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The aim of this paper is to study both the private and the social desirability of a mixed bundling strategy that generates a cost savings effect. We confirm that mixed bundling is the dominant strategy for multiproduct firms, although it may give rise to a prisoner’s dilemma. Moreover, we show that mixed bundling may maximise social welfare, provided that cost savings are sufficiently high. Finally, we highlight the parametric regions where the social and the private interests coincide, and those where they do not. The recent evolution of broadband telecommunications services provides an ideal framework to apply our theoretical predictions.

Las comunicaciones digitales se enseñan tradicionalmente en sesiones de laboratorio desde un punto de vista teórico, utilizando plataformas de simulación. Sin embargo, el sistema de Acreditación Académica incluye la dimensión de "lo que se espera que los estudiantes sean capaces de hacer", lo que plantea la necesidad de disminuir la brecha entre las sesiones de laboratorio simuladas y un enfoque más práctico y realista. En este trabajo, proponemos una metodología para mejorar el aprendizaje de los aspectos prácticos relacionados con los cursos de Comunicaciones Digitales, así como para aumentar la motivación de los estudiantes, mediante el uso de dispositivos de radio definida por software de bajo coste. Esta metodología se ha aplicado en el Grado en Ingeniería Telemática de la Escuela Técnica Superior de Ingeniería de la Universidad de Valencia, España. Con el objetivo de mejorar el compromiso de los estudiantes de máster y de grado, se ha implementado una metodología de aprendizaje basado en proyectos. En el trabajo se describe la metodología, se describen varias actividades de laboratorio basadas en el estándar 802.11 y se dan recomendaciones para la implementación de esta metodología. UV-SFPIE PID-1353656 Digital Communications have been traditionally taught in laboratory sessions from a theoretical point of view, using simulation platforms. However, current Academic Accreditation includes the dimension of “what students are expected to be able to do”, which poses the need of decreasing the gap between standard simulated laboratory sessions and more practical and realistic approaches. In this paper, we propose a methodology to enhance the learning of practical aspects related to Digital Communications courses, as well as increasing the student’s engagement, via the use of low-cost software defined radio devices. This methodology has been applied in the Degree in Telematics Engineering at the School of Engineering from the University of Valencia, Spain. With the aim of improving the engagement of both master and undergraduate students, a project based learning methodology has been implemented. In the paper, the methodology is described, several laboratory activities based on the 802.11 standard are presented, and recommendations for practice are given.

Purpose Digital technology has the potential to support teenagers and young adults (TYAs) with cancer from the onset of their disease into survivorship. We aimed to establish (1) the current pattern of use of TYA digital technologies within our service-user population, and (2) their preferences regarding digital information and support within the service. Methods A cross-sectional survey was administered as a paper and online self-completed questionnaire to TYAs aged 13–24 accessing outpatient, inpatient, and day care cancer services at a regional specialist centre over a 4-week period. Results One hundred two TYAs completed the survey (55.7% male; 39.8% female; 83.3% paper; 16.7% online; mean age 18.5 years [SD = 3.51]). Of the TYAs, 41.6% rated the importance of digital communication as “essential” to their lives. Half (51.0%) kept in contact with other patients they had met during treatment, and 12.0% contacted patients they had not met in person. Respondents wanted to receive clinical information online (66.3%) and use online chat rooms (54.3%). Future online services desired included virtual online groups (54.3%), online counselling or psychological support (43.5%), and receiving (66.3%) and sharing (48.9%) clinical information online. Conclusions Young people with cancer are digital natives. A significant subgroup expressed a desire for digital resources from oncology services, though existing resources are also highly valued. Digital resources have potential to improve patient experience and engagement. Implications for cancer survivors There is considerable scope to develop digital resources with which TYAs can receive information and connect with both professionals and fellow patients, following diagnosis, through treatment and survivorship.

