3,272 research outputs found
Distributed estimation over a low-cost sensor network: a review of state-of-the-art
Proliferation of low-cost, lightweight, and power efficient sensors and advances in networked systems enable the employment of multiple sensors. Distributed estimation provides a scalable and fault-robust fusion framework with a peer-to-peer communication architecture. For this reason, there seems to be a real need for a critical review of existing and, more importantly, recent advances in the domain of distributed estimation over a low-cost sensor network. This paper presents a comprehensive review of the state-of-the-art solutions in this research area, exploring their characteristics, advantages, and challenging issues. Additionally, several open problems and future avenues of research are highlighted
A dynamic distributed multi-channel TDMA slot management protocol for ad hoc networks
With the emergence of new technologies and standards for wireless communications and an increase in application and user requirements, the number and density of deployed wireless ad hoc networks is increasing. For deterministic ad hoc networks, Time-Division Multiple Access (TDMA) is a popular medium access scheme, with many distributed TDMA scheduling algorithms being proposed. However, with increasing traffic demands and the number of wireless devices, proposed protocols are facing scalability issues. Besides, these protocols are achieving suboptimal spatial spectrum reuse as a result of the unsolved exposed node problem. Due to a shortage of available spectrum, a shift from fixed spectrum allocation to more dynamic spectrum sharing is anticipated. For dynamic spectrum sharing, improved distributed scheduling protocols are needed to increase spectral efficiency and support the coexistence of multiple co-located networks. Hence, in this paper, we propose a dynamic distributed multi-channel TDMA (DDMC-TDMA) slot management protocol based on control messages exchanged between one-hop network neighbors and execution of slot allocation and removal procedures between sender and receiver nodes. DDMC-TDMA is a topology-agnostic slot management protocol suitable for large-scale and high-density ad hoc networks. The performance of DDMC-TDMA has been evaluated for various topologies and scenarios in the ns-3 simulator. Simulation results indicate that DDMC-TDMA offers near-optimal spectrum utilization by solving both hidden and exposed node problems. Moreover, it proves to be a highly scalable protocol, showing no performance degradation for large-scale and high-density networks and achieving coexistence with unknown wireless networks operating in the same wireless domain
Reliable load-balancing routing for resource-constrained wireless sensor networks
Wireless sensor networks (WSNs) are energy and resource constrained. Energy limitations make it advantageous to balance radio transmissions across multiple sensor nodes. Thus, load balanced routing is highly desirable and has motivated a significant volume of research. Multihop sensor network architecture can also provide greater coverage, but requires a highly reliable and adaptive routing scheme to accommodate frequent topology changes. Current reliability-oriented protocols degrade energy efficiency and increase network latency. This thesis develops and evaluates a novel solution to provide energy-efficient routing while enhancing packet delivery reliability. This solution, a reliable load-balancing routing (RLBR), makes four contributions in the area of reliability, resiliency and load balancing in support of the primary objective of network lifetime maximisation. The results are captured using real world testbeds as well as simulations. The first contribution uses sensor node emulation, at the instruction cycle level, to characterise the additional processing and computation overhead required by the routing scheme. The second contribution is based on real world testbeds which comprises two different TinyOS-enabled senor platforms under different scenarios. The third contribution extends and evaluates RLBR using large-scale simulations. It is shown that RLBR consumes less energy while reducing topology repair latency and supports various aggregation weights by redistributing packet relaying loads. It also shows a balanced energy usage and a significant lifetime gain. Finally, the forth contribution is a novel variable transmission power control scheme which is created based on the experience gained from prior practical and simulated studies. This power control scheme operates at the data link layer to dynamically reduce unnecessarily high transmission power while maintaining acceptable link reliability
Network Management and Control for mmWave Communications
Millimeter-wave (mmWave) is one of the key technologies that enables the next wireless
generation. mmWave offers a much higher bandwidth than sub-6GHz communications
which allows multi-gigabit-per-second rates. This also alleviates the scarcity of spectrum
at lower frequencies, where most devices connect through sub-6GHz bands. However new
techniques are necessary to overcome the challenges associated with such high frequencies.
