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Introduced pathogens can alter the geographic distribution of susceptible host species. For example, Batrachochytrium dendrobatidis (Bd) is a fungal pathogen that has been linked to the global decline and extinction of numerous amphibian species during the last four decades. A growing number of studies have described the distribution of Bd and susceptible hosts across the globe; however, knowledge on how Bd may shape the climatic niche of susceptible species is still missing. We estimated the effect of Bd on the geographic distribution and niche dynamics of the critically endangered lowland robber frog (Craugastor ranoides) in Costa Rica. We found a reduction of 98% in the geographic range of this species by 1995, following the epizootic outbreaks of Bd that affected Costa Rica in the 1980 and early 1990s. We also quantified niche contraction and found that the species is currently restricted to dry and warm environments that have been considered unsuitable for Bd. Our results contribute to the understanding of how emerging pathogens shape the climatic niches and geographic distribution of susceptible species.

In this chapter, the authors adopt the view of a mobile network operator that, by rolling out its massive multiple input–multiple output (MIMO) based 5G network, aims to offer communication services to both ground users (GUEs) and unmanned aerial vehicles (UAVs) simultaneously, reusing its cellular spectrum and infrastructure. After evaluating the downlink performance of networks with UAV users, they aim to assess whether cellular networks can provide high‐speed uplink aerial links for video streaming purposes. An equally important concern is related to the influence that UAV transmissions have on the uplink performance of terrestrial users. The authors evaluate the network performance and capture the propagation environment between ground base stations and both GUEs and UAVs through the latest 3GPP 3D channel model. They also introduce the network topology and channel model. A common feature of the single‐user and massive MIMO paradigms is an equal time splitting between downlink and uplink data transmissions.

Isthmian Central America (ICA) is one of the most biodiverse regions in the world, hosting an exceptionally high number of species per unit area. ICA was formed

Estadisticas de todos los jugadores y partidos jugados en LaLiga Santander de primera división hasta la fecha 22/03/2022

Treefrogs represent 22% of amphibian species in Costa Rica, but gaps in the knowledge about this group of amphibians can impede conservation efforts. In this study, we first updated the status of Costa Rican treefrogs and found that a total of 38% of treefrog species are threatened according to the most recent IUCN assessment in 2019. Additionally, 21% of Costa Rican treefrog species have a high vulnerability to extinction according to environmental vulnerability scores. Then, we predicted the historical climatic suitability of eight target species that we expected to have exhibited changes in their ranges in the last 20 years. We assessed the location of new occurrence records since 2000 to identify recovery, range expansion, or previously underestimated ranges due to methodological limitations. We also estimated the area of each species’ suitable habitat with two metrics: extent of suitable habitat (ESH) and area of minimum convex polygon (AMCP). Six declined species exhibited recovery (i.e., new occurrences across historical range after 2000), with the widest recovery found in Agalychnis annae. We also found that Isthmohyla pseudopuma appears to have spread after the decline of sympatric species and that the range of I. sukia was originally underestimated due to inadequate detection. We found that the ESH was 32–49% smaller than the AMCP for species that are slowly recovering, however, the ESH is similar or greater than the AMCP for species that are recovering in most of their ranges, as well as rare species with widespread ranges. Results of this work can be used to evaluate the risk of environmental threats and prioritize regions for conservation purposes.

Continental mountain areas cover15% of global land surface, yet these regions concentrate80% of global terrestrial diversity. One prominent hypothesis to explain this pattern proposes that high mountain diversities could be explained by higher diversification rates in regions of high topographic complexity (HTC). While high speciation in mountains has been detected for particular clades and regions, the global extent to which lineages experience faster speciation in mountains remains unknown. Here we addressed this issue using amphibians as a model system (7,000 species), and we found that families showing high speciation rates contain a high proportion of species distributed in mountains. Moreover, we found that lineages inhabiting areas of HTC speciate faster than lineages occupying areas that are topographically less complex. When comparing across regions, we identified the same pattern in five biogeographical realms where higher speciation rates are associated with higher levels of complex topography. Low-magnitude differences in speciation rates between some low and high complex topographies suggest that high mountain diversity is also affected by low extinction and/or high colonization rates. Nevertheless, our results bolster the importance of mountains as engines of speciation at different geographical scales and highlight their importance for the conservation of global biodiversity.

Identifying the source population of invasive species is important to assess the distribution and potential effects in the invaded area. The araneid spider Cyrtophora citricola is widely distributed in Europe, Asia, and Africa; however, in the last twenty years, it has been reported in several countries across the Americas. To date, the geographic origin of the populations established in America remains unclear, but considering the successful colonization after its recent arrival, a high environmental similarity between the invaded and native geographic distributions is expected. In this study, we compared the environmental characteristics of two possible native regions (southern Africa and the Mediterranean) and the invaded region (America), to determine the more likely origin for the populations established in America. We found that the South African populations of C. citricola occupy environments with similar climatic conditions to those of the American populations, and these similarities are greater than the ones shared with the Mediterranean populations. Therefore, our results support a Southern African, rather than a Mediterranean origin for the populations established in America. In addition, our results also show that populations in America are expanding to environments that differ from those of the native populations. Further studies, assessing intrinsic (e.g. physiological tolerances, plasticity, behavior, reproduction) and extrinsic (physical barriers, predator release) factors could provide further information to disentangle the mechanisms behind this expansion.

