1,720,967 research outputs found
Models, Algorithms and Protocols for Innovative Deployment Solutions in 5G And 6G Cellular Networks
Full text linkCellular networks are constantly evolving in order to support the ever-increasing number of mobile users, and the corresponding growth in wireless data traffic, coupled with the emergence of new applications. Specifically, the last generation of mobile networks, i.e., 5G, brought high peak performance and extreme flexibility, making it possible to support a diverse set of applications with heterogeneous yet stringent requirements. One of 5G’s main novelties is represented by the support for millimeter wave (mmWave) frequencies, which unlocks an unprecedented amount of previously unused radio resources. In turn, the latter enables extremely high data rates and low latencies. Moreover, it is envisioned that the upcoming generation, i.e., 6G, will unleash additional bandwidth, by further expanding the supported spectrum bands to include terahertz (THz) frequencies as well. However, despite their theoretical potential, mmWave and THz frequencies exhibit harsh propagation conditions which make it challenging to provide ubiquitous high speed wireless connectivity. To fill this gap, this thesis studies innovative deployment solutions to overcome the unfavorable propagation characteristics of mmWave and THz communications, paving the way for their widespread use in the context of 6G cellular networks. In particular, this thesis (i) presents novel simulation tools, which model innovative coverage enhancement technologies such as Intelligent Reflective Surfaces (IRSs), Amplify-and-Forward (AF) relays, and Non-Terrestrial Networks (NTNs); (ii) presents novel simulation models which improve the computational complexity of Multiple Input, Multiple Output (MIMO) simulations; (iii) introduces schemes for optimizing Integrated Access and Backhaul (IAB) networks; (iv) analyzes the potential of mixed mmWave and THz links for wireless backhauling; and (v) analyzes the impact of non-ideal control channels in IRS-aided deployments, and introduces algorithms for mitigating the corresponding performance degradation. This thesis adopts a system-level approach, thus characterizing the net work behavior in an end-to-end fashion, and capturing the interplay between the physical signal propagation and the different layers of the communications protocol stack. Results demonstrate the effectiveness of the proposed iii solutions, which pave the way towards ubiquitous high-performance mobile networks
Enabling RAN Slicing Through Carrier Aggregation in mmWave Cellular Networks
No full textThe ever increasing number of connected devices and of new and heterogeneous mobile use cases implies that 5G cellular systems will face demanding technical challenges. For example, Ultra-Reliable Low-Latency Communication (URLLC) and enhanced Mobile Broadband (eMBB) scenarios present orthogonal Quality of Service (QoS) requirements that 5G aims to satisfy with a unified Radio Access Network (RAN) design. Network slicing and mmWave communications have been identified as possible enablers for 5G. They provide, respectively, the necessary scalability and flexibility to adapt the network to each specific use case environment, and low latency and multi-gigabit-per-second wireless links, which tap into a vast, currently unused portion of the spectrum. The optimization and integration of these technologies is still an open research challenge, which requires innovations at different layers of the protocol stack. This paper proposes to combine them in a RAN slicing framework for mmWaves, based on carrier aggregation. Notably, we introduce MilliSlice, a cross-carrier scheduling policy that exploits the diversity of the carriers and maximizes their utilization, thus simultaneously guaranteeing high throughput for the eMBB slices and low latency and high reliability for the URLLC flows
Downlink TDMA Scheduling for IRS-aided Communications with Block-Static Constraints
Full text linkIntelligent reflecting surfaces (IRSs) are being studied as possible low-cost
energy-efficient alternatives to active relays, with the goal of solving the
coverage issues of millimeter wave (mmWave) and terahertz (THz) network
deployments. In the literature, these surfaces are often studied by idealizing
their characteristics. Notably, it is often assumed that IRSs can tune with
arbitrary frequency the phase-shifts induced by their elements, thanks to a
wire-like control channel to the next generation node base (gNB). Instead, in
this work we investigate an IRS-aided time division multiple access (TDMA)
cellular network, where the reconfiguration of the IRS may entail an energy or
communication cost, and we aim at limiting the number of reconfigurations over
time. We develop a clustering-based heuristic scheduling, which optimizes the
system sum-rate subject to a given number of reconfigurations within the TDMA
frame. To such end, we first cluster user equipments (UEs) with a similar
optimal IRS configuration. Then, we compute an overall IRS cluster
configuration, which can be thus kept constant while scheduling the whole UEs
cluster. Numerical results show that our approach is effective in supporting
IRSs-aided systems with practical constraints, achieving up to 85% of the
throughput obtained by an ideal deployment, while providing a 50% reduction in
the number of IRS reconfigurations.Comment: 6 pages, 4 figures, submitted to WCNC 2023 Workshop
Clustering-Based Downlink Scheduling of IRS-Assisted Communications With Reconfiguration Constraints
Full text linkIntelligent reflecting surfaces (IRSs) are being widely investigated as a potential low-cost and energy-efficient alternative to active relays for improving coverage in next-generation cellular networks. However, technical constraints in the configuration of IRSs should be taken into account in the design of scheduling solutions and the assessment of their performance. To this end, we examine an IRS-assisted time division multiple access (TDMA) cellular network where the reconfiguration of the IRS incurs a communication cost; thus, we aim at limiting the number of reconfigurations over time. Along these lines, we propose a clustering-based heuristic scheduling scheme that maximizes the cell sum capacity, subject to a fixed number of reconfigurations within a TDMA frame. First, the best configuration of each user equipment (UE), in terms of joint beamforming and optimal IRS configuration, is determined using an iterative algorithm. Then, we propose different clustering techniques to divide the UEs into subsets sharing the same suboptimal IRS configuration, derived through distance- and capacity-based algorithms. Finally, UEs within the same cluster are scheduled accordingly. We provide extensive numerical results for different propagation scenarios, IRS sizes, and phase shifters quantization constraints, showing the effectiveness of our approach in supporting multi-user IRS systems with practical constraints
Safehaul: Risk-Averse Learning for Reliable mmWave Self-Backhauling in 6G Networks
No full textWireless backhauling at millimeter-wave frequencies (mmWave) in static scenarios is a well-established practice in cellular networks. However, highly directional and adaptive beamforming in today’s mmWave systems have opened new possibilities for self-backhauling. Tapping into this potential, 3GPP has standardized Integrated Access and Backhaul (IAB) allowing the same base station to serve both access and backhaul traffic. Although much more cost-effective and flexible, resource allocation and path selection in IAB mmWave networks is a formidable task. To date, prior works have addressed this challenge through a plethora of classic optimization and learning methods, generally optimizing a Key Performance Indicator (KPI) such as throughput, latency, and fairness, and little attention has been paid to the reliability of the KPI. We propose Safehaul, a risk-averse learning-based solution for IAB mmWave networks. In addition to optimizing average performance, Safehaul ensures reliability by minimizing the losses in the tail of the performance distribution. We develop a novel simulator and show via extensive simulations that Safehaul not only reduces the latency by up to 43.2% compared to the benchmarks, but also exhibits significantly more reliable performance, e.g., 71.4% less variance in achieved latency
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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