| 1. |
- Householder, John Ethan, et al.
(författare)
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One sixth of Amazonian tree diversity is dependent on river floodplains
- 2024
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Ingår i: NATURE ECOLOGY & EVOLUTION. - 2397-334X.
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Tidskriftsartikel (refereegranskat)abstract
- Amazonia's floodplain system is the largest and most biodiverse on Earth. Although forests are crucial to the ecological integrity of floodplains, our understanding of their species composition and how this may differ from surrounding forest types is still far too limited, particularly as changing inundation regimes begin to reshape floodplain tree communities and the critical ecosystem functions they underpin. Here we address this gap by taking a spatially explicit look at Amazonia-wide patterns of tree-species turnover and ecological specialization of the region's floodplain forests. We show that the majority of Amazonian tree species can inhabit floodplains, and about a sixth of Amazonian tree diversity is ecologically specialized on floodplains. The degree of specialization in floodplain communities is driven by regional flood patterns, with the most compositionally differentiated floodplain forests located centrally within the fluvial network and contingent on the most extraordinary flood magnitudes regionally. Our results provide a spatially explicit view of ecological specialization of floodplain forest communities and expose the need for whole-basin hydrological integrity to protect the Amazon's tree diversity and its function.
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| 2. |
- Laya, Andres, et al.
(författare)
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Device-to-device communications and small cells : Enabling spectrum reuse for dense networks
- 2014
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Ingår i: IEEE wireless communications. - 1536-1284 .- 1558-0687. ; 21:4, s. 98-105
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Tidskriftsartikel (refereegranskat)abstract
- In the evolution of communication networks, there has always been a need to increase the capacity to cope with the continuous growing demand for data transmission. However, with the arrival of the Internet-of-Things and the commoditization of broadband access through smartphones, tablets, smart-watches, and all types of connecting devices, future networks must be capable of providing higher bandwidth and Quality of Experience, as wellas operating in dense networks with a massive number of simultaneous connections. This high number of connections will be very heterogeneous, spanning from highly-demanding data rate applications to low-complexity and high energy-efficient Machine-to-Machine communications. In such a dense and complex scenario, a more flexible use of spectrum resources is deemed to be the way to meet the growing requirements for data transmission. In particular, this article focuses on Device-to-Device communications and small cell deployments as emerging facilitators of such a demanding and heterogeneous scenario. The pros and cons of both complementary strategies are identified from both a technical and a business point of view, and main standardization activities are discussed. The aim of this article is to identify and describe open challenges and to inspire new areas for research that make viable the next generation of dense networks.
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| 3. |
- Laya, Andres, et al.
(författare)
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Goodbye, ALOHA!
- 2016
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Ingår i: IEEE Access. - : IEEE. - 2169-3536. ; 4, s. 2029-2044
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Tidskriftsartikel (refereegranskat)abstract
- The vision of the Internet of Things (IoT) to interconnect and Internet-connect everyday people, objects, and machines poses new challenges in the design of wireless communication networks. The design of medium access control (MAC) protocols has been traditionally an intense area of research due to their high impact on the overall performance of wireless communications. The majority of research activities in this field deal with different variations of protocols somehow based on ALOHA, either with or without listen before talk, i.e., carrier sensing multiple access. These protocols operate well under low traffic loads and low number of simultaneous devices. However, they suffer from congestion as the traffic load and the number of devices increase. For this reason, unless revisited, the MAC layer can become a bottleneck for the success of the IoT. In this paper, we provide an overview of the existing MAC solutions for the IoT, describing current limitations and envisioned challenges for the near future. Motivated by those, we identify a family of simple algorithms based on distributed queueing (DQ), which can operate for an infinite number of devices generating any traffic load and pattern. A description of the DQ mechanism is provided and most relevant existing studies of DQ applied in different scenarios are described in this paper. In addition, we provide a novel performance evaluation of DQ when applied for the IoT. Finally, a description of the very first demo of DQ for its use in the IoT is also included in this paper.
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| 4. |
- Laya, Andres, et al.