Strawberry Poison Frogs (Oophaga pumilio) are common members of leaf litter lowland communities in Central America and exhibit several color morphs throughout their distribution. Color plays a determinant role during intra- and intermorph interactions in many insular populations, but little is known about the variation and perception of visual signals in mainland populations. In this study, we investigated color variation of four body parts—head, back, belly, and throat—in a bright red O. pumilio population of northeastern Costa Rica. We incorporated frog- and bird-specific visual modeling to evaluate the differences in color and brightness between the sexes, from the perspective of conspecifics and avian predators. Furthermore, we measured the color and brightness contrast against natural backgrounds commonly used by these frogs to forage and patrol within territories. Our results revealed that, from the perspective of conspecifics, there is no dichromatism between males and females. However, females had a greater contrast against green and brown backgrounds than males. The bird visual models indicated that males and females are highly conspicuous against common background substrates but that females are easier to detect than males. This study detailing color variants between sexes within a mainland population of O. pumilio contributes to our understanding of color differences in populations of this species. Fundación Veragua/[]//Costa Rica Museo Argentino de Ciencias Naturales Bernardino Rivadavia/[]/MACN/Argentina Universidad Nacional Autónoma de México/[]/UNAM/México Universidad de Costa Rica/[111-C0-066]/UCR/Costa Rica UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biología

Acoustic signals are distorted by vegetation, wind currents, or other sounds when transmitted through the environment. Consequently, vocalizations with features that optimize sound transmission or behaviors that improve the efficacy of communication have evolved in many animal species. Among behavioral strategies, some species call from perches above the ground to increase the propagation distance of their acoustic signals. However, the orientation in the perch also influences the transmission of the vocalizations, so that frogs calling from different orientations (i.e., horizontal, upward, or downward) may affect differently the quality and efficacy of sound transmission. We implemented a sound transmission experiment to test for the effect of calling orientation (upward, downward, and horizontal) and distance on the attenuation and degradation of advertisement calls in the common dink frog Diasporus diastema. We broadcasted and re-recorded advertisement calls at 2 m height, setting the speaker in three directions (upward, downward, and horizontal) to simulate different signaler orientations. We found that attenuation of the advertisement calls is significantly reduced when the speaker was directed either upward or downward, rather than horizontally. However, the degradation of call is lower when the speaker is direct horizontally. Since calls produced from either upward or downward orientations could travel farther, they could be used to signal male spatial location, while calls produced from a horizontal position could provide information on male quality at shorter distances at advanced phases of courtship. Universidad de Costa Rica/[111-C0-066]/UCR/Costa Rica Universidad Nacional Autónoma de México/[]/UNAM/México Max Planck Institute for Chemical Ecology/[]/IMPRS/Alemania UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biología UCR::Vicerrectoría de Investigación::Sistema de Estudios de Posgrado::Ciencias Básicas::Maestría Académica en Biología

We consider a cellular network deployment where UAV-to-UAV (U2U) transmit-receive pairs share the same spectrum with the uplink (UL) of cellular ground users (GUEs). For this setup, we focus on analyzing and comparing the performance of two spectrum sharing mechanisms: (i) underlay, where the same time-frequency resources may be accessed by both UAVs and GUEs, resulting in mutual interference, and (ii)overlay, where the available resources are divided into orthogonal portions for U2U and GUE communications. We evaluate the coverage probability and rate of both link types and their interplay to identify the best spectrum sharing strategy. We do so through an analytical framework that embraces realistic height-dependent channel models, antenna patterns, and practical power control mechanisms. For the underlay, we find that although the presence of U2U direct communications may worsen the uplink performance of GUEs, such effect is limited as base stations receive the power-constrained UAV signals through their antenna sidelobes. In spite of this, our results lead us to conclude that in urban scenarios with a large number of UAV pairs, adopting an overlay spectrum sharing seems the most suitable approach for maintaining a minimum guaranteed rate for UAVs and a high GUE UL performance., Related Work: Azari, M. M., Rosas, F., & Pollin, S. (2019). Cellular connectivity for UAVs: Network modeling, performance analysis and design guidelines. IEEE Transactions on Wireless Communications. arXiv admin note: text overlap with arXiv:1904.05104

Indoor areas, such as offices and shopping malls, are a natural environment for initial millimeter-wave (mmWave) deployments. While we already have the technology that enables us to realize indoor mmWave deployments, there are many remaining challenges associated with system-level design and planning for such. The objective of this article is to bring together multiple strands of research to provide a comprehensive and integrated framework for the design and performance evaluation of indoor mmWave systems. The paper introduces the framework with a status update on mmWave technology, including ongoing fifth generation (5G) wireless standardization efforts, and then moves on to experimentally-validated channel models that inform performance evaluation and deployment planning. Together these yield insights on indoor mmWave deployment strategies and system configurations, from feasible deployment densities to beam management strategies and necessary capacity extensions., Comment: Proceedings of the IEEE

Wi-Fi technology is continuously evolving to keep the pace with the fast-increasing demand for new digital services and applications. In particular, Wi-Fi 6 is becoming widely available in residential and enterprise scenarios supporting up to eight spatial streams. At the same time, large antenna arrays have already shown their ability and benefits when serving a large number of devices simultaneously. Since enterprise owners are already upgrading their indoor private networks with the next generation of Wi-Fi products, it becomes crucial to understand the capacity limits and the benefits associated to different deployment strategies and large antenna array configurations. The scope of this paper is to provide concrete insights to internet service providers and enterprise owners on how to upgrade, deploy, and efficiently operate their networks with next-generation Wi-Fi access points, showing their potential performance improvements and providing a set of clear guidelines.

In this paper, we investigate the use of highly directional, hybrid antenna arrays in residential Wi-Fi mesh deployments to further improve their performance in challenging conditions where high wall losses are encountered. We also formulate a metric to quantify the quality of the Wi-Fi coverage, and present a deployment procedure to automatically select extender AP locations to maximise such metric. Using the proposed deployment procedure, the performance of highly directional, hybrid antenna arrays in residential Wi-Fi mesh deployments is evaluated through simulations. Compared with the benchmark of omni-directional antennas, we show that using the proposed array increases the areas achieving peak throughput by more than 3 times.

