1,720,998 research outputs found
Communication Modes with Large Intelligent Surfaces in the near Field
Full text linkThis paper proposes a practical method for the definition of communication modes when antennas operate in the near-field region, by realizing ad-hoc beams exploiting the focusing capability of large antennas. The beamspace modeling proposed to define the communication modes is then exploited to derive expressions for their number (i.e., the degrees of freedom) in a generic setup, beyond the traditional paraxial scenario, together with closed-form definitions for the basis set at the transmitting and receiving antennas for several cases of interest, such as for the communication between a large antenna and a small antenna. Numerical results show that quasi-optimal communication can be obtained starting from focusing functions. This translates into the possibility of a significant enhancement of the channel capacity even in line-of-sight channel condition, without the need of implementing optimal but complex phase/amplitude profiles on transmitting/receiving antennas as well as resorting to intensive numerical solutions. Traditional results valid under paraxial approximation are revised in light of the proposed modeling, showing that similar conclusions can be obtained from different perspectives
Holographic Communication Using Intelligent Surfaces
No full textHolographic communication is intended as a holistic way to manipulate, with unprecedented flexibility, the electromagnetic field generated or sensed by an antenna. This is of particular interest when using large antennas at high frequency (e.g., at millimeter-wave or terahertz), whose operating condition may easily fall in the Fresnel region (radiating near-field), where the classical plane wave propagation assumption is no longer valid. This article analyzes the optimal communication involving large intelligent surfaces realized, for example, with metamaterials as possible enabling technology for holographic communication. It is shown that traditional propagation models must be revised and that, when exploiting spherical wave propagation in the near-field region, new opportunities are opened, for example, in terms of feasible orthogonal communication channels
Spatial distribution of genetic variation in a natural beech stand (Fagus sylvatica L.) based on microsatellite markers
No full textThe spatial distribution of alleles is described in a naturally regenerated, isolated pure beech ( Fagus sylvatica L.) stand consisting of 99 adult trees. After testing nine microsatellite loci originally developed for F. crenata, each tree was genotyped at four well-scorable microsatellite loci. Specific primers were developed for one locus of F. sylvatica L. For the characterization of spatial genetic structures, two different statistics were used. One method is based on the mean genetic distance between trees in different spatial distance classes, and the other one is Moran's index I. The results show the same tendency of a strong family structure in the distance classes up to 30 m in comparison with that expected for a spatially non-systematic distribution of genotypes. In general, microsatellites are more useful to detect spatial genetic structures than allozymes. Spatial genetic structures are influenced by unpredictable factors such as wind direction at anthesis and can therefore vary from year to year. We recommend that seed collections should cover large areas in order to prevent a preponderance of few families and a reduction of the adaptive potential of the next generation
Performance Bounds for Velocity Estimation with Extremely Large Aperture Arrays
No full textJoint communication and sensing (JCS) is envisioned as an enabler of future 6G networks. One of the key features of these networks will be the use of extremely large aperture arrays (ELAAs) and high operating frequencies, which will result in significant near-field propagation effects. This unique property can be harnessed to improve sensing capabilities. In this letter, we focus on velocity sensing, as using ELAAs allows the estimation of not just the radial velocity component but also the transverse component. We derive analytical performance bounds for both velocity components, demonstrating how they are affected by the different system parameters and geometries. These results offer insights providing a foundational understanding of how near-field effects play in velocity sensing differently from the far field and from position estimate
LoS MIMO-Arrays vs. LoS MIMO-Surfaces
No full textThe wireless research community has expressed major interest in the sub-terahertz band for enabling mobile communications in future wireless networks. The sub-terahertz band offers a large amount of available bandwidth and, therefore, the promise to realize wireless communications at optical speeds. At such high frequency bands, the transceivers need to have larger apertures and need to be deployed more densely than at lower frequency bands. These factors proportionally increase the far-field limit and the spherical curvature of the electromagnetic waves cannot be ignored anymore. This offers the opportunity to realize spatial multiplexing even in line-of-sight channels. In this paper, we overview and compare existing design options to realize spatial multiplexing in line-of-sight multi-antenna channel
Pathologic factors related to nodal status assessment in colorectal cancer: Analysis of 166 cases with long-term follow-up
No full textFattori patologici inerenti la determinazione dello stato linfonodale nel carcinoma colorettal
OAM-based Holographic MIMO using Large Intelligent Surfaces
No full textThis paper addresses the exploitation of the orbital angular momentum (OAM) property of the electromagnetic waves with large intelligent surfaces (LISs) in near-field and line-of-sight propagation conditions for holographic multiple-input multiple-output (MIMO) communications. The relation-ship between OAM-carrying waves and communication modes established between intelligent surfaces is discussed, and practical strategies for exploiting OAM with LISs are then presented. Nu-merical results characterize the effectiveness of OAM compared to alternative strategies, though highlighting that OAM-based techniques constitute a particular choice of basis set that is sub-optimum with respect to the basis sets corresponding to optimal communication modes, albeit ensuring lower complexity
Beamspace Modeling of Multi-mode Communications with Large Intelligent Surfaces
No full textThe use of large intelligent surfaces as antennas enables the realization of multiple communication modes even in line-of-sight conditions, thanks to the exploitation of the near-field propagation. Despite results for the number of communication modes are known for specific configurations (e.g., small antennas and paraxial scenario), ad-hoc models are needed when adopting large antennas in arbitrary configurations. This paper gives new insights into the communication between large intelligent surfaces exploiting multiple communication modes, considering a beamspace modeling capable of accounting for generic orientations among the antennas and operating conditions following inside the near field, as happens with the increasing of the antenna size and operating frequency towards mm-waves and terahertz
Crowd-based cognitive perception of the physical world: Towards the internet of senses
Full text linkThis paper introduces a possible architecture and discusses the research directions for the realization of the Cognitive Perceptual Internet (CPI), which is enabled by the convergence of wired and wireless communications, traditional sensor networks, mobile crowd-sensing, and machine learning techniques. The CPI concept stems from the fact that mobile devices, such as smartphones and wearables, are becoming an outstanding mean for zero-effort world-sensing and digitalization thanks to their pervasive diffusion and the increasing number of embedded sensors. Data collected by such devices provide unprecedented insights into the physical world that can be inferred through cognitive processes, thus originating a digital sixth sense. In this paper, we describe how the Internet can behave like a sensing brain, thus evolving into the Internet of Senses, with network-based cognitive perception and action capabilities built upon mobile crowd-sensing mechanisms. The new concept of hyper-map is envisioned as an efficient geo-referenced repository of knowledge about the physical world. Such knowledge is acquired and augmented through heterogeneous sensors, multi-user cooperation and distributed learning mechanisms. Furthermore, we indicate the possibility to accommodate proactive sensors, in addition to common reactive sensors such as cameras, antennas, thermometers and inertial measurement units, by exploiting massive antenna arrays at millimeter-waves to enhance mobile terminals perception capabilities as well as the range of new applications. Finally, we distillate some insights about the challenges arising in the realization of the CPI, corroborated by preliminary results, and we depict a futuristic scenario where the proposed Internet of Senses becomes true
Localization in NLOS Conditions using Large Reconfigurable Intelligent Surfaces
No full textThis paper proposes a low-complexity practical algorithm to localize mobile users under NLOS channel conditions using a single base station and a large reconfigurable intelligent surface (RIS). The numerical results show the trade-off between localization accuracy and latency as well as the robustness of the localization algorithm to the presence of synchronization mismatches. An analysis of the soft-coverage capability, i.e., the possibility of maintaining a high level of localization accuracy with RISs that are partially obstructed is also provided
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