Chapter 1
Introduction
By Ömer Bulakçı, Mikko Uusitalo, Patrik Rugeland, Marco Gramaglia,
Xi Li, Mauro Boldi, Anastasius Gavras, et al.1
Copyright © 2023 Ömer Bulakçı, et al.
DOI: 10.1561/9781638282396.ch1
The work will be available online open access and governed by the Creative Commons “Attribution-Non
Commercial” License (CC BY-NC), according to https://creativecommons.org/licenses/by-nc/4.0/
Published in Towards Sustainable and Trustworthy 6G: Challenges, Enablers, and Architectural Design by Ömer
Bulakçı, Xi Li, Marco Gramaglia, Anastasius Gavras, Mikko Uusitalo, Patrik Rugeland and Mauro Boldi (eds.).
2023. ISBN 978-1-63828-238-9. E-ISBN 978-1-63828-239-6.
Suggested citation: Ömer Bulakçı, Mikko Uusitalo, Patrik Rugeland, Marco Gramaglia, Xi Li, Mauro Boldi,
Anastasius Gavras, et al. 2023. “Introduction” in Towards Sustainable and Trustworthy 6G: Challenges, Enablers,
and Architectural Design. Edited by Ömer Bulakçı, Xi Li, Marco Gramaglia, Anastasius Gavras, Mikko Uusitalo,
Patrik Rugeland and Mauro Boldi. pp. 1–10. Now Publishers. DOI: 10.1561/9781638282396.ch1.
1. The full list of chapter authors is provided in the Contributing Authors section of the book.
1.1 Architecting the 6th Generation of Mobile and
Wireless Communications System
Since early generations, mobile and wireless communications systems have played
a crucial role in the establishment of essential connectivity. This has enabled easy
access to information from anywhere and anytime and, thus, has fostered accel-
erated knowledge build-up and timely value-adding actions based on that beyond
telecommunications ecosystems in all sectors of society. The COVID-19 pandemic
has additionally proven the importance of the wireless communication infrastruc-
ture during these challenging times and has supported global stability as well as
faster recovery via maintaining a stable technological environment and seamless
societal connection despite quarantine regulations.
Considering such critical role and importance, the relevant technological
advancements within and for the telecommunications ecosystem are captured by a
non-backward-compatible set of features specified in a new generation of mobile
and wireless communications systems. As advancing from a previous generation
to the new one requires significant efforts, the need for a new generation shall be
1
2 Introduction
Technical
Drive
Economical
Drive xG
Societal
Drive
• Increase in the mobile data traffic
Technical Drive • Diverse Services with Broad Range of Requirements
• Rapid growth of wirelessly-connected Devices
• Demand for Seamless Connectivity Anywhere & Anytime
Societal Drive • Demand for Affordable Access to Broadband
• Demand for Sustainable Access
• The need for cost-efficient cellular communications
Economical Drive • The need for energy-efficient cellular communications
• The need for new business areas
Figure 1.1. Drivers for developing new generation of mobile networks.
justified factoring in the technical, societal, and economical drives (see Figure 1.1).
These drives are not mutually independent, i.e., one boost in any of the drives can
accelerate the whole process. For instance, the need for attaining new business areas
also implies the need for supporting a diverse set of induced requirements.
Accordingly, the development of mobile and wireless networks has followed
around a 10-year cycle, where, up to the 5th generation (5G), previous generations
have been designed for particular use case categories. With 5G, an inherent flexi-
bility has been introduced, and the target customer space has been extended from
mobile broadband users towards vertical industries with diverse requirements [1].
The framework of network slicing has been introduced to cope with such different
requirements. The commercial deployments of the 5G system have been under-
way since 2019 with an original focus on non-standalone (NSA) architecture, while
more and more standalone (SA) architecture has been employed globally. The NSA
deployment implies that 5G new radio (NR) is anchored with the 4th generation
(4G) system, and the 4G core network (CN) is in use. In the case of the SA deploy-
ments, where 5G NR connects to the 5G CN, the full potential of the 5G system
can be unleased, e.g., by means of the utilization of the network slicing. Moreover,
5G-Advanced enhancements, e.g., extended reality (XR) optimizations, are already
being specified in the 3rd Generation Partnership Project (3GPP) Release 18 [2].
Architecting the 6th Generation 3
5G 5G-Advanced 6G era
2023 2030+
High quality video XR - fully immersive Holographic
(4K-8K) user experience communications
Object driven Large scale digital Wide-area realtime synchronous
digital twinning reconstruction digital twins
(e.g. an engine) (e.g. a vertical farm) (e.g., smart city)
Figure 1.2. Example evolution of use case families from 5G towards 6G era.
