1,720,993 research outputs found
Adaptive Holding time and Depth-Based Routing for Underwater Wireless Sensor Networks
Full text linkIn Underwater Wireless Sensor Networks (UWSNs), traditional enhancements of Depth-Based Routing (DBR) scheme rely either on increasing the network overhead or on the adoption of offline localization schemes to improve the network performance in terms of energy consumption, end-to-end delay or network throughput. Unfortunately, localization based techniques are very hard to implement in practice. In this work we show some preliminary results about the performance of a routing scheme called Adaptive Holding time and Depth-based routing (AHD) that we propose to dynamically adapt DBR configuration parameters. Specifically, we show a set of simulation experiments that suggest that networks implementing AHD show a reduced energy consumption with respect to those implementing the standard version of DBR. Simulations are performed by using our simulation library [8] of DBR [11] developed for the simulator AquaSim-Next Generation (NG) underwater simulator, which is based on Network Simulator-3 (NS-3). The characteristics of this library (detailed representation of cross-layer communications and operation modes of the modems) allows us\ud
an accurate prediction of the performance improvement of AHD with respect to standard DBR
Analysis and optimisations in depth-based routing for underwater sensor networks
Full text linkUnderwater Sensor Networks (UWSNs) employ sensor nodes and acoustic communication to detect physical attributes of water such as temperature, pressure, etc. Research on UWSNs has emerged thanks to their wide spectrum of applications which includes the management of the oil reservoirs and the prevention of aqueous disasters, as well as military surveillance. The dynamic conditions of water, the energy constraints and the high error probability during data transmission are prominent challenges in the design of routing protocols in UWSNs. One of the main routing schemes is Depth-based routing (DBR) that performs a specialized anycast routing to the surface sinks, based along the depth measured from pressure sensors. In this thesis, we study and optimise some routing protocols for UWSNs, specifically those based on DBR. To this aim, we designed a novel simulator for studying DBR and its enhancements. Our simulator is based on AquaSim-NG and NS-3 (Network Simulator). With respect to the state of the art, we implemented the cross-layer communication required by DBR and an accurate representation of the operational modes of acoustic modems with the associated energy consumption. We developed some analytical models for UWSNs with the aim of a) identifying the optimal transmission range for sensor nodes given the state of the system, b) finding the optimal number of hops between the source and destination under various network settings, c) evaluating the role of the depth threshold in the definition of the routing scheme. In this work, a pivotal role is played by the energy consumption and expected lifetime of the network. Finally, based on our findings, we designed the Residual energy-Depth (RD) routing protocol which improves the network lifetime
Identifying the Optimal transmission range in Depth-Based Routing For UWSN
Full text linkRouting in Underwater Wireless Sensor Networks (UWSNs) is a challenging problem because of the intrinsic characteristics of this class of wireless networks (long propagation delay, mobility of nodes, etc.) and because of the performance indices that must be taken into account, such as the network throughput, the packet delivery ratio and the energy cost. In particular, routing algorithms must grant a low energy cost in order to maximize the lifetime of the network's nodes. In this study, we focus on a popular routing protocol for UWSNs, namely the Depth-Based Routing (DBR). Specially, we study the impact of the transmission range of the nodes on the network performance indices, with particular attention to its energy efficiency. The study is based on an extensive set of simulations performed in AquaSim-NG using a library that has been developed with the aim of providing an accurate estimation of the nodes' energy consumption. The main outcome of our work is showing the relation between transmission range providing the optimal DBR energy efficiency and the density of the nodes in a UWSN
Radar sensor based machine learning approach for precise vehicle position estimation
Full text linkEstimating vehicles’ position precisely is essential in Vehicular Adhoc Networks (VANETs) for their safe, autonomous, and reliable operation. The conventional approaches used for vehicles’ position estimation, like Global Positioning System (GPS) and Global Navigation Satellite System (GNSS), pose significant data delays and data transmission errors, which render them ineffective in achieving precision in vehicles’ position estimation, especially under dynamic environments. Moreover, the existing radar-based approaches proposed for position estimation utilize the static values of range and azimuth, which make them inefficient in highly dynamic environments. In this paper, we propose a radar-based relative vehicle positioning estimation method. In the proposed method, the dynamic range and azimuth of a Frequency Modulated Continuous Wave radar is utilized to precisely estimate a vehicle’s position. In the position estimation process, the speed of the vehicle equipped with the radar sensor, called the reference vehicle, is considered such that a change in the vehicle’s speed changes the range and azimuth of the radar sensor. For relative position estimation, the distance and relative speed between the reference vehicle and a nearby vehicle are used. To this end, only those vehicles are considered that have a higher possibility of coming in contact with the reference vehicle. The data recorded by the radar sensor is subsequently utilized to calculate the precision and intersection Over Union (IOU) values. You Only Look Once (YOLO) version 4 is utilized to calculate precision and IOU values from the data captured using the radar sensor. The performance is evaluated under various real-time traffic scenarios in a MATLAB-based simulator. Results show that our proposed method achieves 80.0% precision in position estimation and obtains an IOU value up to 87.14%, thereby outperforming the state-of-the-art
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
Implementation of Depth-based routing and its enhancement in Aqua-Sim Next Generation for Underwater Wireless Sensor Networks
No full textIn the last decade, Underwater Wireless Sensor Networks have been widely studied because of their peculiar aspects that distinguish them from common wireless terrestrial networks. Their applications range from environmental monitoring to military defense. The definition of efficient routing protocols in underwater sensor networks is a challenging topic of research because of the intrinsic characteristics of these networks, such as the need of handling the node mobility and the difficulty in balancing the energy consumed by the nodes. Depth-Based Routing protocol is an opportunistic routing protocol for Underwater Sensor Networks which provides good performance both under high and low node mobility scenarios. The main contribution of our work is presenting a novel simulator for studying Depth-Based Routing protocol and its variants as well as novel routing protocols. Our simulator is based on AquaSim-Next-Generation which is a specialized tool for studying underwater networks. With our work, we improve the state of the art of underwater routing protocol simulators by implementing, among other features, a detailed cross-layer communication and an accurate model of the
operational modes of acoustic modem and their energy consumption. The simulator is open source and freely downloadable. Moreover, we propose a novel and completely distributed routing protocol, named Residual energy-Depth based routing. It takes into account the residual energy at the
nodes’ batteries to select the forwarder nodes and improves the network lifetime by providing a more uniform energy consumption among them. We compare its performance with that of Depth-Based Routing protocol and a receiver-based routing protocol implementing a probabilistic opportunistic forwarding scheme
Analysis of performance in Depth Based Routing for Underwater Wireless Sensor Networks
Full text linkIn the last decade, Underwater Wireless Sensor Networks (UWSNs) have been widely studied because of their peculiar aspects that distinguish them from common wireless terrestrial networks. In fact, most UWSNs use acoustic instead of radio-frequency based communications, and nodes are subject to high mobility caused by water currents. As a consequence, specialized routing algorithms have been developed to tackle this challenging scenario. Depth based Routing (DBR) is one of the first protocols that have been developed to this aim, and is still widely adopted in actual implementations of UWSNs. In this paper we propose a stochastic analysis that aims at evaluating the performance of UWSNs using DBR in terms of expected energy consumption and expected end-to-end delay. Under a set of assumptions, we give expressions for these performance indices that can be evaluated efficiently, and hence they can be adopted as the basis for optimizing the configuration parameters of the protocol
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
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