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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Serie: IEEE ComSoc Pocket Guides to Communications Technologies
- Sprache: Englisch
- Veröffentlichungsjahr: 2020
The latest developments and recent progress on the key technologies enabling next-generation 6G mobile networks Toward 6G: A New Era of Convergence offers an up-to-date guide to the emerging 6G vision by describing new human-centric services made possible by combinations of mobile robots, avatars, and smartphones, which will be increasingly replaced with wearable displays and haptic interfaces that provide immersive extended reality (XR) experiences. The authors--noted experts on the topic--include a review of their work and information on the recent progress on the Tactile Internet and multi-sensory haptic communications. The book highlights decentralized edge computing in particular via Ethereum blockchain technologies, most notably the so-called decentralized autonomous organization (DAO) for crowdsourcing of human skills to solve problems that machines (such as autonomous artificial intelligence agents and robots) alone cannot solve well. The book also contains a review of the most recent and ongoing work on XR (including virtual/augmented/mixed reality). Specifically, the book describes the implications of the transition from the current gadgets-based Internet to a future Internet that is evolving from bearables (such as smartphones), moves towards wearables (for example Amazon's recently launched voice-controlled Echo Loop ring, glasses, and earbuds), and then finally progresses to nearables with embedded computing technologies and intelligent provisioning mechanisms for the delivery of human-intended services, including sixth-sense perceptions, in a 6G post-smartphone era. This important text: * Offers a review of the 6G network architectures and key enabling technologies * Explains why 6G should not be a mere exploration of more spectrum at high-frequency bands, but rather a convergence of upcoming technological trends * Describes the Tactile Internet's human-in-the-loop centric design principles and haptic communications models * Includes analytical frameworks to estimate the fluid orchestration of human + machine co-activities across unified communication network infrastructures * Explores the performance gains of cooperative computation offloading with communications and computation limitations in both fronthaul and backhaul Written for students, network researchers, professionals, engineers, and practitioners, Toward 6G: A New Era of Convergence explores the most recent advances on the key technologies enabling next-generation 6G mobile networks, with an emphasis on their seamless convergence.
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Table of Contents
Cover
Title Page
Copyright
Dedication
Author Biographies
Foreword
Preface
Acknowledgments
Acronyms
1 The 6G Vision
1.1 Introduction
1.2 Evolution of Mobile Networks and Internet
1.3 6G Network Architectures and Key Enabling Technologies
1.4 Toward 6G: A New Era of Convergence
1.5 Scope and Outline of Book
2 Immersive Tactile Internet Experiences via Edge Intelligence
2.1 Introduction
2.2 The Tactile Internet: Automation or Augmentation of the Human?
2.3 Haptic Traffic Characterization
2.4 FiWi Access Networks: Revisited for Clouds and Cloudlets
2.5 Delay Analysis
2.6 Edge Sample Forecast
2.7 Results
2.8 Conclusions
Notes
3 Context- and Self-Awareness for Human-Agent-Robot Task Coordination
3.1 Introduction
3.2 System Model
3.3 Context-Aware Multirobot Task Coordination
3.4 Self-Aware Optimal Motion Planning
3.5 Delay and Reliability Analysis
3.6 Results
3.7 Conclusion
Notes
4 Delay-Constrained Teleoperation Task Scheduling and Assignment
4.1 Introduction
4.2 System Model and Network Architecture
4.3 Problem Statement
4.4 Algorithmic Solution
4.5 Delay Analysis
4.6 Results
4.7 Discussion
4.8 Conclusion
Note
5 Cooperative Computation Offloading in FiWi-Enhanced Mobile Networks
5.1 Introduction
5.2 System Model
5.3 Energy-Delay Analysis of the Proposed Cooperative Offloading
5.4 Energy-Delay Trade-off via Self-Organization
5.5 Results
5.6 Conclusions
Notes
6 Decentralization via Blockchain
6.1 Introduction
6.2 Blockchain Technologies
6.3 Blockchain IoT and Edge Computing
6.4 Decentralizing the Tactile Internet
6.5 Nudging: From Judge Contract to Nudge Contract
6.6 Conclusions
7 XR in the 6G Post-Smartphone Era
7.1 Introduction
7.2 6G Vision: Putting (Internet of No) Things in Perspective
7.3 Extended Reality (XR): Unleashing Its Full Potential
7.4 Internet of No Things: Invisible-to-Visible (I2V) Technologies
7.5 Results
7.6 Conclusions
Note
Appendix A: Proof of Lemmas
A.1 Proof of Lemma 3.1
A.2 Proof of Lemma 3.2
A.3 Proof of Lemma 3.3
A.4 Proof of Lemma 5.1
Bibliography
Index
End User License Agreement
List of Tables
Chapter 2
Table 2.1 Classification of intelligent machines along two dimensions: Abilit...
Table 2.2 Summary of the estimated parameters of fitted PDFs using MLE method...
Table 2.3 FiWi network parameters and default values.
Chapter 3
Table 3.1 MR and FiWi network parameters and default values.
Chapter 5
Table 5.1 MEC-enabled FiWi enhanced HetNet parameters and default values.
