. In fact, environmental energy is inherently erratic and intermittent, which may cause a fluctuating energy inflow and produce service outage. A proper control of how the energy is drained and balanced across network elements is therefore necessary for a self-sustainable network design. In this dissertation, we focus on energy harvested through solar panels that is deemed the most appropriate due to the good efficiency of commercial photovoltaic panels as well as the wide availability of the solar source for typical installations. The characteristics of this energy source are analyzed in the first technical part of the dissertation, by considering an approach based on the extraction of features from collected data of solar energy radiation. In the second technical part of the thesis we introduce our proposed scenario. A federation of BSs together with the distributed harvesters and storage devices at the SBS sites form a micro-grid, whose operations are managed by an energy management system in charge of controlling the intermittent and erratic energy budget from the RESs. We consider load control (i.e., enabling sleep mode in the SBSs) as a method to properly manage energy inflow and spending, based on the traffic demand. Moreover, in the third technical part, we introduce the possibility of improving the network energy efficiency by sharing the exceeding energy that may be available at some BS sites within the micro-grid. Finally, a centralized controller based on supervised and reinforcement learning is proposed in the last technical part of the dissertation. The controller is in charge of opportunistically operating the network to achieve efficient utilization of the harvested energy and prevent SBSs blackout.
Durante las últimas décadas, los operadores de redes móviles han sido testigos de un aumento exponencial en la demanda de tráfico, principalmente debido a la gran solicitud de servicios de una gran cantidad de usuarios. La tendencia es un aumento adicional tanto en la demanda de tráfico como en la cantidad de dispositivos conectados en los próximos años. Se espera que la carga de tráfico tenga una tasa de crecimiento anual del 53% solo para la red móvil, y la próxima era industrial, que conectará diferentes tipos de dispositivos a la infraestructura móvil, definitivamente exacerbará tal aumento. Las instrucciones actuales anticipan que las redes móviles futuras estarán compuestas por despliegues ultra densos de estaciones base (BS) heterogéneas. En consecuencia, la capa tradicional de Macro BS se complementará o reemplazará con múltiples niveles superpuestos de pequeños BS (SBS), lo que permitirá ampliar la capacidad del sistema. Sin embargo, el uso masivo de la Tecnología de la Información y la Comunicación (TIC) y el despliegue denso de los elementos de la red aumentará el nivel de energía consumida por la infraestructura de telecomunicaciones y su huella de carbono en el medio ambiente. Las estimaciones actuales indican que el 10% de la generación mundial de electricidad se debe a la industria de las TIC y se prevé que este valor alcance el 51% para 2030, lo que implica que el 23% de la huella de carbono por actividad humana se deberá a las TIC. La sostenibilidad ambiental es, por lo tanto, un requisito clave para diseñar redes móviles de próxima generación. Recientemente, el uso de fuentes de energía renovables (RES) para suministrar elementos de red ha atraído la atención de la comunidad investigadora, donde el interés se ve impulsado por el aumento de la eficiencia y la reducción de los costos de los recolectores y dispositivos de almacenamiento de energía, especialmente cuando se instalan para suministrar SBS. Se ha demostrado que dicha solución es ambiental y económicamente sostenible tanto en áreas rurales como urbanas. Sin embargo, las RES conllevarán una mayor complejidad de gestión. De hecho, la energía ambiental es inherentemente errática e intermitente, lo que puede causar una entrada de energía fluctuante y producir una interrupción del servicio. Por lo tanto, es necesario un control adecuado de cómo se drena y equilibra la energía entre los elementos de la red para un diseño de red autosostenible. En esta disertación, nos enfocamos en la energía cosechada a través de paneles solares que se considera la más apropiada debido a la buena eficiencia de los paneles fotovoltaicos comerciales, así como a la amplia disponibilidad de la fuente solar para instalaciones típicas. Las características de esta fuente de energía se analizan en la primera parte técnica de la disertación, al considerar un enfoque basado en la extracción de características de los datos recopilados de radiación de energía solar. En la segunda parte técnica de la tesis presentamos nuestro escenario propuesto. Una federación de BS junto con los cosechadores distribuidos y los dispositivos de almacenamiento forman una microrred, cuyas operaciones son administradas por un sistema de administración de energía a cargo de controlar el presupuesto de energía intermitente y errático de las RES. Consideramos el control de carga como un método para administrar adecuadamente la entrada y el gasto de energía, en función de la demanda de tráfico. Además, en la tercera parte técnica, presentamos la posibilidad de mejorar la eficiencia energética de la red al compartir la energía excedente que puede estar disponible en algunos sitios dentro de la microrred. Finalmente, se propone un controlador centralizado basado en aprendizaje supervisado y de refuerzo en la última parte técnica de la disertación. El controlador está a cargo de operar la red para lograr una utilización eficiente de energía y previene el apagón de SBS

Wireless sensors networks are used in a variety of environments ranging from environment

monitoring such as humidity and temperature, to environments like patient monitoring, habitat

monitoring etc. Sometimes sensors are deployed in inaccessible or hazardous places, and they

are battery operated; recharging or changing the sensor’s battery is almost impossible.

In such scenarios, where the battery can not be recharged or changed, it is crucial to know in

advance how long the battery will last so that the old sensor node can be replaced by a new

one. Normally, in order to effectively utilize the battery the components of a wireless sensor

node are turned off when not needed.

This paper presents an in-depth analysis of the importance of switching sensor node

components, and its impact on the life time prediction. A new energy model is presented

which caters for the current and time consumed in switching from one mode to another. A

comparison is made between scenarios where current consumption while switching is catered

with the one where it is not catered. This was achieved by using on chip fuel gauge, with

some limitation, which was verified by using digital multimeter.

