Potential key challenges for terahertz communication systems

The vision of 6G communications is an improved performance of the data rate and latency limitations and permit ubiquitous connectivity. In addition, 6G communications will adopt a novel strategy. Terahertz (THz) waves will characterize 6G networks, due to 6G will integrate terrestrial wireless mobile communication, geostationary and medium and low orbit satellite communication and short distance direct communication technologies, as well as integrate communication, computing, and navigation. This study discusses the key challenges of THz waves, including path losses which is considered the main challenge; transceiver architectures and THz signal generators; environment of THz with network architecture and 3D communications; finally, Safety and health issues

Machine-Learning-Based LOS Detection for 5G Signals with Applications in Airport Environments

The operational costs of the advanced Air Traffic Management (ATM) solutions are often prohibitive in low- and medium-sized airports. Therefore, new and complementary solutions are currently under research in order to take advantage of existing infrastructure and offer low-cost alternatives. The 5G signals are particularly attractive in an ATM context due to their promising potential in wireless positioning and sensing via Time-of-Arrival (ToA) and Angle-of-Arrival (AoA) algorithms. However, ToA and AoA methods are known to be highly sensitive to the presence of multipath and Non-Line-of-Sight (NLOS) scenarios. Yet, LOS detection in the context of 5G signals has been poorly addressed in the literature so far, to the best of the Authors’ knowledge. This paper focuses on LOS/NLOS detection methods for 5G signals by using both statistical/model-driven and data-driven/machine learning (ML) approaches and three challenging channel model classes widely used in 5G: namely Tapped Delay Line (TDL), Clustered Delay Line (CDL) and Winner II channel models. We show that, with simulated data, the ML-based detection can reach between 80% and 98% detection accuracy for TDL, CDL and Winner II channel models and that TDL is the most challenging in terms of LOS detection capabilities, as its richness of features is the lowest compared to CDL and Winner II channels. We also validate the findings through in-lab measurements with 5G signals and Yagi and 3D-vector antenna and show that measurement-based detection probabilities can reach 99–100% with a sufficient amount of training data and XGBoost or Random Forest classifiers.publishedVersionPeer reviewe

A Cross-Mode Universal Digital Pre-Distortion Technology for Low-Sidelobe Active Antenna Arrays in 5G and Satellite Communications

A cross-mode universal digital pre-distortion (CMUDPD) technology is proposed here to linearize low-sidelobe active antenna arrays with non-uniform fixed power levels for each branch, which are desired in satellite communications with stringent requirements to minimize interference. In low-sidelobe arrays formed by nonuniform amplitude excitation, conventional digital pre-distortion (DPD) techniques require multiple feedback paths for either one-to-one or average linearization of the PAs, which increases system complexity and is infeasible for large-scale arrays. This is because the power amplifiers (PAs) usually operate in different modes where the supply voltages, bias voltages, and input power levels are different. The proposed CMUDPD method aims at solving this issue by intentionally arranging the PAs to work in different modes but with shared nonlinear characteristics. Based on the nonlinear correlation established among the PAs’ different operating modes, a single feedback path is sufficient to capture the common nonlinearity of all the PAs and determine the parameters of the CMUDPD module. The concept is explained in theory and validated by simulations and experiments using GaN PAs operating with three significantly different output power levels and two orthogonal frequency division multiplexing (OFDM) signal bandwidths

Resource management with adaptive capacity in C-RAN

This work was supported in part by the Spanish ministry of science through the projectRTI2018-099880-B-C32, with ERFD funds, and the Grant FPI-UPC provided by theUPC. It has been done under COST CA15104 IRACON EU project.Efficient computational resource management in 5G Cloud Radio Access Network (CRAN) environments is a challenging problem because it has to account simultaneously for throughput, latency, power efficiency, and optimization tradeoffs. This work proposes the use of a modified and improved version of the realistic Vienna Scenario that was defined in COST action IC1004, to test two different scale C-RAN deployments. First, a large-scale analysis with 628 Macro-cells (Mcells) and 221 Small-cells (Scells) is used to test different algorithms oriented to optimize the network deployment by minimizing delays, balancing the load among the Base Band Unit (BBU) pools, or clustering the Remote Radio Heads (RRH) efficiently to maximize the multiplexing gain. After planning, real-time resource allocation strategies with Quality of Service (QoS) constraints should be optimized as well. To do so, a realistic small-scale scenario for the metropolitan area is defined by modeling the individual time-variant traffic patterns of 7000 users (UEs) connected to different services. The distribution of resources among UEs and BBUs is optimized by algorithms, based on a realistic calculation of the UEs Signal to Interference and Noise Ratios (SINRs), that account for the required computational capacity per cell, the QoS constraints and the service priorities. However, the assumption of a fixed computational capacity at the BBU pools may result in underutilized or oversubscribed resources, thus affecting the overall QoS. As resources are virtualized at the BBU pools, they could be dynamically instantiated according to the required computational capacity (RCC). For this reason, a new strategy for Dynamic Resource Management with Adaptive Computational capacity (DRM-AC) using machine learning (ML) techniques is proposed. Three ML algorithms have been tested to select the best predicting approach: support vector machine (SVM), time-delay neural network (TDNN), and long short-term memory (LSTM). DRM-AC reduces the average of unused resources by 96 %, but there is still QoS degradation when RCC is higher than the predicted computational capacity (PCC). For this reason, two new strategies are proposed and tested: DRM-AC with pre-filtering (DRM-AC-PF) and DRM-AC with error shifting (DRM-AC-ES), reducing the average of unsatisfied resources by 99.9 % and 98 % compared to the DRM-AC, respectively

Visible Light Communications for Industrial Applications—Challenges and Potentials