Recent years have seen a sequence of “moral panics” regarding accessibility of information on the internet and its exercise for criminal/harmful activity. Such problems and wider availability of internet raises the public policy concerns among governments over whether the internet should be regulated or not. Some believe it should not, considering that internet regulation will discourage what really internet is purported to encourage i.e. ‘free flow of information’. They see internet regulation as a potential threat to the ‘freedom of expression’, which is possibly one of the most prominent aspects that are instrumental in the growth and popularity of this technology. On the other hand, the others who are against the free access of internet underscores the danger of problematic content and illegal activities on the internet. They claim that much of these activities and content are illegal in most jurisdictions. Adding to this, unrestricted right to freedom of speech and expression may possibly threaten other’s rights. Thus many government organizations and internet users call for the regulation of internet. In this backdrop, paper revisits relevant literature and attempt to respond to the contentious problem of internet regulation. In this process, the paper also examines the experiences from several countries grappling with the problem of internet regulation. It concludes that any regulation on the internet has to be multi-faceted, culturally sensitive, and globally coordinated.

The use of digital communications has created a fundamental shift in how information is distributed and consumed. Digital communications hold possibilities for cost-effectively engaging larger numbers of stakeholders while promoting better public understanding of science. This paper evaluates the status of digital communication use for CCUS and explores its potential to improve the outreach efforts of the Regional Carbon Sequestration Partnerships. The paper includes a background on digital communication tools, a benchmark assessment of current use by the RCSPs and other carbon sequestration websites, a brief literature review examining the rationale for digital outreach, best practices, evaluation, and special considerations.

Can the power of digital communications create opportunities for overcoming generational renewal problems on farms? This interdisciplinary review explores the reported impacts of digital communication on career initiation into farming from a global perspective via the lens of career theories. Seventy-three papers were synthesized into two domains: (1) the impact of digital communication interactions on farming career initiation, and (2) the dynamics of digital communication initiatives that create opportunities to inspire youth into farming. The finding shows that the mainstream literature primarily aims to support the continuity of farming careers but pay little attention to the potential of digital communication to attract youth into farming. This review argues that career communications for farming receives insufficient attention, and could be better integrated into agricultural communications strategies by using the potential of digital communications. Study concludes that while economic and geographic factors, as well as societal and cultural norms, lead to negative perceptions on farming careers, there are three pathways that may contribute to breaking down these negative perceptions. Firstly, taking the changing nature of career motivations, such as the trend towards sustainable farming linked to self-fulfillment, among today’s youth into consideration is essential. Secondly, highlighting technological advances in digital agriculture practices, like geographical flexibility or innovation capacity of farming, for example, is important to increase awareness about new opportunities in the profession. Lastly, communication campaigns with targeted groups (e.g., young females) play a role to change the negative perceptions of the rural way of life and the farming profession.

5 pages; Phase noise is a topic of theoretical and practical interest in electronic circuits. Although progress has been made in the characterization of its description, there still considerable gaps in its effect especially on the multi carrier spreading systems. In this paper, we investigate the impact of a local oscillator phase noise on the multi carrier 2 dimensional spreading systems known as OFDM-CDMA. The contribution of this paper is twofold. First, we use some properties of random matrix and free probability theory to give a simplified expression of the Signal to Interference and Noise Ratio SINR obtained after equalization and despreading. The latter is independent of the actual value of the spreading codes of different users and depends principally on the complex amplitudes of the estimated channel coefficients. Second, we use this expression to derive new weighting functions which are very interesting for the RF engineers when they design the frequency synthesizer. Simulation results are provided to discuss and validate our model.

Tranchenko L. V., Tereshchuk N. V., Lopatiuk R. I., Tranchenko O. M. The impact of digital communications on tourism marketing. Journal of Education, Health and Sport. 2020;10(5):394-402. eISSN 2391-8306. DOI http://dx.doi.org/10.12775/JEHS.2020.10.05.041 https://apcz.umk.pl/czasopisma/index.php/JEHS/article/view/JEHS.2020.10.05.041 https://zenodo.org/record/4947420 The journal has had 5 points in Ministry of Science and Higher Education parametric evaluation. § 8. 2) and § 12. 1. 2) 22.02.2019. © The Authors 2020; This article is published with open access at Licensee Open Journal Systems of Nicolaus Copernicus University in Torun, Poland Open Access. This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author (s) and source are credited. This is an open access article licensed under the terms of the Creative Commons Attribution Non commercial license Share alike. (http://creativecommons.org/licenses/by-nc-sa/4.0/) which permits unrestricted, non commercial use, distribution and reproduction in any medium, provided the work is properly cited. The authors declare that there is no conflict of interests regarding the publication of this paper. Received: 04.05.2020. Revised: 16.05.2020. Accepted: 29.05.2020. UDC 316.46.058.5 THE IMPACT OF DIGITAL COMMUNICATIONS ON TOURISM MARKETING L. V. Tranchenko, N. V. Tereshchuk, R. I. Lopatiuk, O. M. Tranchenko Uman National University of Horticulture Abstract The influence of digital communications on marketing in the field of tourism is investigated. The need to develop strategies for the formation of business communications in the field of tourism and indicators that allow to evaluate their effectiveness and risks is emphasized. Attention is paid to the feasibility in applying strategies of differentiated, differentiated and concentrated marketing. The relevant indicators were proposed to assess the economic effectiveness of business communication strategies: income multipliers, breakeviate level assessment formula, methodology for checking the stability of the performance indicator to change factors, and Hurwitz criterion. The considered formulas and strategies for the formation of business communications in tourism create the necessary basis for scientifically justified strategic planning of the travel company's relations with counterparties. Keywords: tourism; tourism activities; travel companies; tourist product; digital communications; information technology; information support.