Chapter 6
Table 6.1 Public vs. private blockchains.
List of Illustrations
Chapter 2
Figure 2.1 The three lenses of 5G, Internet of things (IoT), and the Tactile...
Figure 2.2 Teleoperation system based on bidirectional haptic communications...
Figure 2.3 Next-generation passive optical network (NG-PON) roadmap as of 20...
Figure 2.4 Teleoperation system based on bidirectional haptic communications...
Figure 2.5 Histogram of experimental 6-DoF teleoperation packet interarrival...
Figure 2.6 Complementary cumulative distribution function (CCDF) of fitted p...
Figure 2.7 Mean packet rate (in packets/s) vs.
for 6-DoF teleoperation: (a...
Figure 2.8 Summary of best fitting packet interarrival time distributions fo...
Figure 2.9 Estimation of the autocorrelation of the haptic samples in the fe...
Figure 2.10 Hierarchical frame aggregation involving different aggregation l...
Figure 2.11 Local and non-local teleoperation in fiber-wireless (FiWi) enhan...
Figure 2.12 Two-dimensional Markov process.
Figure 2.13 Generic architecture of a multilayer perceptron artificial neura...
Figure 2.14 Average end-to-end delay of mobile users (MUs) vs. mean backgrou...
Figure 2.15 Average end-to-end delay of human operators (HOs) vs. mean backg...
Figure 2.16 End-to-end delay cumulative distribution function (CDF)
of loc...
Figure 2.17 Average end-to-end delay of human operators (HOs) vs. backhaul t...
Figure 2.18 Comparison of forecasting accuracy between proposed multilayer p...
Chapter 3
Figure 3.1 Generic architecture of fiber-wireless (FiWi) based Tactile Inter...
Figure 3.2 Trapezoidal velocity profile of mobile robots (MRs).
Figure 3.3 An illustrative case study demonstrating the trade-off between de...
Figure 3.4 Different mobile robot (MR) operational regions represented by
,...
Figure 3.5 Delay components of average channel access delay in IEEE 802.11 d...
Figure 3.6 Average cost,
, per executed task vs. user- to network-owned ope...
Figure 3.7 Average operational expenditures (OPEX),
, per executed task vs....
Figure 3.8
vs. waiting deadline
(
fixed).
Figure 3.9 Average task completion time vs. waiting deadline
.
Figure 3.10 2-D Pareto-front of our proposed context-aware dynamic multirobo...
Figure 3.11 Average task completion time vs. ownership spreading factor. sou...
Figure 3.12 Human–robot (HR) connectivity probability vs.
for different va...
Figure 3.13 Human–robot (HR) connection reliability function
and failure r...
Chapter 4
Figure 4.1 Generic architecture of fiber-wireless (FiWi)-based Tactile Inter...
Figure 4.2 An illustrative case study of the delay/cost performance of two d...
Figure 4.3 Average weighted completion time of tasks vs. total number of ava...
Figure 4.4 Maximum tardiness of tasks vs. total number of available human op...
Figure 4.5 Rate
of tardy tasks vs.
for different task classes (
and
f...
Figure 4.6 Average operational expenditures (OPEX) per task vs. total number...
Figure 4.7 Average operational expenditures (OPEX) per task vs. total number...
Figure 4.8 Average operational expenditures (OPEX) per task vs.
for differ...
Figure 4.9 Average operational expenditures (OPEX) per task vs.
for differ...
Figure 4.10 Average end-to-end packet delay of local teleoperation vs. backg...
Figure 4.11 Average end-to-end packet delay of nonlocal teleoperation vs. ba...
Chapter 5
Figure 5.1 Generic multi-access edge computing (MEC)-enabled fiber-wireless ...
Figure 5.2 Schematic of task scheduler and queueing system for mobile user (...
Figure 5.3 Illustration of the search space for problem
for different valu...
Figure 5.4 (a) Average response time vs. mobile user (MU) offloading probabi...
Figure 5.5 Comparison of average response time performance of edge-only, clo...
Figure 5.6 Average response time vs. edge-server offloading probability
fo...
Figure 5.7 Average response time vs. edge-server offloading probability
fo...
Figure 5.8 Average energy per task vs.
for different values of local clock...
Figure 5.9 Cumulative distribution function (CDF) of response time for diffe...
Figure 5.10 Average response time vs. edge server offloading probability
f...
Figure 5.11 Pareto front solutions of self-organization problem (
) for
Mc...
Figure 5.12 (a) Optimal offloading probability
vs. energy constraint
and...
Figure 5.13 Average uplink delay vs. human-to-human (H2H) background traffic...
Chapter 6
Figure 6.1 Bitcoin and Ethereum blockchains: commonalities and differences....
Figure 6.2 Decentralized autonomous organizations (DAOs) vs. artificial inte...
Figure 6.3 Average computational task completion time (in seconds) vs. compu...
Figure 6.4 Average physical task completion time (in seconds) vs. probabilit...
Figure 6.5 Learning loss (in seconds) vs. subtask learning probability for d...
Chapter 7
Figure 7.1 The reality–virtuality continuum, ranging from pure reality (offl...
