Redes mesh basadas en puntos de acceso inteligentes 802.11 open source (II)

El creciente éxito que las tecnologías inalámbricas basadas en 802.11 experimentan actualmente, está haciendo que cada vez más se opte por implementar soluciones basadas en este estándar para redes de ámbito doméstico, corporativo o incluso metropolitano. Gran parte de su éxito se basa en la compatibilidad con las redes Ethernet actuales, unido a unos precios cada vez más asequibles y la libertad de usarla sin licencia gracias a la banda en la que opera, pero es el mismo éxito el que amenaza el futuro de este tipo de redes ya que 802.11 dispone de un espectro muy limitado y la coexistencia de las cada vez más numerosas redes resulta cada vez más difícil. La solución pasa por diseñar una sistema que permita realizar una distribución frecuencial eficiente y global para minimizar el impacto de las interferencias entre los distintos nodos. Con una herramienta de estas características será posible llevar a cabo una distribución dinámica de las frecuencias de modo que nuestro sistema pueda evitar, en la medida de lo posible, interferencias entre sus propios nodos y con sistemas externos que escapen a nuestra gestión. El objetivo de este proyecto es encontrar una plataforma de código abierto con la suficiente potencia y flexibilidad para llevar a cabo esta tarea y desarrollar sobre ella un algoritmo distribuido capaz de construir, en cada nodo, un mapa completo de la red que reúna los datos necesarios para efectuar la distribución frecuencial

Scalability study of Guifi.net and mesh networks

A día de hoy, existen multitud de comunidades y asociaciones de usuarios particulares que crean y desarrollan iniciativas de conectividad ciudadana. De forma casual o profesionalizada, en pequeños grupos u organizados en estructuras de mayor tamaño, estas agrupaciones utilizan múltiples de tecnologías de comunicación, predominando las abiertas e inalámbricas, como base tecnológica para impulsar sus proyectos. Los expertos que materializan estas redes utilizan su tiempo libre, un recurso valioso, para el diseño e implementación de estas. Algunas de las tareas más costosas en tiempo son las relacionadas con la confección, prueba y validación de las configuraciones de red, fases fundamentales en el crecimiento y expansión de estas redes. En muchos casos, especialmente en lo referente a los protocolos de comunicaciones, es difícil prever cómo se comportará una la red, con una determinada configuración, sometida a las inclemencias del medio radio. Toda variación no prevista en el diseño, puede cambiar su topología, afectar a la distribución de carga de la red y al rendimiento general, en un entorno en el que realizar modificaciones o ajustes in-situ requiere coordinación entre los miembros de la comunidad y un esfuerzo que comporta desplazamientos, acceso a azoteas y trabajo en exteriores. Este proyecto reúne la documentación, el software y los procedimientos necesarios para emular redes Ethernet y probar su desempeño bajo condiciones propias de entornos radio. Virtualizando los nodos y utilizando los mismos sistemas operativos con las mismas aplicaciones, servicios, protocolos y configuraciones que en los escenarios reales, se estudia el impacto provocado por las problemáticas características del medio radio tales como pérdida de datos y variaciones en la velocidad de transferencia o la topología

A MIMO-OFDM testbed, channel measurements, and system considerations for outdoor-indoor WiMAX

The design, implementation, and test of a real-time flexible 2×2 (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing) MIMO-OFDM IEEE 802.16 prototype are presented. For the design, a channel measurement campaign on the 3.5GHz band has been carried out, focusing on outdoor-indoor scenarios. The analysis of measured channels showed that higher capacity can be achieved in case of obstructed scenarios and that (Channel Distribution Information at the Transmitter) CDIT capacity is close to (Channel State Information at the Transmitter) CSIT with much lower complexity and requirements in terms of channel estimation and feedback. The baseband prototype used an (Field Programmable Gate Array) FPGA where enhanced signal processing algorithms are implemented in order to improve system performance. We have shown that for MIMO-OFDM systems, extra signal processing such as enhanced joint channel and frequency offset estimation is needed to obtain a good performance and approach in practice the theoretical capacity improvements

The coexistence of diabetic retinopathy and diabetic nephropathy is associated with worse kidney outcomes

Up to 50-60% of patients with diabetes have non-diabetic kidney disease (NDKD) on kidney biopsy. Diabetic retinopathy (DR) is a microvascular complication of diabetes frequently associated with diabetic nephropathy (DN). The objective of the current study was to investigate the kidney outcomes and survival in patients with biopsy diagnoses of DN and NDKD according to the presence of DR. We conducted an observational, multicentre and retrospective study of the pathological findings of renal biopsies from 832 consecutive patients with diabetes from 2002 to 2014 from 18 nephrology departments. The association of DR with kidney replacement therapy (KRT) or survival was assessed by Kaplan-Meier and Cox regression analyses. Of 832 patients with diabetes and renal biopsy, 768 had a retinal examination and 221/768 (22.6%) had DR. During a follow-up of 10 years, 288/760 (37.9%) patients with follow-up data needed KRT and 157/760 (20.7%) died. The incidence of KRT was higher among patients with DN (alone or with NDKD) and DR [103/175 (58.9%)] than among patients without DR [88/216 (40.7%), P <.0001]. The incidence of KRT was also higher among patients with only NDKD and DR than among those without DR [18/46 (39.1%) versus 79/331 (23.9%), P <.0001]. In multivariate analysis, DR or DN were independent risk factors for KRT {hazard ratio [HR] 2.48 [confidence interval (CI) 1.85-3.31], P <.001}. DN (with or without DR) was also identified as an independent risk factor for mortality [HR 1.81 (CI 1.26-2.62), P =.001]. DR is associated with a higher risk of progression to kidney failure in patients with histological DN and in patients with NDKD

