On the use of Hidden Markov Processes and auto-regressive filters to incorporate indoor bursty wireless channels into network simulation platforms

In this paper we thoroughly analyze two alternatives to replicate the bursty behavior that characterizes real indoor wireless channels within Network Simulation platforms. First, we study the performance of an improved Hidden Markov Process model, based on a time-wise configuration so as to decouple its operation from any particular traffic pattern. We compare it with the behavior of Bursty Error Model Based on an Auto-Regressive Filter, a previous proposal of ours that emulates the received Signal to Noise Ratio by means of an auto-regressive filter that captures the “memory” assessed in real measurements. We also study the performance of one of the legacy approaches intrinsically offered by most network simulation frameworks. By means of a thorough simulation campaign, we demonstrate that our two models are able to offer a much more realistic behavior, yet maintaining an affordable response in terms of computational complexity.The authors would like to express their gratitude to the Spanish government for its funding in the project “Connectivity as a Service: Access for the Internet of the Future”, COSAIF (TEC2012-38574-C02-01

Wireless Real-Time Communication in Tunnel-like Environments using Wireless Mesh Networks: The WICKPro Protocol

En los últimos años, las redes inalámbricas se están utilizando cada vez más en entornos industriales debido a sus ventajas respecto a redes cableadas: menor coste de instalación, soporte de movilidad, instalación en lugares donde los cables pueden ser problemáticos y mayor facilidad de reconfiguración. Estas redes inalámbricas normalmente deben proporcionar comunicación en tiempo real para satisfacer los requerimientos de las aplicaciones. Podemos encontrar ejemplos de comunicación en tiempo real con redes inalámbricas para entornos industriales en el campo de la automatización industrial y en el control de procesos, donde redes inalámbricas de radiofrecuencia han sido utilizadas para posibilitar comunicación en tiempo real con un despliegue sencillo. Asimismo, la industria también está interesada en comunicaciones en tiempo real en entornos subterráneos, puesto que existen diversas actividades que se llevan a cabo en escenarios tales como túneles y minas, incluyendo operaciones de minería, vigilancia, intervención y rescate. Las redes inalámbricas malladas (Wireless Mesh Networks, WMNs) representan una solución prometedora para conseguir comunicaci ón en tiempo real en entornos inalámbricos, dado que proporcionan una red troncal inalámbrica formada por encaminadores (routers) que es utilizada por terminales móviles. Sin embargo, las WMNs también presentan algunos retos: la naturaleza multisalto de estas redes causa interferencias entre flujos e interferencias de un flujo consigo mismo, además de que la propagación inalámbrica sufre shadowing y propagación multicamino. El estándar IEEE 802.11 ha sido ampliamente utilizado en redes WMNs debido a su bajo coste y la operación en bandas frecuenciales sin licencia. El problema es que su protocolo de acceso al medio (Medium Access Control, MAC) no es determinista y que sus comunicaciones sufren los problemas del terminal oculto y expuesto. Esta tesis doctoral se centra en el soporte de comunicaciones en tiempo real en entornos tipo túnel utilizando redes WMNs. Con este objetivo, desarrollamos un protocolo MAC y de nivel de red denominado WIreless Chain networK Protocol (WICKPro) que funciona sobre IEEE 802.11. Más concretamente, en este trabajo diseñamos dos versiones de este protocolo para proporcionar soporte de tráfico de tiempo real firme (Firm Real-Time, FRT) y de tiempo real no estricto (Soft Real-Time, SRT): FRT-WICKPro y SRT-WICKPro. Asimismo, proponemos un algoritmo de hand-off conocido como Double-Threshold Hand-off (DoTHa) para el manejo de la movilidad en SRT-WICKPro WICKPro utiliza un esquema de paso de testigo para solventar las interferencias entre flujos y de un flujo consigo mismo, así como los problemas del terminal oculto y expuesto, dado que este esquema no permite que dos nodos transmitan al mismo tiempo. Esta solución es razonable para redes pequeñas donde el re uso espacial es imposible o limitado. Para tratar la naturaleza no determinista de IEEE 802.11, combinamos el esquema de paso de testigo con una planificación cíclica global. Como es habitual en planificación cíclica, el hiperperiodo es dividido en un conjunto de ciclos secundarios. FRT-WICKPro inicia el paso de testigo de forma síncrona para satisfacer estrictamente dichos ciclos secundarios, mientras que SRT-WICKPro implementa un paso de testigo asíncrono y permite sobrepasar los ciclos secundarios, por lo que desacopla los ciclos secundarios reales de los te_oricos. Finalmente, DoTHa lidia con el shadowing y la propagación multicamino. Para abordar el shadowing, DoTHa permite llevar a cabo el proceso de hand-off en la región conectada y en la región de transición de un enlace, mientras que la propagación multicamino es ignorada para