Figure 7.2 The Multiverse as an architecture of advanced XR experiences: thr...
Figure 7.3 Extrasensory perception network (ESPN) architecture integrating u...
Figure 7.4 Experimental set-up for demonstrating eternalism in locally conne...
Figure 7.5 Regret (given in seconds) vs. misforecast sample rate
for diffe...
Figure 7.6 Average empathic AI score of four different positive emotions exp...
Appendix A
Figure A.1 Two-dimensional Markov chain for distributed coordination functio...
Guide
Cover
Table of Contents
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IEEE Press445 Hoes LanePiscataway, NJ 08854
IEEE Press Editorial BoardEkram Hossain, Editor in Chief
Jón Atli Benediktsson
David Alan Grier
Elya B. Joffe
Xiaoou Li
Peter Lian
Andreas Molisch
Saeid Nahavandi
Jeffrey Reed
Diomidis Spinellis
Sarah Spurgeon
Ahmet Murat Tekalp
Toward 6G: A New Era of Convergence
Amin Ebrahimzadeh
Martin Maier
Copyright © 2021 by The Institute of Electrical and Electronics Engineers, Inc. All rights reserved.
Published by John Wiley & Sons, Inc., Hoboken, New Jersey.
Published simultaneously in Canada.
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Library of Congress Cataloging-in-Publication Data
Names: Ebrahimzadeh, Amin, author. | Maier, Martin, 1969- author.
Title: Toward 6G : a new era of convergence / Amin Ebrahimzadeh, Martin Maier.
Description: Hoboken, New Jersey : John Wiley & Sons, Inc., [2021] | Includes bibliographical references and index.
Identifiers: LCCN 2020034076 (print) | LCCN 2020034077 (ebook) | ISBN 9781119658023 (paperback) | ISBN 9781119658030 (adobe pdf) | ISBN 9781119658047 (epub)
Subjects: LCSH: Wireless communication systems–Technological innovations. | Network performance (Telecommunication)
Classification: LCC TK5103.2 .E34 2021 (print) | LCC TK5103.2 (ebook) | DDC 621.3845/6–dc23
LC record available at https://lccn.loc.gov/2020034076
LC ebook record available at https://lccn.loc.gov/2020034077
Cover Design: Wiley
Cover Image: © John Wiley & Sons, Inc
For my soulmate, Atefeh, who dreams and who knows magic is real.
— Amin Ebrahimzadeh
To Alexie and our two children Coby and Ashanti Diva. May J. M. Keynes' “Economic Possibilities” predicted for 2030 become a reality for them.
— Martin Maier
Author Biographies
Amin Ebrahimzadeh received the BSc[S3G1] and MSc degrees in Electrical Engineering from the University of Tabriz, Iran, in 2009 and 2011, respectively, and the PhD degree (Hons.) in telecommunications from the Institut National de la Recherche Scientifique (INRS), Montréal, QC, Canada, in 2019. From 2011 to 2015, he was with the Sahand University of Technology, Tabriz, Iran. He is currently a Horizon Post-Doctoral Fellow with Concordia University, Montréal. His research interests include Tactile Internet, 6G, FiWi networks, multi-access edge computing, and multi-robot task allocation. He was a recipient of the doctoral research scholarship from the B2X program of Fonds de Recherche du Québec-Nature et Technologies (FRQNT).
Martin Maier is a full professor with the Institut National de la Recherche Scientifique (INRS), Montréal, Canada. He was educated at the Technical University of Berlin, Germany, and received MSc and PhD degrees both with distinctions (summa cum laude) in 1998 and 2003, respectively. He was a recipient of the two-year Deutsche Telekom doctoral scholarship from 1999 through 2001. He was a visiting researcher at the University of Southern California (USC), Los Angeles, CA, in 1998 and Arizona State University (ASU), Tempe, AZ, in 2001. In 2003, he was a postdoc fellow at the Massachusetts Institute of Technology (MIT), Cambridge, MA. Before joining INRS, Dr. Maier was a research associate at CTTC, Barcelona, Spain, 2003 through 2005. He was a visiting professor at Stanford University, Stanford, CA, 2006 through 2007. He was a co-recipient of the 2009 IEEE Communications Society Best Tutorial Paper Award. Further, he was a Marie Curie IIF Fellow of the European Commission from 2014 through 2015. In 2017, he received the Friedrich Wilhelm Bessel Research Award from the Alexander von Humboldt (AvH) Foundation in recognition of his accomplishments in research on FiWi-enhanced mobile networks. In 2017, he was named one of the three most promising scientists in the category “Contribution to a better society” of the Marie Skłodowska-Curie Actions (MSCA) 2017 Prize Award of the European Commission. In 2019/2020, he held a UC3M-Banco de Santander Excellence Chair at Universidad Carlos III de Madrid (UC3M), Madrid, Spain.