The scaling of MOS transistors into the nanometer regime opens the possibility for creating large Network-on-Chip (NoC) architectures containing hundreds of integrated processing elements with on-chip communication. NoC architectures, with structured on-chip networks are emerging as a scalable and modular solution to global communications within large systems-on-chip. NoCs mitigate the emerging wire-delay problem and addresses the need for substantial interconnect bandwidth by replacing today’s shared buses with packet-switched router networks. With on-chip communication consuming a significant portion of the chip power and area budgets, there is a compelling need for compact, low power routers. While applications dictate the choice of the compute core, the advent of multimedia applications, such as three-dimensional (3D) graphics and signal processing, places stronger demands for self-contained, low-latency floating-point processors with increased throughput. This work demonstrates that a computational fabric built using optimized building blocks can provide high levels of performance in an energy efficient manner. The thesis details an integrated 80- Tile NoC architecture implemented in a 65-nm process technology. The prototype is designed to deliver over 1.0TFLOPS of performance while dissipating less than 100W. This thesis first presents a six-port four-lane 57 GB/s non-blocking router core based on wormhole switching. The router features double-pumped crossbar channels and destinationaware channel drivers that dynamically configure based on the current packet destination. This enables 45% reduction in crossbar channel area, 23% overall router area, up to 3.8X reduction in peak channel power, and 7.2% improvement in average channel power. In a 150-nm sixmetal CMOS process, the 12.2 mm2 router contains 1.9-million transistors and operates at 1 GHz at 1.2 V supply. We next describe a new pipelined single-precision floating-point multiply accumulator core (FPMAC) featuring a single-cycle accumulation loop using base 32 and internal carry-save arithmetic, with delayed addition techniques. A combination of algorithmic, logic and circuit techniques enable multiply-accumulate operations at speeds exceeding 3GHz, with singlecycle throughput. This approach reduces the latency of dependent FPMAC instructions and enables a sustained multiply-add result (2FLOPS) every cycle. The optimizations allow removal of the costly normalization step from the critical accumulation loop and conditionally powered down using dynamic sleep transistors on long accumulate operations, saving active and leakage power. In a 90-nm seven-metal dual-VT CMOS process, the 2 mm2 custom design contains 230-K transistors. Silicon achieves 6.2-GFLOPS of performance while dissipating 1.2 W at 3.1 GHz, 1.3 V supply. We finally present the industry's first single-chip programmable teraFLOPS processor. The NoC architecture contains 80 tiles arranged as an 8×10 2D array of floating-point cores and packet-switched routers, both designed to operate at 4 GHz. Each tile has two pipelined singleprecision FPMAC units which feature a single-cycle accumulation loop for high throughput. The five-port router combines 100 GB/s of raw bandwidth with low fall-through latency under 1ns. The on-chip 2D mesh network provides a bisection bandwidth of 2 Tera-bits/s. The 15-FO4 design employs mesochronous clocking, fine-grained clock gating, dynamic sleep transistors, and body-bias techniques. In a 65-nm eight-metal CMOS process, the 275 mm2 custom design contains 100-M transistors. The fully functional first silicon achieves over 1.0TFLOPS of performance on a range of benchmarks while dissipating 97 W at 4.27 GHz and 1.07-V supply. It is clear that realization of successful NoC designs require well balanced decisions at all levels: architecture, logic, circuit and physical design. Our results demonstrate that the NoC architecture successfully delivers on its promise of greater integration, high performance, good scalability and high energy efficiency.

Noise pollution is becoming an increasing concern in many urban regions all over the world. An important step in fighting and mitigating noise pollution is its quantification. Wireless sensor networks (WSNs) can potentially help with these efforts, as they enable the simultaneous and continuous gathering of data over wide geographic regions. The need to replace batteries however makes the maintenance of such physically very large networks impractical. As an alternative to batteries, noise-sensing WSNs could also be powered by energy harvesting. While energy-harvesting WSNs have been demonstrated before, utilizing energy harvesting for powering noise-sensing WSNs still pose a significant challenge because of application’s unique requirements, such as a high power consumption profile for extended periods of time. In this thesis, we address four key areas of research necessary on to make energy-harvesting noise-sensing WSNs possible and, more importantly, practical to use in large-scale settings. The first key area that we address is that of new and emerging energy storage technologies, and how current algorithms and infrastructures must be modified to take advantage of them. The second key area is that of currently-accepted technical requirements, and their assessment on whether they would indeed lead to the attainment of long-term goals. The third key area is that of test methodologies for energy-harvesting designs, and how they should be modified to facilitate validation of results between researchers. The final key area is that of techniques and algorithms for future capabilities that energy-harvesting noise-sending WSNs will or can have, and how we should prepare for them, even though they may not yet exist. We provide research to support all four key areas in this work and provide concrete examples for each.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 73-78).
Network Coding (NC) has been shown to provide several advantages in communication networks in terms of throughput, data robustness and security. However, its applicability to networks with resource constrained nodes, like Body Area Networks (BANs), has been questioned due to its complexity requirements. Proposed NC implementations are based on high-end CPUs and GPUs, consuming hundreds of Watts, without providing enough insight about its energy requirements. As more and more mobile devices, sensors and other low power systems are used in modern communication protocols, a highly efficient and optimized implementation of NC is required. In this work, an effort is made to bridge NC theory with ultra low power applications. For this reason, an energy-scalable, low power accelerator is designed in order to explore the minimum energy requirements of NC. Based on post-layout simulation results using a TSMC 65nm process, the proposed encoder consumes 22.15 uW at 0.4V, achieving a processing throughput of 80 MB/s. These numbers reveal that NC can indeed be incorporated into resource constrained networks with battery-operated or even energy scavenging nodes. Apart from the hardware design, a new partial packet recovery mechanism based on NC, called PPRNC, is proposed. PPRNC exploits information contained in partial packets, similarly to existing Hybrid-ARQ schemes, but with a PHY-agnostic approach. Minimization of the number of retransmitted packets saves transmission energy and results in higher total network throughput, making PPRNC an attractive candidate for energy constrained networks, such as BANs, as well as modern, high-speed wireless mesh networks. The proposed mechanism is analyzed and implemented using commercial development boards, validating its ability to extract information contained from partial packets.
by Georgios Angelopoulos.
S.M.