el proceso de hand-off porque la potencia recibida es promediada. Nuestras propuestas fueron validadas en experimentos de laboratorio y de campo, así como en simulación. Como un estudio de caso, llevamos a cabo la teleoperación de un robot móvil en dos entornos confinados: los pasillos de un edificio y el túnel del Somport. El túnel del Somport es un antiguo túnel ferroviario fuera de servicio que conecta España y Francia por los Pirineos Centrales. Aunque los robots autónomos son cada vez más importantes, la tecnología no está suficientemente madura para manejar entornos con alto dinamismo como sistemas de fabricación reconfigurables, o para realizar decisiones de vida o muerte, por ejemplo después de un desastre con contaminación radiactiva. Las aplicaciones que pueden beneficiarse de la teleoperación de robots móviles incluyen la monitorización en tiempo real y el uso de maquinaria robotizada, por ejemplo camiones dumper y máquinas tuneladoras, que podrían ser operadas remotamente para evitar poner en peligro vidas humanas.Industrial applications have been shifting towards wireless networks in recent years because they present several advantages compared with their wired counterparts: lower deployment cost, mobility support, installation in places where cables may be problematic, and easier reconfiguration. These industrial wireless networks usually must provide real-time communication to meet application requirements. Examples of wireless real-time communication for industrial applications can be found in factory automation and process control, where Radio Frequency wireless communication technologies have been employed to support flexible real-time communication with simple deployment. Likewise, industry is also interested in real-time communication in underground environments, since there are several activities that are carried out in scenarios such as tunnels and mines, including mining, surveillance, intervention, and rescue operations. Wireless Mesh Networks (WMNs) are promising enablers to achieve wireless real-time communication because they provide a wireless backbone comprised by dedicated routers that is utilized by mobile terminals. However, WMNs also present several challenges: wireless multi-hopping causes inter-flow and intra-flow interferences, and wireless propagation suffers shadowing and multi-path fading. The IEEE 802.11 standard has been widely used in WMNs due to its low cost and the operation in unlicensed frequency bands. The downside is that its Medium Access Control (MAC) protocol is non-deterministic, and that its communications suffer from the hidden and exposed terminal problems. This PhD thesis focuses on real-time communication in tunnel-like environments by using WMNs. Particularly, we develop a MAC and network protocol on top of the IEEE 802.11 standard to provide real-time capabilities, so-called WIreless Chain networK Protocol (WICKPro). Two WICKPro versions are designed to provide Firm Real-Time (FRT) or Soft Real-Time (SRT) traffic support: FRT-WICKPro and SRT-WICKPro. We also propose a hand-off algorithm dubbed Double-Threshold Hand-off (DoTHa) to manage mobility in SRT-WICKPro. WICKPro employs a token-passing scheme to solve the inter-flow and intra-flow interferences as well as the hidden and exposed terminal problems, since this scheme does not allow two nodes to transmit at the same time. This is a reasonable solution for small-scale networks where spatial reuse is impossible or limited. The non-deterministic nature of IEEE 802.11 is faced by combining the token-passing mechanism with a polling approach based on a global cyclic packet schedule. As usual in cyclic scheduling, the hyper-period is divided into minor cycles. FRT-WICKPro triggers the token synchronously and fulfills strictly minor cycles, whereas SRT-WICKPro carries out asynchronous token-passing and lets minor cycles be overrun, thereby decoupling the theoretic and the actual minor cycles. Finally, DoTHa deals with shadowing and multi-path fading. Shadowing is addressed by providing the opportunity of triggering hand-off in the connected and transitional regions of a link, while multi-path fading is neglected for hand-off purposes by smoothing the received signal power. We tested our proposals in laboratory and field experiments, as well as in simulation. As a case study, we carried out the tele-operation of a mobile robot within two confined environments: the corridors of a building and the Somport tunnel. The Somport tunnel is an old out-of-service railway tunnel that connects Spain and France through the Central Pyrenees. Although autonomous robots are becoming more and more important, technology is not mature enough to manage highly dynamic environments such as reconfigurable manufacturing systems, or to make life-and-death decisions, e.g., after a disaster with radioactivity contamination. Applications that can benefit from mobile robot tele-operation include real-time monitoring and the use of robotized machinery, for example, dumper trucks and tunneling machines, which could be remotely operated to avoid endangering human lives