Foreword
A new generation of cellular standards was introduced by the industry once every 10 years since 1979. Each generation provides a big improvement in performance, functionality, and efficiency over the previous generation. These standards were driven mainly by the International Telecommunication Union Radio Communication Sector (ITU-R) and the third generation partnership project (3GPP). As 5G started deployment in 2019, different study groups are poised to examine the possibility of 6G to appear around 2030. One such study group is the ITU-T Focus Group on Technologies for Network 2030. In May 2019, the group issued a white paper entitled “Network 2030 – A Blueprint of Technology, Application and Market Drivers Towards the Year 2030 and Beyond.” Among the new applications being studied by the group are holographic media and multi-sense communication services which include transmission of touch and feel as well as smell and taste, in addition to sight and sound that we already enjoy today. Such new applications are expected to give rise to a brand new class of vertical market in entertainment, healthcare, automotive, education, and manufacturing.
It is perfect timing for researchers Amin Ebrahimzadeh and Martin Maier to write their book on “Toward 6G: A New Era of Convergence.” The authors surveyed the literature on different 6G proposals including their own work and wrote this book on what 6G would look like in the future. 6G is expected to be built on the strong foundation of 5G, in particular its ultra-high speed and reliability with ultra-low latency. These features enable 6G to support new applications involving human senses such as haptic communication as in the Tactile Internet, as well as high-resolution immersive media beyond today's virtual reality (VR) and augmented reality (AR). The transmission of realistic hologram involves sending volumetric data from multiple viewpoints to account for the 6 degrees of freedom (tilt, angle, and shift of the observer relative to the hologram). The authors provided quantitative examples of such 6G applications requiring the complex interplay of human, robots, avatars, and sophisticated digital twins of objects.
I am particularly intrigued by the last chapter, where the authors summarized their discussions in earlier chapters as the evolution to the “Internet of No Things” in the 6G post-smartphone era, in which smartphones may not be needed anymore. They presented the concept of extended reality (XR) which spans the continuum from pure reality (offline) at one end to pure virtuality (online) at the other end. The middle of the continuum is the region of mixed reality that covers the space from AR to Augmented Virtuality. The authors further expanded the XR concept to extrasensory perception (ESP) as a nonlocal awareness of space and time, mimicking the principle of nonlocality of the quantum realm. The authors undoubtedly provided us plenty of food for thought as we continue our journey from the well-defined 5G standards to the new world of 6G.
Nim Cheung
26 May 2020
Preface
In March 2019, I was approached to publish a book with Wiley-IEEE Press to give visibility to our pioneering work on fiber wireless access. After a short period of reflection, I was willing to accept the invitation and prepare a manuscript, making the following two suggestions. First, we should extend the scope of the book significantly by including technologies that are starting to play a key role in the future 6G vision. Based on the position taken in a commissioned paper back in 2014, where I advocated that we enter an age of convergence, I suggested that 6G will not be a mere exploration of more spectrum at high-frequency bands, but it will rather be a convergence of upcoming technological trends, most notably connected robotics, extended reality, and blockchain technologies. Second, I suggested to involve Dr. Amin Ebrahimzadeh as lead author, with whom I have been closely collaborating on those research topics during his doctoral and postdoctoral studies over the last four to five years, while my role will be more that of a spiritus rector, much like a quarterback in modern American football. Gratefully, our Wiley-IEEE book proposal was very well received by all reviewers and the book project was underway to become the first book on 6G.
What will 6G be? Among others, 6G envisions four-tier network architectures that will extend the 5G space-air-ground networks by integrating underwater networks and incorporating key enabling technologies such as millimeter-wave and Terahertz communications as well as brand-new wireless communication technologies, most notably reconfigurable intelligent surfaces. Furthermore, 6G will take network softwarization to a new level, namely toward network intelligentization. Arguably more interesting, while smartphones were central to 4G and 5G, there has been an increase in wearable devices (e.g., Google and Levi's smart jacket or Amazon's recently launched voice-controlled Echo Loop ring, glasses, and earbuds) whose functionalities are gradually replacing those of smartphones. The complementary emergence of new human-centric and human-intended Internet services, which appear from the surrounding environment when needed and disappear when not needed, may bring an end to smartphones and potentially drive a majority of 6G use cases in an anticipated post-smartphone era. Given that the smartphone is sometimes called the new cigarette of the twenty-first century and using it is considered the new smoking, the anticipated 6G post-smartphone era may allow us to rediscover the offline world by co-creating technology together with a philosophy of technology use toward Digital Minimalism, as recently suggested by computer scientist Cal Newport.
As this book is ready to go to press, the currently most intriguing 6G vision out there at the time of writing was outlined by Harish Viswanathan and Preben E. Mogensen, two Nokia Bell Labs Fellows, in an open access article titled “Communications in the 6G Era” that was published just recently last month. In this article, the authors focus not only on the technologies but they also expect the human transformation in the 6G era through unifying experiences across the physical, biological, and digital worlds in what they refer to as the network with the sixth sense. This book aims at providing a comprehensive overview of these and other aforementioned developments as well as up-to-date achievements, results, and trends in the research on next-generation 6G mobile networks.
