736 research outputs found

    Polar communications: Status and recommendations. Report of the Science Working Group

    Get PDF
    The capabilities of the existing communication links within the polar regions, as well as between the polar regions and the continental United States, are summarized. These capabilities are placed in the context of the principal scientific disciplines that are active in polar research, and in the context of how scientists both utilize and are limited by present technologies. Based on an assessment of the scientific objectives potentially achievable with improved communication capabilities, a list of requirements on and recommendations for communication capabilities necessary to support polar science over the next ten years is given

    A Network Tomography Approach for Traffic Monitoring in Smart Cities

    Get PDF
    Traffic monitoring is a key enabler for several planning and management activities of a Smart City. However, traditional techniques are often not cost efficient, flexible, and scalable. This paper proposes an approach to traffic monitoring that does not rely on probe vehicles, nor requires vehicle localization through GPS. Conversely, it exploits just a limited number of cameras placed at road intersections to measure car end-to-end traveling times. We model the problem within the theoretical framework of network tomography, in order to infer the traveling times of all individual road segments in the road network. We specifically deal with the potential presence of noisy measurements, and the unpredictability of vehicles paths. Moreover, we address the issue of optimally placing the monitoring cameras in order to maximize coverage, while minimizing the inference error, and the overall cost. We provide extensive experimental assessment on the topology of downtown San Francisco, CA, USA, using real measurements obtained through the Google Maps APIs, and on realistic synthetic networks. Our approach provides a very low error in estimating the traveling times over 95% of all roads even when as few as 20% of road intersections are equipped with cameras

    A network tomography approach for traffic monitoring in smart cities

    Get PDF
    Various urban planning and managing activities required by a Smart City are feasible because of traffic monitoring. As such, the thesis proposes a network tomography-based approach that can be applied to road networks to achieve a cost-efficient, flexible, and scalable monitor deployment. Due to the algebraic approach of network tomography, the selection of monitoring intersections can be solved through the use of matrices, with its rows representing paths between two intersections, and its columns representing links in the road network. Because the goal of the algorithm is to provide a cost-efficient, minimum error, and high coverage monitor set, this problem can be translated into an optimization problem over a matroid, which can be solved efficiently by a greedy algorithm. Also as supplementary, the approach is capable of handling noisy measurements and a measurement-to-path matching. The approach proves a low error and a 90% coverage with only 20% nodes selected as monitors in a downtown San Francisco, CA topology --Abstract, page iv

    Overlay networks monitoring

    Get PDF
    The phenomenal growth of the Internet and its entry into many aspects of daily life has led to a great dependency on its services. Multimedia and content distribution applications (e.g., video streaming, online gaming, VoIP) require Quality of Service (QoS) guarantees in terms of bandwidth, delay, loss, and jitter to maintain a certain level of performance. Moreover, E-commerce applications and retail websites are faced with increasing demand for better throughput and response time performance. The most practical way to realize such applications is through the use of overlay networks, which are logical networks that implement service and resource management functionalities at the application layer. Overlays offer better deployability, scalability, security, and resiliency properties than network layer based implementation of services. Network monitoring and routing are among the most important issues in the design and operation of overlay networks. Accurate monitoring of QoS parameters is a challenging problem due to: (i) unbounded link stress in the underlying IP network, and (ii) the conflict in measurements caused by spatial and temporal overlap among measurement tasks. In this context, the focus of this dissertation is on the design and evaluation of efficient QoS monitoring and fault location algorithms using overlay networks. First, the issue of monitoring accuracy provided by multiple concurrent active measurements is studied on a large-scale overlay test-bed (PlanetLab), the factors affecting the accuracy are identified, and the measurement conflict problem is introduced. Then, the problem of conducting conflict-free measurements is formulated as a scheduling problem of real-time tasks, its complexity is proven to be NP-hard, and efficient heuristic algorithms for the problem are proposed. Second, an algorithm for minimizing monitoring overhead while controlling the IP link stress is proposed. Finally, the use of overlay monitoring to locate IP links\u27 faults is investigated. Specifically, the problem of designing an overlay network for verifying the location of IP links\u27 faults, under cost and link stress constraints, is formulated as an integer generalized flow problem, and its complexity is proven to be NP-hard. An optimal polynomial time algorithm for the relaxed problem (relaxed link stress constraints) is proposed. A combination of simulation and experimental studies using real-life measurement tools and Internet topologies of major ISP networks is conducted to evaluate the proposed algorithms. The studies show that the proposed algorithms significantly improve the accuracy and link stress of overlay monitoring, while incurring low overheads. The evaluation of fault location algorithms show that fast and highly accurate verification of faults can be achieved using overlay monitoring. In conclusion, the holistic view taken and the solutions developed for network monitoring provide a comprehensive framework for the design, operation, and evolution of overlay networks

    Body attenuation and path loss exponent estimation for RSS-based positioning in WSN

    Get PDF
    The influence of the human body in antenna systems has significant impact in the received signal strength (RSS) of wireless transmissions. Accounting for body effect is generally considered as being able to improve position estimation based on RSS measurements. In this work we perform several experiments with a wireless sensor network, using a sensor node equipped with an inertial measurement unit (IMU), in order to obtain the relative orientation between the sensor node and multiple anchor nodes. A model of the RSS attenuation induced by the body was created using experimental measurements in a controlled environment and applied to a real-time positioning system. A path loss exponent (PLE) estimation method using RSS information from neighbor anchors was also implemented and evaluated. Weighted centroid localization (WCL) algorithm was the positioning method used in this work. When the sensor node was placed on the user’s body, accounting for body effect produced negligible improvements (6%) in the best-case scenario and consistently degraded accuracy under real conditions, whether the node was placed on the user’s body (in the order of 3%), 10 cm away (from 14% to 35%) or 20 cm away from the body (from 42% to 105%) for results in the 70th percentile. The PLE estimation method showed improvements (in the order of 11%) when the sensor node is further away from the body. Results demonstrate that the distance between sensor node and the body has an extremely important influence on the accuracy of the position estimate.This work has been supported by FCT (Fundação para a Ciência e Tecnologia) in the scope of the project UID/EEA/04436/2013. Helder D. Silva is supported by FCT under the grant SFRH/BD/78018/2011info:eu-repo/semantics/publishedVersio

