1,720,973 research outputs found
A Markov Game of Age of Information From Strategic Sources With Full Online Information
No full textWe investigate the performance of concurrent remote sensing from independent strategic sources, whose goal is to minimize a linear combination of the freshness of information and the updating cost. In the literature, this is often investigated from a static perspective of setting the update rate of the sources a priori, either in a centralized optimal way or with a distributed game-theoretic approach. However, we argue that truly rational sources would better make such a decision with full awareness of the current age of information, resulting in a more efficient implementation of the updating policies. To this end, we investigate the scenario where sources independently perform a stateful optimization of their objective. Their strategic character leads to the formalization of this problem as a Markov game, for which we find the resulting Nash equilibrium. This can be translated into practical smooth threshold policies for their update. The results are eventually tested in a sample scenario, comparing a centralized optimal approach with two distributed approaches with different objectives for the players
Biogas upgrading by 2-steps methanation of its CO2 – Thermodynamics analysis
No full textA thermodynamic analysis of the methanation of CO2 within biogas sets the limits to the achievable perfor-mances, directing process and catalyst development. Practical indications of thermodynamics are elaborated. The large presence of CH4 in the biogas does not hinder the achievement of an almost complete CO2 methanation, even with CH4/CO2 = 3. The smaller the temperature, the higher the CH4 concentration in the dry biomethane, and the lower the residual H2. Results comply with some grid specification even operating at 1 bar, below 400 degrees C, where active commercial catalysts are available. CO in the product is never a concern, in this temperature range. There is no advantage in operating above approx. 400 degrees C. The H2 slip can be further reduced increasing the pressure, but the improvement is most effective with a few bars; 15 bar is already quite good. H2 in excess of the stoichiometric is not useful. The process can be completely autothermal, but adiabatic operation must be avoided. Significant improvements in biomethane purity can be achieved with two methanation steps, with steam condensation in between. Residual H2 can be reduced from 7% (single stage, 1 bar, 300 degrees C), to 1.8% (two stages, at 300 degrees C, and 1 and 15bars, respectively). Partial steam condensation allows to limit coking in the second step, without a remarkable increase of residual H2. The second step cannot be autothermal above 150 degrees C, but the first step provides heat in excess, at 300 degrees C, to support also the second step
Improving the Efficiency of MIMO Simulations in ns-3
No full textChannel modeling is a fundamental task for the design and evaluation of wireless technologies and networks, before actual prototyping, commercial product development and real deployments. The recent trends of current and future mobile networks, which include large antenna systems, massive deployments, and high-frequency bands, require complex channel models for the accurate simulation of massive MIMO (m-MIMO) in millimeter wave (mmWave) and Terahertz (THz) bands. To address the complexity/accuracy trade-off, a spatial channel model has been defined by 3GPP (TR 38.901), which has been shown to be the main bottleneck of current system-level simulations in ns-3. In this paper, we focus on improving the channel modeling efficiency for large-scale MIMO system-level simulations. Extensions are developed in two directions. First, we improve the efficiency of the current 3GPP TR 38.901 implementation code in ns-3, by allowing the use of the Eigen library for more efficient matrix algebra operations, among other optimizations and a more modular code structure. Second, we propose a new performance-oriented MIMO channel model for reduced complexity, as an alternative model suitable for mmWave/THz bands, and calibrate it against the 3GPP TR 38.901 model. Simulation results demonstrate the proper calibration of the newly introduced model for various scenarios and channel conditions, and exhibit an effective reduction of the simulation time (up to 16 times compared to the previous baseline) thanks to the various proposed improvements
Resource Management for 5G NR Integrated Access and Backhaul: a Semi-centralized Approach