espanolEl presente articulo reconstruye las dinamicas y condiciones generadas entre 2003 y 2015, para la adopcion de decisiones y la planificacion en los medios del Estado nacional de Argentina. La investigacion aborda el periodo dividido por la sancion de la Ley de Servicios de Comunicacion Audiovisual en 2009. El abordaje desde el indicador de participacion ciudadana se enfoca, particularmente, en la adopcion de decisiones y la planificacion, y retoma un modelo metodologico con criterios especificos para reconocer tendencias, contradicciones, continuidades y cambios desde informacion cualitativa. Se concluye que las dinamicas para la toma de decisiones y la planificacion en las instituciones ofrecieron un avance notorio en sus tendencias democratizadoras, a partir de la deliberacion sobre la ley audiovisual y, posteriormente, con su institucionalizacion en los medios estatales nacionales. Sin embargo, existieron limitaciones normativas (en una primera etapa) y de implementacion (en una segunda etapa) que condicionaron seriamente la participacion ciudadana. EnglishThis paper reconstructs the dynamics and conditions generated between 2003 and 2015 for the decision making and planning processes in Argentina’s national media. The research addresses a period divided by the enactment of the Audiovisual Communication Services Law. The approach from the citizen participation indicator focuses particularly on the levels related to decision making and planning processes. It uses a methodological model with specific criteria to recognize trends, contradictions, continuities, and changes based on qualitative information. The article concludes the dynamics reproduced for decision making and planning processes in the institutions offered a remarkable advance in their democratizing tendencies from the deliberation around the audiovisual law, and later with its institutionalization in the national state media. However, there were limitations in the regulation (in a first stage) and in the implementation of the law (in a second stage) that seriously conditioned the citizen participation indicator.

Recently, massive research works have been accomplished for augmenting privacy and security requirements for cybersecurity applications in wireless communication networks. This is attributed to the fact that conventional security processes are not appropriate for robust, efficient, and reliable multimedia streaming over unsecure media. Therefore, this paper presents an efficient color image cryptosystem based on RC6 with different modes of operation. The proposed cryptosystem is composed of two phases: encryption and decryption. The encryption phase starts by decomposing the color plainimage with few details into its RGB components, which in turn, are segmented into 128-bit blocks. These blocks are then enciphered using RC6 with an appropriate mode of operation. After that, the corresponding enciphered blocks of RGB components are multiplexed for constructing the final cipherimage. This scenario is reversed in the decryption phase. The performance of the proposed cryptosystem is gauged via simulation using a set of encryption quality metrics. The simulation results reveal that the proposed cryptosystem with cipher block chaining (CBC), cipher feedback (CFB), and output feedback (OFB) modes can efficiently and effectively hide all information of the color images with few details even in the presence of some input blocks with similar data. On the other hand, the results show that the electronic codebook (ECB) mode is not effective at all in hiding all details of images. Finally, the obtained results ensure the applicability of the proposed cryptosystem and its efficiency in encrypting images in terms of security, encryption quality, and noise immunity.

