1,720,988 research outputs found
Data dissemination scheme for distributed storage for IoT observation systems at large scale
No full textIn the emerging field of the Internet of Things (IoT), Wireless Sensor Networks (WSNs) have a key role to play in sensing and collecting measures on the surrounding environment. In the deployment of large scale observation systems in remote areas, when there is not a permanent connection with the Internet, WSNs are calling for replication and distributed storage techniques that increase the amount of data stored within the WSN and reduce the probability of data loss. Unlike conventional network data storage, WSN-based distributed storage is constrained by the limited resources of the sensors. In this paper, we propose a low-complexity distributed data replication mechanism to increase the resilience of WSN-based distributed storage at large scale. In particular, we propose a simple, yet accurate, analytical modeling framework and an extensive simulation campaign, which complement experimental results on the SensLab testbed. The impact of several key parameters on the system performance is investigated
Redundant distributed data storage: experimentation with the SensLab testbed
No full textWireless sensor network (WSN)-based applications typically require to store data in the network. For instance, in the surveillance of isolated areas, if no sink nodes are present, WSNs may archive observation data that are periodically retrieved by an external agent. In contrast to conventional network data storage, storing data in WSNs is challenging because of the limited power, memory, and communication bandwidth of WSNs. In our study, we review the state-of-art techniques for data replication and storage in WSNs, and we propose a lowcomplexity distributed data replication mechanism to increase the resilience of WSN storage capacity against node failure and local memory shortage. We evaluate our approach through experimental results collected on the SensLab large-scale real testbed. In particular, we show how the performance is affected by changing the configuration of several key system parameters, such as (i) the transmission power of the nodes; (ii) the control message overhead; (iii) the number of deployed nodes; and (iv) the redundancy. To the best of our knowledge, this is one of the first works presenting experimental results at a really large scale on SensLab
Cross-layer design and analysis of WSN-based mobile target detection systems
No full textThe limited node capabilities typical of Wireless Sensor Networks (WSNs) call for crosslayer design optimization. In this paper, we address the problem of designing and operating long-lasting surveillance mobile target detection applications for unattended WSNs with a priori knowledge of the nodes’ positions. In particular, we focus on the cross-layer interaction between the sensing layer (devoted to the detection of a mobile target crossing the monitored area) and the communication layer (devoted to the transmission of the alert, upon detection, from a sensing node to the network sink). The performance of the sensing layer is characterized by the probability of target missed detection and the delay before the first sensor detection act. The communication layer is investigated considering two Medium Access Control (MAC) protocols: X-MAC [1] and the novel Cascade (Cas)-MAC protocol, inspired by the principles of the D-MAC protocol [2]. At both layers, we validate analytical models through realistic simulations and experiments. The cross layer interaction between the two layers is achieved considering a proper model for the network lifetime, based on the average energy depletion at the node level. Finally, to highlight the benefits of the proposed framework, we present a cross-layer optimization approach for the configuration of the system parameters, considering several relevant network topologies
Distributed Data Storage and Retrieval Schemes in RPL/IPv6-based networks
No full textThis chapter deals with distributed data storage and retrieval techniques in WSNs. The focus is on WSN systems for the Internet of Things (IoT), a new vision of the Internet aiming at pushing IP conne tivity into smart objects. The range of objects involved in the Internet of Things also encompasses Radio Frequency Identi ation (RFID) and Machine-to-Machine (M2M) systems, to cite a few. These technologies will be also described in detail
Data storage and retrieval with RPL routing
No full textIn scenarios like the surveillance of isolated areas, when the border node of a network does not have a permanent connection with the Internet, Wireless Sensor Networks (WSNs) are calling for resilient in-network data storage techniques which minimize the risk of data loss. The efficiency of these techniques can be largely improved exploiting information on the status of the network, such as that used by routing protocols. In particular, one of the most used protocol in Internet of Things (IoT) scenarios is the IPv6 Routing Protocol for Low power and lossy networks (RPL). In this paper, we propose a redundant distributed data storage and retrieval mechanism to increase the resilience and storage capacity of a RPL-based WSN against local memory shortage. We evaluate our approach in the Contiki operating system through extensive analysis with the Cooja simulator
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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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