1,720,963 research outputs found
Experimental results for a passive forward scatter radar based on OFDM waveforms of opportunity
No full textRecently, it has been demonstrated that OFDM waveforms of opportunity have a non-negligible impact on the performance of a passive forward scatter radar (PFSR) when employing conventional processing schemes. Therefore, ad-hoc signal processing techniques have been proposed for improving both the interference cancellation stage and the target signature extraction in OFDM-based PFSR. This paper reports on the performance obtained with the resulting PFSR sensor in dedicated experimental tests. To this purpose a Digital Video Broadcasting - Terrestrial transmitter is employed as illuminator of opportunity and the detection capability of a commercial off-the-shelf (COTS) based receiver is investigated against aerial targets. The results demonstrate the benefits of the proposed approach in a real-world scenario
Fusing measurements from wi-fi emission-based and passive radar sensors for short-range surveillance
Full text linkIn this work, we consider the joint use of different passive sensors for the localization and tracking of human targets and small drones at short ranges, based on the parasitic exploitation of Wi-Fi signals. Two different sensors are considered in this paper: (i) Passive Bistatic Radar (PBR) that exploits the Wi-Fi Access Point (AP) as an illuminator of opportunity to perform uncooperative target detection and localization and (ii) Passive Source Location (PSL) that uses radio frequency (RF) transmissions from the target to passively localize it, assuming that it is equipped with Wi-Fi devices. First, we show that these techniques have complementary characteristics with respect to the considered surveillance applications that typically include targets with highly variable motion parameters. Therefore, an appropriate sensor fusion strategy is proposed, based on a modified version of the Interacting Multiple Model (IMM) tracking algorithm, in order to benefit from the information diversity provided by the two sensors. The performance of the proposed strategy is evalu-ated against both simulated and experimental data and compared to the performance of the single sensors. The results confirm that the joint exploitation of the considered sensors based on the proposed strategy largely improves the positioning accuracy, target motion recognition capability and continuity in target tracking
Fusing active and passive measurements for drone localization
No full textThis paper investigates the joint exploitation of Wi-Fi based Passive Bistatic Radar (PBR) and Wi-Fi based Passive Source Location (PSL) for drone localization. The inherent features of the two strategies and the results obtained from their comparison on experimental data show an interesting complementarity between them. Following this consideration, a proper sensor fusion strategy combining these two methodologies is investigated in order to achieve improved results in terms of positioning capability. The three strategies (PBR, PSL and sensor fusion) are evaluated against experimental data. The comparison between the use of the sensor fusion approach and the localization based on a single sensor (PBR or PSL) shows the benefits coming from the exploitation of multiple sensors
Detection and 3D localization of ultralight aircrafts and drones with a WiFi-based passive radar
Full text linkThis paper investigates the possibility to localize small aircrafts and drones in three-dimensions by exploiting a passive radar based on WiFi transmissions. Specifically, following the latest results of the authors, where the effectiveness of the WiFi-based passive radar has been demonstrated for the detection and 2D localization of small aircrafts, the advanced capability to estimate their height is demonstrated in this paper. In addition, the new capability is explored to detect and localize small commercial drones and UAVs in 3D. The experimental results achieved by means of a demonstrator developed at Sapienza University of Rome support the practical applicability of WiFi-based passive radar for improving security of small airfields and outdoor areas
Comparing phase-locked and non-phase-locked architectures for dual-channel DVB-S passive radar
No full textThis paper addresses the possibility to obtain low-cost passive radar that exploits DVB-S satellite transmissions as signals of opportunity using Commercial-Off The Shelf (COTS) hardware. In particular, low-noise down-conversion blocks (LNB) are typically available on the market, which include the Local Oscillator. Their use does not guarantee the fully coherent acquisition of surveillance and reference signal, required for passive radar operation. However, we estimate the frequency drift between the two channels, from the collected signals, and operate effectively for short-range surveillance applications. Using an ad-hoc experimental setup with 'less commercial' LNBs that can be locked to a reference, we compare two different types of receiver architectures: The non-phase-locked and a phase-locked architecture where the two LNBs are locked to the same 10 MHz oscillator. It is found that for small coherent integration times, the two schemes have very similar performance, whereas the phase-locked architecture is required to allow longer integration times and thus greater correlation gains. However, the lower-cost prototype is shown to be effective to detect and follow cars at least in the short ranges of typical parking-lots
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
Non-Coherent DVB-S Passive Radar Demonstrator
No full textIn recent years passive radar systems research has been increasingly focused on the use of satellite opportunity signals, and DVB-S signals in particular, since these offer virtually global coverage. Several papers have been published recently proving the effectiveness of very simple demonstrators based on COTS. However, conventional architectures struggle to employ coherent channels on the receiver impacting directly in their cost. In this work we show preliminary results for ground targets obtained using a very low-cost non-coherent COTS architecture
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