1 2 3
Pre-X Standardizaon Commercializaon
X: Compeon Well-rounded Feature Porolio Base Rel. 21
X: Standardizaon Respond to Business & Societal Needs Deployments ~2030
Exploratory Global 6G System for 2030+
Digital World
6G
Physical World Human World
Figure 1.3. Three-phase approach to realize the complete value chain of 6G.
While 5G deployments and 5G-Advanced standardization are progressing well,
as highlighted in Chapter 9, research into the new generation of mobile and wire-
less communications systems, i.e., the 6th Generation (6G), has already started.
Like in the case for other generations, the creation of 6G has started with the
identification as well as prediction of the use cases and the associated requirements
(see Section 2.1). An illustration of the evolution of use case families is shown in
Figure 1.2. As depicted, digital twinning of objects is already supported by a 5G
system, and this support can be expanded via 5G-Advanced. Nevertheless, it is fore-
seen that a wide-area synchronous digital twinning can be possible only during the
6G era. Accordingly, it can be stated that 5G-Advanced provides the stepping stone
towards 6G, where 6G will enable new use cases as well as existing use cases at scale.
It is worth noting that the wireless networks are designed to be flexible to address
the requirements of new use cases that may not be predicted today.
On this basis, a three-phase approach is being followed to realize the complete
value chain of the 6G system, as depicted in Figure 1.3. These phases are outlined
in the following.
Pre-X Phase: This is the exploratory research phase, where X can refer to compe-
tition or standardization. During this phase, the key stakeholders, e.g., academia,
vendors, diverse industries, and mobile network operators (MNOs), come together
4 Introduction
to set the vision, design guidelines, and the foundation for the 6G system. The
main motivation for such a phase is the build-up and expansion of the 6G ecosys-
tem. This phase is essential for rapid and efficient standardization process that will
follow.
Standardization Phase: In this phase, a well-rounded feature portfolio is speci-
fied, e.g., radio access network (RAN) and CN by 3GPP, that shall respond to the
business and societal needs, as highlighted in Figure 1.1, which have been iden-
tified during the Pre-X Phase as well as the standardization phase. It is expected
that, differently from 5G specification, many architecture options shall be avoided
to enable the full potential of 6G already in the early deployments. Moreover, to
make use of the economies of scale and the proven benefits of previous generations,
a global 6G standard should be aimed for.
Commercialization Phase: Based on the established standardization, which is
envisioned to be 3GPP Release 21, the first commercial 6G deployments can be
seen around 2030. It should be noted that the 6G system will be designed at least
for the full next decade (2030s) and even beyond.
With the seamless execution of all three phases, the promises of the 6G system
on the integration of digital, physical, and human worlds can be realized, which
can transform the world while maximizing human potential. The details on the
standardization and regulatory processes are provided in Chapter 9.
1.2 Approach and Timing of the Book
This book is a result of the collaborative work performed at European level during
the Pre-X phase of the 6G system’s creation. In particular, the main content of the
book has been provided by the 5G Public Private Partnership (5G PPP) Phase 3
research projects [3]. 5G PPP Phase 3 projects are categorized under different calls
that pertain to specific requirements set by the European Commission (EC); see the
corresponding book preface. Among the Phase 3 calls, the most relevant ones for the
scope of the book have been the information and communication technologies 20
(ICT 20) and ICT 52 calls, where the former has comprised projects that work on
the longer-term vision of 5G, i.e., 5G evolution [4], and the latter has comprised
projects that work on the foundation of the beyond 5G/6G system [5]. As part
of the ICT 52 call, the Hexa-X project is the system flagship project [6]. Yet, since
various enhancements considered for the 5G system by other Phase 3 projects could
be employed by 6G with its full potential, such enhancements are also captured
herein.
Approach and Timing of the Book 5
V1.0 released June 2016 V2.0 released Jan. 2018 V4.0 released October 2021
V3.0 released Fen 2020
Novel trends and key Key architectural Consolidation of large-scale
Architecture enhancements and
architectural enablers for 5G findings and overall vertical trials and beyond 5G
verticals-enabled architecture
vision architecture definition concepts
V6.0 Released for Public Consultation Dec 2022 and Final Version Published in Feb. 2023
Sets the foundation of the 6G Architecture Design, e.g., based on inputs from ICT 52 projects.
Concise Version, where the detailed version to be published as an open access book during 2023.
Figure 1.4. White papers released by the 5G PPP Architecture WG.