The paper covers questions related to the creation of the comprehensive device designed for long-term autonomous operations as part of the radio networks for various purposes in short-wave bands. Such radio networks are intended for remote monitoring and control over facilities at distances of hundreds and thousands of kilometres. The device and features of functioning of autonomous nodes in short-wave radio networks are based on daily and seasonal characteristics of distribution of radio waves, operation under conditions of self-provision with electricity and in areas of harsh climate, as well as on impossibility of their timely repair and maintenance. The authors have proposed solutions to the issue of a reliable communication channel using advanced low-energy types of angle modulation with low-value signal-to-noise ratios and the choice of the best frequency for a given time of the day for specific nodes. There is an overview of issues related to the choice of an antenna type for the autonomous radio network node, taking into account changes of working ranges. The issue of power supply to the radio network node is solved by applying the combination of a photovoltaic panel and wind generator working from a frost-resistant battery. Thermal modes for electronic equipment are provided through the use of a thermostatically controlled container. Authors have presented a possible architecture for the short-wave range radio network node. The study results include advice for developers of autonomous nodes of shortwave radio networks.

Orientador: Vera Regina Toledo Camargo Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Estudos da Linguagem Resumo: Este estudo é vinculado ao projeto científico "Geração de cenários de produção de álcool como apoio para a formulação de políticas públicas aplicadas à adaptação do setor sucroalcooleiro nacional às mudanças climáticas". Seu objetivo é produzir e divulgar informações científicas para públicos distintos sobre o tema das mudanças climáticas no âmbito da internet. O estudo se justifica graças à sua relevância, no universo digital, como canal de difusão de informação e de conhecimento na vida contemporânea. Enquanto em um primeiro momento enfatiza o uso de sites, blogs e redes sociais on-line para compartilhar ciência, permitindo identificar o público-alvo e, consequentemente, atraindo novos pesquisadores e interessados nas mudanças climáticas e seus impactos, o segundo aborda a criação de um site como horizonte de ação para tornar a informação acessível ao maior número de pessoas possível. A introdução de temas científicos na web requer estudo, compreensão e análise do conteúdo quanto à propagação das informações resultantes desse projeto científico. Considerando que o objeto da pesquisa é como usar a sociedade em rede para transmitir conhecimento, enfatizam-se as principais características deste trabalho: recuperar informações acessíveis e detalhadas geradas pela equipe científica, fatos recentes e de grande repercussão sobre temas de interesse do público-alvo do projeto e difundi-los na rede. De forma sistemática, este estudo mapeou o processo de divulgação científica mediado pelas tecnologias de comunicação e informação. Além do uso em conjunto das redes sociais on-line e o emprego de estratégias de divulgação científica que foram exploradas como tentativa de transmitir e promover amplo acesso ao conhecimento gerado pelos pesquisadores, os principais resultados do trabalho foram o aprimoramento e análise das informações científicas colocadas à disposição do público na web, e as estratégias empregadas para favorecer o acesso ao conhecimento gerado pelo projeto, além do site que foi desenvolvido com recursos técnicos de acessibilidade, usabilidade e design responsivo e que serviu de base para preservar e divulgar o conteúdo científico produzido pelo projeto de pesquisa. Os resultados visam contribuir com a circulação da informação científica na internet e tornar acessíveis artigos, dissertações, teses, entrevistas, vídeos, áudios, textos, fotos, imagens, matérias jornalísticas e informações sobre eventos científicos no contexto das mudanças climáticas. A expectativa é que o uso da internet possa levar as pessoas a identificar os posicionamentos que sustentam os estudos sobre o tema e estimule outras leituras que auxiliem na tomada de decisões sobre o mundo contemporâneo e as mudanças, que nele acontecem, causadas pela atividade humana Abstract: This research is linked to the scientific project in global climate changes "Generation of Alcohol Production Scenarios as Support for the Formulation of Public Policies Applied to the Adaptation of the National Sugar and Alcohol Industry to the Climate Changes". Its aim is to focus more extensive disclosures, for different audiences, on the topic of global climate changes within the internet. This study is justified by its relevance as a channel for diffusion of information and knowledge of contemporary life. It emphasizes, in the first place, how the use of sites, blog and digital social networks, as science communication platforms, serves to identify the target audience and hence attracting new researchers and stakeholders on climate change and its impacts. Still at the process of adjustment to social networks and medias, the introduction of scientific subjects on those networks demands studies, comprehension and analyses of the content in relation to the spread of information and knowledge resulting of this scientific project. When the object of the research is "how to use the network society" to impart knowledge, it is emphasized that the main features of the work are: to recover accessible and detailed information generated by the scientific staff, to retrieve recent and highly publicized events on topics of interest to the target audience of the project and spread them online. Systematically, the purpose of this study was to map the process of scientific dissemination mediated by communication and information technologies. Besides the use of digital social network together with scientific dissemination strategies that have been explored as attempts of conveying and promoting a broad access to the knowledge generated by the researchers, the main results of the work were the improvement and analyses of the scientific information made available to public on the web, and the strategies employed to facilitate access to knowledge generated by the project, together with the website, that was developed with technical features of accessibility, usability and responsive design and that has been the basis for preserving and disclosing the scientific and technological content produced by the research. And, more broadly, contribute to the circulation of scientific information on the Internet and make available papers, dissertations, theses, interviews, videos, audios, texts, photos, newspaper articles and images, information and news about national and international scientific events in context of climate change. The expectation is that the use of the internet can lead users to identify positions that support the studies on the subject and stimulate other readings that help in making decisions about the contemporary world and the changes that happen in it, caused by human activity Mestrado Divulgação Científica e Cultural Mestre em Divulgação Científica e Cultural

