21 research outputs found
Toward End-to-End, Full-Stack 6G Terahertz Networks
Recent evolutions in semiconductors have brought the terahertz band in the
spotlight as an enabler for terabit-per-second communications in 6G networks.
Most of the research so far, however, has focused on understanding the physics
of terahertz devices, circuitry and propagation, and on studying physical layer
solutions. However, integrating this technology in complex mobile networks
requires a proper design of the full communication stack, to address link- and
system-level challenges related to network setup, management, coordination,
energy efficiency, and end-to-end connectivity. This paper provides an overview
of the issues that need to be overcome to introduce the terahertz spectrum in
mobile networks, from a MAC, network and transport layer perspective, with
considerations on the performance of end-to-end data flows on terahertz
connections.Comment: Published on IEEE Communications Magazine, THz Communications: A
Catalyst for the Wireless Future, 7 pages, 6 figure
Empirical Validation of a Class of Ray-Based Fading Models
As new wireless standards are developed, the use of higher operation
frequencies comes in hand with new use cases and propagation effects that
differ from the well-established state of the art. Numerous stochastic fading
models have recently emerged under the umbrella of generalized fading
conditions, to provide a fine-grain characterization of propagation channels in
the mmWave and sub-THz bands. For the first time in literature, this work
carries out an experimental validation of a class of such ray-based models, in
a wide range of propagation conditions (anechoic, reverberation and indoor) at
mmWave bands. We show that the independently fluctuating two-ray (IFTR) model
has good capabilities to recreate rather dissimilar environments with high
accuracy. We also put forth that the key limitations of the IFTR model arise in
the presence of reduced diffuse propagation, and also due to a limited phase
variability for the dominant specular components.Comment: 9 pages, 13 figure
Terahertz Communications for 6G and Beyond Wireless Networks: Challenges, Key Advancements, and Opportunities
The unprecedented increase in wireless data traffic, predicted to occur
within the next decade, is motivating academia and industries to look beyond
contemporary wireless standards and conceptualize the sixth-generation (6G)
wireless networks. Among various promising solutions, terahertz (THz)
communications (THzCom) is recognized as a highly promising technology for the
6G and beyond era, due to its unique potential to support terabit-per-second
transmission in emerging applications. This article delves into key areas for
developing end-to-end THzCom systems, focusing on physical, link, and network
layers. Specifically, we discuss the areas of THz spectrum management, THz
antennas and beamforming, and the integration of other 6G-enabling technologies
for THzCom. For each area, we identify the challenges imposed by the unique
properties of the THz band. We then present main advancements and outline
perspective research directions in each area to stimulate future research
efforts for realizing THzCom in 6G and beyond wireless networks.Comment: This work has been submitted to the IEEE for possible publication.
Copyright may be transferred without notice, after which this version may no
longer be accessibl
Channel Power Gain Estimation for Terahertz Vehicle-to-infrastructure Networks
The use of terahertz (THz) frequencies has been recommended to achieve high-speed and ultra-low latency transmissions. Although there exist very large bandwidths in the THz frequency bands, THz channels are significantly dynamic and complicated, which is challenging for channel estimation. To improve the energy efficiency of wireless networks, THz channel power gains need to be precisely evaluated for determining optimal THz transmission frequencies and power control. Therefore, this work presents a novel conditional generative adversarial networks (GAN) based channel power gain estimation solution in the THz vehicle-to-infrastructure (V2I) networks with leaky-wave antennas, where the THz frequency has a big effect on the antenna gain, path loss and atmospheric attenuation. Simulation results confirm that our solution can accurately estimate the channel power gains versus the THz frequencies at a fast speed.acceptedVersionPeer reviewe
V2I-aided Tracking Design
In this paper, we design the vehicle tracking in the terahertz (THz) vehicle-to-infrastructure (V2I) networks, where roadside units (RSUs) equipped with leaky-wave antennas help to estimate the driving states of multiple vehicles after receiving the vehicles’ feedback. Different from the conventional phased arrays, the leaky-wave antenna has the potential of improving the sensing accuracy with lower system overhead thanks to its unique spatial-spectral coupling feature. The generalized mobile scenario is studied in which vehicles drive at time-varying speeds. A novel unscented Kalman filter (UKF) based solution is proposed to track the vehicles without requirement of addressing the Doppler effect. Simulation results confirm that the proposed tracking solution can evaluate the propagation angle, vehicle’s states and inter-vehicle distance accurately.acceptedVersionPeer reviewe
6G to Take the Digital Divide by Storm: Key Technologies and Trends to Bridge the Gap
The pandemic caused by COVID-19 has shed light on the urgency of bridging the digital
divide to guarantee equity in the fruition of different services by all citizens. The inability to access
the digital world may be due to a lack of network infrastructure, which we refer to as service-delivery
divide, or to the physical conditions, handicaps, age, or digital illiteracy of the citizens, that is
mentioned as service-fruition divide. In this paper, we discuss the way how future sixth-generation
