1,720,963 research outputs found
Field measurements for practical unlicensed communication in the UHF band
No full textThis paper presents the result of a measurement campaign conducted in Italy, Spain, and Romania to obtain empirical values for the parameters upon which unlicensed devices could distinguish in a hidden node scenario between empty and occupied TV channels. Signal power measurements in the UHF frequency band (470–860 MHz) have been carried out on rural, sub-urban, and urban sites, at different heights over the ground by using different analysis bandwidths. The results have been analyzed with respect to the hidden node margin problem, spectrum sensing bandwidth, and occupancy threshold, to produce a set of practical parameters upon which harmless unlicensed communication in the UHF TV bands is feasible
Co-channel and adjacent channel interference and protection issues for DVB-T2 and IEEE 802.22 WRAN operation
No full textThis paper presents a study on the coexistence issue of digital terrestrial TV broadcasting and cognitive broadband access operation in the TV white spaces (TVWS). Extended measurements were performed to evaluate the protection of the existing Second generation of digital video broadcasting terrestrial standard (DVB-T2) services in the presence of IEEE 802.22 WRAN co-channel and adjacent channel interference. The absence of picture failure over 30 consecutive seconds on decoded DVB-T2 streams has been monitored to obtain the maximum tolerable level of IEEE 802.22 WRAN interference, which ensures the protection of the primary broadcast system. This paper considers practical DVB-T2 system configuration options by varying parameters of the standard, such as constellation and code rate, FFT size, pilot pattern and guard interval, and rotated constellations and compares them in terms of robustness with respect to the interference generated by IEEE 802.22 WRAN operation. The goal is to provide cognitive broadband operators in the TVWS with guidelines to optimize their network by choosing the parameters that best fit their needs in case of coexistence with DVB-T2 broadcasting services
Heuristic performance evaluation for DVB-T/T2 SFN network
No full textIn DVB-T/T2 broadcasting single frequency network (SFN) multipath interference (MPI) at the receiver antenna is a critical issue. The capability to elaborate those signals depends on both synchronization strategy used and coded orthogonal frequency-division multiplexing (COFDM) modulation properties. An efficient COFDM system requires the guard interval as short as possible and such as to protect the system from the MPI. To cope with this problem a static delay adjustment obtained by fitting the launching time of each broadcast station is introduced so that the time difference of the incoming signals within the reception area falls into the COFDM guard interval. This work investigates the use of advanced simulated annealing to optimize transmission parameters such as the static delay, gain and orientation of sector antennas of DVB-T/T2 transmitters in SFNs. In particular, we identify the static delay adjustment map to maximize the coverage area according to quality of service requirements. The proposed approach has been validated for DVB-T/T2 network planning in the Basque Country (Spain) and Sardinia island (Italy). Different density of transmitters, generalized geography of territory are considered for the best setting of the parameters involved. Reliability studies are included to demonstrate the efficacy of the method
Protection ratios and interference curves for broadcast and cognitive co-channel and adjacent channel operation
No full textThis paper presents an extended study of the performance of an 802.22 WRAN system operating into the same coverage range of a DTT receiver. We performed extended measurements for evaluating the protection of the existing broadcasting services. In order to evaluate the performance of DTT systems interfered by 802.22 transmission in their adjacent channels, the Picture Failure levels have been monitored for different operation modes of the 802.22 standard. The goal of the present study is to find the maximum transmission power level and bandwidth configuration of an 802.22 signal operating in the adjacent channels of an active DTT system that ensures the protection of the primary broadcast system. The results from the measurements performed in the various scenarios have been analyzed and conclusions have been drawn. © 2013 IEEE
Hidden Node Margin and Man-Made Noise Measurements in the UHF Broadcasting Bands
No full textThis paper presents an extended study of the spectrum occupancy in the UHF frequency band (470-870MHz) in Spain and in Italy. The objective of the study is to establish by signal power measuring if cognitive devices are able to detect and distinguish in a Hidden Node scenario between empty and occupied TV channels. The study has been performed, for each of these two countries, at three different sites and at different heights over the ground for assessing the hidden node margin. The measurements in Spain were carried out in urban, suburban and rural environments close to the city of Bilbao while the measurements in Italy were carried out in Sardinia, in different urban areas of the city of Cagliari, surrounding suburban spots and a rural location 50 km west. The measurement methodology was the same in both scenarios. The results from the spectrum measurements performed in the various scenarios have been analyzed and conclusions have been drawn. © 2012 IEEE
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
Spectrum Occupancy and Hidden Node Margins for Cognitive Radio Applications in the UHF band
No full textVariations 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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