(författare)
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Green MTC, M2M, Internet of Things
- 2015
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Ingår i: Green Communications. - Chichester, UK : John Wiley & Sons. - 9781118759257 ; , s. 217-236
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Bokkapitel (refereegranskat)abstract
- The capability of having any type of object interconnected and Internet-connected creates an unprecedented access and exchange of information that has been baptized as the Internet of Things (IoT). With the advancement of integrated technologies, improved batteries, and electronic miniaturization, everyday things will be equipped with sensors and microprocessors to collect information around them and execute smart applications. In addition, they will be able to communicate with each other. The IoT has the potential to revolutionize innovations; create new products, services, business; and reshape consumer’s behavior. IoT represents a major player for the future of Information and Communications Technologies (ICT).The development of the IoT must be environment friendly. ICT have shown to be a key contributor to global warming and environmental pollution; it is predicted that the global greenhouse gas (GHG) emissions from ICT will account for 12% of all emissions by 2020 at a growth rate of 6% per year. Therefore, it is mandatory to develop environmentally friendly - or “green” - technologies for the IoT, and ICT in general.Machine-to-Machine (M2M) communications constitute a fundamental part of the IoT. The term M2M refers to the exchange of data between two or more entities, objects, or machines that do not necessarily need human interaction. The envisioned market for such kind of communications is broader than the one traditional human-based communications in terms of number of users and variety of applications. Some forecasts predict figures up to 50 billion machines that will be connecting to communication networks by 2020. This is a very big number compared to the entire world population of around 7 billion people. Therefore, there are some challenges that need to be addressed in order to fully supportM2Mservices in current communication networks. From the technical point of view, M2M communications are substantially different from Human-to-Human (H2H) communications. For example, network operators should provide communication services at low cost in order to face the low Average Revenue Per User (ARPU). Despite the large number of expected M2M connections, most of them will generate very little and infrequent data traffic. Communication networks shall also provide suitable congestion and overload control solutions in order to handle a huge number of simultaneous connections. Features such as low mobility, time-controlled data delivery, group-based policing and addressing, low connection delays, and a wide variety of Quality of Service requirements are among other challenges that need to be addressed. All of them must have the “green” concept embedded. In order to ensure that devices can operate autonomously for years or even decades without human intervention, it is necessary to provide networks with highly efficient communication protocols. This is the main focus of this chapter.The European Telecommunications Standards Institute (ETSI) created in 2009 a dedicated technical committee to identify key M2M use cases, understand the service requirements, and promote standards for the complete end-to-end M2M functional architecture. Later, in 2012, the global One M2M project was also established by ETSI, with other international standardization bodies, in order to define M2M standards that can accelerate the deployment and success of M2M applications.
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| 5. |
- Laya, Andres, et al.
(författare)
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Is the Random Access Channel of LTE and LTE-A Suitable for M2M Communications? A Survey of Alternatives
- 2014
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Ingår i: IEEE Communications Surveys and Tutorials. - : IEEE Communications Society. - 1553-877X. ; 16:1, s. 4-16
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Tidskriftsartikel (refereegranskat)abstract
- The 3GPP has raised the need to revisit the design of next generations of cellular networks in order to make them capable and efficient to provide M2M services. One of the key challenges that has been identified is the need to enhance the operation of the random access channel of LTE and LTE-A. The current mechanism to request access to the system is known to suffer from congestion and overloading in the presence of a huge number of devices. For this reason, different research groups around the globe are working towards the design of more efficient ways of managing the access to these networks in such circumstances. This paper aims to provide a survey of the alternatives that have been proposed over the last years to improve the operation of the random access channel of LTE and LTE-A. A comprehensive discussion of the different alternatives is provided, identifying strengths and weaknesses of each one of them, while drawing future trends to steer the efforts over the same shooting line. In addition, while existing literature has been focused on the performance in terms of delay, the energy efficiency of the access mechanism of LTE will play a key role in the deployment of M2M networks. For this reason, a comprehensive performance evaluation of the energy efficiency of the random access mechanism of LTE is provided in this paper. The aim of this computer-based simulation study is to set a baseline performance upon which new and more energy-efficient mechanisms can be designed in the near future.
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| 6. |
- Laya, Andres, et al.
(författare)
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Reliable Machine-to-Machine Multicast Services with Multi-Radio Cooperative Retransmissions
- 2015
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Ingår i: Mobile Networks and Applications. - : Springer-Verlag New York. - 1383-469X .- 1572-8153. ; 20:6, s. 734-744
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Tidskriftsartikel (refereegranskat)abstract
- The 3GPP is working towards the definition of service requirements and technical solutions to provide support for energy-efficient Machine Type Communications (MTC) in the forthcoming generations of cellular networks. One of the envisioned solutions consists in applying group management policies to clusters of devices in order to reduce control signaling and improve upon energy efficiency, e.g., multicast Over-The-Air (OTA) firmware updates. In this paper, a Multi-Radio Cooperative Retransmission Scheme is proposed to efficiently carry out multicast transmissions in MTC networks, reducing both control signaling and improving energy-efficiency. The proposal can be executed in networks composed by devices equipped with multiple radio interfaces which enable them to connect to both a cellular access network, e.g., LTE, and a short-range MTC area network, e.g., Low-Power Wi-Fi or ZigBee, as foreseen by the MTC architecture defined by ETSI. The main idea is to carry out retransmissions over the M2M area network upon error in the main cellular link. This yields a reduction in both the traffic load over the cellular link and the energy consumption of the devices. Computer-based simulations with ns-3 have been conducted to analyze the performance of the proposed scheme in terms of energy consumption and assess its superior performance compared to non-cooperative retransmission schemes, thus validating its suitability for energy-constrained MTC applications.