ITC/USA 2012 Conference Proceedings / The Forty-Eighth Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2012 / Town and Country Resort & Convention Center, San Diego, California
Systems that monitor environments often rely on cumbersome wires to supply power to the sensing equipment or batteries that require monitoring and replacement. As technologies continue to advance, the use of self-sustaining, wireless powering becomes more essential to satisfy challenging requirements that necessitate continuous measurement and general functionality. This paper focuses on the creation of a wireless sensor network with emphasis on the implementation of wirelessly charged sensing nodes by utilizing microwaves. Three subsystems make up this "proof of concept" wireless sensor system: a power transmitting base station, three sensor nodes, and a communication base station. Interfacing and power regulation are of the utmost importance in order to ensure all of the subsystems are able to communicate with one another and power all necessary functions. The power transmitting base station transmits microwaves to the nodes. A rectenna on each node converts the transmitted microwaves into DC power. Each node contains sensors to monitor the temperature and light of the environment. For the communication aspect of the system, Zigbee protocol, which belongs to IEEE 802.15.4 protocol, is used fore wireless communication between the base station and the nodes. Through the combination of power regulation, microwave energy, and radio transmission, users are able to utilize this system to collect environmental sensor data wirelessly.

With the addition of mesh capability to Bluetooth low energy(BLE) in 2017 new possibilities open up for the Internet of Things applications of Bluetooth. With the rapidly increasing number of connected devices a few new standards are competing for being the standard protocol for low power mesh communication. BLE is mostly aimed towards low bandwidth data such as sensor readings or light control. However, this thesis attempts to investigate the viability of adapting BLE mesh nodes to communicate DMX-data which is a protocol widely used in lightning and stage effects. The system is implemented on Bluetooth development kits and the latency and power consumption are measured. The results show that the latency is significant and with high variance if the full DMX frame is transmitted, rendering the application non-applicable on many real-time applications. It can however be justified in some applications due to Bluetooth's well established eco-system of devices and functionality where the nodes could extend their capabilities by implementing already established BLE models. By only transmitting the updated channels the latency can be lowered to values that would in some applications be indistinguishable from wired connection. The energy consumption of BLE mesh suffers greatly with the addition of mesh due to its constant scanning but by implementing low power nodes which keep the radio off during certain intervals this consumption could be greatly decreased. The results also show a high variance of latency depending on the node configuration regarding to the placements and the number of hops required to reach the intended recipient.
Bluetooth har länge varit standardprotokollet för kommunikation mellan två stycken enheter. 2017 kom tillägget med mesh till Bluetooth. Mesh innebär att andra enheten i närheten ska skicka vidare meddelanden och därigenom tillåta kommunikation mellan enheter som är utanför direkt radiokontakt. DMX är ett protokoll som används inom ljus- och sceneffekter. Bluetooth mesh är utformat för att skicka små datamängder som till exempel sensordata eller styra glödlampor. Denna uppsats kommer utvärdera om det är användbart att skicka DMX-data över Bluetooth mesh. En implementation gjordes på Bluetooth utvecklingskort och resultatet visar på en signifikant fördröjning och med hög varians vid överföring av alla DMX-kanaler, vilket innebär att denna implementation inte är användbar vid många användningsområden. Men trots det kan den vid vissa fall vara användningsbar, mycket till hjälp av Bluetooths billiga och utbyggda ekosystem av produkter och tilläggsfunktioner. Eftersom Bluetooth mesh byggs in i en del befintliga byggnader kan de uppoffringar man får göra vid överföringar av DMX-data vara acceptabel då man kan uttnyttja befintliga nät. Strömförbrukningen ökar avsevärt vid mesh jämfört med klassisk lågenergi Bluetooth då mesh måste skanna radiotrafiken konstant. Vid implementationen av lågenergi noder kan dock radio vara i stand-by och starta endast vid speciella tidpunkter och man kan därigenom få avsevärt lägre strömförbrukning, med uppoffringen att DMX-datan inte kan överföras omgående. Det visade sig också att noduppställningen kraftigt påverkade variansen i överföringshastighet och att detta måste ta i hänsyn vid valet om DMX över Bluetooth mesh är användbart i just det fallet.

Artificial Neural Network as a universal function approximators can be used for mapping any nonlinear function. Used in different fields of application (congnitive science, engineering, biology, finance..), ANN have become popular in finance for their power in pattern recognition, classification and forecasting. This paper specifically examines the used of ANN in the energy market in order to build a forecast price on the energy commodities. A brief study on the feature of the energy market, in particular crude oil and natural gas prices, will be followed by an implementation of an ANN system for the forecast. Finally a comparison between a real and estimated price will be done to see if the ANN could be considered a good forecasting tool also in the energy market.

Modern data centers host hundreds of thousands of servers to achieve economies of scale. Such a huge number of servers create challenges for the data center network (DCN) to provide proportionally large bandwidth. In addition, the deployment of virtual machines (VMs) in data centers raises the requirements for efficient resource allocation and find-grained resource sharing. Further, the large number of servers and switches in the data center consume significant amounts of energy. Even though servers become more energy efficient with various energy saving techniques, DCN still accounts for 20% to 50% of the energy consumed by the entire data center. The objective of this dissertation is to enhance DCN performance as well as its energy efficiency by conducting optimizations on both host and network sides. First, as the DCN demands huge bisection bandwidth to interconnect all the servers, we propose a parallel packet switch (PPS) architecture that directly processes variable length packets without segmentation-and-reassembly (SAR). The proposed PPS achieves large bandwidth by combining switching capacities of multiple fabrics, and it further improves the switch throughput by avoiding padding bits in SAR. Second, since certain resource demands of the VM are bursty and demonstrate stochastic nature, to satisfy both deterministic and stochastic demands in VM placement, we propose the Max-Min Multidimensional Stochastic Bin Packing (M3SBP) algorithm. M3SBP calculates an equivalent deterministic value for the stochastic demands, and maximizes the minimum resource utilization ratio of each server. Third, to provide necessary traffic isolation for VMs that share the same physical network adapter, we propose the Flow-level Bandwidth Provisioning (FBP) algorithm. By reducing the flow scheduling problem to multiple stages of packet queuing problems, FBP guarantees the provisioned bandwidth and delay performance for each flow. Finally, while DCNs are typically provisioned with full bisection bandwidth, DCN traffic demonstrates fluctuating patterns, we propose a joint host-network optimization scheme to enhance the energy efficiency of DCNs during off-peak traffic hours. The proposed scheme utilizes a unified representation method that converts the VM placement problem to a routing problem and employs depth-first and best-fit search to find efficient paths for flows.