We study support for unmanned aerial vehicle (UAV) communications through a cell-free massive MIMO architecture, wherein a large number of access points (APs) is deployed in place of large co-located massive MIMO arrays. We consider also a variation of the pure cell-free architecture by applying a user-centric association approach, where each user is served only from a subset of APs in the network. Under the general assumption that the propagation channel between the mobile stations, either UAVs or ground users (GUEs), and the APs follows a Ricean distribution, we derive closed-form spectral efficiency lower bounds for uplink and downlink with linear minimum mean square error channel estimation. We consider several power allocation and user scheduling strategies for such a system, and, among these, also minimum-rate maximizing power allocation strategies to improve the system fairness. Our numerical results reveal that cell-free massive MIMO architecture and its low-complexity user-centric alternative may provide better performance than a traditional multi-cell massive MIMO network deployment., double-column, 14 pages, 8 figure, journal paper

As hordes of data-hungry devices challenge its current capabilities, Wi-Fi strikes back with 802.11be, alias Wi-Fi 7. This brand-new amendment promises a (r)evolution of unlicensed wireless connectivity as we know it. With its standardisation process being consolidated, we provide an updated digest of 802.11be essential features, vouching for multi-AP coordination as a must-have for critical and latency-sensitive applications. We then get down to the nitty-gritty of one of its most enticing implementations-coordinated beamforming-, for which our standard-compliant simulations confirm near-tenfold reductions in worst-case delays., Comment: 7 pages

In this article, we evaluate the performance of the parameterized spatial reuse (PSR) framework of IEEE 802.11ax, mainly focusing on its impact on transmission latency. Based on detailed standard-compliant system-level simulations, we provide a realistic analysis of the effects of PSR considering different scenario densities, traffic loads, and access points (APs) antenna capabilities to quantify its performance gains under various scenarios. Our results show that, in medium-density scenarios, PSR can offer up to a 3.8x reduction in the 5% worst-case latencies for delay-sensitive stations with respect to an 802.11ax system without PSR. Moreover, our study demonstrates that, for low-latency communications, providing the network with PSR capabilities may be an appealing alternative to the deployment of more costly multi-antenna APs., Comment: Accepted to IEEE Globecom 2020, SAC - Access Networks and Systems

In this article, we consider a cellular network deployment where UAV-to-UAV (U2U) transmit-receive pairs coexist with the uplink (UL) of cellular ground users (GUEs). Our analysis focuses on comparing two spectrum sharing mechanisms: i) overlay, where the available time-frequency resources are split into orthogonal portions for U2U and GUE communications, and ii) underlay, where the same resources may be accessed by both link types, resulting in mutual interference. We evaluate the coverage probability and rate of all links and their interplay to identify the best spectrum sharing mechanism. Among other things, our results demonstrate that, in scenarios with a large number of UAV pairs, adopting overlay spectrum sharing seems the most suitable approach for maintaining a minimum guaranteed rate for UAVs and a high GUE UL performance. We also find that increasing the density of U2U links degrades their rates in the overlay-where UAVs only receive interference from other UAVs-, but not significantly so in the underlay -- where the effect of GUE-generated interference is dominant., Comment: Accepted to present at IEEE GLOBECOM 2020. arXiv admin note: substantial text overlap with arXiv:1912.07534

A spatially correlated large antenna array operating at millimeter-wave (mmWave) frequencies is considered. Based on a Saleh–Valenzuela channel model, closed-form expressions of the 3-D spatial correlation (SC) for wide, narrow, and Von Mises power elevation spectra (PESs) are analytically derived. The effects of the PES on the convergence to massive multiple-input-multiple-output properties are then illustrated by defining and deriving a diagonal dominance metric. Numerically, the effects of antenna element mutual coupling (MC) are shown on the effective SC, eigenvalue structure, and mmWave user rate for different antenna topologies. It is concluded that although MC can significantly reduce SC for side-by-side dipole antenna elements, the change in antenna effective gain (and, therefore, signal-to-noise ratio) caused by MC becomes a dominating effect and ultimately determines the antenna array performance. The user rate of an mmWave system with hybrid beamforming, using an orthogonal matching pursuit (OMP) algorithm, is then shown for different antenna topologies with dipole and cross-polarized (x-pol) antenna elements. It is seen that even for small numbers of radio frequency chains, the OMP algorithm works well relative to the fully digital case for channels with high SC, such as the x-pol antenna array.

The purpose of this article is to bestow the reader with a timely study of UAV cellular communications, bridging the gap between the 3GPP standardization status quo and the more forward-looking research. Special emphasis is placed on the downlink command and control (C&C) channel to aerial users, whose reliability is deemed of paramount technological importance for the commercial success of UAV cellular communications. Through a realistic side-by-side comparison of two network deployments -- a present-day cellular infrastructure versus a next-generation massive MIMO system -- a plurality of key facts are cast light upon, with the three main ones summarized as follows: (i) UAV cell selection is essentially driven by the secondary lobes of a base station's radiation pattern, causing UAVs to associate to far-flung cells; (ii) over a 10 MHz bandwidth, and for UAV heights of up to 300 m, massive MIMO networks can support 100 kbps C&C channels in 74% of the cases when the uplink pilots for channel estimation are reused among base station sites, and in 96% of the cases without pilot reuse across the network; (iii) supporting UAV C&C channels can considerably affect the performance of ground users on account of severe pilot contamination, unless suitable power control policies are in place., arXiv admin note: text overlap with arXiv:1802.01527

We propose to operate massive multiple-input multiple-output (MIMO) cellular base stations (BSs) in unlicensed bands. We denote such systems as massive MIMO unlicensed (mMIMO-U) ones. We design the key procedures required at a cellular BS to guarantee coexistence with nearby Wi-Fi devices operating in the same band. In particular, spatial reuse is enhanced by actively suppressing interference toward neighboring Wi-Fi devices. Wi-Fi interference rejection is also performed during an enhanced listen-before-talk phase. These operations enable Wi-Fi devices to access the channel as though no cellular BSs were transmitting, and vice versa. Under concurrent Wi-Fi and BS transmissions, the downlink rates attainable by cellular user equipment (UEs) are degraded by the Wi-Fi-generated interference. To mitigate this effect, we select a suitable set of UEs to be served in the unlicensed band accounting for a measure of the Wi-Fi/UE proximity. Our results show that the so-designed mMIMO-U allows simultaneous cellular and Wi-Fi transmissions by keeping their mutual interference below the regulatory threshold. Compared with a system without interference suppression, Wi-Fi devices enjoy a median interference power reduction of between 3 dB with 16 antennas and 18 dB with 128 antennas. With mMIMO-U, cellular BSs can also achieve large data rates without significantly degrading the performance of Wi-Fi networks deployed within their coverage area.

