347 research outputs found
Adaptive Transmission Techniques for Mobile Satellite Links
Adapting the transmission rate in an LMS channel is a challenging task
because of the relatively fast time variations, of the long delays involved,
and of the difficulty in mapping the parameters of a time-varying channel into
communication performance. In this paper, we propose two strategies for dealing
with these impairments, namely, multi-layer coding (MLC) in the forward link,
and open-loop adaptation in the return link. Both strategies rely on
physical-layer abstraction tools for predicting the link performance. We will
show that, in both cases, it is possible to increase the average spectral
efficiency while at the same time keeping the outage probability under a given
threshold. To do so, the forward link strategy will rely on introducing some
latency in the data stream by using retransmissions. The return link, on the
other hand, will rely on a statistical characterization of a physical-layer
abstraction measure.Comment: Presented at the 30th AIAA International Communications Satellite
Systems Conference (ICSSC), Ottawa, Canada, 2012. Best Professional Paper
Awar
Generalized Propagation Channel Model for 2GHz Low Elevation Links Using a Ray-tracing Method
Unmanned Aerial Vehicles (UAV) will increasingly be used for responding to emergencies or for law enforcement in civil surveillance applications. Transferring the enormous amounts of information from UAV-mounted cameras or sensors will require large bandwidths, unlike the information required for remotely controlling a UAV, thus necessitating higher frequency bands typically in the vicinity of 2 or 5 GHz. Novel hardware developments will need to rely on a versatile propagation channel model for the envisaged scenarios ranging from deep shadow urban areas to open fields. This paper studies more complex intermediate scenarios, which fall between the aforementioned ones, and which are more difficult to model. A semi-deterministic model, first developed for open, flat areas, has been generalized to accommodate any possible operational scenario and was tested in built-up areas. The model involves a stochastic part and a determinist which is a ray-tracing based part used to compute the long term mean (LTM) of the signal's coherent component
Estimation of the Radio Channel Parameters using the SAGE Algorithm
This paper presents the problem of estimating the parameters of a given number of superimposed signals, as is the case of the received signal in wireless communications. Based on the description of the received signal in the frequency domain, one version of the SAGE (Space-Alternating Generalized Expectation-Maximization) algorithm is presented, allowing the estimation, for each impinging ray, the delay, azimuth, elevation and complex amplitude. Ray retrieval results are presented in synthetic channels, using data generated with the extended Saleh Valenzuela (ESV) model, and also in real channels
How a bottom-up multi-stakeholder initiative helped transform the renal replacement therapy landscape in Spain
[Abstract] Healthcare reforms aim to change certain parts of the health system to improve quality of care, access, or financial sustainability. Traditionally, healthcare reform is understood as an action undertaken by a government at a national or local level. However, bottom-up changes can also lead to improvements in the health system. This paper describes the efforts of a coordinated multi-stakeholder advocacy group in Spain to promote a more cost-effective and patient-centred treatment for people receiving renal replacement therapy and assesses the outcomes of their advocacy for health system financing and patient satisfaction. It concludes that bottom-up initiatives do indeed have the power to change health policy and that policy makers should pay attention to their arguments
A Three-Component Model Based on Macropropagation Phenomena Approach for Complex Building Scattering
Multipaths represent a common predominant and
uncontrolled component on channel impairments for all terrestrial
and Land Mobile Satellite systems. Without restrictions w.r.t mobile terrestrial applications, the addressed multipath problematic
in this paper is focused on Land Mobile Satellite applications
where delayed signal replicas are highly impacting performances
on communication systems while they induce strong positioning
errors for navigation systems. The actual trend in propagation
channel modelling is to improve the multipath characterisation
and representation by using semideterministic and hybrid
physical-statistical models into channel simulators instead of
narrow-band empirical approaches. In this context, this paper
presents a new simplified model, called 3CM (3-Component Model) to reproduce building scattering in an efficient way
which strongly improves computation performances. This model
is based on asymptotic methods, namely, PO (Physical Optics)
which allows the 3CM to be frequency scalable, polarimetric, and
dielectric materials oriented. Note that the proposed model and
the retained approach can be integrated into more complex tools
such as existing ray tracers. However, this issue is not discussed
in this paper
A Model for the Detailed Analysis of Radio Links Involving Tree Canopies
Detailed analysis of tree canopy interaction with incident radiowaves has mainly been limited to remote sensing for the purpose of forest classification among many other applications. This represents a monostatic configuration, unlike the case of communication links, which are bistatic. In general, link analyses have been limited to the application of simple, empirical formulas based on the use of specific attenuation values in dB/m and the traversed vegetated mass as, e.g., the model in Recommendation ITU-R P.833-8 [1]. In remote sensing, two main techniques are used: Multiple Scattering Theory (MST) [2][5] and Radiative Transfer Theory (RT), [5] and [6]. We have paid attention in the past to MST [7][10]. It was shown that a full application of MST leads to very long computation times which are unacceptable in the case where we have to analyze a scenario with several trees. Extensive work using MST has been also presented by others in [11][16] showing the interest in this technique. We have proposed a simplified model for scattering from tree canopies based on a hybridization of MST and a modified physical optics (PO) approach [16]. We assume that propagation through a canopy is accounted for by using the complex valued propagation constant obtained by MST. Unlike the case when the full MST is applied, the proposed approach offers significant benefits including a direct software implementation and acceptable computation times even for high frequencies and electrically large canopies. The proposed model thus replaces the coherent component in MST, significant in the forward direction, but keeps the incoherent or diffuse scattering component present in all directions. The incoherent component can be calculated within reasonable times. Here, we present tests of the proposed model against MST using an artificial single-tree scenario at 2 GHz and 10 GHz
Smart zero carbon city readiness level: sistema de indicadores para el diagnostico de las ciudades en su camino hacia la descarbonizacion y su aplicacion en el Pais Vasco
Nowadays urban environments concentrate more than half
the world’s population, reaching up to 70% on 2050 according
to forecasts. This concentration implies that most of future
challenges will take place in cities as well as the opportunities
coming from their potential solutions.