This contribution discusses the latest opportunities and challenges that affected higher educational institutions, following the outbreak of the Coronavirus (COVID-19) pandemic. It sheds light on the effects of an unprecedented COVID-19 on higher education services. Educational institutions were suddenly expected to abide by COVID-19 preventative measures, including social distancing and hygienic practices, among others. As a result, many of them migrated to virtual and remote course delivery. This reflective paper urges education leaders and policymakers to embrace online teaching models and virtual systems, as they are here to stay in a post-COVID-19 era. In conclusion, it puts forward key implications to practitioners and identifies future research avenues to academia., peer-reviewed

Tranchenko L. V., Tereshchuk N. V., Lopatiuk R. I., Tranchenko O. M. Use of information support for marketing in tourist enterprises. Journal of Education, Health and Sport. 2021;11(2):200-207. eISSN 2391-8306. DOI http://dx.doi.org/10.12775/JEHS.2021.11.02.020 https://apcz.umk.pl/czasopisma/index.php/JEHS/article/view/JEHS.2021.11.02.020 https://zenodo.org/record/4958675 The journal has had 5 points in Ministry of Science and Higher Education parametric evaluation. § 8. 2) and § 12. 1. 2) 22.02.2019. © The Authors 2021; This article is published with open access at Licensee Open Journal Systems of Nicolaus Copernicus University in Torun, Poland Open Access. This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author (s) and source are credited. This is an open access article licensed under the terms of the Creative Commons Attribution Non commercial license Share alike. (http://creativecommons.org/licenses/by-nc-sa/4.0/) which permits unrestricted, non commercial use, distribution and reproduction in any medium, provided the work is properly cited. The authors declare that there is no conflict of interests regarding the publication of this paper. Received: 11.01.2021. Revised: 10.02.2021. Accepted: 26.02.2021. Use of information support for marketing in tourist enterprises L. V. Tranchenko1, N. V. Tereshchuk1, R. I. Lopatiuk2, O. M. Tranchenko1 1Uman National University of Horticulture 2Vinnytsia National Agrarian University Abstract Every year Ukraine integrates more and more into the world economic economy. Tourist services are one of the most important socio-economic sectors of the world economy. However, Ukraine, having a variety of tourism resources, has little experience in this area. For these reasons, the relevance of the article on the promotion of tourist services is determined. The article investigates the means of promoting tourist services, determining the theoretical and methodological principles of building an effective process of marketing communications at the enterprises of the tourist sphere. It is proved that in order to achieve the effect of synergy, the main principle when deciding on the use of several means of communication is the choice of one means as the main and several - auxiliary. The main thing is to be able to independently and effectively influence consumers. Auxiliary - should fill possible gaps in the reach of the target audience, supporting the main means of communication. Key words: tourism; tourist activity; tourist firms; marketing; digital communications; information technologies; information support.

