Energy efficiency in next generation wireless networks: methodologies, solutions and algorithms

Mobile Broadband Wireless Access (BWA) networks will offer in the forthcoming years multiple and differentiated services to users with high mobility requirements, connecting via portable or wearable devices which rely on the use of batteries by necessity. Since such devices consume a relatively large fraction of energy for transmitting/receiving data over-the-air, mechanisms are needed to reduce power consumption, in order to increase the lifetime of devices and hence improve user’s satisfaction. Next generation wireless network standards define power saving functions at the Medium Access Control (MAC) layer, which allow user terminals to switch off the radio transceiver during open traffic sessions for greatest energy consumption reduction. However, enabling power saving usually increases the transmission latency, which can negatively affect the Quality of Service (QoS) experienced by users. On the other hand, imposing stringent QoS requirements may limit the amount of energy that can be saved. The IEEE 802.16e standard defines the sleep mode is power saving mechanism with the purpose of reducing energy consumption. Three different operation classes are provided, each one to serve different class of traffic: class I, best effort traffic, class II real time traffic and class III multicast traffic. Several aspects of the sleep mode are left unspecified, as it is usually done in standards, allowing manufacturers to implement their own proprietary solutions, thus gaining a competitive advantage over the rivals. The work of this thesis is aimed at verifying, the effectiveness of the power saving mechanism proposed into IEEE 802.16e standard, focusing on the mutual interaction between power saving and QoS support. Two types of delay constrained applications with different requirements are considered, i.e., Web and Voice over IP (VoIP). The performance is assessed via detailed packet-level simulation, with respect to several system parameters. To capture the relative contribution of all the factors on the energy- and QoS-related metrics, part of the evaluation is carried out by means of 2k · r! analysis. Our study shows that the sleep mode can achieve significant power consumption reduction, however, when real time traffic is considered a wise configuration of the parameters is mandatory in order to avoid unacceptable degradation of the QoS. Finally, based on the guidelines drawn through the analysis, we extend our contribution beyond a simple evaluation, proposing a power saving aware scheduling framework aimed at reducing further the energy consumption. Our framework integrates with existing scheduling policies that can pursue their original goals, e.g. maximizing throughput or fairness, while improving the energy efficiency of the user terminals. Its effectiveness is assessed through an extensive packet level simulation campaign

Contributions to QoS and energy efficiency in wi-fi networks

The Wi-Fi technology has been in the recent years fostering the proliferation of attractive mobile computing devices with broadband capabilities. Current Wi-Fi radios though severely impact the battery duration of these devices thus limiting their potential applications. In this thesis we present a set of contributions that address the challenge of increasing energy efficiency in Wi-Fi networks. In particular, we consider the problem of how to optimize the trade-off between performance and energy effciency in a wide variety of use cases and applications. In this context, we introduce novel energy effcient algorithms for real-time and data applications, for distributed and centralized Wi-Fi QoS and power saving protocols and for Wi-Fi stations and Access Points. In addition, the di¿erent algorithms presented in this thesis adhere to the following design guidelines: i) they are implemented entirely at layer two, and can hence be easily re-used in any device with a Wi-Fi interface, ii) they do not require modi¿cations to current 802.11 standards, and can hence be readily deployed in existing Wi-Fi devices, and iii) whenever possible they favor client side solutions, and hence mobile computing devices implementing them can benefit from an increased energy efficiency regardless of the Access Point they connect to. Each of our proposed algorithms is thoroughly evaluated by means of both theoretical analysis and packet level simulations. Thus, the contributions presented in this thesis provide a realistic set of tools to improve energy efficiency in current Wi-Fi networks

Contributions towards softwarization and energy saving in passive optical networks