Martin Maier
Montréal, April 2020
Acknowledgments
The completion of this book would have never been possible without the support and collaboration of a number of amazing people. We would like to thank Professor Eckehard Steinbach, Dr. Claudio Pacchierotti, and Dr. Leonardo Meli for providing us with the teleoperation and telesurgery traces. We thank Abdeljalil Beniiche for his collaboration in surveying the state-of-the-art of blockchain technologies and developing our proposed nudge contract in Chapter 6. Special thanks go to Sajjad Rostami for his endless efforts in our lab toward developing the experimental framework used in Chapter 7. In particular, we are grateful to Nim Cheung, the former President of IEEE Communications Society, who invited Martin to write this book, as a new entry to the ComSoc Guide to Communications Series. At Wiley-IEEE Press, we would like to thank Mary Hatcher, Victoria Bradshaw, Louis Vasanth Manoharan, and Teresa Netzler for their guidance throughout the whole process of preparing the book. We would like to acknowledge the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Fonds de Recherche du Québec-Nature et Technologies (FRQNT) for funding our research. Finally, and most importantly, Amin would like to take this opportunity to express his great depth of gratitude to his parents for their endless support, love, and encouragement.
Acronyms
1G
First generation
2G
Second generation
3G
Third generation
3GPP
3rd generation partnership project
6Genesis
6G enabled smart society and ecosystem
6GFP
6Genesis flagship program
A2A
Avatar-to-avatar
A2H
Avatar-to-human
ACCs
Access control contracts
ADC
Analog-to-digital converter
AGI
Artificial general intelligence
AI
Artificial intelligence
ANN
Artificial neural network
API
Application programming interface
APT
Advanced persistent threat
AR
Augmented reality
ART
Audi robotic telepresence
AV
Augmented virtuality
B5G
Beyond 5G
BBU
Baseband unit
BIoT
Blockchain-based IoT
BS
Base station
CAeC
Contextually agile eMBB communications
CAPSTA
Context-aware prioritized scheduling and task assignment
CCDF
Complementary cumulative distribution function
CCSC
Crypto currency smart card
CNRS
Centre National de la Recherche Scientifique
CoC
Computation oriented communications
co-DBA
Cooperative dynamic bandwidth allocation
CoMP
Coordinated multipoint
CPRI
Common public radio interface
CPU
Central processing unit
C-RAN
Cloud radio access network
DAC
Digital-to-analog converters
DAO
Decentralized autonomous organization
DApps
Decentralized applications
DBA
Dynamic bandwidth allocation
DC
Direct current
DCF
Distributed coordination function
DFR
Decreasing failure rate
DIFS
DCF interframe space
DLT
Distributed ledger technology
DNS
Domain name system
DoF
Degrees-of-freedom
DSOC
Decentralized self-organizing cooperative
DVB
Digital video broadcasting
DVS
Dynamic voltage scaling
ECDSA
Elliptic curve digital signature algorithm
eMBB
Enhanced mobile broadband
EPON
Ethernet passive optical network
ESF
Edge sample forecast
ESPN
Extrasensory perception network
EVM
Ethereum virtual machine
FiWi
Fiber-wireless
FRF
Failure rate function
FTTN
Fiber-to-the-node
FTTx
Fiber-to-the-x
Fx-FH
Fx fronthaul
GP
Generalized Pareto
GSM
Global system for mobile communication
HABA
Humans-are-better-at
HART
Human-agent-robot teamwork
HITL
Human-in-the-loop
HMI
Human–machine interaction
HSI
Human system interface
I2V
Invisible-to-visible
IA
Intelligence amplification
ICT
Information and communication technology
IFR
Increasing failure rate
IMT 2020
ITU's international mobile telecommunications 2020
IoE
Internet of everything
IoS
Internet of skills
IoT
Internet of Things
IP
Internet protocol
IPACT
Interleaved polling with adaptive cycle time
ITU-T
ITU's telecommunication standardization sector
JC
Judge contract
JND
Just noticeable difference
KPI
Key performance indicator
LoRa
Long range
LPWA
Low-power wide-area
LTE
Long-term evolution
LTE-A
LTE-advanced
M2M
Machine-to-machine
MABA
Machines-are-better-at
MAC
Medium access control
MAP
Mesh access point
MCC
Mobile cloud computing
MEC
Multi-access edge computing
MIMO
Multiple-input multiple-output
MLE
Maximum likelihood estimation
MLP
Multi-layer perceptron
mMTC
Massive machine type communications
mmWave
Millimeter-wave
MP
Mesh point
MPCP
Multipoint control protocol
MPP
Mesh portal point
MR
Mobile robot
MU
Mobile user
NAT
Network address translation
NG-PON
Next-generation PON
NOMA
Non-orthogonal multiple access
OFDM
Orthogonal frequency division multiplexing
OLT
Optical line terminal
ONU
Optical network unit
OPEX
Operational expenditures
Probability distribution function
pHRI
Physical human–robot interaction
PON
Passive optical network
PoS
Proof-of-stake
PoW
Proof-of-work
QoE
Quality of experience
QoS
Quality of service
qubit
Quantum bit
R&F
Radio-and-fiber
RACS
Remote APDU call secure
RF
Radio frequency
RIS
Reconfigurable intelligent surface
RoF
Radio-over-fiber
RRH
Remote radio head
RTP
Real-time transport protocol
SDN
Software-defined networking
SDONs
Software-defined optical networks
SDR
Software-defined radio
SDS
Software-defined surface
SLAM
Simultaneous localization and mapping
SMS
Short message service
STA
Station
