217 research outputs found
6G Wireless Systems: Vision, Requirements, Challenges, Insights, and Opportunities
Mobile communications have been undergoing a generational change every ten
years or so. However, the time difference between the so-called "G's" is also
decreasing. While fifth-generation (5G) systems are becoming a commercial
reality, there is already significant interest in systems beyond 5G, which we
refer to as the sixth-generation (6G) of wireless systems. In contrast to the
already published papers on the topic, we take a top-down approach to 6G. We
present a holistic discussion of 6G systems beginning with lifestyle and
societal changes driving the need for next generation networks. This is
followed by a discussion into the technical requirements needed to enable 6G
applications, based on which we dissect key challenges, as well as
possibilities for practically realizable system solutions across all layers of
the Open Systems Interconnection stack. Since many of the 6G applications will
need access to an order-of-magnitude more spectrum, utilization of frequencies
between 100 GHz and 1 THz becomes of paramount importance. As such, the 6G
eco-system will feature a diverse range of frequency bands, ranging from below
6 GHz up to 1 THz. We comprehensively characterize the limitations that must be
overcome to realize working systems in these bands; and provide a unique
perspective on the physical, as well as higher layer challenges relating to the
design of next generation core networks, new modulation and coding methods,
novel multiple access techniques, antenna arrays, wave propagation,
radio-frequency transceiver design, as well as real-time signal processing. We
rigorously discuss the fundamental changes required in the core networks of the
future that serves as a major source of latency for time-sensitive
applications. While evaluating the strengths and weaknesses of key 6G
technologies, we differentiate what may be achievable over the next decade,
relative to what is possible.Comment: Accepted for Publication into the Proceedings of the IEEE; 32 pages,
10 figures, 5 table
Terahertz Communications and Sensing for 6G and Beyond: A Comprehensive View
The next-generation wireless technologies, commonly referred to as the sixth
generation (6G), are envisioned to support extreme communications capacity and
in particular disruption in the network sensing capabilities. The terahertz
(THz) band is one potential enabler for those due to the enormous unused
frequency bands and the high spatial resolution enabled by both short
wavelengths and bandwidths. Different from earlier surveys, this paper presents
a comprehensive treatment and technology survey on THz communications and
sensing in terms of the advantages, applications, propagation characterization,
channel modeling, measurement campaigns, antennas, transceiver devices,
beamforming, networking, the integration of communications and sensing, and
experimental testbeds. Starting from the motivation and use cases, we survey
the development and historical perspective of THz communications and sensing
with the anticipated 6G requirements. We explore the radio propagation, channel
modeling, and measurements for THz band. The transceiver requirements,
architectures, technological challenges, and approaches together with means to
compensate for the high propagation losses by appropriate antenna and
beamforming solutions. We survey also several system technologies required by
or beneficial for THz systems. The synergistic design of sensing and
communications is explored with depth. Practical trials, demonstrations, and
experiments are also summarized. The paper gives a holistic view of the current
state of the art and highlights the issues and challenges that are open for
further research towards 6G.Comment: 55 pages, 10 figures, 8 tables, submitted to IEEE Communications
Surveys & Tutorial
Seven Defining Features of Terahertz (THz) Wireless Systems: A Fellowship of Communication and Sensing
Wireless communication at the terahertz (THz) frequency bands (0.1-10THz) is
viewed as one of the cornerstones of tomorrow's 6G wireless systems. Owing to
the large amount of available bandwidth, THz frequencies can potentially
provide wireless capacity performance gains and enable high-resolution sensing.
