1,720,958 research outputs found
Estimating Nonlinear Parameters Present in OFDM-based System Using Non-linear Least Squares
No full textAbstractWireless communication systems are omnipresent in our everyday life and high standards regarding capacity, re- liability, speed and power are naturally expected. In order to satisfy these requirements, more sophisticated and efficient technology is needed. This is especially true for the integrated amplifiers at the transmitter side, which are responsible for the majority of the power consumption. In order to obtain high gain at the low power levels, these amplifiers are operated into their nonlinear region. However, many communication schemes cannot handle the nonlinear distortion generated by such amplifiers. The nonlinear distortions generated at the transmitter side can be compensated through the use of digital predistortion. This method compensates the non-linear effects by first esti- mating a non-linear model for the amplifier, and then applying the inverse model onto the data during transmission such that the nonlinearities are canceled. The main advantage of this approach is that it allows to use the classical linear communication scheme once the precompensation is performed.In this work, Special attention goes to the estimation of the nonlinear model used for the predistortion. Most nonlinear models are not only nonlinear in behavior but also nonlinear in their parametrization, which requires spe- cial care during estimation of the model parameters. Performance of the simple linear least square estimator and nonlinear least square estimator is investigated using a National Instrument student setup
EH-CRAM: A Sustainable Energy Harvesting Algorithm for LPWANs
No full textLow Power Wide Area Network (LPWAN) technologies offer the advantage of wide coverage areas and low power consumption for low data-rate Internet-of-Things (IoT) applications. LoRaWAN, the Long Range Wide Area Network is a key technology in this space, with a growing worldwide presence. LoRa devices are expected to operate autonomously for extended periods in order to support diverse IoT applications. Despite being energy efficient, frequent battery replacements are typically required over the lifetime of a LoRa device. This increases maintenance costs and furthermore, disposing of large numbers of dead batteries is damaging to the environment. Energy harvesting offers a potential solution, but it is difficult to ensure sustainability. In this paper, we propose EH-CRAM, a centralized Kalman filter-based optimization algorithm where the gateway is responsible for controlling End-Device configurations (i.e: data transmission rates, spreading factors, and energy harvesting period) based upon incoming traffic and solar energy, thus balancing energy supply and demand. In addition, by using a time-synchronized cryptographic frequency hopping scheme, EH-CRAM also tackles the issues of energy efficiency and performance. Our evaluation shows that EH-CRAM significantly reduces contention while maximizing reliability and energy efficiency to support sustainable energy-harvesting for LoRa End- Devices (ED’s).sponsorship: This research is partially funded by the Research Fund KU Leuven, by imec, and by the Flemish Research Programme Cybersecurity. (Research Fund KU Leuven, Flemish Research Programme Cybersecurity, imec)status: Published onlin
Smart-Hop: Low-Latency Multi-hop Networking for LoRa
No full textThis research is partially funded by the Research Fund KU Leuven, and by imec and Flanders Innovation Entrepreneurship (VLAIO) in the context of the WiPeR project
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Investigation of the impact of a wireless Fog Warning System with respect to road traffic on a highway
No full textSudden visibility reductions on highways due to foggy weather conditions often lead to a drastic increase in car crash risks. Indeed, fog formation distorts drivers' perception and judgment of inter-vehicular distances, vehicles' speeds, and braking distances. In order to support drivers in dealing with the impact of fog, various on-board warning systems are being deployed today. Despite their added value, these systems are still in need of efficient solutions supporting smooth vehicle's acceleration/deceleration profiles. This is to avoid sudden braking (hence, higher car crash risks) incurred by sensor technologies restricted to line of sight measurements. To meet this goal, we advocate in this paper a Wireless Fog Warning System (WFWS) where cooperative awareness messages are disseminated and used for calculating acceleration/deceleration activities. Without loss of generality, we build on IEEE 802.11p WLAN as a basis technology. Using simulations on the open-source vehicular network simulation framework Veins, we demonstrate both the potential of such a system for increasing safety and smoothing traffic flow-as well as of computer simulation as a means of its evaluation.Outay, F (reprint author), Zayed Univ, Dubai, U Arab Emirates.
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Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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