    Langattomien anturiverkkojen sotilas-, agroteknologia- ja energiatutkimussovelluksia

    Get PDF
    The physical quantities nowadays are widely measured by using electronic sensors. Wireless sensor networks (WSNs) are low-cost, low-power electronic devices capable of collecting data using their onboard sensors. Some wireless sensor nodes are equipped with actuators, providing the possibility to change the state of the physical world. The ability to change the state of a physical system means that WSNs can be used in control and automation applications. This research focuses on appropriate system design for four different wireless measurement and control cases. The first case provides a hardware and software solution for camera integration to a wireless sensor node. The images are captured and processed inside the sensor node using low power computational techniques. In the second application, two different wireless sensor networks function in cooperation to overcome seeding problems in agricultural machinery. The third case focuses on indoor deployment of the wireless sensor nodes into an area of urban crisis, where the nodes supply localization information to friendly assets such as soldiers, firefighters and medical personnel. The last application focuses on a feasibility study for energy harvesting from asphalt surfaces in the form of heat.Fysikaaliset suureet mitataan nykyisin elektronisten anturien avulla. Langattomat anturiverkot ovat kustannustasoltaan edullisia, matalan tehonkulutuksen elektronisia laitteita, jotka kykenevät suorittamaan mittauksia niissä olevilla antureilla. Langattomat anturinoodit voidaan myös liittää toimilaitteisiin, jolloin ne voivat vaikuttaa fyysiseen ympäristöönsä. Koska langattomilla anturi- ja toimilaiteverkoilla voidaan vaikuttaa niiden fysikaalisen ympäristön tilaan, niiden avulla voidaan toteuttaa säätö- ja automaatiosovelluksia. Tässä väitöskirjaty össä suunnitellaan ja toteutetaan neljä erilaista langattomien anturi- ja toimilaiteverkkojen automaatiosovellusta. Ensimmäisenä tapauksena toteutetaan elektroniikka- ja ohjelmistosovellus, jolla integroidaan kamera langattomaan anturinoodiin. Kuvat tallennetaan ja prosessoidaan anturinoodissa vähän energiaa kuluttavia laskentamenetelmiä käyttäen. Toisessa sovelluksessa kahdesta erilaisesta langattomasta anturiverkosta koostuvalla järjestelmällä valvotaan siementen syöttöä kylvökoneessa. Kolmannessa sovelluksessa levitetään kaupunkiympäristössä kriisitilanteessa rakennuksen sisätiloihin langaton anturiverkko. Sen anturinoodit välittävät paikkatietoa rakennuksessa operoiville omille joukoille, jotka voivat tilanteesta riippuen olla esimerkiksi sotilaita, palomiehiä tai lääkintähenkilökuntaa. Neljännessä sovelluksessa toteutetaan langaton anturiverkko, jonka keräämää mittausdataa käytetään arvioitaessa lämpöenergian keräämismahdollisuuksia asfalttipinnoilta.fi=vertaisarvioitu|en=peerReviewed

    Master of Science

    Get PDF
    thesisLocation of an object or person in in-door environments is a vital piece of in-formation. Traditionally, global positioning system-based devices do an excellent job in providing location information but are limited in in-door environments due to lack of an unobstructed line of sight. Wireless environments, with their extreme sensitivity to the positioning of objects inside them, provide excellent opportunities for obtaining location information of subjects. Received signal strength (RSS) based localization methods attract special attention as they can be readily implemented with "off-the-shelf" hardware and software. Device-free localization (DFL) presents a new and promising dimension in RSS-based localization research by providing a non-intrusive method of localization. However, existing RSS-based localization schemes assume a fixed or known transmit power. Any unexpected change in transmit power, not known to the receivers in the wireless network, can introduce errors in location estimate. Previous work has shown that meticulously planned power attacks can result in expected errors, in location of a transmitting sensor, in excess of 18 meters for an area of 75 X 50 m2. We find that the localization error in DFL can increase by four-fold when under power attack of 15 dB amplitude by multiple adversaries. Certain nonadversarial circumstances can also lead to unexpected changes in transmit power which would result in increased localization error. In this thesis, we focus on detection and isolation of wireless sensor nodes in a network which vary their transmit power to cause unexpected changes in RSS measurements and lead to increased localization errors in DFL. In the detection methods presented in this thesis, we do not require a training phase and hence, our methods are robust for use in dynamic environments where the training data may get obsolete frequently. We present our work with special focus on DFL methods using wireless sensor networks. However, the methods developed are generic and can be easily extended to active localization methods using both wireless sensor networks (WSN) and IEEE 802.11 protocols. To evaluate the effectiveness of our detection method, we perform extensive experiments in indoor settings using a network of 802.15.4 (Zigbee) compliant wireless sensor nodes and present evaluation results in the form of average detection rate, ROC curves, probability of missed detection and false alarm

    Wireless sensor systems in indoor situation modeling II (WISM II)

    Get PDF
    fi=vertaisarvioimaton|en=nonPeerReviewed
    • …
    corecore