Ths thesis is a result of contributions to optimize and improve the network management systme and power consumption in Passive Optical Network (PON). Passive Optical Network elements such as Optical Line Terminal (OLT) and Optical Network Units (ONUs) are currently managed by inflexible legacy network management systems. Software-Defined Networking (SDN) is a new networking paradigm that improves the operation and management of networks by decoupling control plane from data plane. Currently, network management in PON networks is not always automated nor normalized. One goal of the researchers in optical networking is to improve the programmability, efficiency, and global optimization of network operations, in order to minimize both Capital Expenditure (CAPEX) and Operational Expenditure (OPEX) by reducing the complexity of devices and its operation. Therefore, it makes sense to use an SDN approach in order to manage the passive optical network functionalities and migrating must of the upper layer functions to the SDN controller. Many approaches have already addressed the topic of applying the SDN architecture in PON networks. However; the focus was usually on facilitating the deployment of SDN-based service and so Service Interoperability remains unexplored in detail. The main challenge toward this goal is how to make compatible the synchronous nature of the EPON media access control protocols with the asynchronous architecture of SDN, and in particular, OpenFlow. In our proposed architecture, the OLT is partially virtualized and some of its functionalities are allocated to the core network management system, while the OLT itself is replaced by an OpenFlow switch. A new MultiPoint MAC Control (MPMC) sublayer extension based on the OpenFlow protocol is presented. The OpenFlow switch is extended with synchronous ports to retain the time-critical nature of the EPON network. Our simulation-based results demonstrate the effectiveness of the new architecture, while retaining a similar (or improved) performance in term of delay and throughput when compared to legacy PONs. Nowadays, many researchers are working simultaneously to develop power saving techniques and improves energy efficiency in the PON network, and since the contribution of access networks to the global energy consumption is large, energy efficiency has become an increasingly important requirement in designing access networks. Therefore, energy-saving approaches are being investigated to provide high performance and consume less energy. Several techniques have been proposed to increase energy efficiency in PON networks. Such techniques are related to the centeralized DBA but the advantage of power saving in a distributed DBA remains untouched. We present a distributed energy-efficient Dynamic Bandwidth Allocation (DBA) algorithm for both the upstream and downstream channels of EPON to improve energy efficiency in EPON networks. The proposed algorithm analyzes the queue status of the ONUs and OLT in order to power-off the transmitter and/or receiver of an ONU whenever there is no upstream or downstream traffic. We have been able to combine the advantage of a distributed DBA such as DDSPON (a smaller packet delay, due to the shorter time needed by DDSPON to allocate the transmission slots) and the energy-saving features (that come at a price of longer packet delays due to the fact that switching off the transmitters make the packet queues grow). Our proposed DBA algorithm minimizes the ONU energy consumption across a wide range of network loads, while maintaining at an acceptable level the penalty introduced in terms of channel utilization and packet delay.Las contribuciones de esta tesis se centran en mejorar el sistema de gestión de red y el consumo de energía en redes de acceso ópticas pasivas (PON). Los elementos de las redes PON, como el terminal de línea óptica (OLT) y las unidades de red ópticas (ONU), se gestionan actualmente mediante sistemas poco flexibles. El nuevo paradigma de redes definidas por software (SDN) mejora la gestión de redes al desacoplar el plano de control del plano de datos. Actualmente, la gestión de redes PON no está automatizada ni normalizada. Uno de los objetivos de los investigadores en redes ópticas es mejorar la programabilidad, la eficiencia y la optimización global de las operaciones de red, con el fin de minimizar tanto el gasto de capital (CAPEX) como el gasto operativo (OPEX) al reducir la complejidad de los dispositivos y su funcionamiento. Por lo tanto, tiene sentido utilizar un enfoque SDN para gestionar las funciones de red óptica pasiva y migrar algunas de las funciones PON de capas superiores al controlador SDN. Otros investigadores han estudiado esta aproximación. sin embargo; el enfoque generalmente estaba en facilitar la implementación del servicio basado en SDN y, por lo tanto, la interoperabilidad de los servicios permanecía sin ser explorado en detalle. El principal desafío hacia este objetivo es cómo compatibilizar la naturaleza síncrona de los protocolos de control de acceso a medios EPON con la arquitectura asíncrona de SDN y, en particular, OpenFlow. En nuestra propuesta de arquitectura, la OLT se virtualiza parcialmente y algunas de sus funcionalidades se asignan al sistema de gestión de red centralizado, mientras que la OLT se reemplaza por un conmutador OpenFlow. Proponemos una nueva extensión de la subcapa de control múltiple de MAC (MPMC) basada en el protocolo OpenFlow. El conmutador OpenFlow se amplía con puertos síncronos para asegurar la naturaleza de tiempo real de la red EPON. Nuestros resultados basados ¿¿en simulaciones demuestran la efectividad de la nueva arquitectura, al tiempo que se mantiene un rendimiento similar (o mejorado) en términos de retardos y rendimiento en comparación con las PON clásicas. Por otro lado, se están desarrollando técnicas de ahorro de energía y mejora de la eficiencia energética en redes PON, y dado que la contribución de las redes de acceso al consumo total de energía es importante, la eficiencia energética se ha convertido en un requisito cada vez más importante. Se han propuesto varias técnicas por parte de otros autores para aumentar la eficiencia energética en las redes PON, relacionadas con algoritmos DBA (Dynamic Bandwidth Allocation) centralizados, pero las ventaja del ahorro de energía en un DBA distribuido no se ha explorado todavía. Por ello nuestra segunda contiribución es un algoritmo distribuido de asignación dinámica de ancho de banda energéticamente eficiente tanto para los canales ascendentes como descendentes de EPON para mejorar la eficiencia energética en las redes EPON. El algoritmo propuesto analiza el estado de cola de las ONU y la OLT para apagar el transmisor y/o el receptor de una ONU cuando no hay tráfico en sentido ascendente o descendente. Hemos podido combinar la ventaja de un DBA distribuido como DDSPON (que asegura retardos más pequeños, debido al menor tiempo que DDSPON necesita para asignar las ranuras de transmisión) y las características de ahorro de energía (al precio de tener retardos de paquete más grandes debido al hecho de que apagar los transmisores hace que las colas de paquetes crezcan). Nuestro algoritmo de DBA propuesto minimiza el consumo de energía de la ONU en una amplia gama de cargas de red, mientras mantiene a un nivel aceptable la penalización introducida en términos de utilización del canal y retardos.Postprint (published version