Most of these challenges come from the high spatial attenuation at the mmWave band,
which requires new paradigms that differ from sub-6GHz communications. Most notably
mmWave telecommunications are characterized by the need to be directional in order to
extend the operational range. This is achieved by using electronically steerable antenna
arrays, that focus the energy towards the desired direction by combining each antenna
element constructively or destructively. Additionally, most of the energy comes from
the Line Of Sight (LOS) component which gives mmWave a quasi-optical behaviour
where signals can reflect off walls and still be used for communication. Some other
challenges that directional communications bring are mobility tracking, blockages and
misalignments due to device rotation. The IEEE 802.11ad amendment introduced wireless
telecommunications in the unlicensed 60 GHz band. It is the first standard to address
the limitations of mmWave. It does so by introducing new mechanisms at the Medium
Access Control (MAC) and Physical (PHY) layers. It introduces multi-band operation,
relay operation mode, hybrid channel access scheme, beam tracking and beam forming
among others.
In this thesis we present a series of works that aim to improve mmWave
telecommunications. First we give an overview of the intrinsic challenges of mmWave
telecommunications, by explaining the modifications to the MAC and PHY layers. This
sets the base for the rest of the thesis. Then do a comprehensive study on how mmWave
behaves with existing technologies, namely TCP. TCP is unable to distinguish losses
caused by congestion or by transmission errors caused by channel degradation. Since
mmWave is affected by blockages more than sub-6GHz technologies, we propose a set
of parameters that improve the channel quality even for mobile scenarios. The next job
focuses on reducing the initial access overhead of mmWave by using sub-6GHz information
to steer towards the desired direction. We start this work by doing a comprehensive High Frequency (HF) and Low Frequency (LF) correlation, analyzing the similarity of
the existing paths between the two selected frequencies. Then we propose a beam
steering algorithm that reduces the overhead to one third of the original time. Once
we have studied how to reduce the initial access overhead, we propose a mechanism
to reduce the beam tracking overhead. For this we propose an open platform based
on a Field Programmable Gate Arrays (FPGA) where we implement an algorithm that
completely removes the need to train on the Station (STA) side. This is achieved by
changing beam patterns on the STA side while the Access Point (AP) is sending the
preamble. We can change up to 10 beam patterns without losing connection and we reduce
the overhead by a factor of 8.8 with respect to the IEEE 802.11ad standard. Finally
we present a dual band location system based on Commercial-Off-The-Shelve (COTS)
devices. Locating the STA can improve the quality of the channel significantly, since the
AP can predict and react to possible blockages. First we reverse engineer existing 60
GHz enabled COTS devices to extract Channel State Information (CSI) and Fine Timing
Measurements (FTM) measurements, from which we can estimate angle and distance.
Then we develop an algorithm that is able to choose between HF and LF in order to
improve the overall accuracy of the system. We achieve less than 17 cm of median error
in indoor environments, even when some areas are Non Line Of Sight (NLOS).This work has been supported by IMDEA Networks Institute.Programa de Doctorado en IngenierĂa Telemática por la Universidad Carlos III de MadridPresidente: Matthias Hollick.- Secretario: Vincenzo Mancuso.- Vocal: Paolo Casar
A study of the applicability of software-defined networking in industrial networks