This paper deals with the computation of integralsof centred bivariate Gaussian densities over any domain defined as an angular sector of R^2. Based on an accessible geometrical approach of the problem, we suggest to transform the double integral into a single one, leading to a tractable closed-form expression only involving trigonometric functions. This solution can also be seen as the angular cumulative distribution of bivariate centered Gaussian variables (X,Y). We aim to provide a didactic approach of our results, and we validate them by comparing with those of the literature.

In this paper, we propose the theoretical framework for a reconfigurable radiation pattern modulation (RRPM) scheme, which is reminiscent of the index modulation technique. In the proposed scheme, information is encoded using far-field radiation patterns generated by a set of programmable radiating elements. A considerable effort has been invested to allow for high transmission of the reconfigurable radiation pattern symbols, yet, the receiving system has received little attention and has always been considered ideal. Depending on the number of receivers and their respective positions, two variables are considered here for data transmission: the sampling resolution and the fraction of the covered space by the receiving antennas. Hence, we quantitatively investigate their effect on the bit-error-rate (BER) by making use of a limited number of measurements that approximate the behavior of the system under real-field conditions.

Based on a case study, the paper analyses the possibilities of social media as a tool for science communication in the context of information and communication technology (ICT) usage in archaeology. Aside from discussing the characteristics of digital archaeology, the social networking sites (SNS) Twitter, Sketchfab, and ResearchGate are integrated into a digital research data dissemination tool. As a result, above-average engagement rates with few impressions were observed. Compared with that, status updates focusing on actual fieldwork and other research activities gain high numbers of impressions with below-average engagement rates. It is believed that most of the interactions are restricted to a core audience and that a clearly defined social media strategy is obligatory for successful research data dissemination in archaeology, combined with regular posts in the SNS. Additionally, active followers are of highest importance.

The article of record as published may be found at http://dx.doi.org/10.1109/ICASSP.2017.7952523 Published in: 2017 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) In this paper, a covert communication method is proposed that embeds a digital communication signal onto the radar return of a pulse Doppler radar. The interfering radar signal at the receiver is estimated and coherently subtracted from combined signal prior to demodulation of the communications signal to baseband and symbol detection. The robustness of the communication method to various estimation errors is investigated for several phase shift keying digital communication modulations through Monte Carlo simulations. It is demonstrated that differential encoding systems with non-coherent detection perform best in the presence of frequency estimation errors. However, it was also demonstrated that the system is not very robust to phase estimation errors. The performance of non-coherent differential phase shift keying and differential quaternary phase shift keying are investigated to determine the impact of varying different parameters upon symbol error rate.