Wireless Sensor Networks (WSNs) have been widely studied in the last decade because of the large set of applications that can be potentially enabled by this novel network paradigm, as environmental monitoring, home automation, localization and tracking of mobile users, seamless and ubiquitous data exchange. However, the severe constraints in terms of energy, processing, memory and reliability of the low--cost sensor devices left a number of unresolved problems, open to research. This thesis tackles two of the most interesting problems concerning WSNs, namely localization and traffic management. Accurate sensor localization is crucial for a wide variety of WSN applications and protocols, including monitoring, routing, scheduling, data fusion and so on. Typically, localization algorithms are based on an infrastructure of nodes which are aware of their geographical positions, called beacons. These nodes broadcast their coordinates in order to let the other nodes in the network, referred to as stray nodes, infer their own position by means of some estimation technique. The topic has been widely investigated, both in simulation and, more recently, in experimental testbeds. Nonetheless, the performance obtained by most of the proposed algorithms is still unsatisfactory, in particular in indoor environments. Therefore, further research is needed. In this thesis, the problem has been tackled from different perspectives, in order to gain a deep and clear understanding of the several facets that characterize this interesting domain. As a consequence, we collected a rather wide set of results that apparently may not seem to be strongly correlated, though they all fit within the same research project. As a first step, we compare well known localization algorithms in indoor environments for static networks, based on a Received Signal Strength Indicator (RSSI) ranging estimation technique. Results shed light on the actual potentialities and limits of common localization algorithms in indoor environments in a real testbed. In particular, we observed the strong impact of the shadowing random attenuation of the power of the received signal on the performance of the localization algorithms. Therefore, research has been addressed to the reduction of the shadowing term in the RSSI measures. To this end, we investigated the effect of the carrier frequency and of the antenna anisotropy on the randomness of the shadowing component, again using real measurements collected in different testbeds. Successively, our attention turned to the problem of beacon positioning that we observed may strongly affect the localization performance. We analyzed the optimal beacons placement both using an exhaustive but very complex approach and a heuristic scheme that provides close to optimal solutions while maintaining a linear complexity with the number of beacons. Looking at the localization performance separating the different effects of localization algorithms, channel parameters and beacon positioning, has been important to understand the contribution of each one of these aspects to the localization error and how much is it possible to improve the localization accuracy by means of a single technique, that usually is chosen depending on the particular scenario and available resources. Then nodes mobility has been included into the framework. We first considered an Autonomous Mobile Robot (AMR) that can interact with sensors, but is also capable to self--localize using onboard odometry. Leveraging on the complementarities of WSN and AMR, we considered the Simultaneous Localization and Mapping (SLAM) problem that consists in creating the map of an area without any a priori knowledge of the environment, while localizing the nodes in the WSN by combining the information provided by the WSN and by the AMR odometry. Second, we considered a completely mobile wireless networks in which heterogeneous nodes with different self--localization capabilities can interact one another on an opportunistic basis, exchanging localization information with other nodes that occasionally happen to be in geographical proximity. The performance of this scheme has been analyzed through a mathematical framework. We considered a Maximum Likelihood (ML) approach, a Linear Matrix Inequality (LMI) system and a simple heuristic strategy to define opportunistic localization algorithms. The validity of the mathematical model has been confirmed through experimental measures. We considered two main settings, one in which a node can rely on a single opportunistic interaction and one in which multiple contacts can be set while the node remains in the same position. We analyzed the different techniques, finding that in the first scenario, if the channel is not very noisy and the self--localization of the cooperative node quite accurate, the heuristic algorithm performs very well, in some case slightly better than ML, while the ML approach is very robust and improves localization accuracy even in difficult scenarios. If multiple interactions are available, then the heuristic technique is quite poor and it is better to rely on the LMI technique. Moreover LMI is quite flexible, because it does not require an initial guess of the position by the stray node and it can be used both with and without ranging information. The static scenario analysis was very useful to focus on the mobile localization. The design of the proposed algorithms and scenarios, the simulation parameters and limits, are strictly related to the knowledge of the channel behavior and localization performance gained from the previous studies. The opportunistic idea raises from two main considerations: the limited accuracy of the beacon based RSSI localization in a real scenario and the quite good ranging accuracy of RSSI when limiting the distance. Alongside the main research line concerning localization in WSN, during the Ph.D. we also investigated other research topics, namely traffic management and underwater sensor network, which are not directly related to the previous ones but still of great scientific and educational interest. The most significant achievements obtained in these areas have also been collected in the thesis for two reasons. First, these topics still belong to the context of wireless sensor networks, sharing some basic characteristics such as the assumptions of simplicity and energy constraints. Second, the excursion on different but correlated fields may potentially open new perspectives to well known problems, thus contributing to the innovation and the progress of the research. As mentioned, the second problem addressed in this thesis regards the traffic management in WSN. Usually all the nodes in a WSN send packets to a common node, called sink. This traffic pattern, under a certain load, can lead to congestion problems, causing packet losses, high delays and waste of energy. The proposed solutions in literature usually aim at detecting the occurence of congestion by involving in this task many nodes, sometimes the entire network. We propose a different protocol, called Efficient Packet Converge Casting (EPC$^2$), that mitigates the congestion at the sink involving only a fixed number of nodes, namely the sink's neighbors. Another scenario we look into was that of underwater wireless sensor networks (UWSNs), which enable a number of applications as for radio WSNs, fostering interest in this research field. Similarly to radio networks, the energy efficiency remains a main issue. Nodes are powered by battery and it is very important to extend the network lifetime as much as possible. The different characteristics of the environment in which nodes are deployed raise new research challenges that require novel protocol design. We addressed the energy efficiency problem in UWSN with two different approaches. First, we investigated the effect of duty--cycle and node density on the energy consumption of the network, assuming that nodes can use different power levels to transmit. Second, we proposed a channel management scheme to optimize the energy consumption, considering the strong relationship between distance, frequency and channel attenuation. Both solutions are very simple and suitable for the low--complexity underwater sensor devices and do not need any central unit to coordinate, but they work asyncronously and distributely.
Negli ultimi anni, le reti wireless di sensori (WSN) sono state molto studiate a causa delle numerose applicazioni in cui possono essere usate, come il monitoraggio ambientale, la domotica, la localizzazione e il tracking di utenti mobili. Le forti limitazioni dei nodi sensori in termini di energia, processamento, memoria e affidabilita', lasciano ancora aperti molti problemi per la ricerca. Questa tesi affronta due problemi molto importanti relativi alle reti wireless di sensori: la localizzazione e la gestione del traffico. Un'accurata localizzazione dei sensori e' importante per molte applicazioni per WSN, come monitoraggio, routing, scheduling, data fusion e molte altre. Tipicamente, gli algoritmi di localizzazione si basano su una infrastruttra di nodi, detti nodi ancora che conoscono la loro posizione geografica. Questi nodi trasmettono in broadcast le loro coordinate agli altri nodi della rete, che da queste informazioni ricavano la loro posizione tramite tecniche di stima. L'argomento e' stato largamente studiato, sia con simulazioni sia, piu' recentemente, con testbed sperimentali. Ciononostante, l'accuratezza ottenuta dalla maggior parte degli algoritmi proposti e' ancora insufficiente, soprattutto in ambienti interni. E' quindi necessario cercare nuove metodologie e nuovi approcci. In questa tesi, il problema e' stato affrontato da diversi punti di vista, in modo da capire in maniera piu' chiara e accurata i diversi aspetti che lo caratterizzano. Come conseguenza, abbiamo raccolto una vasta quantita' di dati che potrebbero apparire come non molto legati uno all'altro, ma che in realta' rientrano tutti nello stesso progetto di ricerca. Come primo passo, abbiamo confrontato algoritmi di localizzazione proposti in letteratura in uno scenario indoor e con nodi statici, stimando la distanza tra i nodi utilizzando la potenza del segnale ricevuto (RSSI). I risultati ci hanno permesso di capire le potenzialita' e i limiti dei piu' diffusi algoritmi di localizzazione in ambiente indoor e in un testbed reale. In particolare, abbiamo osservato il grande impatto che ha sulle prestazioni di localizzazione l'aleatorieta', data dal termine di shadowing, della misura di potenza ricevuta. Abbiamo quindi cercato delle strategie per ridurre la varianza di questo termine aleatorio. A questo scopo, abbiamo studiato l'effetto della frequenza della portante, utilizzando una stima della potenza ricevuta multi--canale, e l'impatto dell'anisotropia dell'antenna sulle oscillazioni dei valori di potenza ricevuta. Entrambi glil studi sono stati fatti con misure reali raccolte in diversi testbed. Successivamente, abbiamo analizzato il problema del posizionamento dei nodi ancora, dopo aver osservato l'incidenza che questo ha sull'accuratezza della localizzazione. Abbiamo confrontato il posizionamento ottimo dei nodi ancora usando sia una tecnica esaustiva, ma computazionalmente molto complessa, sia uno schema euristico che raggiunge prestazioni molto vicine all'ottimo pur mantenendo una complessita' lineare con il numero di ancore. Guardare alle prestazioni di localizzazione separando i diversi effetti degli algoritmi, dei parametri di canale e del posizionamento dei nodi ancora e' stato importante per capire il contributo dei diversi aspetti all'interno dell'errore di localizzazione e quanto sia possibile migliorare la precisione della localizzazione ottimizzando uno di questi aspetti, che solitamente viene scelto in base allo scenario e alle risorse disponibili. Quindi, abbiamo incluso nel nostro scenario anche nodi mobili. All'inizio abbiamo considerato un robot mobile (AMR) che poteva interagire con i sensori, ma anche capace di localizzarsi grazie all'odometria. Facendo leva sulla complementarieta' della rete di sensori e del robot mobile, abbiamo studiato e implementato un algoritmo di localizzazione e mappatura simultanea (SLAM), problema che consiste nel creare la mappa di un'area senza nessuna conoscenza a priori dell'ambiente e in contemporanea localizzare i nodi sensore confrontando le informazioni provenienti dai sensori e quelle ricavate dall'odometria del robot. Poi abbiamo considerato uno scenario piu' generale composto da nodi mobili ed eterogenei, con diverse capacita' di autolocalizzazione, che possono interagire uno con l'altro in modo opportunistico, scambiandosi informazioni di localizzazione con altri nodi che occasionalmente si trovano in prossimita'. Le prestazioni di questo schema sono state analizzate in un modello matematico. Abbiamo studiato un approccio a Massima Verosimiglianza (ML), uno basato su Linear Matrix Inequalities (LMI) e una semplice strategia euristica per definire gli algoritmi di localizzazione opportunistica. La validita' del modello matematico e' stata confermata attraverso misure sperimentali. Abbiamo considerato due scenari principali, uno in cui un nodo puo' contare su una sola interazione opportunistica e uno dove possono essere fatti contatti multipli mentre il nodo resta nella stessa posizione. Abbiamo analizzato le diverse tecniche, trovando che nel primo caso, se le informazioni di autolocalizzazione del nodo cooperatore e di ranging sono buone, l'algoritmo euristico ha buone prestazioni, a volte addirittura meglio della Massima Verosimiglianza, che invece e' estremamente robusto e riesce a migliorare la stima di localizzazione anche in scenari molto difficili. Se invece sono disponibili numerose interazioni, allora l'algoritmo euristico porta prestazioni scarse ed e' meglio utilizzare la tecnica LMI, specialmente utilizzando l'informazione di ranging. Inoltre l'LMI non richiede una conoscenza della posizione iniziale del nodo incognito. Lo scenario statico e' stato molto utile per studiare in maniera efficace la localizzazione mobile. La scelta degli algoritmi proposti e dello scenario, i parametri di simulazione e i limiti, sono strettamente legati a quello che abbiamo studiato riguardo al canale wireless e alle prestazioni di localizzazione nei lavori precedenti. L'idea dello scenario opportunistico infatti e' venuta a partire da due considerazioni: la limitata precisione della localizzazione con ancore basata su RSSI in uno scenario reale e la buona precisione nella stima di distanza con RSSI quando la distanza e' limitata. Affianco al principale filone di ricerca riguardante la localizzazione nelle WSN, durante il dottorato di ricerca abbiamo approfondito anche altri argomenti, come la gestione del traffico e le reti di sensori sottomarine, che non sono direttamente collegate con il tema principale, ma sono comunque di grande interesse scientifico. I risultati piu' significativi ottenuti in questi temi sono stati inseriti all'interno della tesi per due motivi. Innanzitutto, questi argomenti appartengono al contesto delle reti di sensori wireless, condividendo alcune caratteristiche di base quali l'assunzione di semplicita' e le limitazioni energetiche. Inoltre, il trattare campi diversi ma correlati, puo' aprire nuove prospettive a problemi noti, contribuendo cosi' all'innovazione della ricerca. Il secondo problema affrontato in questa tesi e' stato la gestione del traffico in reti di sensori wireless. Spesso, i nodi di una rete di sensori mandano i pacchetti ad un nodo comune, chiamato sink. Questo modello di traffico, quando il carico cresce, puo' portare a problemi di congestione, causando perdita di pacchetti, ritardi e spreco di energia. Le soluzioni proposte in letteratura solitamente cercando di individuare l'inizio di una congestione, utilizzando in questo compito molti nodi, talvolta l'intera rete. Il protocollo proposto, chiamato Efficient Packet Converge Casting (EPC$^2$), mitiga la congestione al sink, ma coinvolgnedo solo un numero fissato di nodi, i vicini del sink. Un altro scenario che abbiamo analizzato in questa tesi, sono state le reti sottomarine di sensori che, come nel caso delle reti radio, possono essere utilizzato per molteplici applicazioni e quindi hanno ricevuto molta attenzione dal mondo della ricerca. Similmente alle reti radio, l'efficienza energetica e' un problema molto sentito. I nodi sono alimentati a batteria ed e' molto importante incrementare la vita della rete il piu' possibile. La profonda diversita' dell'ambiente in cui i nodi sono disposti crea nuove sfide per la ricerca che richiedono la progettazione di nuovi protocolli. Abbiamo affrontato il problema dell'efficienza energetica in reti sottomarine con due diversi approcci. Abbiamo studiato l'effetto del duty--cycle and della densita' dei nodi sul consumo energetico della rete, assumendo che i nodi potessero usare diversi livelli di potenza in trasmissione. Quindi abbiamo proposto uno schema di utilizzazione della banda disponibile per ottimizzare il consumo energetico, facendo leva sulla forte relazione tra distanza, frequenza e attenuazione del canale. Entrambe le soluzioni sono molto semplici e adatte ai dispositivi sottomarini che hanno forti limitazioni. Inoltre non richiedono una unita' centrale per essere coordinate, ma operano in modo asincrono e distribuito.