173 p.Las redes industriales interconectan sensores y actuadores para llevar a cabo funciones de monitorizaciĂłn, control y protecciĂłn en diferentes entornos, tales como sistemas de transporte o sistemas de automatizaciĂłn industrial. Estos sistemas ciberfĂsicos generalmente están soportados por mĂşltiples redes de datos, ya sean cableadas o inalámbricas, a las cuales demandan nuevas prestaciones, de forma que el control y gestiĂłn de tales redes deben estar acoplados a las condiciones del propio sistema industrial. De este modo, aparecen requisitos relacionados con la flexibilidad, mantenibilidad y adaptabilidad, al mismo tiempo que las restricciones de calidad de servicio no se vean afectadas. Sin embargo, las estrategias de control de red tradicionales generalmente no se adaptan eficientemente a entornos cada vez más dinámicos y heterogĂ©neos.Tras definir un conjunto de requerimientos de red y analizar las limitaciones de las soluciones actuales, se deduce que un control provisto independientemente de los propios dispositivos de red añadirĂa flexibilidad a dichas redes. Por consiguiente, la presente tesis explora la aplicabilidad de las redes definidas por software (Software-Defined Networking, SDN) en sistemas de automatizaciĂłn industrial. Para llevar a cabo este enfoque, se ha tomado como caso de estudio las redes de automatizaciĂłn basadas en el estándar IEC 61850, el cual es ampliamente usado en el diseño de las redes de comunicaciones en sistemas de distribuciĂłn de energĂa, tales como las subestaciones elĂ©ctricas. El estándar IEC 61850 define diferentes servicios y protocolos con altos requisitos en terminos de latencia y disponibilidad de la red, los cuales han de ser satisfechos mediante tĂ©cnicas de ingenierĂa de tráfico. Como resultado, aprovechando la flexibilidad y programabilidad ofrecidas por las redes definidas por software, en esta tesis se propone una arquitectura de control basada en el protocolo OpenFlow que, incluyendo tecnologĂas de gestiĂłn y monitorizaciĂłn de red, permite establecer polĂticas de tráfico acorde a su prioridad y al estado de la red.Además, las subestaciones elĂ©ctricas son un ejemplo representativo de infraestructura crĂtica, que son aquellas en las que un fallo puede resultar en graves pĂ©rdidas econĂłmicas, daños fĂsicos y materiales. De esta forma, tales sistemas deben ser extremadamente seguros y robustos, por lo que es conveniente la implementaciĂłn de topologĂas redundantes que ofrezcan un tiempo de reacciĂłn ante fallos mĂnimo. Con tal objetivo, el estándar IEC 62439-3 define los protocolos Parallel Redundancy Protocol (PRP) y High-availability Seamless Redundancy (HSR), los cuales garantizan un tiempo de recuperaciĂłn nulo en caso de fallo mediante la redundancia activa de datos en redes Ethernet. Sin embargo, la gestiĂłn de redes basadas en PRP y HSR es estática e inflexible, lo que, añadido a la reducciĂłn de ancho de banda debida la duplicaciĂłn de datos, hace difĂcil un control eficiente de los recursos disponibles. En dicho sentido, esta tesis propone control de la redundancia basado en el paradigma SDN para un aprovechamiento eficiente de topologĂas malladas, al mismo tiempo que se garantiza la disponibilidad de las aplicaciones de control y monitorizaciĂłn. En particular, se discute cĂłmo el protocolo OpenFlow permite a un controlador externo configurar mĂşltiples caminos redundantes entre dispositivos con varias interfaces de red, asĂ como en entornos inalámbricos. De esta forma, los servicios crĂticos pueden protegerse en situaciones de interferencia y movilidad.La evaluaciĂłn de la idoneidad de las soluciones propuestas ha sido llevada a cabo, principalmente, mediante la emulaciĂłn de diferentes topologĂas y tipos de tráfico. Igualmente, se ha estudiado analĂtica y experimentalmente cĂłmo afecta a la latencia el poder reducir el nĂşmero de saltos en las comunicaciones con respecto al uso de un árbol de expansiĂłn, asĂ como balancear la carga en una red de nivel 2. Además, se ha realizado un análisis de la mejora de la eficiencia en el uso de los recursos de red y la robustez alcanzada con la combinaciĂłn de los protocolos PRP y HSR con un control llevado a cabo mediante OpenFlow. Estos resultados muestran que el modelo SDN podrĂa mejorar significativamente las prestaciones de una red industrial de misiĂłn crĂtica
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Integration of unidirectional technologies into wireless back-haul architecture
This thesis was submitted for the degree of Docter of Philosophy and awarded by Brunel University.Back-haul infrastructures of today's wireless operators must support the triple-play services demanded by the market or regulatory bodies. To cope with increasing capacity demand, the EU FP7 project CARMEN has developed a cost-effective heterogeneous
multi-radio wireless back-haul architecture, which may also leverage the native multicast
capabilities of broadcast technologies such as DVB-T to off-load high-bandwidth broadcast