Contributions towards softwarization and energy saving in passive optical networks

Ths thesis is a result of contributions to optimize and improve the network management systme and power consumption in Passive Optical Network (PON). Passive Optical Network elements such as Optical Line Terminal (OLT) and Optical Network Units (ONUs) are currently managed by inflexible legacy network management systems. Software-Defined Networking (SDN) is a new networking paradigm that improves the operation and management of networks by decoupling control plane from data plane. Currently, network management in PON networks is not always automated nor normalized. One goal of the researchers in optical networking is to improve the programmability, efficiency, and global optimization of network operations, in order to minimize both Capital Expenditure (CAPEX) and Operational Expenditure (OPEX) by reducing the complexity of devices and its operation. Therefore, it makes sense to use an SDN approach in order to manage the passive optical network functionalities and migrating must of the upper layer functions to the SDN controller. Many approaches have already addressed the topic of applying the SDN architecture in PON networks. However; the focus was usually on facilitating the deployment of SDN-based service and so Service Interoperability remains unexplored in detail. The main challenge toward this goal is how to make compatible the synchronous nature of the EPON media access control protocols with the asynchronous architecture of SDN, and in particular, OpenFlow. In our proposed architecture, the OLT is partially virtualized and some of its functionalities are allocated to the core network management system, while the OLT itself is replaced by an OpenFlow switch. A new MultiPoint MAC Control (MPMC) sublayer extension based on the OpenFlow protocol is presented. The OpenFlow switch is extended with synchronous ports to retain the time-critical nature of the EPON network. Our simulation-based results demonstrate the effectiveness of the new architecture, while retaining a similar (or improved) performance in term of delay and throughput when compared to legacy PONs. Nowadays, many researchers are working simultaneously to develop power saving techniques and improves energy efficiency in the PON network, and since the contribution of access networks to the global energy consumption is large, energy efficiency has become an increasingly important requirement in designing access networks. Therefore, energy-saving approaches are being investigated to provide high performance and consume less energy. Several techniques have been proposed to increase energy efficiency in PON networks. Such techniques are related to the centeralized DBA but the advantage of power saving in a distributed DBA remains untouched. We present a distributed energy-efficient Dynamic Bandwidth Allocation (DBA) algorithm for both the upstream and downstream channels of EPON to improve energy efficiency in EPON networks. The proposed algorithm analyzes the queue status of the ONUs and OLT in order to power-off the transmitter and/or receiver of an ONU whenever there is no upstream or downstream traffic. We have been able to combine the advantage of a distributed DBA such as DDSPON (a smaller packet delay, due to the shorter time needed by DDSPON to allocate the transmission slots) and the energy-saving features (that come at a price of longer packet delays due to the fact that switching off the transmitters make the packet queues grow). Our proposed DBA algorithm minimizes the ONU energy consumption across a wide range of network loads, while maintaining at an acceptable level the penalty introduced in terms of channel utilization and packet delay.Las