Energy is a critical resource in the design of wireless networks since wireless devices are usually powered by batteries. Battery capacity is finite and the progress of battery technology is very slow, with capacity expected to make little improvement in the near future. Under these conditions, many techniques for conserving power have been proposed to increase battery life. In this dissertation we consider two approaches to conserving the energy consumed by a wireless network interface. One technique is to use power saving mode, which allows a node to power off its wireless network interface (or enter a doze state) to reduce energy consumption. The other is to use a technique that suitably varies transmission power to reduce energy consumption. These two techniques are closely related to theMAC (Medium Access Control) layer. With respect to power saving mode, we study IEEE 802.11 PSM (Power Saving Mechanism) and propose a scheme that improves its energy efficiency. We also investigate the interaction between power saving mode and TCP (Transport Control Protocol). As a second approach to conserving energy, we investigate a simple power control protocol, called BASIC, which uses the maximum transmission power for RTS-CTS and the minimum necessary power for DATA-ACK. We identify the deficiency of BASIC, which increases collisions and degrades network throughput, and propose a power control protocol that addresses these problems and achieves energy savings. Since energy conservation is not an issue limited to one layer of the protocol stack, we study a cross layer design that combines power control at the MAC layer and power aware routing at the network layer. One poweraware routing metric is minimizing the aggregate transmission power on a path from source to destination. This metric has been used along with BASIC-like power control under the assumption that it can save energy, which we show to be false. Also, we show that the power aware routing metric leads to a lower throughput. We show that using the shortest number of hops in conjunction with BASIC-like power control conserves more energy than power aware routing with BASIC-like power control.