Comunicació presentada a: The 30th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), celebrat a Istambul,Turquia, del 8 a l'11 de setembre de 2019. Reliable and direct communication between un-manned aerial vehicles (UAVs) could facilitate autonomous flight, collision avoidance, and cooperation in UAV swarms. In this paper, we consider UAV-to-UAV (U2U) communica-tions underlaying a cellular network, where UAV transmit-receive pairs share the same spectrum with the uplink (UL) of cellular ground users (GUEs). We evaluate the performance of this setup through an analytical framework that embraces realistic height-dependent channel models, antenna patterns, and practical power control mechanisms. Our results demonstrate that, although the presence of U2U communications may worsen the performance of the GUEs, such effect is limited as base stations receive UAV interference through their antenna sidelobes. Moreover, we illustrate that the quality of all links degrades as the UAV height increases—due to a larger number of line-of-sight interferers—, and how the performance of the U2U links can be traded off against that of the GUEs by varying the UAV power control policy. The work of G. Geraci was supported by the Postdoctoral Junior Leader Fellowship Programme from “la Caixa” Banking Foundation.

We investigate the interfering channel estimation in radar and communication coexistence, where a multi-input-multi-output (MIMO) radar is operated in a “search and track” mode, and a MIMO base station (BS) is attempting to acquire the interfering channel state information (ICSI) between them, which is required for the precoding designs. In contrast to conventional training based techniques, we exploit radar probing waveforms as pilot signals, which requires no coordination between the systems. As the radar randomly transmits searching and tracking waveforms, it is challenging for the BS to directly obtain the ICSI. We therefore propose a Rao test approach to firstly identify the working mode of the radar, and then estimate the channel. We further provide theoretical performance analysis for the Rao detector. Finally, we assess the effectiveness of the proposed approach by numerical simulations, which show that the BS is able to estimate the ICSI with limited information from the radar.

A new dink frog (Eleutherodactylidae: Diasporus) is described from the Tropical Wet Forest, in the northeastern foothills of Cordillera de Talamanca in Costa Rica at an elevation of ca. 1000 m. Analysis of DNA sequences of the 16S rRNA (16S) and cytochrome oxidase 1 (COI) mitochondrial genes revealed a distinct lineage within the genus Diasporus. Additional morphological, morphometric, and acoustic analyses support the differences of this lineage, which we recognize as a new species. This new taxon is distinguished from other members of the genus Diasporus inhabiting Isthmian Central America by its unique coloration: dorsum brown to brown-grayish and venter gray-bluish with pale blotches. The new species is distinguished from other members of the genus Diasporus by very significant genetic distances (higher than 5.6 % in 16S and 16.7 % in COI). The new taxon is most closely related to D. vocator from the south pacific of Costa Rica and to an unnamed taxon from western Panama.

Together with ultra‐dense networks, massive MIMO (mMIMO) has also emerged as one of the disruptive technologies for the next‐generation wireless communications systems, where APs are envisioned to be equipped with a large number of antennas. This chapter describes the fundamentals behind mMIMO‐unlicensed (mMIMO‐U), a technology that, if adopted, could provide significant improvements to existing licensed assisted access (LAA), MulteFire, and even Wi‐Fi systems. It summarizes the procedures carried out by mMIMO‐U systems for downlink data transmissions: channel covariance estimation, enhanced listen before talk, neighboring‐node‐aware scheduling, acquisition of channel state information, and beamforming with radiation nulls. The chapter presents the performance evaluation of mMIMO‐U for both outdoor and indoor scenarios. It dissects the main challenges to realize mMIMO‐U and its potential in enhancing spectrum reuse. Overall, the substantial enhancements attainable over existing alternatives make mMIMO‐U a key solution for future unlicensed ultra‐dense network deployments.