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| 7. |
- Luize, Bruno Garcia, et al.
(författare)
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Geography and ecology shape the phylogenetic composition of Amazonian tree communities
- 2024
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Ingår i: JOURNAL OF BIOGEOGRAPHY. - 0305-0270 .- 1365-2699.
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Tidskriftsartikel (refereegranskat)abstract
- Aim: Amazonia hosts more tree species from numerous evolutionary lineages, both young and ancient, than any other biogeographic region. Previous studies have shown that tree lineages colonized multiple edaphic environments and dispersed widely across Amazonia, leading to a hypothesis, which we test, that lineages should not be strongly associated with either geographic regions or edaphic forest types. Location: Amazonia. Taxon: Angiosperms (Magnoliids; Monocots; Eudicots). Methods: Data for the abundance of 5082 tree species in 1989 plots were combined with a mega-phylogeny. We applied evolutionary ordination to assess how phylogenetic composition varies across Amazonia. We used variation partitioning and Moran's eigenvector maps (MEM) to test and quantify the separate and joint contributions of spatial and environmental variables to explain the phylogenetic composition of plots. We tested the indicator value of lineages for geographic regions and edaphic forest types and mapped associations onto the phylogeny. Results: In the terra firme and v & aacute;rzea forest types, the phylogenetic composition varies by geographic region, but the igap & oacute; and white-sand forest types retain a unique evolutionary signature regardless of region. Overall, we find that soil chemistry, climate and topography explain 24% of the variation in phylogenetic composition, with 79% of that variation being spatially structured (R-2 = 19% overall for combined spatial/environmental effects). The phylogenetic composition also shows substantial spatial patterns not related to the environmental variables we quantified (R-2 = 28%). A greater number of lineages were significant indicators of geographic regions than forest types. Main Conclusion: Numerous tree lineages, including some ancient ones (>66 Ma), show strong associations with geographic regions and edaphic forest types of Amazonia. This shows that specialization in specific edaphic environments has played a long-standing role in the evolutionary assembly of Amazonian forests. Furthermore, many lineages, even those that have dispersed across Amazonia, dominate within a specific region, likely because of phylogenetically conserved niches for environmental conditions that are prevalent within regions.
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| 8. |
- ter Steege, Hans, et al.
(författare)
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Mapping density, diversity and species-richness of the Amazon tree flora
- 2023
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Ingår i: COMMUNICATIONS BIOLOGY. - 2399-3642. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- Using 2.046 botanically-inventoried tree plots across the largest tropical forest on Earth, we mapped tree species-diversity and tree species-richness at 0.1-degree resolution, and investigated drivers for diversity and richness. Using only location, stratified by forest type, as predictor, our spatial model, to the best of our knowledge, provides the most accurate map of tree diversity in Amazonia to date, explaining approximately 70% of the tree diversity and species-richness. Large soil-forest combinations determine a significant percentage of the variation in tree species-richness and tree alpha-diversity in Amazonian forest-plots. We suggest that the size and fragmentation of these systems drive their large-scale diversity patterns and hence local diversity. A model not using location but cumulative water deficit, tree density, and temperature seasonality explains 47% of the tree species-richness in the terra-firme forest in Amazonia. Over large areas across Amazonia, residuals of this relationship are small and poorly spatially structured, suggesting that much of the residual variation may be local. The Guyana Shield area has consistently negative residuals, showing that this area has lower tree species-richness than expected by our models. We provide extensive plot meta-data, including tree density, tree alpha-diversity and tree species-richness results and gridded maps at 0.1-degree resolution. A study mapping the tree species richness in Amazonian forests shows that soil type exerts a strong effect on species richness, probably caused by the areas of these forest types. Cumulative water deficit, tree density and temperature seasonality affect species richness at a regional scale.
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| 9. |
- Antonakoglou, Konstantinos, et al.
(författare)
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On the needs and requirements arising from connected and automated driving
- 2020
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Ingår i: Journal of Sensor and Actuator Networks. - : MDPI AG. - 2224-2708. ; 9:2
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Tidskriftsartikel (refereegranskat)abstract
- Future 5G systems have set a goal to support mission-critical Vehicle-to-Everything (V2X) communications and they contribute to an important step towards connected and automated driving. To achieve this goal, the communication technologies should be designed based on a solid understanding of the new V2X applications and the related requirements and challenges. In this regard, we provide a description of the main V2X application categories and their representative use cases selected based on an analysis of the future needs of cooperative and automated driving. We also present a methodology on how to derive the network related requirements from the automotive specific requirements. The methodology can be used to analyze the key requirements of both existing and future V2X use cases.
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| 10. |
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