During the recent years, a huge augmentation of the data traffic volume has been noticed, while a further steep increase is expected in the following years. As a result, questions have been raised over the years about the energy consumption needs of the wireless telecommunication networks, their carbon dioxide emissions and their operational expenses. Aiming at meeting the high traffic demands with flat energy consumption and flat incurred expenses, mobile network operators (MNOs) have opted to improve their position (i) by deploying heterogeneous networks (HetNets), which are consisted of macrocell base stations (MBSs) and small cell base stations (SBSs) and (ii) by sharing their infrastructure. However, questions could be raised about the extend to which HetNet densification is of aid. Given that network planning is executed according to high traffic load volumes, BS underutilisation during low-traffic hours cannot be neglected. Similarly, the aggregated energy needs of multiple SBSs equals the ones of an energy hungry MBS, having thus a respectable share of the net energy consumption. In this context, a set of research opportunities have been identified. This thesis provides contribution toward the achievement of a greener and more cost efficient operation of HetNet deployments, where multiple stakeholders develop their activity and where energy support can have the form of various alternate schemes, including renewable energy (RE) sources. Depending on the network energy support, i.e., whether RE sources are used in the network or not, the main body of this thesis is divided in two research directions. The first part of the thesis uses the technology of switching off strategies in order to explore their efficiency in terms of both energy and costs in a HetNet. The HetNet is assumed to be a roaming-based cooperative activity of multiple MNOs that is powered exclusively by grid energy. A switching off and a cost allocation scheme are proposed, using as criteria the BS type, the BS load and the roaming cost for traffic offloading. The performance of the proposed schemes is evaluated with respect to energy efficiency, cost savings and fairness, using computer-based simulations. The second part of the thesis explores energy and cost management issues in energy harvesting (EH) HetNet deployments where EH-BSs use an EH system (EHS), an energy storage system (ESS) and the smart grid (SG) as energy procurement sources. The EH-HetNet is assumed a two-tier network deployment of EH-MBSs that are passively shared among an MNO set and EH-SBSs that are provided to MNOs by an infrastructure provider. Taking into consideration the infrastructure location and the variety of stakeholders involved in the network deployment, approaches of RE exchange (REE) are proposed as a cooperative RE sharing for the shared EH-MBSs, based on bankruptcy theory, and a non-cooperative, aggregator-assisted RE trading, based on double auctions, for the EH-SBSs. The performance of the proposed schemes is evaluated in terms of the hours of independence of the studied system from the SG, the fairness regulated by the provided solution and the economical payoffs extracted for the stakeholders
Durante los últimos años, se ha notado un aumento enorme del volumen de tráfico de datos, mientras que se espera un nuevo aumento en los próximos años. Como resultado, se han planteado preguntas sobre las necesidades de consumo de energía de las redes inalámbricas de telecomunicaciones, sus emisiones de dióxido de carbono y sus gastos operativos. Con el objetivo de satisfacer las altas demandas de tráfico con consumo de energía constante y con gastos incurridos constantes, además de utilizar soluciones basadas en la nube, los operadores de redes móviles (MNOs) han optado por mejorar su posición (i) desplegando redes heterogéneas (HetNets), que consisten en estaciones base de macro-células (MBSs) y estaciones base de células pequeñas (SBSs), y (ii) compartiendo su infraestructura. Sin embargo, podrían plantearse preguntas sobre hasta qué punto la densificación de una HetNet es de ayuda. Dado que la planificación de la red se ejecuta de acuerdo con los volúmenes de carga de tráfico más elevados, no se puede descuidar la subutilización de las estaciones base (BS) durante las horas de poco tráfico. De manera similar, las necesidades de energía agregadas de múltiples SBSs son iguales a las de una MBS que consume mucha energía, teniendo así una parte respetable del consumo neto de energía. En este contexto, se ha identificado un conjunto de oportunidades de investigación. Esta tesis contribuye al logro de una operación más ecológica y rentable de las implementaciones de HetNet, donde múltiples partes interesadas desarrollan su actividad y donde el apoyo energético puede tener la forma de varios esquemas alternativos, incluidas las fuentes de energía renovables (RE). Dependiendo del soporte de energía de red, es decir, si las fuentes de RE se usan en la red o no, el cuerpo principal de esta tesis se divide en dos direcciones de investigación. La primera parte de la tesis utiliza la tecnología de las estrategias de apagado con el objetivo de explorar su eficiencia en términos de energía y gastos en una HetNet. Se asume que la HetNet es una actividad cooperativa basada en la itinerancia de múltiples MNO que se alimenta exclusivamente de energía de la red. Se propone un esquema de desconexión y de asignación de costes, que utiliza como criterios el tipo de BS, la carga de BS y el coste de la itinerancia para la descarga de tráfico. El rendimiento de los esquemas propuestos se evalúa con respecto a la eficiencia energética, el ahorro de costes y la equidad, usando simulaciones en computadora. La segunda parte de la tesis explora los problemas de gestión de energía y de costes en las implementaciones de HetNet donde las estaciones base recolectan energía usando un sistema EH (EHS), un sistema de almacenamiento de energía (ESS) y la red eléctrica inteligente (SG) como sistemas de adquisición de energía. Se asume que el EH-HetNet es una implementación de redes de dos niveles donde los EH-MBSs se comparten pasivamente entre un conjunto de MNOs y EH-SBSs se proporcionan a los MNOs de un proveedor de infraestructura. Teniendo en cuenta la ubicación de la infraestructura y la variedad de partes interesadas e involucradas en el despliegue de la red, se proponen enfoques de intercambio de RE (REE) como un intercambio cooperativo de RE para los EH-MBS compartidos, basado en la teoría de bancarrota, y un no cooperativo comercio de RE para los EH-SBSs, que es asistido por un agregador y basado en las subastas dobles. El rendimiento de los esquemas propuestos se evalúa en términos de las horas de independencia del sistema estudiado con respecto al SG, la imparcialidad regulada por la solución proporcionada y los beneficios económicos extraídos para las interesadas.