El sistema de comunicació ràdio d’alta freqüència (HF, en anglès) és usat arreu del món per agències governamentals i no governamentals sempre que calgui una alternativa a les comunicacions via satèl•lit: vaixells a alta mar, avions fora de cobertura de xarxes ràdio amb visió directa, operacions militars, zones on la infraestructura ha estat destruïda per algun tipus de desastre o bé zones llunyanes sense cap altre tipus de comunicació. La ràdio HF representa una alternativa, o un sistema de backup al satèl•lit per a comunicacions de llarg abast i en redueix els costos, evita la vulnerabilitat i els problemes de sobirania. En aquesta tesi s’ha estudiat l’enllaç HF entre la base antàrtica espanyola Juan Carlos I, situada a l’illa Livingston a l’arxipèlag de les Shetland del Sud, i Espanya. L’objectiu d’aquest treball és estudiar els problemes que afecten la propagació; és a dir, la relació senyal a soroll i interferència, la dispersió multicamí i la dispersió per efecte Doppler, i dissenyar la capa física d’un enllaç HF de baixa velocitat, poca potència i llarg abast. Pel que fa aquest últim punt es fan un parell de propostes: espectre eixamplat per seqüència directa (DSSS, en anglès) i multiplexació per divisió en freqüència ortogonal (OFDM, en anglès). El repte que es planteja és el de la definició de les característiques dels símbols que millor encaixen en aquest canal per tal d’obtenir un benefici de la diversitat temporal i freqüencial que ofereix el canal. Des de l’any 2003 diverses campanyes han permès estudiar aquest canal HF, però no va ser fins la campanya 2009/2010 que s’obtingué un foto de les característiques, diürnes i nocturnes, de la ionosfera. En els articles que es presenten en aquesta tesi hem estès el rang freqüencial d’estudi respecte a investigacions prèvies i hem mostrat diferències de comportament entre el dia i la nit. Hem usat els resultats de la caracterització del canal per a dissenyar i comparar la bondat dels símbols DSSS i OFDM. Ambdues possibilitats han resultat ser candidates a implementar l’enllaç HF entre l’Antàrtida i Espanya. Tot i així, ambdues tècniques representen visions diferents de la implementació del mòdem: mentre que DSSS obté bons resultats a baixa velocitat en entorns amb baixa relació senyal a soroll, OFDM aconsegueix tasses de velocitat més elevades en canals més benignes., Los sistemas de radio de alta frecuencia (HF, en inglés) son usados por agencias gubernamentales y no gubernamentales en todo el mundo siempre que se necesite una alternativa a las comunicaciones por satélite: barcos en alta mar, aviones fuera del rango de cobertura de las redes radio de visión directa, operaciones militares, zonas donde la infraestructura ha sido destruida por algún desastre. Ésta ofrece una alternativa, o representa un sistema de backup, a las comunicaciones vía satélite, evitando los costes, la vulnerabilidad y los problemas de soberanía de las comunicaciones por satélite. En esta tesis se ha estudiado el enlace HF entre la base antártica española Juan Carlos I en la isla Livingston, en las Shetland del sur y España. El objetivo de este trabajo es el estudio de las limitaciones de la propagación ionosférica (como la relación señal a ruido e interferencia, la dispersión multicamino y la dispersión por efecto Doppler) y el diseño de la capa física de un enlace HF de baja velocidad, baja potencia y largo alcance. Se han estudiado un par de propuestas para este enlace, como son el espectro ensanchado por secuencia directa (DSSS, en inglés) y la multiplexación por división en frecuencia ortogonal (OFDM, en inglés). El reto ha sido definir las características que mejor se adecuan a este enlace para poder aprovechar la diversidad temporal y frecuencial que ofrece el canal HF. Desde el año 2003 diversas campañas de sondeo han permitido estudiar el canal HF pero no es hasta la campaña 2009/2010 que se consigue una fotografía de la actividad ionosférica tanto nocturna como diurna. En los artículos que se presentan en esta tesis hemos extendido los estudios previos a todo el rango de frecuencias HF y hemos mostrado las diferencias entre el día y la noche. Hemos usado estos resultados de caracterización del canal para diseñar y comparar símbolos DSSS y símbolos OFDM. Ambas posibilidades han resultado ser posibles candidatas para implementar un enlace HF de baja velocidad entre la Antártida y España. Sin embargo ambas técnicas representan dos aproximaciones distintas a la implementación del módem. Mientras que DSSS consigue un buen funcionamiento a baja velocidad en escenarios con baja relación señal a ruido, OFDM consigue tasas de transmisión más altas en escenarios más benignos., High Frequency (HF) radio is used by governmental and non nongovernmental agencies worldwide whenever an alternative to satellites for sky wave communication is needed: ships at sea, aircraft out of range of line-of-sight radio networks, military operations, disaster areas with communication infrastructure destroyed or distant regions lacking other communications. It offers an alternative to satellites, or a backup, for long-haul communications, thus avoiding the costs, vulnerabilities and sovereignty concerns of satellite communications. In this thesis the HF link between the Antarctic Spanish Station Juan Carlos I in Livingston Island, South Shetlands and Spain is studied. The aim of this study is to address the impairments that affect HF propagation (i.e., signal-to-noise plus interference ratio, multipath and Doppler shift and spread) and to design the physical layer of a low rate, low power and long-haul HF link. Some proposals regarding this last issue are addressed, i.e., direct sequence spread spectrum (DSSS) and orthogonal frequency division multiplexing (OFDM). The challenge is to define the symbol characteristics that best fit the link to benefit from time and frequency diversity that offers the HF channel. Since 2003 several transmission campaigns have allowed to study the HF channel but it is not until the 2009/2010 campaign that we have achieved a whole picture of both diurnal and nocturnal ionospheric activity. In the papers presented in this thesis we have extended the previous research to the whole range of HF frequencies and we have shown the differences on performance between day and night. We have used the results from channel characterization to design and compare the performance of DSSS and OFDM symbols. Both techniques have turned out to be possible candidates to implement a low rate HF link between Antarctica and Spain. However, both techniques stand for different approaches of the modem: DSSS achieves good performance at low data rate in low SNR scenarios, whereas OFDM achieves higher data rate in benign channels