TDM
Time division multiplexing
THz
Terahertz
TLD
Top-level domain
ToD
Teleoperated driving
TOR
Teleoperator robot
UAV
Unmanned aerial vehicle
UDP
User datagram protocol
URLLC
Ultra-reliable and low-latency communications
UX
User experience
VHT
Very high throughput
VR
Virtual reality
WDM
Wavelength division multiplexing
WLAN
Wireless local area network
XR
Extended reality
1The 6G Vision
1.1 Introduction
With the completion of third generation partnership project (3GPP) Release 15 of the 5G standard in June 2018, the research community has begun to shift their focus to 6G. In July 2018, ITU's Telecommunication standardization sector (ITU-T) Study Group 13 has established the ITU-T Focus Group Technologies for Network 2030 (FG NET-2030). FG NET-2030 will study the requirements of networks for the year 2030 and beyond and will investigate future network infrastructures, use cases, and capabilities. According to Yastrebova et al. (2018), current networks are not able to guarantee new application delivery constraints. The application time delivery constraints will differ in terms of required quality of service (QoS). For instance, for Internet of things (IoT) applications, the delay can be up to 25 ms, but connected cars will need 5–10 ms to get information about road conditions from the cloud to make the drive safe. Current cellular networks are not able to guarantee these new application delivery constraints. For illustration of these shortcomings, the authors of Yastrebova et al. (2018) mentioned that the end-to-end latency in today's 4G long-term evolution (LTE) networks increases with the distance, e.g. 39 ms are needed to reach the gateway to the Internet and additional 5 ms are needed to receive a reply from the server. Furthermore, the number of active devices per cell greatly affect the network latency. Measurements of highly loaded cells showed an increase of the average latency from 50 to 85 ms. Among others, the authors of Yastrebova et al. (2018) expect that future mobile networks will enable the following applications:
Holographic calls
Avatar robotics applications
Nanonetworks
Flying networks
Teleoperated driving
(ToD)
Electronic health
(e-Health)
Tactile Internet
Internet of skills
(IoS).
As a consequence, the network traffic will increase significantly with these new applications that will be enabled by technologies like virtual reality (VR) and augmented reality (AR). Even more exciting will be the widespread use and distribution of avatars for the reproduction and implementation of user actions. According to Yastrebova et al. (2018), avatar robotics applications can become one of the most important sources of traffic in future FG NET-2030 networks, involving new types of communications such as human-to-avatar (H2A), avatar-to-human (A2H), and avatar-to-avatar (A2A) communications. Importantly, taking into account the limited speed of propagation of light, the requirements for ultra-low latency should lead to the decentralization of future networks.
In academia, researchers from the University of Oulu's Centre for Wireless Communications launched an eight-year research program called 6G enabled smart society and ecosystem(6Genesis) to conceptualize 6G. The first open 6Genesis seminar was held in August 2018. In Katz et al. (2018), an initial vision of what the sixth generation mobile communication system might be was presented by outlining the primary ideas of the 6Genesis Flagship Program (6GFP) created by the University of Oulu together with a Finish academic and industrial consortium. In this 6GFP program, 6G is investigated from a wide and realistic perspective, considering not only the communicational part of it but also looking into other highly relevant parts such as computer science, engineering, electronics, and material science. This integral approach is claimed to be instrumental in achieving truly novel solutions. Among others, the interrelated research areas of 6GFP aim at achieving distributed intelligent wireless computing by means of mobile edge, cloud, and fog computing. More specifically, intelligent distributed computing and data analytics is becoming an inseparable part of wireless networks, which call for self-organizing solutions to provide strong robustness in the event of device and link failures. Furthermore, VR/AR over wireless is considered one of the key application drivers for the future, whereby the information theory and practical performance requirements from the perspective of human psychology and physiology must be accounted for. As a consequence, perception-based coding should be considered to mitigate the shortcomings of existing compression–decompression algorithms in VR/AR. Future applications need distributed high-throughput local computing nodes and ubiquitous sensing to enable intelligent cyber-physical systems that are critical for future smart societies. Finally, techno-economic and business considerations need to address the question how network ownership and service provisioning models affect the design of radio access systems, including the potential analysis of high-risk technology enablers such as quantum theory and communications.