Recent advances in Micro-Electro-Mechanical Systems (MEMS) and low-power short-range radios have enabled rapid development of wireless sensor networks. Future sensor networks are anticipated to include hundreds or thousands of these devices in many applications, such as capturing multimedia content for surveillance, structural health monitoring, tracking of accidental chemical leaks, machine failures, earthquakes and intrusion detection. With the increase of sensor applications, a number of challenging problems related to the network protocol design has emerged - the most important ones relating to energy efficiency and lifetime maximisation. Techniques devised for sensor networks should deal with a large number of sensors distributed in the field. Wireless sensor nodes are deployed with limited energy reserves, so the networks should operate with minimum energy overhead. In fact, the network should take into account not only individual node's energy efficiency but also consider the global picture, because surviving nodes' energy reserves in a failed network are wasted energy. This thesis examines a node organisation technique to deal with the above challenges. The focus is on improving network lifetime via organising the nodes in a distributed and energy efficient manner. The main goal is lowering wasted energy via energy balancing and exploiting node redundancy in case of node failure. In particular, this thesis proposes Energy Balanced Clustering (EBC) method for node self-organisation where network tasks (such as data aggregation and data forwarding) are shifted to high-energy neighbours to reduce the energy consumption of low energy nodes. After showing how to extend network lifetime by energy balanced node organisation, the effect of redundant node deployments on network lifetime is addressed. Redundant nodes consume energy by performing unnecessary tasks so a method called Self-Calculated Redundancy Check (SCRC) is proposed to deactivate redundant nodes. A deactivated redundant node can be used as a replacement for a failed node. The Asynchronous Failed Sensor node Detection (AFSD) proposed in this thesis uses the data packets exchanged between neighbours to identify failed neighbours. To restore coverage for network holes caused by failed nodes, policies are given for re-activating redundant nodes. Detailed analytical analysis and simulation of the proposed methods demonstrate that by taking into account energy balancing, eliminating redundant tasks and replacing failed nodes sensor network lifetime can significantly be improved.