Full text linkThe next generations of mobile networks will be deployed as ultra-dense networks, to match the demand for increased capacity and the challenges that communications in the higher portion of the spectrum (i.e., the mmWave band) introduce. Ultra-dense networks, however, require pervasive, high-capacity backhaul solutions, and deploying fiber optic to all base stations is generally considered to be too expensive for network operators. The 3gpp has thus introduced iab, a wireless backhaul solution in which the access and backhaul links share the same hardware, protocol stack, and also spectrum. The multiplexing of different links in the same frequency bands, however, introduces interference and capacity sharing issues, thus calling for the introduction of advanced scheduling and coordination schemes. This paper proposes a semi-centralized resource allocation scheme for iab networks, designed to be flexible, with low complexity, and compliant with the 3gpp iab specifications. We develop a version of the mwm problem that can be applied on a spanning tree that represents the iab network and whose complexity is linear in the number of iab-nodes. The proposed solution is compared with state-of-the-art distributed approaches through end-to-end, full-stack system-level simulations with a 3gpp-compliant channel model, protocol stack, and a diverse set of user applications. The results show that our scheme can increase the throughput of cell-edge users up to 3 times, while decreasing the overall network congestion with an end-to-end delay reduction of up to 25 times
6G Integrated Access and Backhaul Networks with Sub-Terahertz Links
No full textIntegrated Access and Backhaul (IAB) is a flexible and low-cost solution to deploy ultra-dense fifth and sixth generation (5G and 6G) systems, as it enables wireless backhaul links based on the same technology and specifications as for the access links. In this paper, we consider the deployment of mixed millimeter wave (mmWave) and sub-terahertz links to increase the capacity of the backhaul network, and provide the first performance evaluation of the potential of sub-terahertz frequencies for 6G IAB. To do so, we develop a greedy algorithm that allocates frequency bands to the backhaul links (considering constraints on spectrum licenses, sharing, and congestion) and generates the wireless network mesh. We then profile the performance through a custom extension of the open-source system-level simulator Sionna that supports Release 17 IAB specifications and channel models up to 140 GHz. Our results show that IAB with sub-terahertz links can outperform a mmWave-only deployment with improvements of 4×for average user throughput and a reduction of up to 50% for median latency
Implementation of a Channel Model for Non-Terrestrial Networks in ns-3
No full textWhile the 5th generation (5G) of mobile networks has landed in the commercial area, the research community is exploring new functionalities for 6th generation (6G) networks, for example non-terrestrial networks (NTNs) via space/air nodes such as Unmanned Aerial Vehicles (UAVs), High Altitute Platforms (HAPs) or satellites. Specifically, satellite-based communication offers new opportunities for future wireless applications, such as providing connectivity to remote or otherwise unconnected areas, complementing terrestrial networks to reduce connection downtime, as well as increasing traffic efficiency in hot spot areas. In this context, an accurate characterization of the NTN channel is the first step towards proper protocol design. Along these lines, this paper provides an ns-3 implementation of the 3rd Generation Partnership Project (3GPP) channel and antenna models for NTN described in Technical Report 38.811. In particular, we extend the ns-3 code base with new modules to implement the attenuation of the signal in air/space due to atmospheric gases and scintillation, and new mobility and fading models to account for the Geocentric Cartesian coordinate system of satellites. Finally, we validate the accuracy of our ns-3 module via simulations against 3GPP calibration results
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
5G NR-Light at Millimeter Waves: Design Guidelines for Mid-Market IoT Use Cases
Full text link5th generation (5G) systems have been designed with three main objectives in mind: increasing throughput, reducing latency, and enabling reliable communications. To meet these (often conflicting) constraints, the 3GPP released a set of specifications for 5G NR, one of the main innovations being the support for communications in the millimeter wave (mmWave) bands. However, how to implement lower complexity, energy efficient, mid-market Internet of Things (IoT) applications is still an on-going investigation, currently led by the 3GPP which is extending the NR standard with NR-Light specifications to support devices with reduced capabilities (REDCAP). While REDCAP devices may also operate at mmWaves to improve the network performance, hardware/software simplifications are needed to support balanced and mixed requirements compared to 5G NR systems. In this context, the contributions of this paper are threefold. First, we present some NR-Light use cases for which the support of the mmWave bands is desirable. Second, we describe how 5G NR can be simplified to achieve NR-Light requirements and expectations. Finally, we evaluate via simulation the performance of NR-Light devices operating at mmWaves in an industrial IoT setup, in terms of cost and complexity, throughput, and latency
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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