1,720,977 research outputs found
On the feasibility of unlicensed communications in the TV white space: Field measurements in the UHF band
Full text linkIn practical unlicensed communications in TV band, radio devices have to identify, at first, the transmission opportunities, that is, the portion of the spectrum licensed for broadcasting services unoccupied in a certain region at certain time, that is, the so-called TV white space. In this paper the outcome of field measurements in the UHF TV band (470-860 MHz) conducted in EU is presented. To obtain empirical values for the parameters upon which unlicensed radio devices are able to distinguish in a real scenario between empty and occupied TV channels, signal power measurements have been performed in Italy, Spain, and Romania on rural, suburban, and urban sites, at different heights over the ground by using different analysis bandwidths. The aim of this work is to provide a set of practical parameters upon which harmless unlicensed communication in the UHF TV white space is feasible. The results have been analyzed with respect to the hidden node margin problem, spectrum sensing bandwidth, and occupancy threshold
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
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
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
Multimedia Multicast Services in 5G Networks: Subgrouping and Non-Orthogonal Multiple Access Techniques
No full textThe expected growth in mobile video demand over broadband cellular networks is one of the key factors driving the wireless industry to develop the fifth generation of network technology. This scenario is fueling the need for group-oriented services (i.e., multicast and broadcast) in order to efficiently manage the radio resources, and consequently grant different groups of users simultaneous access to the same multimedia content with differentiated quality of service. The evolved multimedia broadcast multicast service (eMBMS), standardized by the Third Generation Partnership Project, is one of the technologies likely to be extended to 5G systems with the aim of addressing point-to-multipoint services. In addition, non-orthogonal multiple access (NOMA) techniques are also being considered as a driver to increase the efficient use of the spectrum in multi-user environments with asymmetric data delivery. The present article proposes the joint use of subgrouping multicast techniques and NOMA in an eMBMS-like scenario. Performance is evaluated in envisaged 5G environments, where different quality video services are delivered to a group of users interested in the same contents
Network Selection Over 5G-Advanced Heterogeneous Networks Based on Federated Learning and Cooperative Game Theory
Full text link5G-Advanced and Beyond claims a 3D ecosystem with cooperation between terrestrial and non-terrestrial networks to achieve seamless coverage, improve capacity, and enable advanced applications with strict quality of service (QoS) requirements. This complex environment requires a disaggregated Radio Access Network (RAN) deployment with open interfaces, such as the architecture promoted by the O-RAN Alliance. This architecture, supporting the slicing paradigm, is a prominent solution to guarantee dynamism and differentiated traffic management. Furthermore, intelligence is critical for future wireless networks to enable Machine Learning (ML)-based optimization for autonomous RANs, handling ultra-dense heterogeneous environments, and adapting to numerous scenarios. This paper presents an enhanced Dynamic Radio Access Network Selection (eDRANS) algorithm based on Federated Double Deep Q-Network (F-DDQN) and inserted in the novel O-RAN architecture. The proposal selects the most suitable base station (BS) to satisfy multiple service requests, optimizing QoS and slicing resource utilization. Moreover, the solution employs a Cooperative Game Theory (CGT) approach to manage resources in overload situations. This load-balancing process enables the acceptance of new clients without abruptly degrading the active users' perception. eDRANS is adapted to diverse network conditions, multiple service constraints, and several user types with different priorities and mobility behaviors. The proposal is validated through network-level simulations, recreating a heterogeneous environment composed of terrestrial-airborne nodes and using the Max-SINR criterion, a heuristic algorithm, and centralized and distributed ML solutions as benchmarks. Results show that eDRANS correctly learns during multiple trial-and-error interactions with the environment, fulfilling the Service Level Agreement (SLA) and maximizing user satisfaction
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
- …
