Architectures and Key Technical Challenges for 5G Systems Incorporating Satellites

Satellite Communication systems are a promising solution to extend and complement terrestrial networks in unserved or under-served areas. This aspect is reflected by recent commercial and standardisation endeavours. In particular, 3GPP recently initiated a Study Item for New Radio-based, i.e., 5G, Non-Terrestrial Networks aimed at deploying satellite systems either as a stand-alone solution or as an integration to terrestrial networks in mobile broadband and machine-type communication scenarios. However, typical satellite channel impairments, as large path losses, delays, and Doppler shifts, pose severe challenges to the realisation of a satellite-based NR network. In this paper, based on the architecture options currently being discussed in the standardisation fora, we discuss and assess the impact of the satellite channel characteristics on the physical and Medium Access Control layers, both in terms of transmitted waveforms and procedures for enhanced Mobile BroadBand (eMBB) and NarrowBand-Internet of Things (NB-IoT) applications. The proposed analysis shows that the main technical challenges are related to the PHY/MAC procedures, in particular Random Access (RA), Timing Advance (TA), and Hybrid Automatic Repeat reQuest (HARQ) and, depending on the considered service and architecture, different solutions are proposed.Comment: Submitted to Transactions on Vehicular Technologies, April 201

The Floodplain Woods of Tuscany

The contraction of lowland forests throughout Europe began in remote times and then intensified strongly with land reclamation by agriculture and urbanization during the first half of the last century. We present a map of the Floodplain Woods of Tuscany on a scale of 1:300,000 as a synthesis of that built at the scale of 1:10,000 and the methods used to obtain it. Nearly 90% of the patches contain habitats of concern to conservation, according to the Habitat Directive. The Tuscan Floodplain Woods remained prevalent in coastal areas, where some levels of protection are guaranteed by the presence of several protected areas, whereas they have practically vanished in the other parts of the regional territory. The resulting patches are very small and distant from each other, so only in-depth management of all potential floodplain forest areas, taking into consideration patches for their regeneration, can be useful to assure their conservation

Unravelling the ultrafast dynamics of a N-BODIPY compound

Although the photophysics of BODIPY compounds has been widely investigated in the last few years, their analogues N-BODIPY, with nitrogen substitution at the boron center, did not receive comparable attention. In this work we report the synthesis and photochemical characterization of a substituted N-BODIPY compound, by means of a combined theoretical and spectroscopic approach. Compared to a standard BODIPY, the compound under investigation presents a lower fluorescence quantum yield (QY) in the visible region. The excited state relaxation dynamics of the dye was studied in different solvents, showing further fluorescence quenching in polar solvents, and excited state decay rates strongly dependent on the environment polarity. The role of the pendant moieties and the involvement of charge transfer states in the excited state dynamics was experimentally addressed by transient absorption spectroscopy, and further analyzed with TD-DFT calculations, which allowed precise assignment of the transient signals to the correspondent electronic configuration. The complete picture of the N-BODIPY behavior shows the presence of both charge transfer and localized states, influencing the observed photophysics to different amounts, depending on the excitation conditions and the surrounding environment

Postglacial colonization history reflects in the genetic structure of natural populations of Festuca rubra in Europe

We conducted a large-scale population genetic survey of genetic diversity of the host grass Festuca rubra s.l., which fitness can be highly dependent on its symbiotic fungus Epichloe festucae, to evaluate genetic variation and population structure across the European range. The 27 studied populations have previously been found to differ in frequencies of occurrence of the symbiotic fungus E. festucae and ploidy levels. As predicted, we found decreased genetic diversity in previously glaciated areas in comparison with nonglaciated regions and discovered three major maternal genetic groups: southern, northeastern, and northwestern Europe. Interestingly, host populations from Greenland were genetically similar to those from the Faroe Islands and Iceland, suggesting gene flow also between those areas. The level of variation among populations within regions is evidently highly dependent on the postglacial colonization history, in particular on the number of independent long-distance seed colonization events. Yet, also anthropogenic effects may have affected the population structure in F. rubra. We did not observe higher fungal infection rates in grass populations with lower levels of genetic variability. In fact, the fungal infection rates of E. festucae in relation to genetic variability of the host populations varied widely among geographical areas, which indicate differences in population histories due to colonization events and possible costs of systemic fungi in harsh environmental conditions. We found that the plants of different ploidy levels are genetically closely related within geographic areas indicating independent formation of polyploids in different maternal lineages.Peer reviewe