contribuciones de esta tesis se centran en mejorar el sistema de gestión de red y el consumo de energía en redes de acceso ópticas pasivas (PON). Los elementos de las redes PON, como el terminal de línea óptica (OLT) y las unidades de red ópticas (ONU), se gestionan actualmente mediante sistemas poco flexibles. El nuevo paradigma de redes definidas por software (SDN) mejora la gestión de redes al desacoplar el plano de control del plano de datos. Actualmente, la gestión de redes PON no está automatizada ni normalizada. Uno de los objetivos de los investigadores en redes ópticas es mejorar la programabilidad, la eficiencia y la optimización global de las operaciones de red, con el fin de minimizar tanto el gasto de capital (CAPEX) como el gasto operativo (OPEX) al reducir la complejidad de los dispositivos y su funcionamiento. Por lo tanto, tiene sentido utilizar un enfoque SDN para gestionar las funciones de red óptica pasiva y migrar algunas de las funciones PON de capas superiores al controlador SDN. Otros investigadores han estudiado esta aproximación. sin embargo; el enfoque generalmente estaba en facilitar la implementación del servicio basado en SDN y, por lo tanto, la interoperabilidad de los servicios permanecía sin ser explorado en detalle. El principal desafío hacia este objetivo es cómo compatibilizar la naturaleza síncrona de los protocolos de control de acceso a medios EPON con la arquitectura asíncrona de SDN y, en particular, OpenFlow. En nuestra propuesta de arquitectura, la OLT se virtualiza parcialmente y algunas de sus funcionalidades se asignan al sistema de gestión de red centralizado, mientras que la OLT se reemplaza por un conmutador OpenFlow. Proponemos una nueva extensión de la subcapa de control múltiple de MAC (MPMC) basada en el protocolo OpenFlow. El conmutador OpenFlow se amplía con puertos síncronos para asegurar la naturaleza de tiempo real de la red EPON. Nuestros resultados basados ¿¿en simulaciones demuestran la efectividad de la nueva arquitectura, al tiempo que se mantiene un rendimiento similar (o mejorado) en términos de retardos y rendimiento en comparación con las PON clásicas. Por otro lado, se están desarrollando técnicas de ahorro de energía y mejora de la eficiencia energética en redes PON, y dado que la contribución de las redes de acceso al consumo total de energía es importante, la eficiencia energética se ha convertido en un requisito cada vez más importante. Se han propuesto varias técnicas por parte de otros autores para aumentar la eficiencia energética en las redes PON, relacionadas con algoritmos DBA (Dynamic Bandwidth Allocation) centralizados, pero las ventaja del ahorro de energía en un DBA distribuido no se ha explorado todavía. Por ello nuestra segunda contiribución es un algoritmo distribuido de asignación dinámica de ancho de banda energéticamente eficiente tanto para los canales ascendentes como descendentes de EPON para mejorar la eficiencia energética en las redes EPON. El algoritmo propuesto analiza el estado de cola de las ONU y la OLT para apagar el transmisor y/o el receptor de una ONU cuando no hay tráfico en sentido ascendente o descendente. Hemos podido combinar la ventaja de un DBA distribuido como DDSPON (que asegura retardos más pequeños, debido al menor tiempo que DDSPON necesita para asignar las ranuras de transmisión) y las características de ahorro de energía (al precio de tener retardos de paquete más grandes debido al hecho de que apagar los transmisores hace que las colas de paquetes crezcan). Nuestro algoritmo de DBA propuesto minimiza el consumo de energía de la ONU en una amplia gama de cargas de red, mientras mantiene a un nivel aceptable la penalización introducida en términos de utilización del canal y retardos