[Abstract] Time-modulated arrays (TMAs) are electromagnetic systems whose radiated power pattern is controlled by the application of variable-width periodical pulses to the individual elements. The nonlinear nature of the array operation causes the appearance of radiation patterns at the harmonic frequencies of such periodic pulses. The technique can be used for improving the side-lobe level (SLL) topology of the radiation pattern at the central frequency and/or to profitably exploit the harmonic patterns in order to supply smart antenna capabilities. Among the latter features, the TMA harmonic beamforming takes on special importance due to its attractive trade-off performance-hardware complexity. From this perspective, TMAs are sensors capable of transforming the spatial diversity of a communication channel into frequency diversity, thus improving the performance of a wireless communication. In addition to a walk through the origins of the concept, and a brief analysis of the mathematical fundamentals, this paper organizes the prolific state of the art of TMAs in two major thematic blocks: (1) TMA design from an antenna perspective; and (2) TMA design from a signal processing perspective. Ministerio de Economía, Industria y Competitividad; TEC2013-47141-C4-1-R Ministerio de Economía, Industria y Competitividad; TEC2015-69648-REDC

This paper analyses the determinants of broadband Internet access prices in a group of 15 EU countries between 2008 and 2011. Using a rich panel dataset of broadband plans, we show the positive effect of downstream speed on prices, and report that cable and fibre-to-the-home technologies are available at lower prices per Mbps than x DSL technology. Operators’marketing strategies are also analysed as we show how much prices rise when the broadband service is offered in a bundle with voice telephony and/or television, and how much they fall when download volume caps are included. The most insightful results of this study are provided by a group of metrics that represent the situation of competition and entry patterns in the broadband market. We show that consumer segmentation positively affects prices. On the other hand, broadband prices are higher in countries where entrants make greater use of bitstream access and lower when they use more intensively direct access -local loop unbundling-. However, we do not find a significant effect of inter-platform competition on prices.

International audience; This paper deals with the problem of Blind Source Separation. Contrary to the vast majority of works, we do not assume the statistical independence between sources and explicitly consider that they are dependent. We introduce three particular types of dependent sources and show that their cumulants have interesting properties. Based on these properties, we investigate the behavior of classical Blind Source Separation algorithms when applied to these sources: depending on the source vector, the separation may be successful or some additionnal indeterminacies can be identified.

The power of social media is virtually untameable. The advent of social media has shrunk the world to what Marshal McLuhan once termed ‘global village’. This paper has examined into the amount of time government and private school students spent on social media vis-à-vis on physical activities. It has attempted to answer the questions: (i) How much time government and private school students spend using different social media applications?, (ii) Is there any association between government and private school students regarding time spent on social media applications?, (iii) Whether they use social media applications primarily to communicate with others, and (iv) how much time, on an average, school students spend on outdoor games after school hours. For the purpose of the study, a self administered survey was conducted among five government and private schools each.

Transmit antenna diversity has been exploited to develop high-performance space-time coders and simple maximum-likelihood decoders for transmissions over flat fading channels. Relying on block precoding, this paper develops generalized space-time coded multicarrier transceivers appropriate for wireless propagation over frequency-selective multipath channels. Multicarrier precoding maps the frequency-selective channel into a set of flat fading subchannels, whereas space-time encoding/decoding facilitates equalization and achieves performance gains by exploiting the diversity available with multiple transmit antennas. When channel state information is unknown at the receiver, it is acquired blindly based on a deterministic variant of the constant-modulus algorithm that exploits the structure of space-time block codes. To benchmark performance, the Cramer-Rao bound of the channel estimates is also derived. System performance is evaluated both analytically and with simulations.

The ability of orthogonal frequency-division multiplexing systems to mitigate frequency-selective channels is impaired by the presence of carrier frequency offsets (CFOs). In this paper, we investigate identifiability issues involving high-resolution techniques that have been proposed for blind CFO estimation based on null subcarriers. We propose new approaches that do not suffer from the lack of identifiability and adopt adaptive algorithms that are computationally feasible. The performance of these techniques in relation to the location of the null subcarriers is also investigated via computer simulations and compared with the modified Cramer-Rao bound.