Biological communities are experiencing rapid shifts of composition in Neotropical ecosystems due to several factors causing population declines. However, emerging evidence has provided insights on the adaptive potential of multiple species to respond to illnesses and environmental pressures. In Costa Rica, the decline of amphibian populations is a remarkable example of these changes. Here we provide evidence of variation in the amphibian richness of a premontane forest of San Ramón (Costa Rica) across a ~30 year period. We also quantified changes in the composition and abundance of the leaf-litter frog community occurring in the same premontane forest, by comparing diversity data with a difference of ~18 years. We evaluated the similarity of species richness from 1980s to 2010s based on several sources, and the dissimilarity of species diversity in the site comparing 28 standardized surveys from 1994-1995 and 2011-2012. We compared the relative abundance of some frogs that inhabit the leaf-litter layer between these same periods. Our results show that there is more similarity in amphibian richness between 1980s and 2010s (~ 52 %) than between 1980s and 1990s (~ 40 %). The richness of leaf-litter anurans was ~ 65 % similar between 1990s and 2010s. The diversity of leaf-litter anuran was clearly different between 1994-1995 and 2011-2012, and it was clustered among those periods. We determined that the amphibian community in this premontane forest drastically changed: many species have disappeared, or gradually declined through the decades (e.g. Pristimantis ridens, P. cruentus, Craugastor bransfordii) as in other well studied localities of Costa Rica, while some few species flourished after being almost absent from the site in the 1990s (e.g. Craugastor crassidigitus, Lithobates warszewistchii). Currently dominant species such as C. crassidigitus would be using developed resistance against Bd-fungus as an advantage (apparent competition) in the premontane forest where the disease is more virulent than in lowlands. Our analysis supports the hypothesis of individualized responses of anuran populations under distinct site and elevations. We suggest to continue monitoring the amphibian communities of premontane tropical forests to understand how this ecosystem gradually resist and adapts to this catastrophic time of biodiversity loss. Resumen Las comunidades biológicas están experimentando rápidos cambios de composición en los ecosistemas neotropicales debido a varios factores que causan disminuciones de las poblaciones. Sin embargo, la evidencia emergente ha proporcionado información sobre el potencial de adaptación de múltiples especies para responder a enfermedades y presiones ambientales. En Costa Rica, el declive de las poblaciones de anfibios es un ejemplo notable de estos cambios. Aquí proporcionamos evidencia de variación en la riqueza de anfibios de un bosque premontano de San Ramón (Costa Rica) en un período de ~ 30 años. También cuantificamos los cambios en el ensamblaje, y las oscilaciones poblacionales, de la comunidad de ranas de hojarasca que ocurren en el mismo bosque premontano, tras comparar datos de diversidad con una diferencia de ~ 18 años. Evaluamos la similitud de la riqueza de especies desde la década de 1980 hasta la de 2010 basados en varias fuentes, así como la disimilitud de la diversidad de especies en el sitio comparando 28 muestreos estandarizados entre 1994-1995 y 2011-2012. Comparamos la abundancia relativa de algunas ranas que habitan la hojarasca entre 1994-1995 y 2011-2012. Nuestros resultados muestran que existe una similitud un poco mayor en la riqueza de anfibios entre los años 1980 y 2010 que entre los 1980 y 1990 (~ 40 %). La riqueza de los anuros de la hojarasca fue aproximadamente un 65 % similar entre la década de 1990 y 2010. La diversidad de anuros de la hojarasca fue claramente diferente entre 1994-1995 y 2011-2012, y se agrupó entre esos períodos. Determinamos que la comunidad de anfibios en este bosque premontano cambió drásticamente: muchas especies han desaparecido o han disminuido gradualmente a lo largo de las décadas como en otras localidades bien estudiadas de Costa Rica (por ejemplo, Pristimantis ridens, P. cruentus, Craugastor bransfordii), mientras algunas pocas especies florecieron tras casi desaparecer de nuestro sitio en la década de 1990 (por ejemplo, Craugastor crassidigitus, Lithobates warszewistchii). Actualmente, las especies dominantes como C. crassidigitus podrían tener resistencia contra el hongo quitridio, desarrollada como una ventaja (competición aparente) en el bosque premontano donde la enfermedad es más virulenta que en las tierras bajas. Nuestro análisis apoya la hipótesis de las respuestas individualizadas de las poblaciones de anuros en distintos sitios y elevaciones. Sugerimos continuar con el monitoreo de las comunidades de anfibios de los bosques neotropicales premontanos para comprender cómo este ecosistema resiste gradualmente y se adapta a este momento catastrófico de pérdida de biodiversidad.

Wi-Fi technology is continuously innovating to cater to the growing customer demands, driven by the digitalisation of everything, both in the home as well as the enterprise and hotspot spaces. In this article, we introduce to the wireless community the next generation Wi-Fi$-$based on IEEE 802.11be Extremely High Throughput (EHT)$-$, present the main objectives and timelines of this new 802.11be amendment, thoroughly describe its main candidate features and enhancements, and cover the important issue of coexistence with other wireless technologies. We also provide simulation results to assess the potential throughput gains brought by 802.11be with respect to 802.11ax., Comment: 6 pages, 4 figures

We study support for unmanned aerial vehicle (UAV) communications through a cell-free massive MIMO architecture. Under the general assumption that the propagation channel between the mobile stations, either UAVs or ground users, and the access points follows a Ricean distribution, we derive closed form spectral efficiency lower bounds for uplink and downlink with linear minimum mean square error (LMMSE) channel estimation. We also propose power allocation and user scheduling strategies for such a system. Our numerical results reveal that a cell-free massive MIMO architecture may provide better performance than a traditional multicell massive MIMO network deployment., Comment: Submitted to 2019 ICC Workshop on "Integrating UAVs into 5G and Beyond"

In this paper, we focus on the coexistence between a MIMO radar and cellular base stations. We study the interfering channel estimation, where the radar is operated in the "search and track" mode, and the BS receives the interference from the radar. Unlike the conventional methods where the radar and the cellular systems fully cooperate with each other, in this work we consider that they are uncoordinated and the BS needs to acquire the interfering channel state information (ICSI) by exploiting the radar probing waveforms. For completeness, both the line-of-sight (LoS) and Non-LoS (NLoS) channels are considered in the coexistence scenario. By further assuming that the BS has limited a priori knowledge about the radar waveforms, we propose several hypothesis testing methods to identify the working mode of the radar, and then obtain the ICSI through a variety of channel estimation schemes. Based on the statistical theory, we analyze the theoretical performance of both the hypothesis testing and the channel estimation methods. Finally, simulation results verify the effectiveness of our theoretical analysis and demonstrate that the BS can effectively estimate the interfering channel even with limited information from the radar., 15 pages, 10 figures. This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessible

Resumen 26. Las señales acústicas producidas por animales pueden ser enmascaradas por el ruido del medio ambiente en que se encuentran, tanto de origen natural como antropogénico. Una especie que puede ver afectada su comunicación por el ruido medio ambiental es la rana de vidrio Hyalinobatrachium fleischmanni (Centrolenidae), porque la distribución actual de esta especie en gran parte se encuentra en ambientes urbanos con altos niveles de ruido. En este trabajo analizamos si existe una relación entre la variación de los niveles de ruido antropogénico a través de la noche y la actividad vocal (cantidad de vocalizaciones por unidad de tiempo) de H. fleischmanni, a lo largo de un gradiente de ruido urbano. El trabajo lo realizamos en tres sitios dentro del Campus Universitario Rodrigo Facio, San José, Costa Rica durante el mes de junio de 2015. Para contabilizar la actividad vocal de la especie en cada sitio instalamos grabadores programables de 17:00 a las 6:00 por dos días consecutivos cada dos semanas. De forma simultánea, cuantificamos el ruido en dB cada hora a lo largo del periodo de grabación utilizando sonómetros. Comparamos la abundancia promedio de vocalizaciones por hora contra los niveles de ruido promedio por hora y sitio utilizando modelos lineales mixtos. Nuestros resultados demuestran que, tanto el ruido como la actividad vocal de H. fleischmanni variaron a lo largo de la noche. Sin embargo, encontramos que en el sitio más ruidoso el patrón de actividad de H. fleischmanni difiere de los dos sitios menos ruidosos.El sitio menos ruidoso fue el que presento una mayor actividad vocal a lo largo de todo el periodo de muestreo. A pesar de que no se encontró una relación directa entre el nivel de ruido antropogénico y la actividad acústica de H. fleischmanni, sí observamos un efecto de los niveles de ruido en los patrones de actividad de la especie. Abstract 23. Acoustic signals produced by animals can be masked by natural or anthropogenic environmental noise. A high proportion of the current distribution of the glass-frog Hyalinobatrachium fleischmanni (Centrolenidae) overlaps with noisy urban habitats, and this may affect the species acoustic communication. In this work, we analyzed the relationship between changes in anthropogenic noise level throughout the night and the diel acoustic variation (vocalization per time) in H. fleischmanni, within three sites with different noise level. We conducted this study in three sites inside the Rodrigo Facio University Campus, San José, Costa Rica in June 2015. We used an automated recorder per site to record glass-frog vocalizations, from 17:00 to 6:00 h, during two consecutive days, every two weeks, for a month. Simultaneously, we measured the noise levels in dB each hour using a soundmeter. We used linear mixed models to compare the vocalization mean per hour against the noise levels per hour and site. Our results showed that noise levels and H. fleischmanni acoustic activity varied throughout the night. The H. fleischmanni acoustic activity at the noisier site was different from sites with lower noise levels. The highest acoustic activity was found in the less noisy site throughout the sampled period. Although we fail to found a direct relationship between noise level and H. fleischmanni acoustic activity, noise level variation affects vocal activity pattern in this species.

In this letter, we revisit hybrid analog–digital precoding systems with emphasis on the modeling of their radio-frequency (RF) losses, to realistically evaluate their benefits in 5G system implementations. We focus on fully-connected analog beamforming networks (FC-ABFNs) and on discrete Fourier transform implementations, and decompose these as a bank of commonly used RF components. We then model their losses based on their S-parameters. Our results reveal that the performance and energy efficiency of hybrid precoding systems are severely affected once these, commonly ignored, losses are considered in the overall design. In this context, we also show that hybrid precoder designs similar to Butler matrices are capable of providing better performances than FC-ABFN for systems with a large number of RF chains.

An adaptive interference detector based on compressive sensing is introduced in this paper. The proposed detector is part of a narrowband interference mitigation system for wideband cognitive HF front-ends that self-adapts its configuration hinging on the behaviour of the automatic gain control. The use of a compressive sensing architecture allows us to significantly reduce the cost of the additional hardware required to perform the detection of harmful narrowband interfering signals. The proposed detector has been verified with real wideband HF signals and the results show that the adopted approach is a suitable alternative to detect a number of narrowband interfering signals without prior knowledge of their frequency location.

The genus of direct-developing frogs Diasporus is currently composed of 11 species ranging from Honduras to Ecuador. Body size variability, advertisement call divergence, and polychromatism have all been reported at the interpopulation level, suggesting that the existence of some species may be masked within the current nomenclature of this group. This pattern highlights the need for integrative approaches to resolve the taxonomy of the genus and provide a robust delimitation of the species it contains. Here, we provide novel data on morphology, genetics, habitat use, and bioacoustics for D. tigrillo, the least known species in the genus. Then we use an integrative approach to assess the divergence between this species and D. citrinobapheus a recently described species. D. tigrillo was indicated as the most similar species to D. citrinobapheus by its authors; however, given the lack of available information for D. tigrillo this conclusion was based only on morphological data obtained from a few deteriorat...

A key aspect of the fifth-generation wireless communication network will be the integration of different services and technologies to provide seamless connectivity. In this paper, we consider using massive multiple-input multiple-output (mMIMO) to provide backhaul links to a dense deployment of self-backhauling (s-BH) small cells (SCs) that provide cellular access within the same spectrum resources of the backhaul. Through a comprehensive system-level simulation study, we evaluate the interplay between access and backhaul and the resulting end-to-end user rates. Moreover, we analyze the impact of different SCs deployment strategies, while varying the time resource allocation between radio access and backhaul links. We finally compare the above mMIMO-based s-BH approach to a mMIMO direct access (DA) architecture accounting for the effects of pilot reuse schemes, together with their associated overhead and contamination mitigation effects. The results show that dense SCs deployments supported by mMIMO s-BH provide significant rate improvements for cell-edge users (UEs) in ultra-dense deployments with respect to mMIMO DA, while the latter outperforms mMIMO s-BH from the median UEs' standpoint.

Reliable command and control channels to unmanned aerial vehicles (UAVs) are needed to allow beyond visual line of sight (LoS) operations. Cellular networks, with their almost ubiquitous coverage, are an obvious candidate to provide such conditions. However, up to which extent the current networks designed for ground users can support UAV communications is an open question. In this paper, we provide a comprehensive theoretical analysis, using stochastic geometry, of the performance that operators could expect from traditional cellular networks with omnidirectional antennas when supporting UAV downlink command and control channels. Our study employs the latest UAV height-dependent path loss model defined by the 3GPP, with LoS and non-LoS transmissions and a probabilistic model to switch between them. We derive analytical expressions for the coverage probability and area spectral efficiency, while accounting for base stations with idle mode capabilities, a practical finite UAV density, and different UAV heights. Results show that networks based on base stations with omnidirectional coverage can support low-height UAVs but will struggle with high-height ones. Network densification helps to provide a better performance.