In September 2019, the world's first 6G white paper was published as an outcome of the first 6G wireless summit, which was held in Levi, Finland, earlier in March 2019 with almost 300 participants from 29 countries, including major infrastructure manufacturers, operators, regulators as well as academia (Latva-aho and Leppänen, 2019). Each year, the white paper will be updated following the annual 6G wireless summit. While 5G was primarily developed to address the anticipated capacity growth demand from consumers and to enable the increasing importance of the IoT, 6G will require a substantially more holistic approach, embracing a much wider community. Many of the key performance indicators (KPIs) used for 5G are valid also for 6G. However, in the beyond 5G (B5G) and 6G, KPIs in most of the technology domains once again point to an increase by a factor of 10–100, though a 1000 times price reduction from the customer's view point may be also key to the success of 6G (Zhang et al., 2020). Note that price reduction is particularly important for providing connectivity to rural and underprivileged areas, where the cost of backhaul deployment is the major limitation. According to Yaacoub and Alouini (2020), providing rural connectivity represents a key 6G challenge and opportunity given that around half of the world population lives in rural or underprivileged areas. Among other important KPIs, 6G is expected to be the first wireless standard exceeding a peak throughput of 1 Tbit/s per user. Furthermore, 6G needs a network with embedded trust given that the digital and physical worlds will be deeply entangled by 2030. Toward this end, blockchain also known as distributed ledger technology (DLT) may play a major role in 6G networks due to its capability to establish and maintain trust in a distributed fashion without requiring any central authority.
Arguably more interestingly, the 6G white paper envisions that totally new services such as telepresence, as a surrogate for actual travel, will be made possible by combinations of graphical representations (e.g. avatars), wearable displays, mobile robots and drones, specialized processors, and next-generation wireless networks. Similarly, smartphones are likely to be replaced by pervasive extended reality (XR) experiences through lightweight glasses, whereby feedback will be provided to other senses via earphones and haptic interfaces.
1.2 Evolution of Mobile Networks and Internet
The general evolution of global mobile network standards was first to maximize coverage in the first and second generations and then to maximize capacity in the third and fourth generations. In addition to higher capacity, research on 5G mobile networks has focused on lower end-to-end latency, higher spectral efficiency and energy efficiency, and more connection nodes (Rowell and Han, 2015). More specifically, the first generation (1G) mobile network was designed for voice services with a data rate of up to 2.4 kbit/s. It used analog signal to transmit information, and there was no universal wireless standard. Conversely, 2G was based on digital modulation technologies and offered data rates of up to 384 kbit/s, supporting not only voice services but also data services such as short message service (SMS). The dominant 2G standard was the global system for mobile (GSM) communication. The third generation (3G) mobile network provided a data rate of at least 2 Mbit/s and enabled advanced services, including web browsing, TV streaming, and video services. For achieving global roaming, 3GPP was established to define technical specifications and mobile standards. 4G mobile networks were introduced in the late 2000s. 4G is an all Internet Protocol (IP) based network, which is capable of providing high-speed data rates of up to 1 Gbit/s in the downlink and 500 Mbit/s in the uplink in support of advanced applications like digital video broadcasting (DVB), high-definition TV content, and video chat. LTE-Advanced (LTE-A) has been the dominant 4G standard, which integrates techniques such as coordinated multipoint (CoMP) transmission and reception, multiple-input multiple-output (MIMO), and orthogonal frequency division multiplexing (OFDM). The main goal of 5G has been to use not only the microwave band but also the millimeter-wave (mmWave) band for the first time in order to significantly increase data rates up to 10 Gbit/s. Another feature of 5G is a more efficient use of the spectrum, as measured by increasing the number of bits per hertz. ITU's International Mobile Telecommunications 2020 (IMT 2020) standard proposed the following three major 5G usage scenarios: (i) enhanced mobile broadband (eMBB), (ii) ultra-reliable and low latency communications (URLLC), and (iii) massive machine type communications (mMTC). As 5G is entering the commercial deployment phase, research has started to focus on 6G mobile networks, which are anticipated to be deployed by 2030 (Huang et al., 2019).
Typically, next-generation systems do not emerge from the vacuum, but follow the industrial and technological trends from previous generations. Potential research directions of 6G consistent with these trends were provided by Bi (2019), including among others:
6G will continue to move to higher frequencies with wider system bandwidth
: Given that the spectrum at lower frequencies has almost been depleted, the current trend is to obtain wider bandwidth at higher frequencies in order to increase the data rate more than 10 times for each generation.
Massive MIMO
will remain a key technology for 6G
: Massive MIMO has been the defining technology for 5G that has enabled the antenna number to increase from 2 to 64. Given that the performance gains have saturated in the areas of channel coder and modulator, the hope of increasing spectral efficiency for 6G will remain in the multiple antenna area.
6G
will take the cloud service to the next level
: With the ever higher data rates, short delays, and low transmission costs, many of the computational and storage functions have been moved from the smartphone to the cloud. As a result, most of the computational power of the smartphone can focus on presentation rendering, making VR, AR, or XR more impressive and affordable. Many
artificial intelligence
(AI) services that are intrinsically cloud based may prevail more easily and broadly. In addition to smartphones, less expensive functional terminals may once again flourish, providing growth opportunities in more application areas.
Grant-free transmissions could be more prominent in 6G
: In past cellular network generations, transmissions were primarily based on grant-oriented design with strong centralized system control. More advanced grant-free protocols and approaches will be needed for 6G. It is possible that the
non-orthogonal multiple access
(NOMA) technology may have another opportunity to prevail due to its short delay performance even though it failed to take off during the 5G time period.
mMTC is more likely to take shape in the older generation before it can succeed in the next generation
: mMTC has been one of the major directions for the next-generation system design since the market growth of communications between people has saturated. High expectations have been put on 5G mMTC to deliver significant growth for the cellular industry. Until now, however, this expectation has been mismatched with the reality on the ground. Therefore, the current trend appears to indicate that mMTC would be more likely to prevail by utilizing older technology that operates in the lower band at lower cost.