Modern power generation aims to utilize renewable energy sources such as solar power and wind to supply customers with power. This approach avoids exhaustion of fossil fuels as well as provides clean energy. Microgrids have become popular over the years, as they contain multiple renewable power sources and battery storage systems to supply power to the entities within the network. These microgrids can share power with the main grid or operate islanded from the grid. During an islanded scenario, self-sustainability is crucial to ensure balance between supply and demand within the microgrid. This can be accomplished by a smart microgrid that can monitor system conditions and respond to power imbalance by shedding loads based on priority. Such a method ensures security of the most important loads in the system and manages energy by automatically disconnecting lower priority loads until system conditions have improved. This thesis introduces a prioritized load shedding algorithm for the microgrid at the University of North Texas Discovery Park and highlight how such an energy management algorithm can add reliability to an islanded microgrid.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 128-129).
The Energy Mobility Network is a mobile, networked energy production, consumption and sharing system that is designed to motivate users to be more aware of their energy consumption. In particular, the system provides a just-in-time message to the user before using the device, which allows the user to evaluate his/her needs and the cost of the device. Furthermore, the idea of minimizing electrical costs are extended into the social realm; the system creates a social network among users which allow social energy etiquettes to come into play. With these etiquettes, the system aims to use social means as a way to minimize the use of electricity. In the thesis, I discuss the goals and ideas developed that led to the creation of the network and the technical infrastructure behind the system. I will be going in depth with the prototyping, the pros and cons, as well as the multiple versions of the system that have been prototyped. Finally, I will discuss the future possibilities the Energy Mobility Network will bring when introduced to the general public.
by Natalie Wen Yua Cheung.
M.Eng.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 137-142).
The popularity of mobile devices has stimulated rapid progress in both Wi-Fi and cellular technologies. Before LTE was widely deployed, Wi-Fi speeds dominated cellular network speeds. But that is no longer true today. In a study we conducted with a crowd-sourced measurement tool used by over 1,000 users in 16 countries, we found that 40% of the time LTE outperforms Wi-Fi, and 75% of the time the difference between LTE and Wi-Fi throughput is higher than 1 Mbits/s. Thus, instead of the currently popular "always prefer Wi-Fi" policy, we argue that mobile devices should use the best available combination of networks: Wi-Fi, LTE, or both. Selecting the best network combination, however, is a challenging problem because: 1) network conditions vary with both location and time; 2) many network transfers are short, which means that the decision must be made with low overhead; and, 3) the best choice is determined not only by best network performance, but also constrained by practical factors such as monetary cost and battery life. In this dissertation, we present Delphi, a software controller for network selection on mobile devices. Delphi makes intelligent network selection decisions according to current network conditions and monetary cost concerns, as well as battery-life considerations. Our experiments show that Delphi reduces application network transfer time by 46% for web browsing and by 49% for video streaming, compared with Android's default policy of always using Wi-Fi when it is available. Delphi can also be configured to achieve high throughput while being energy efficient; in this configuration, it achieves 1.9 x the through-put of Android's default policy while only consuming 6% more energy. Delphi improves performance but uses the cellular network more extensively than the status quo, consuming more energy than before. To address this problem, we develop a general method to reduce the energy consumption of cellular interfaces on mobile devices. The key idea is to use the statistics of data transfers to determine the best times at which to put the radio in different power states. These techniques not only make Delphi more useful in practice but can be deployed independently without Delphi to improve energy efficiency for any cellular-network-enabled devices. Experiments show that our techniques reduce energy consumption by 15% to 60% across various traffic patterns.
by Shuo Deng.
Ph. D.

Master of Science
Department of Electrical and Computer Engineering
William B. Kuhn and Balasubramaniam Natarajan
This thesis presents an energy harvesting wireless sensor network (EHWSN) architecture customized for use within a space suit. The contribution of this research spans both physical (PHY) layer energy harvesting transceiver design and appropriate medium access control (MAC) layer solutions. The EHWSN architecture consists of a star topology with two types of transceiver nodes: a powered Gateway Radio (GR) node and multiple energy harvesting (EH) Bio-Sensor Radio (BSR) nodes. A GR node works as a central controller to receive data from BSR nodes and manages the EHWSN via command packets; low power BSR nodes work to obtain biological signals, packetize the data and transmit it to the GR node. To demonstrate the feasibility of an EHWSN at the PHY layer, a representative BSR node is designed and implemented. The BSR node is powered by a thermal energy harvesting system (TEHS) which exploits the difference between the temperatures of a space suit's cooling garment and the astronaut's body. It is shown that through appropriate control of the duty-cycle in transmission and receiving modes, it is possible for the transceiver to operate with less than 1mW power generated by the TEHS. A super capacitor, energy storage of TEHS, acts as an energy buffer between TEHS and power consuming units (processing units and transceiver radio). The super capacitor charges when a BSR node is in sleep mode and discharges when the node is active. The node switches from sleep mode to active mode whenever the super capacitor is fully charged. A voltage level monitor detects the system's energy level by measuring voltage across the super capacitor. Since the power generated by the TEHS is extremely low(less than 1mW) and a BSR node consumes relatively high power (approximately 250mW) during active mode, a BSR node must work under an extremely low duty cycle (approximately 0.4%). This ultra-low duty cycle complicates MAC layer design because a BSR node must sleep for more than 99.6% of overall operation time. Another challenge for MAC layer design is the inability to predict when the BSR node awakens from sleep mode due to unpredictability of the harvested energy. Therefore, two feasible MAC layer designs, CSA (carrier sense ALOHA based)-MAC and GRI (gateway radio initialized)-MAC, are proposed in this thesis.