Mobile Networks

The growth in the use of mobile networks has come mainly with the third generation systems and voice traffic. With the current third generation and the arrival of the 4G, the number of mobile users in the world will exceed the number of landlines users. Audio and video streaming have had a significant increase, parallel to the requirements of bandwidth and quality of service demanded by those applications. Mobile networks require that the applications and protocols that have worked successfully in fixed networks can be used with the same level of quality in mobile scenarios. Until the third generation of mobile networks, the need to ensure reliable handovers was still an important issue. On the eve of a new generation of access networks (4G) and increased connectivity between networks of different characteristics commonly called hybrid (satellite, ad-hoc, sensors, wired, WIMAX, LAN, etc.), it is necessary to transfer mechanisms of mobility to future generations of networks. In order to achieve this, it is essential to carry out a comprehensive evaluation of the performance of current protocols and the diverse topologies to suit the new mobility conditions

Scalable base station switching framework for green cellular networks

With the recent unprecedented growth in the wireless market, network operators are obliged not only to find new techniques including dense deployment of base stations (BSs) in order to support high data rate services and high user density, but also to reduce the operating costs and energy consumption of various network elements. To solve these challenges, powering down certain BSs during low-traffic periods, so-called BS sleeping, has emerged as an effective green communications paradigm. While BS sleeping offers the potential to significantly lower energy consumption, it also raises many challenges, since when a BS is switched off, this can lead to, for example, coverage holes, sudden degradation in quality of service (QoS), higher transmit power dissipation in off-cell mobile stations (MSs), an inability to rapidly power up/down equipment and finally, a failure to uphold regulatory requirements. In order to realise greener network designs which both maximise energy savings whilst guaranteeing QoS, innovative BS switching mechanisms need to be developed. This thesis presents a novel BS switching framework which improves energy efficiency (EE) in comparison with existing approaches, while guaranteeing the minimum QoS and seamless services. The major technical contributions in this framework are: i) a new BS to relay station (RS) switching model where certain BSs are switched to RS mode rather than being turned off, firstly using a fixed threshold based switching algorithm utilizing temporal traffic diversity, and ii) then subsequently by means of an adaptive threshold by exploiting the inherently asymmetric traffic profile between cells, i.e., by exploiting both the temporal and spatial traffic diversity; iii) a traffic-and-interference-aware BS switching strategy that considers the impact of inter-cell interference in the decision making process to dynamically determine the best BS set to be kept active for improved EE; and finally iv) a novel scalable multimode BS switching model which enables each BS to operate in different power modes i.e., macro/micro/sleep to explore energy savings potential even at higher traffic conditions. The thesis findings conclusively confirm this new BS switching framework provides significant EE improvements from both BS and MS perspectives, under diverse network conditions and represents a notable step towards greener communications

Synchronous and Concurrent Transmissions for Consensus in Low-Power Wireless

With the emergence of the Internet of Things, autonomous vehicles and the Industry 4.0, the need for dependable yet adaptive network protocols is arising. Many of these applications build their operations on distributed consensus. For example, UAVs agree on maneuvers to execute, and industrial systems agree on set-points for actuators.Moreover, such scenarios imply a dynamic network topology due to mobility and interference, for example. Many applications are mission- and safety-critical, too.Failures could cost lives or precipitate economic losses.In this thesis, we design, implement and evaluate network protocols as a step towards enabling a low-power, adaptive and dependable ubiquitous networking that enables consensus in the Internet of Things. We make four main contributions:- We introduce Orchestra that addresses the challenge of bringing TSCH (Time Slotted Channel Hopping) to dynamic networks as envisioned in the Internet of Things. In Orchestra, nodes autonomously compute their local schedules and update automatically as the topology evolves without signaling overhead. Besides, it does not require a central or distributed scheduler. Instead, it relies on the existing network stack information to maintain the schedules.- We present A2 : Agreement in the Air, a system that brings distributed consensus to low-power multihop networks. A2 introduces Synchrotron, a synchronous transmissions kernel that builds a robust mesh by exploiting the capture effect, frequency hopping with parallel channels, and link-layer security. A2 builds on top of this layer and enables the two- and three-phase commit protocols, and services such as group membership, hopping sequence distribution, and re-keying.- We present Wireless Paxos, a fault-tolerant, network-wide consensus primitive for low-power wireless networks. It is a new variant of Paxos, a widely used consensus protocol, and is specifically designed to tackle the challenges of low-power wireless networks. By utilizing concurrent transmissions, it provides a dependable low-latency consensus.- We present BlueFlood, a protocol that adapts concurrent transmissions to Bluetooth. The result is fast and efficient data dissemination in multihop Bluetooth networks. Moreover, BlueFlood floods can be reliably received by off-the-shelf Bluetooth devices such as smartphones, opening new applications of concurrent transmissions and seamless integration with existing technologies

Cryptography for Ultra-Low Power Devices

Ubiquitous computing describes the notion that computing devices will be everywhere: clothing, walls and floors of buildings, cars, forests, deserts, etc. Ubiquitous computing is becoming a reality: RFIDs are currently being introduced into the supply chain. Wireless distributed sensor networks (WSN) are already being used to monitor wildlife and to track military targets. Many more applications are being envisioned. For most of these applications some level of security is of utmost importance. Common to WSN and RFIDs are their severely limited power resources, which classify them as ultra-low power devices. Early sensor nodes used simple 8-bit microprocessors to implement basic communication, sensing and computing services. Security was an afterthought. The main power consumer is the RF-transceiver, or radio for short. In the past years specialized hardware for low-data rate and low-power radios has been developed. The new bottleneck are security services which employ computationally intensive cryptographic operations. Customized hardware implementations hold the promise of enabling security for severely power constrained devices. Most research groups are concerned with developing secure wireless communication protocols, others with designing efficient software implementations of cryptographic algorithms. There has not been a comprehensive study on hardware implementations of cryptographic algorithms tailored for ultra-low power applications. The goal of this dissertation is to develop a suite of cryptographic functions for authentication, encryption and integrity that is specifically fashioned to the needs of ultra-low power devices. This dissertation gives an introduction to the specific problems that security engineers face when they try to solve the seemingly contradictory challenge of providing lightweight cryptographic services that can perform on ultra-low power devices and shows an overview of our current work and its future direction