6G will transform a transmission network into a computing network
: One of the possible trademarks of 6G could be the harmonious operations of transmission, computing, AI, machine learning, and big data analytics such that 6G is expected to detect the users' transmission intent autonomously and automatically provide personalized services based on a user's intent and desire.
In his latest book “The Inevitable,” Kevin Kelly described the 12 technological forces that will shape our future (Kelly, 2016). According to Kelly, nothing has happened yet in terms of the Internet. The Internet linked humans together into one very large thing. From this embryonic net will be born a collaborative interface, a sensing, cognitive apparatus with power that exceeds any previous invention. The hard version of it is a future brought about by the triumph of a superintelligence. According to Kelly, however, a soft singularity is more likely where AI and robots converge – humans plus machines – and together we move to a complex interdependence. This phase has already begun. We are connecting all humans and all machines into a global matrix, which some call the global mind or world brain. It is a new regime wherein our creations will make us better humans. This new platform will include the collective intelligence of all humans combined with the collective behavior of all machines, plus the intelligence of nature, plus whatever behavior emerges from this whole. Kelly estimates that by the year 2025 every person will have access to this platform via some almost-free device.
The importance of convergence of emerging key technologies, e.g. AI, robots, and XR, lies also at the heart of the 6G era with standards and enabled devices anticipated to roll out around 2030. 6G research is just now starting, even though 5G networks have not been widely deployed yet. A few countries, most notably Finland as well as China and South Korea, have taken the lead by launching 6G programs to avoid getting left behind.
1.3 6G Network Architectures and Key Enabling Technologies
1.3.1 Four-Tier Networks: Space-Air-Ground-Underwater
6G network architectures are anticipated to extend the 5G three-tier space-air-ground networks by integrating underwater networks, thus giving rise to four-tier space-air-ground-underwater networks with near-instant and unlimited superconnectivity in the sky, at sea, and on land. According to Zhang et al. (2019b), these large-dimensional integrated nonterrestrial and terrestrial networks will consist of the following four network tiers:
Space-network tier
: This network tier will support orbit or space Internet services in such applications such as space travel and provide wireless coverage via satellites. For long-distance intersatellite transmission in free space, laser communications represents a promising solution. The use of mmWave frequencies to establish high-capacity (inter)satellite communications may be another feasible solution to complement terrestrial 6G networks with computing stations placed on satellite platforms (Giordani and Zorzi,
2020
). The integration of terrestrial and non-terrestrial networks poses a number of challenges and new open problems such as (i) large propagation delays, (ii) Duppler effect due to fast moving satellites, and (iii) severe path loss of mmWave transmission.
Air-network tier
: This network tier works in the low-frequency, microwave, and mmWave bands to provide more flexible and reliable connectivity for urgent events or in remote areas by densely employing flying base stations, e.g.
unmanned aerial vehicle
s (UAVs).
Terrestrial-network tier
: Similar to 5G, this network tier will still be the main solution for providing wireless coverage for most human activities. It will support low-frequency, microwave, mmWave, and THz bands in ultradense heterogeneous networks, which require the deployment of ultra-high-capacity backhaul infrastructures. Optical fiber will still be important for 6G, though THz wireless backhaul will be an attractive alternative.
Underwater-network tier
: Finally, this network tier will provide coverage and Internet services for broad-sea and deep-sea activities for military or commercial applications. Given that water exhibits different propagation characteristics, acoustic and laser communications can be used to achieve high-speed data transmission for bidirectional underwater communications. According to Huang et al. (
2019
), however, there is a lot of controversy about whether undersea networks are able to become a part of future 6G networks. Unpredictable and complex underwater environments lead to intricate network deployments, severe signal attenuation, and physical damage to equipment, leaving plenty of issues to be resolved.
1.3.2 Key Enabling Technologies
1.3.2.1 Millimeter-Wave and Terahertz Communications
Higher frequencies from 100 GHz to 3 THz are promising bands for the next generation of wireless communication systems, offering the potential for revolutionary applications. Technically, the formal definition of the THz region is 300 GHz through 3 THz, though sometimes the terms sub-THz or sub-mmWave are used to define the 100–300 GHz spectrum. The short wavelengths at mmWave and THz will allow massive spatial multiplexing in hub and backhaul communications. The THz band from 100 GHz through 3 THz can enable secure communications due to the fact that small wavelengths allow for extremely high-gain antennas with extremely small physical dimensions. The ultra-high data rates facilitated by mmWave and THz wireless local area and cellular networks will enable super-fast download speeds for computer communication, autonomous vehicles, robotic control, the so-called information shower, high-definition holographic gaming, and high-speed wireless data distribution in data centers. In addition to the extremely high data rates, there are promising applications for future mmWave and THz systems that are likely to evolve in 6G networks and beyond. These applications can be categorized into the main areas of wireless cognition, sensing, imaging, wireless communications, and position location/THz navigation (Rappaport et al., 2019).