Submarine canyons and related features in the Alboran Sea: continental margins and major isolated reliefs

The analysis of a data set of multibeam bathymetry plus high resolution seismic and parametric profiles allow us to characterize the geomorphologic units on the Alboran Sea-floor as well as the evolution of morpho-sedimentary systems along the Pliocene and Quaternary, later than the main erosive Messinian event. Since the opening of the Gibraltar Straits, the sedimentary evolution of this basin has been controlled by the interchange of water masses between the Atlantic Ocean and the Mediterranean Sea. Basin physiography is also a consequence of the Pliocene-Quaternary compression which has progressively uplifted the sourrounding reliefs and deforms the interior and the margins of the basin. On this scenario, several submarine canyons and gullies have been developed in this basin which traverse especially the northern margin and the flanks of the Northern Alboran Ridge, without affecting the African margins. This fact must be related to the action of bottom contour currents which constitute the main morpho-sedimentary process. The influence of water masses distributed the sedimentary input carried by rivers and coming from the erosion of surrounding ranges. In the southern margin of this basin this influence is stronger and inhibits the development of transversal submarine canyons

The nowcasting SAF products and services: recent improvements in the new SW packages PPS v2018 and GEO v2018 and future plans

Presentación realizada en la 3rd European Nowcasting Conference, celebrada en la sede central de AEMET en Madrid del 24 al 26 de abril de 2019

From chemosynthesis-based communities to cold-water corals: Vulnerable deep-sea habitats of the Gulf of Cádiz

The Gulf of Cádiz (GoC) represents an area of ecological importance within the northeastern Atlantic Ocean due to the presence of Mediterranean and Atlantic water masses, a heterogeneous seafloor and a biological confluence. Nevertheless, information on the presence of vulnerable deep-sea habitats is still very scarce and it is of importance for further habitat monitoring within the context of the Habitats and Marine Strategy Framework Directives and for improving conservation and resource extraction management. From 2010 to 2012, fluid migration and emission related edifices (e.g., mud volcanoes, diapirs) from the Spanish continental margin of the GoC have been explored using a remotely operated vehicle (ROV; Liropus 2000) and an underwater camera sled (UCS; APHIA 2012) as well as several devices for collecting sediment and fauna. Different vulnerable deep-sea habitats have been observed, including anoxic bottoms with bacterial mats, sea-pen communities, sponge aggregations, antipatharian and gorgonian communities and also cold-water coral banks. Some of these habitats are included in conservation lists of the habitat directive and in international conventions (OSPAR, RAC/SPA), however some of them are located in areas of the GoC that are exposed to intense trawling. The diversity of habitats detected in the Spanish continental margin of the GoC highlights the importance of seepage related edifices as inducers of seabed and habitat heterogeneity in deep-sea areas.En prens

Asociaciones de crustáceos decápodos de volcanes de fango y fondos adyacentes en aguas españolas del Golfo de Cádiz

Publicado

Underwater imagery-study of sediment and fauna for habitat characterization in mud volcanoes of the Spanish margin (Gulf of Cádiz)

Habitat characterization using underwater images has been carried out in 4 mud volcanoes (Gazul, Almazán, St. Petersburg and Aveiro) and one mud volcano/diapir complex (Hespérides) located at the middle slope of the Spanish margin of the Gulf of Cádiz (360-1200m depth). A total of 126 species, mostly cnidarians, sponges, brachiopods, crustaceans and echinoderms and 19 habitats have been observed in the underwater images, including anoxic bottoms with cold seep fauna or remains (Siboglinum sp., Lucinoma asapheus, Solemya elarraichensis), bottoms with authigenic carbonates colonized by gorgonians and anthipatharians, extensive muddy bottoms with sea pens (Kophobelemnon sp., Protoptilum sp.) and bamboo corals (Isidella elongata) and cold-water coral banks (Madrepora oculata). Habitat type and distribution seem influenced by sedimentary features, presence of hard substrates with authigenic carbonates, seepage activity, depth and hydrodynamic conditions. Cold seep related species and heterotrophic species not directly linked to fluid venting represent seepage activity indicators and induce habitat and biodiversity differentiation among the fluid venting edifices

Spatial assessment of trawling activity in a shallow mud volcano field of the Gulf of Cádiz

The Gulf of Cadiz display a wide continental shelf at its northwestern part with a complex oceanographic circulation, large extensions with soft bottoms, diapiric ridges, mud volcanoes, channels, that promote geological and biological heterogeneity and also a wide variety of commercial resources that are exploited by an important fishing sector. Fisheries activity in this area has been studied using VMS and logbooks data during 2011. Fishing effort and captures maps for some important species (Nephrops norvegicus and Parapenaeus longirostris) have been developed for different areas which may be able to improve the spatial and quantitative information on fisheries, and implement measures to improve ecosystem management and conservation of the different vulnerable habitats of the Gulf of CadizVersión del edito