Prediction-based techniques for the optimization of mobile networks

Mención Internacional en el título de doctorMobile cellular networks are complex system whose behavior is characterized by the superposition of several random phenomena, most of which, related to human activities, such as mobility, communications and network usage. However, when observed in their totality, the many individual components merge into more deterministic patterns and trends start to be identifiable and predictable. In this thesis we analyze a recent branch of network optimization that is commonly referred to as anticipatory networking and that entails the combination of prediction solutions and network optimization schemes. The main intuition behind anticipatory networking is that knowing in advance what is going on in the network can help understanding potentially severe problems and mitigate their impact by applying solution when they are still in their initial states. Conversely, network forecast might also indicate a future improvement in the overall network condition (i.e. load reduction or better signal quality reported from users). In such a case, resources can be assigned more sparingly requiring users to rely on buffered information while waiting for the better condition when it will be more convenient to grant more resources. In the beginning of this thesis we will survey the current anticipatory networking panorama and the many prediction and optimization solutions proposed so far. In the main body of the work, we will propose our novel solutions to the problem, the tools and methodologies we designed to evaluate them and to perform a real world evaluation of our schemes. By the end of this work it will be clear that not only is anticipatory networking a very promising theoretical framework, but also that it is feasible and it can deliver substantial benefit to current and next generation mobile networks. In fact, with both our theoretical and practical results we show evidences that more than one third of the resources can be saved and even larger gain can be achieved for data rate enhancements.Programa Oficial de Doctorado en Ingeniería TelemáticaPresidente: Albert Banchs Roca.- Presidente: Pablo Serrano Yañez-Mingot.- Secretario: Jorge Ortín Gracia.- Vocal: Guevara Noubi

Analyzing Granger causality in climate data with time series classification methods

Attribution studies in climate science aim for scientifically ascertaining the influence of climatic variations on natural or anthropogenic factors. Many of those studies adopt the concept of Granger causality to infer statistical cause-effect relationships, while utilizing traditional autoregressive models. In this article, we investigate the potential of state-of-the-art time series classification techniques to enhance causal inference in climate science. We conduct a comparative experimental study of different types of algorithms on a large test suite that comprises a unique collection of datasets from the area of climate-vegetation dynamics. The results indicate that specialized time series classification methods are able to improve existing inference procedures. Substantial differences are observed among the methods that were tested

Future Transportation

Greenhouse gas (GHG) emissions associated with transportation activities account for approximately 20 percent of all carbon dioxide (co2) emissions globally, making the transportation sector a major contributor to the current global warming. This book focuses on the latest advances in technologies aiming at the sustainable future transportation of people and goods. A reduction in burning fossil fuel and technological transitions are the main approaches toward sustainable future transportation. Particular attention is given to automobile technological transitions, bike sharing systems, supply chain digitalization, and transport performance monitoring and optimization, among others