However, operating a wireless system at the THz-band is limited by a highly
uncertain channel. Effectively, these channel limitations lead to unreliable
intermittent links as a result of a short communication range, and a high
susceptibility to blockage and molecular absorption. Consequently, such
impediments could disrupt the THz band's promise of high-rate communications
and high-resolution sensing capabilities. In this context, this paper
panoramically examines the steps needed to efficiently deploy and operate
next-generation THz wireless systems that will synergistically support a
fellowship of communication and sensing services. For this purpose, we first
set the stage by describing the fundamentals of the THz frequency band. Based
on these fundamentals, we characterize seven unique defining features of THz
wireless systems: 1) Quasi-opticality of the band, 2) THz-tailored wireless
architectures, 3) Synergy with lower frequency bands, 4) Joint sensing and
communication systems, 5) PHY-layer procedures, 6) Spectrum access techniques,
and 7) Real-time network optimization. These seven defining features allow us
to shed light on how to re-engineer wireless systems as we know them today so
as to make them ready to support THz bands. Furthermore, these features
highlight how THz systems turn every communication challenge into a sensing
opportunity. Ultimately, the goal of this article is to chart a forward-looking
roadmap that exposes the necessary solutions and milestones for enabling THz
frequencies to realize their potential as a game changer for next-generation
wireless systems.Comment: 26 pages, 6 figure
A Prospective Look: Key Enabling Technologies, Applications and Open Research Topics in 6G Networks
The fifth generation (5G) mobile networks are envisaged to enable a plethora
of breakthrough advancements in wireless technologies, providing support of a
diverse set of services over a single platform. While the deployment of 5G
systems is scaling up globally, it is time to look ahead for beyond 5G systems.
This is driven by the emerging societal trends, calling for fully automated
systems and intelligent services supported by extended reality and haptics
communications. To accommodate the stringent requirements of their prospective
applications, which are data-driven and defined by extremely low-latency,
ultra-reliable, fast and seamless wireless connectivity, research initiatives
are currently focusing on a progressive roadmap towards the sixth generation
(6G) networks. In this article, we shed light on some of the major enabling
technologies for 6G, which are expected to revolutionize the fundamental
architectures of cellular networks and provide multiple homogeneous artificial
intelligence-empowered services, including distributed communications, control,
computing, sensing, and energy, from its core to its end nodes. Particularly,
this paper aims to answer several 6G framework related questions: What are the
driving forces for the development of 6G? How will the enabling technologies of
6G differ from those in 5G? What kind of applications and interactions will
they support which would not be supported by 5G? We address these questions by
presenting a profound study of the 6G vision and outlining five of its
disruptive technologies, i.e., terahertz communications, programmable
metasurfaces, drone-based communications, backscatter communications and
tactile internet, as well as their potential applications. Then, by leveraging
the state-of-the-art literature surveyed for each technology, we discuss their
requirements, key challenges, and open research problems
Near-Space Communications: the Last Piece of 6G Space-Air-Ground-Sea Integrated Network Puzzle
This article presents a comprehensive study on the emerging near-space
communications (NS-COM) within the context of space-air-ground-sea integrated
network (SAGSIN). Specifically, we firstly explore the recent technical
developments of NS-COM, followed by the discussions about motivations behind
integrating NS-COM into SAGSIN. To further demonstrate the necessity of NS-COM,
a comparative analysis between the NS-COM network and other counterparts in
SAGSIN is conducted, covering aspects of deployment, coverage, channel
characteristics and unique problems of NS-COM network. Afterwards, the
technical aspects of NS-COM, including channel modeling, random access, channel
estimation, array-based beam management and joint network optimization, are
examined in detail. Furthermore, we explore the potential applications of
NS-COM, such as structural expansion in SAGSIN communication, civil aviation
communication, remote and urgent communication, weather monitoring and carbon
neutrality. Finally, some promising research avenues are identified, including
stratospheric satellite (StratoSat) -to-ground direct links for mobile
terminals, reconfigurable multiple-input multiple-output (MIMO) and holographic
MIMO, federated learning in NS-COM networks, maritime communication,
electromagnetic spectrum sensing and adversarial game, integrated sensing and
communications, StratoSat-based radar detection and imaging, NS-COM assisted
enhanced global navigation system, NS-COM assisted intelligent unmanned system
and free space optical (FSO) communication. Overall, this paper highlights that
the NS-COM plays an indispensable role in the SAGSIN puzzle, providing
substantial performance and coverage enhancement to the traditional SAGSIN
architecture.Comment: 28 pages, 8 figures, 2 table
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