Emerging infectious diseases are a growing threat to biodiversity worldwide. Outbreaks of the infectious disease chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), have caused the decline and extinction of numerous amphibian species. In Costa Rica, a major decline event occurred in 1987, more than two decades before this pathogen was discovered. The loss of many species in Costa Rica is assumed to be due to Bd-epizootics, but there are few studies that provide data from amphibians in the time leading up to the proposed epizootics. In this study, we provide new data on Bd infection rates of amphibians collected throughout Costa Rica, in the decades prior to the epizootics. We used a quantitative PCR assay to test for Bd infection in 1016 specimens collected throughout Costa Rica. We found Bd-infected hosts collected as early as 1964, and a infection prevalence average per decade of just 4%. The infection prevalence remained relatively low and geographically constrained until the 1980s when epizootics are hypothesized to have occurred. After that time, infection prevalence increased three-fold and Bd-infected hosts we collected throughout the entire country. Our results, suggest that Bd may either have invaded Costa Rica earlier than previously known, and spread more slowly than previously reported, or that an endemic lineage of the pathogen may exists. To help visualize areas where future studies should take place, we provide a Bd habitat suitability model trained with local data. Studies that provide information on genetic lineages of Bd are needed to determine whether an endemic lineage of Bd or the Global Panzootic Lineage (identified from mass die off sites globally) was present in Costa Rica and responsible for the epizootics that caused amphibian communities to collapse.

In this paper, we focus on one of the key technologies for the fifth-generation wireless communication networks, massive multiple-input-multiple-output (mMIMO), by investigating two of its most relevant architectures: 1) to provide in-band backhaul for the ultra-dense network (UDN) of self-backhauled small cells (SCs), and 2) to provide direct access (DA) to user equipments (UEs). Through comprehensive 3GPP-based system-level simulations and analytical formulations, we show the end-to-end UE rates achievable with these two architectures. Differently from the existing works, we provide results for two strategies of self-backhauled SC deployments, namely random and ad-hoc, where in the latter SCs are purposely positioned close to UEs to achieve line-of-sight (LoS) access links. We also evaluate the optimal backhaul and access time resource partition due to the in-band self-backhauling (s-BH) operations. Our results show that the ad-hoc deployment of self-backhauled SCs closer to the UEs with optimal resource partition and with directive antenna patterns, provides rate improvements for cell-edge UEs that amount to 30% and tenfold gain, as compared to mMIMO DA architecture with pilot reuse 3 and reuse 1, respectively. On the other hand, mMIMO s-BH underperforms mMIMO DA above the median value of the UE rates when the effect of pilot contamination is less severe, and the LoS probability of the DA links improves., The paper is published at IEEE Transactions on Vehicular Technology (TVT 2019). arXiv admin note: text overlap with arXiv:1806.10969

The rapid growth of consumer Unmanned Aerial Vehicles (UAVs) is creating promising new business opportunities for cellular operators. On the one hand, UAVs can be connected to cellular networks as new types of user equipment, therefore generating significant revenues for the operators that can guarantee their stringent service requirements. On the other hand, UAVs offer the unprecedented opportunity to realize UAV-mounted flying base stations that can dynamically reposition themselves to boost coverage, spectral efficiency, and user quality of experience. Indeed, the standardization bodies are currently exploring possibilities for serving commercial UAVs with cellular networks. Industries are beginning to trial early prototypes of flying base stations or user equipments, while academia is in full swing researching mathematical and algorithmic solutions to address interesting new problems arising from flying nodes in cellular networks. In this article, we provide a comprehensive survey of all of these developments promoting smooth integration of UAVs into cellular networks. Specifically, we survey (i) the types of consumer UAVs currently available off-the-shelf, (ii) the interference issues and potential solutions addressed by standardization bodies for serving aerial users with the existing terrestrial base stations, (iii) the challenges and opportunities for assisting cellular communications with UAV-based flying relays and base stations, (iv) the ongoing prototyping and test bed activities, (v) the new regulations being developed to manage the commercial use of UAVs, and (vi) the cyber-physical security of UAV-assisted cellular communications., Accepted in the JOURNAL OF COMMUNICATIONS SURVEYS AND TUTORIALS, Feb 2019, 26 pages, 9 Tables, 9 Figures Submitted to JOURNAL OF COMMUNICATIONS SURVEYS AND TUTORIALS, June 2018, 20 pages, 9 Tables, 9 Figures

What will it take for drones -- and the whole associated ecosystem -- to take off? Arguably, infallible command and control (C&C) channels for safe and autonomous flying, and high-throughput links for multi-purpose live video streaming. And indeed, meeting these aspirations may entail a full cellular support, provided through 5G-and-beyond hardware and software upgrades by both mobile operators and manufacturers of these unmanned aerial vehicles (UAVs). In this article, we vouch for massive MIMO as the key building block to realize 5G-connected UAVs. Through the sheer evidence of 3GPP-compliant simulations, we demonstrate how massive MIMO can be enhanced by complementary network-based and UAV-based solutions, resulting in consistent UAV C&C support, large UAV uplink data rates, and harmonious coexistence with legacy ground users.