(6G) systems can remedy actual limitations in the realization of a truly digital world. Hence, we
introduce the key technologies for bridging the digital gap and show how they can work in two
use cases of particular importance, namely eHealth and education, where digital inequalities have
been dramatically augmented by the pandemic. Finally, considerations about the socio-economical
impacts of future 6G solutions are drawn
Uninterrupted Connectivity Time in THz Systems Under User Micromobility and Blockage
Terahertz (THz) band is considered as the main candidate for new radio access technology in sixth-generation (6G) cellular systems. However, the performance of these systems will be severely affected by not only blockage but user equipment (UE) micromobility in hands of a user. The negative effects of these phenomena can be alleviated by utilizing the multi-connectivity functionality that allows UE to maintain two or more links to nearby base stations (BS) and use them when the currently active link is lost. By accounting for THz specific propagation, antenna and beamsearching design, the density of THz BS deployment, and multi-connectivity operation, we investigate the successful session completion probability under both types of impairments. Our results indicate that the gains of multi-connectivity are observed up to 5 simultaneously supported links and heavily depend on the application outage tolerance time and is mostly affected by micromobility. To improve it, one needs to ensure that the application may tolerate outage caused by beamsearching time which is on the order of milliseconds.acceptedVersionPeer reviewe
On the Properties of Next Generation Wireless Backhaul
With the advent of 5G, cellular networks require a high number of base stations, possibly interconnected with wireless links, an evolution introduced in the last revision of 5G as the Integrated Access and Backhaul (IAB). Researchers are now working to optimize the complex topologies of the backhaul network, using synthetic models for the underlying visibility graph, i.e., the graph of possible connections between the base stations. The goal of this paper is to provide a novel methodology to generate visibility graphs starting from real data (and the data sets themselves together with the source code for their manipulation), in order to base the IAB design and optimization on assumptions that are as close as possible to reality. We introduce a GPU-based method to create visibility graphs from open data, we analyze the properties of the realistic visibility graphs, and we show that different geographic areas produce very different graphs. We run state-of-the-art algorithms to create wireless backhaul networks on top of visibility graphs, and we show that the results that exploit synthetic models are far from those that use our realistic graphs. Our conclusion is that the data-based approach we propose is essential to design mobile networks that work in a variety of real-world situations
Max-min Rate Optimization of Low-Complexity Hybrid Multi-User Beamforming Maintaining Rate-Fairness
A wireless network serving multiple users in the millimeter-wave or the
sub-terahertz band by a base station is considered. High-throughput multi-user
hybrid-transmit beamforming is conceived by maximizing the minimum rate of the
users. For the sake of energy-efficient signal transmission, the
array-of-subarrays structure is used for analog beamforming relying on
low-resolution phase shifters. We develop a convexsolver based algorithm, which
iteratively invokes a convex problem of the same beamformer size for its
solution. We then introduce the soft max-min rate objective function and
develop a scalable algorithm for its optimization. Our simulation results
demonstrate the striking fact that soft max-min rate optimization not only
approaches the minimum user rate obtained by max-min rate optimization but it
also achieves a sum rate similar to that of sum-rate maximization. Thus, the
soft max-min rate optimization based beamforming design conceived offers a new
technique of simultaneously achieving a high individual quality-of-service for
all users and a high total network throughput
Spectrum Allocation with Adaptive Sub-band Bandwidth for Terahertz Communication Systems
We study spectrum allocation for terahertz (THz) band communication (THzCom)
systems, while considering the frequency and distance-dependent nature of THz
channels. Different from existing studies, we explore multi-band-based spectrum
allocation with adaptive sub-band bandwidth (ASB) by allowing the spectrum of
interest to be divided into sub-bands with unequal bandwidths. Also, we
investigate the impact of sub-band assignment on multi-connectivity (MC)
enabled THzCom systems, where users associate and communicate with multiple
access points simultaneously. We formulate resource allocation problems, with
the primary focus on spectrum allocation, to determine sub-band assignment,
sub-band bandwidth, and optimal transmit power. Thereafter, we propose
reasonable approximations and transformations, and develop iterative algorithms
based on the successive convex approximation technique to analytically solve
the formulated problems. Aided by numerical results, we show that by enabling
and optimizing ASB, significantly higher throughput can be achieved as compared
to adopting equal sub-band bandwidth, and this throughput gain is most profound
when the power budget constraint is more stringent. We also show that our
sub-band assignment strategy in MC-enabled THzCom systems outperforms the
state-of-the-art sub-band assignment strategies and the performance gain is
most profound when the spectrum with the lowest average molecular absorption
coefficient is selected during spectrum allocation.Comment: This work has been accepted for publication in IEEE Transaction on
Communication