Visible Light Communication (VLC) is a short-range optical wireless communication technology that has been gaining attention due to its potential to offload heavy data traffic from the congested radio wireless spectrum. At the same time, wireless communications are becoming crucial to smart manufacturing within the scope of Industry 4.0. Industry 4.0 is a developing trend of high-speed data exchange in automation for manufacturing technologies and is referred to as the fourth industrial revolution. This trend requires fast, reliable, low-latency, and cost-effective data transmissions with fast synchronizations to ensure smooth operations for various processes. VLC is capable of providing reliable, low-latency, and secure connections that do not penetrate walls and is immune to electromagnetic interference. As such, this paper aims to show the potential of VLC for industrial wireless applications by examining the latest research work in VLC systems. This work also highlights and classifies challenges that might arise with the applicability of VLC and visible light positioning (VLP) systems in these settings. Given the previous work performed in these areas, and the major ongoing experimental projects looking into the use of VLC systems for industrial applications, the use of VLC and VLP systems for industrial applications shows promising potential

Designing antennas and RF components for upper millimeter frequencies using advanced substrate technology

Abstract. When shifting towards high frequency range, integration in the RF-front end becomes crucial. The ongoing planning of 6G communications systems causes a need to explore the possibilities beyond current 5G systems. To address the compactness and smaller sizes of the RF circuit components, the Integrated Passive Devices (IPD) multilayer technology provides us one solution to this problem. There are options already being tested in terms of implementing on-chip components, especially Antenna-in-Package (AiP) designs with a variety of different substrates. Among these technologies, Low Temperature Co-Fired Ceramic (LTCC) can be seen as a choice offering the freedom of multiple metal layers. IPD can be used for providing AiP solutions, as well as passive components such as baluns, filters, and power dividers. The main target of this thesis is to explore the possibilities and limitations for high frequency designs offered by IPD technology developed by (VTT) Technical Research Centre of Finland. The technology has already been tested at 20 GHz, but the focus was to reach the D-band (110–170 GHz) frequency range and subsequently up to even G-band (220–330 GHz). The technology utilizes 3 metal layers and a high resistivity silicon substrate (a lossy material). Starting off with simple transmission line structures (microstrip lines, strip lines and coplanar waveguides), the designs up to 330 GHz, provided information on the possibilities offered by this technology. After that, different AiP options were simulated with frequencies ranging from D- band to G- band. In addition to single elements, also antenna arrays were studied. Additionally, bandpass filters were designed. The dielectric thickness and the width and thickness of 3 the metal layers play a pivotal role in defining the performance of all the RF components designed using this technology. Furthermore, the size and pitch of the RF probe pads used to excite the structures show an impact on the overall behavior of the transmission lines.Antennien ja RF-komponenttien suunnittelu ylemmille millimetritaajuuksille edistynyttä substraattitekniikkaa käyttäen. Tiivistelmä. Siirryttäessä korkeammille taajuuskaistoille RF-etupään integrointi on entistä tärkeämpää. Käynnissä oleva kuudennen sukupolven (6G) viestintäjärjestelmien suunnittelu edellyttää nykyisiä 5G-järjestelmiä edistyksellisempien teknologisten mahdollisuuksien tarkastelua. Entistä pienempien RF-piirikomponenttien toteuttaminen vaatii uusia teknisiä ratkaisuja, ja yksi mahdollisuus komponenttien pienentämiseen on käyttää integroituihin passiivirakenteisiin (Integrated Passive Devices, IPD) pohjautuvaa monikerrosteknologiaa. Eri vaihtoehtoja on jo testattu sirulle sijoitettavien komponenttien toteuttamiseen eri substraattimateriaaleilla, etenkin paketoitujen antenniratkaisujen (Antenna-in-Package, AiP) suunnittelemiseksi. Eräs vaihtoehto IPD:lle on matalan lämpötilan yhteissintrattava keraamiteknologia (Low Temperature Co-Fired Ceramic, LTCC), joka mahdollistaa useamman metallikerroksen hyödyntämisen suunniteltaessa AiP-rakenteita sekä muita passiivikomponentteja (kuten symmetrointimuuntajia, suodattimia sekä tehonjakajia). Tämän opinnäytetyön päätavoitteena on tarkastella Valtion teknillisen tutkimuskeskuksen (VTT:n) kehittämän IPD-teknologian mahdollisuuksia ja rajoitteita korkean taajuuden rakenteiden suunnitteluun. IPD-teknologiaa on tähän mennessä testattu 20 GHz:n taajuudelle asti, mutta tässä työssä tarkoituksena on tutkia teknologiaa 110–170 GHz:n taajuuksille (D-kaista) sekä myöhemmin aina 220–330 GHz:iin saakka (G-kaista). Teknologia hyödyntää kolmea metallikerrosta sekä häviöllistä korkean ominaisvastuksen piisubstraattia. Yksinkertaisten siirtojohtorakenteiden (mikroliuskajohto, liuskajohto, koplanaarijohto) suunnittelu aina 330 GHz:n taajuudelle asti antoi tietoa teknologian mahdollisuuksista, minkä jälkeen erilaisia AiP-rakenteita simuloitiin D- ja G-kaistoilla. Yksittäisten antennielementtien ohella tarkasteltiin antenniryhmiä. Työssä suunniteltiin myös kaistanpäästösuodattimia. Käytettävissä olevien metalli- ja substraattikerrosten paksuudella sekä niiden mahdollistamilla liuskanleveyksillä on keskeinen rooli IPD-teknologialla suunniteltujen komponenttien suorituskyvyn kannalta. Lisäksi RF-mittapäiden kontaktikohtien koko ja välimatka vaikuttavat siirtojohtojen ominaisuuksiin