content delivery. However, the integration of such unidirectional technologies into a packet-switched architecture requires careful considerations. The contribution of this thesis is the investigation, design and evaluation of protocols and mechanisms facilitating the integration of such unidirectional technologies into the wireless
back-haul architecture so that they can be configured and utilized by the spectrum and
capacity optimization modules. This integration mainly concerns the control plane and, in particular, the aspects related to resource and capability descriptions, neighborhood, link and Multi Protocol Label Switching (MPLS) Label-Switched Path (LSP) monitoring, unicast and multicast LSP signalling as well as topology forming and maintenance. During the course of this study we have analyzed the problem space, proposed solutions to the resulting research questions and evaluated our approach. Our results show that the now Unidirectional Technology (UDT)-aware architecture can readily consider
Unidirectional Technologies (UDTs) to distribute, for example, broadcast content
A cross-layer middleware architecture for time and safety critical applications in MANETs
Mobile Ad hoc Networks (MANETs) can be deployed instantaneously and adaptively, making them highly suitable to military, medical and disaster-response scenarios. Using real-time applications for provision of instantaneous and dependable communications, media streaming, and device control in these scenarios is a growing research field. Realising timing requirements in packet delivery is
essential to safety-critical real-time applications that are both delay- and loss-sensitive.
Safety of these applications is compromised by packet loss, both on the network and by the applications themselves that will drop packets exceeding delay bounds. However, the provision of this required Quality of Service (QoS) must overcome issues relating to the lack of reliable existing infrastructure, conservation of safety-certified functionality. It must also overcome issues relating to the layer-2 dynamics with causal factors including hidden transmitters and fading channels. This thesis proposes that bounded maximum delay and safety-critical application support can be achieved by using cross-layer middleware. Such an approach benefits from the use of established protocols without requiring modifications to safety-certified ones. This research proposes ROAM: a novel, adaptive and scalable cross-layer Real-time Optimising Ad hoc Middleware framework for the provision and maintenance of performance guarantees in self-configuring MANETs. The ROAM framework is designed to be scalable to new optimisers and MANET protocols and requires no modifications of protocol functionality. Four original contributions are proposed: (1) ROAM, a middleware entity abstracts information from the protocol stack using application programming interfaces (APIs) and that implements optimisers to monitor and autonomously tune conditions at protocol layers in response to dynamic network conditions. The cross-layer approach is MANET protocol generic, using minimal imposition on the protocol stack, without protocol modification requirements. (2) A horizontal handoff optimiser that responds to time-varying link quality to ensure optimal and most robust channel usage. (3) A distributed contention reduction optimiser that reduces channel contention and related delay, in response to detection of the presence of a hidden transmitter. (4) A feasibility evaluation of the ROAM architecture to bound maximum delay and jitter in a comprehensive range of ns2-MIRACLE simulation scenarios that demonstrate independence from the key causes of network dynamics:
application setting and MANET configuration; including mobility or topology. Experimental results show that ROAM can constrain end-to-end delay, jitter and packet loss, to support real-time applications with critical timing requirements
Towards enabling cross-layer information sharing to improve today's content delivery systems