In this article, we provide a much-needed study of UAV cellular communications, focusing on the rates achievable for the UAV downlink command and control (C&C) channel. For this key performance indicator, we perform a realistic comparison between existing deployments operating in single-user mode and next-generation multi-user massive MIMO systems. We find that in single-user deployments under heavy data traffic, UAVs flying at 50 m, 150 m, and 300 m achieve the C&C target rate of 100 kbps -- as set by the 3GPP -- in a mere 35%, 2%, and 1% of the cases, respectively. Owing to mitigated interference, a stronger carrier signal, and a spatial multiplexing gain, massive MIMO time division duplex systems can dramatically increase such probability. Indeed, we show that for UAV heights up to 300 m the target rate is met with massive MIMO in 74% and 96% of the cases with and without uplink pilot reuse for channel state information (CSI) acquisition, respectively. On the other hand, the presence of UAVs can significantly degrade the performance of ground users, whose pilot signals are vulnerable to UAV-generated contamination and require protection through uplink power control.

Providing consistently high wireless capacity is becoming increasingly important to support the applications required by future digital enterprises. In this paper, we propose Eigen-direction-aware ZF (EDA-ZF) with partial coordination among base stations (BSs) and distributed interference suppression as a practical approach to achieve this objective. We compare our solution with Zero Forcing (ZF), entailing neither BS coordination or inter-cell interference mitigation, and Network MIMO (NeMIMO), where full BS coordination enables centralized inter-cell interference management. We also evaluate the performance of said schemes for three sub-6 GHz deployments with varying BS densities -- sparse, intermediate, and dense -- all with fixed total number of antennas and radiated power. Extensive simulations show that: (i) indoor massive MIMO implementing the proposed EDA-ZF provides uniformly good rates for all users; (ii) indoor network densification is detrimental unless full coordination is implemented; (iii) deploying NeMIMO pays off under strong outdoor interference, especially for cell-edge users.

We present new distribution information for 19 species of Costa Rican birds. Thirteen species show changes in altitudinal distribution, 9 are recorded at higher elevations such as Egretta rufescens (Gmelin, 1789), Heliomaster constantii (Delattre, 1843), Myiozetetes cayanensis (Linnaeus, 1766), and Lonchura malacca (Linnaeus, 1766), and 4 are recorded at lower elevations, Panterpe insignis Cabanis & Heine, 1860, Empidonax albigularis Sclater & Salvin, 1859, Sayornis nigricans (Swainson, 1827), and Dacnis venusta (Lawrence, 1862). We recorded 2 forest understory species, Geotrygon montana (Linnaeus, 1758), and Grallaria guatimalensis Prévost & Des Murs, 1842, inside the area of the county with the most urban development. Finally, Saltator grossus (Linnaeus, 1766), which was restricted to Caribbean forest, was recorded at the South Pacific rainforest for the first time.

Nowadays, the demand for wireless mobile services is copious, and will continue increasing in the near future. Mobile cellular operators are therefore looking at the unlicensed spectrum as an economical supplement to augment the capacity of their soon-to-be overloaded networks. The same unlicensed bands are luring internet service providers, venue owners, and authorities into autonomously setting up and managing their high-performance private networks. In light of this exciting future, ensuring coexistence between multiple unlicensed technologies becomes a pivotal issue. So far this issue has been merely addressed via inefficient sharing schemes based on intermittent transmission. In this article, we present the fundamentals and the main challenges behind massive MIMO unlicensed, a brand-new approach for technology coexistence in the unlicensed bands, which is envisioned to boost spectrum reuse for a plethora of use cases., Comment: 6 pages, 6 figures

We provide a checklist of the amphibians and reptiles of Río Macho Biological Station (RMBS), Costa Rica. During a period of a year (2012–2013) we conducted visual and acoustic surveys in a natural mature forest plot (>50 years old) (MF), secondary forest plot (~17 years old) (SF), in open areas and riparian forest at RMBS. We found a total of 11 species of amphibians and 15 species of reptiles belonging to 11 taxonomic families. We also compared the diversity of the MF against the SF. The MF contained 10 species (five amphibians and five reptiles) and the SF seven (three amphibians and four reptiles), with similar dominance between sites. Unfortunately, some forest and riparian species have vanished at this elevation after an enigmatic decline, according to historical literature pristine areas should contain higher species richness. Perhaps, the secondary forest will provide an available habitat for an important percentage of the remaining forest species. Proporcionamos una lista de verificación de los anfibios y reptiles de la Estación Biológica Río Macho (RMBS), Costa Rica. Durante un período de un año (2012–2013) realizamos estudios visuales y acústicos en una parcela de bosque maduro natural (> 50 años) (MF), parcela de bosque secundario (~ 17 años) (SF), en áreas abiertas y bosque ribereño en RMBS. Encontramos un total de 11 especies de anfibios y 15 especies de reptiles pertenecientes a 11 familias taxonómicas. También comparamos la diversidad del MF con el SF. El MF contenía 10 especies (cinco anfibios y cinco reptiles) y el SF siete (tres anfibios y cuatro reptiles), con un dominio similar entre los sitios. Desafortunadamente, algunas especies forestales y ribereñas se han desvanecido en esta elevación después de una disminución enigmática; De acuerdo con la literatura histórica, las áreas prístinas deben contener una mayor riqueza de especies. Quizás, el bosque secundario proporcionará un hábitat disponible para un porcentaje importante de las especies forestales restantes. Universidad Nacional, Costa Rica Escuela de Ciencias Biológicas

Extreme climatic events such as the El Nino Southern Oscillation profoundly affect many plants and animals, including amphibians, which are strongly negatively affected by drought conditions. How amphibians respond to exceptionally high precipitation as observed in La Nina events, however, remains unclear. We document the correlation between the exceedingly wet 2010–2012 La Nina and community-level changes in a leaf litter frog assemblage in Costa Rica. Relative abundances of species shifted, diversity and plot occupancy decreased, and community composition became homogenized with the onset of La Nina. These aspects remained altered for over 20 months but rebounded to pre-La Nina levels after approximately 12 months. We hypothesize that complex ecological cascades associated with excess moisture caused short-term declines in abundances of species and associated changes in community structure. If additional stressors such as disease or habitat loss are not co-occurring, frog communities can rapidly recover to pre-disturbance levels following severe climatic events.