Current technological innovation can provide support in facing
one of main challenges society is facing: reducing carbon
footprint from our cities. This ambitious transition, steered by
the Smart Zero Carbon City (SZCC) concept, needs a flexible
characterisation method, which can be adapted to different
kinds of cities to evaluate the main features of each city, hence
proposing and prioritising most suitable interventions.
The aim of this study is focused on the characterisation of cities
according to the SZCC concept through a set of indicators: the
Smart Zero Carbon City Readiness Level (SZCC Readiness Level),
able to analyse key aspects of cities according to SZCC concept
(Characteristics of the city; City plans and strategies; Energy;
Mobility; Infrastructures and ICT services; Citizen Engagement).
This characterisation enlightens the development of SZCC
concept in the city, identifying its strengths and weaknesses
in order to ease the alternatives’ selection towards
decarbonisation, being handy at a time for those small and
medium-sized municipalities, so common in the European
context, which usually hold less resources than big capitals to
implement decision-making support diagnoses.
In order to validate this set of indicators, SZCC Readiness Level
has been implemented in 5 Basque cities, which represent
different urban typologies, analysing its current situation
regarding SZCC concept.Los autores quieren expresar su profundo agradecimiento a las administraciones
de Donostia-San Sebastián, Eibar, Irún, Sestao y Vitoria-Gasteiz por la estrecha
colaboración e involucración de sus técnicos en la tarea. Del mismo modo,
agradecer al Departamento de Medio Ambiente, PlanificaciĂłn Territorial y
Vivienda del Gobierno Vasco, mediante la convocatoria Eraikal, y a la ComisiĂłn
Europea, a través del proyecto SmartEnCity, por hacer posible este estudio
Short-term regulation of peptide YY secretion by a mixed meal or peritoneal glucose-based dialysate in patients with chronic renal failure
This is a pre-copyedited, author-produced version of an article accepted for publication in "Nephrology Dialysis Trasnplantation" following peer review. The version of the record is avaliable online at Oxford Academic website.Instituto de Salud Carlos III, PI051024Instituto de Salud Carlos III, PI070413Xunta de Galicia, PS07/12Xunta de Galicia, 2006/2
Inadequate use of antibiotics in the covid-19 era: effectiveness of antibiotic therapy
Background: Since December 2019, the COVID-19 pandemic has changed the concept of medicine. This work aims to analyze the use of antibiotics in patients admitted to the hospital due to SARS-CoV-2 infection. Methods: This work analyzes the use and effectiveness of antibiotics in hospitalized patients with COVID-19 based on data from the SEMI-COVID-19 registry, an initiative to generate knowledge about this disease using data from electronic medical records. Our primary endpoint was all-cause in-hospital mortality according to antibiotic use. The secondary endpoint was the effect of macrolides on mortality. Results: Of 13, 932 patients, antibiotics were used in 12, 238. The overall death rate was 20.7% and higher among those taking antibiotics (87.8%). Higher mortality was observed with use of all antibiotics (OR 1.40, 95% CI 1.21–1.62; p <.001) except macrolides, which had a higher survival rate (OR 0.70, 95% CI 0.64–0.76; p <.001). The decision to start antibiotics was influenced by presence of increased inflammatory markers and any kind of infiltrate on an x-ray. Patients receiving antibiotics required respiratory support and were transferred to intensive care units more often. Conclusions: Bacterial co-infection was uncommon among COVID-19 patients, yet use of antibiotics was high. There is insufficient evidence to support widespread use of empiric antibiotics in these patients. Most may not require empiric treatment and if they do, there is promising evidence regarding azithromycin as a potential COVID-19 treatment. © 2021, The Author(s)
Icodextrin does not impact infectious and culture-negative peritonitis rates in peritoneal dialysis patients: a 2-year multicentre, comparative, prospective cohort study
Background. Icodextrin is a glucose polymer derived by hydrolysis of cornstarch. The different biocompatibility profile of icodextrin-containing peritoneal dialysis (PD) solutions may have a positive influence on peritoneal host defence. Furthermore, cases of sterile peritonitis potentially associated with icodextrin have been reported
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