Content is omnipresent and without content the Internet would not be what it is today. End users consume content throughout the day, from checking the latest news on Twitter in the morning, to streaming music in the background (while working), to streaming movies or playing online games in the evening, and to using apps (e.g., sleep trackers) even while we sleep in the night. All of these different kinds of content have very specific and different requirements on a transport—on one end, online gaming often requires a low latency connection but needs little throughput, and, on the other, streaming a video requires high throughput, but it performs quite poorly under packet loss. Yet, all content is transferred opaquely over the same transport, adhering to a strict separation of network layers. Even a modern transport protocol such as Multi-Path TCP, which is capable of utilizing multiple paths, cannot take the (above) requirements or needs of that content into account for its path selection. In this work we challenge the layer separation and show that sharing information across the layers is beneficial for consuming web and video content. To this end, we created an event-based simulator for evaluating how applications can make informed decisions about which interfaces to use delivering different content based on a set of pre-defined policies that encode the (performance) requirements or needs of that content. Our policies achieve speedups of a factor of two in 20% of our cases, have benefits in more than 50%, and create no overhead in any of the cases. For video content we created a full streaming system that allows an even finer grained information sharing between the transport and the application. Our streaming system, called VOXEL, enables applications to select dynamically and on a frame granularity which video data to transfer based on the current network conditions. VOXEL drastically reduces video stalls in the 90th-percentile by up to 97% while not sacrificing the stream's visual fidelity. We confirmed our performance improvements in a real-user study where 84% of the participants clearly preferred watching videos streamed with VOXEL over the state-of-the-art.Inhalte sind allgegenwärtig und ohne Inhalte wäre das Internet nicht das, was es heute ist. Endbenutzer konsumieren Inhalte von früh bis spät - es beginnt am Morgen mit dem Lesen der neusten Nachrichten auf Twitter, dem online hören von Musik während der Arbeit, wird fortgeführt mit dem Schauen von Filmen über Online-Streaming Dienste oder dem spielen von Mehrspieler Online Spielen am Abend, und sogar dem, mit dem Internet synchronisierten, Überwachens des eigenen Schlafes in der Nacht. All diese verschiedenen Arten von Inhalten haben sehr spezifische und unterschiedliche Ansprüche an den Transport über das Internet - auf der einen Seite sind es Online Spiele, die eine sehr geringe Latenz, aber kaum Durchsatz benötigen, auf der Anderen gibt es Video-Streaming Dienste, die einen sehr hohen Datendurchsatz benötigen, aber, sehr nur schlecht mit Paketverlust umgehen können. Jedoch werden all diese Inhalte über den selben, undurchsichtigen, Transportweg übertragen, weil an eine strikte Unterteilung der Netzwerk- und Transportschicht festgehalten wird. Sogar ein modernes Übertragungsprotokoll wie MPTCP, welches es ermöglicht mehrere Netzwerkpfade zu nutzen, kann die (oben genannten) Anforderungen oder Bedürfnisse des Inhaltes, nicht für die Pfadselektierung, in Betracht ziehen. In dieser Arbeit fordern wir die Trennung der Schichten heraus und zeigen, dass ein Informationsaustausch zwischen den Netzwerkschichten von großem Vorteil für das Konsumieren von Webseiten und Video Inhalten sein kann. Hierzu haben wir einen Ereignisorientierten Simulator entwickelt, mit dem wir untersuchten wie Applikationen eine informierte Entscheidung darüber treffen können, welche Netzwerkschnittstellen für verschiedene Inhalte, basierend auf vordefinierten Regeln, welche die Leistungsvorgaben oder Bedürfnisse eines Inhalts kodieren, benutzt werden sollen. Unsere Regeln erreichen eine Verbesserung um einen Faktor von Zwei in 20% unserer Testfälle, haben einen Vorteil in mehr als 50% der Fälle und erzeugen in keinem Fall einen Mehraufwand. Für Video Inhalte haben wir ein komplettes Video-Streaming System entwickelt, welches einen noch feingranulareren Informationsaustausch zwischen der Applikation und des Transportes ermöglicht. Unser, VOXEL genanntes, System ermöglicht es Applikationen dynamisch und auf Videobild Granularität zu bestimmen welche Videodaten, entsprechend der aktuellen Netzwerksituation, übertragen werden sollen. VOXEL kann das stehenbleiben von Videos im 90%-Perzentil drastisch, um bis zu 97%, reduzieren, ohne dabei die visuelle Qualität des übertragenen Videos zu beeinträchtigen. Wir haben unsere Leistungsverbesserung in einer Studie mit echten Benutzern bestätigt, bei der 84% der Befragten es, im vergleich zum aktuellen Stand der Technik, klar bevorzugten Videos zu schauen, die über VOXEL übertragen wurden
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