Moreover, a key part of the 5G PPP framework is a set of cross-project work-
ing groups (WGs). The outcome of the work from these groups is presented in
white papers [7]. As highlighted in the prefaces of this book, the Architecture WG
brings the research projects together to build a consolidated view of the architectural
efforts, including the overall architecture of mobile and wireless communications
networks across different network domains, such as RAN, Transport, and CN, as
well as cloud or edge infrastructure.
The outcome of the Architecture WG has been published in a series of
white papers and presented during various technical workshops at international
conferences and webinars. As shown in Figure 1.4, the latest white paper of the
WG is “The 6G Architecture Landscape – European Perspective” [8], which is Ver-
sion 6.0. The first version of the architecture white paper from the Architecture
WG was back in July 2016. Since then, this effort has continuously captured the
technology trends as developed by the different phases of 5G PPP projects: the first
phase (Phase 1) laid the foundation of the network slicing-aware operations we are
seeing these days; the second phase (Phase 2) provided the first proof of concepts;
and the third phase (Phase 3) has targeted the first large-scale platforms. All these
efforts were captured in the subsequent releases of the white paper (Version 2 in
January 2018, Version 3 in February 2020, and Version 4 in November 2021). It
is worth noting that Version 6.0 is intentionally the next version after Version 4.0
as an indication of the focus on 6G.
Capitalizing on the Version 6.0 of the white paper, this book is a joint effort by
the Architecture WG and the Hexa-X project, extending significantly the concise
content of the published white paper [8]. Within the framework of the Architecture
WG and the joint work, the content of the book has been based on the following
projects (in alphabetical order) [3]:
• 5G-COMPLETE, which aims at revolutionizing beyond 5G architecture,
by efficiently combining compute and storage resource functionality over
a unified, ultra-high capacity converged digital/analogue Fiber-Wireless
(FiWi) RAN.
• 5G-CLARITY, which brings forward the design of a system beyond 5G pri-
vate networks to address challenges in spectrum flexibility, delivery of critical
services, and autonomic network management using heterogeneous wireless
access that integrates 5G, Wi-Fi, and LiFi technologies managed through
novel Artificial Intelligence (AI)-based autonomic networking.
6 Introduction
• 5G ERA, which aims at providing third-party application developers with an
experimentation facility as a playground to test and qualify their applications.
• 5GASP, which aims at shortening the idea-to-market process through the
creation of a European testbed for Small and Medium-sized Enterprises
(SMEs) that is fully automated and self-service, in order to foster rapid devel-
opment and testing of new and innovative 5G network applications.
• 6G BRAINS, which brings reinforcement learning into radio-light network
for massive connections.
• AI@EDGE, which develops a connect-compute fabric – specifically leverag-
ing the serverless paradigm – for creating and managing resilient, elastic, and
secure end-to-end slices.
• ARIADNE, which proposes to exploit bandwidth-rich D-band, the capa-
bilities of Reconfigurable Intelligent Surfaces (RIS), and powerful Machine
Learning (ML) tools in order to realize a novel Communication Theory
framework beyond Shannon and design suitable technology enablers for
highly reliable and reconfigurable 6G connectivity.
• DAEMON, which develops and implements innovative and pragmatic
approaches to Network Intelligence (NI) design that enable high perfor-
mance, sustainability, and an extremely reliable zero-touch network system.
• DEDICAT 6G, which addresses techniques for achieving and maintaining
efficient dynamic connectivity and intelligent placement of computation in
the mobile network.
• EVOLVED-5G, which designs and develops an open facility for the long-
term support of third-party applications that interact with the network core.
• Hexa-X, which is the European 6G flagship research project, defining the
vision, and developing technological enablers for connecting the physical,
digital, and human worlds.
• MARSAL, which targets the development of a complete framework for the
management and orchestration of network resources in 5G and beyond, by
utilizing a converged optical wireless network infrastructure in the access and
fronthaul/midhaul segments.
• MonB5G, which targets zero-touch management and orchestration in sup-
port of network slicing at massive scales for 5G evolution and beyond.
• REINDEER, which develops a new smart connect-compute platform with a
capacity that is scalable to quasi-infinite, and that offers perceived zero latency
and interaction with an extremely high number of embedded devices.
• RISE 6G, which aims at investigating innovative solutions that capitalize on
the latest advances in the emerging technology of RISs and offers dynamic
and goal-oriented radio wave propagation control, enabling the concept of
the wireless environment as a service.
Scope and Structure of the Book 7
• TeraFlow, which aims to deliver a new generation open-source cloud-native
Software-Defined Networking (SDN) controller to provide smart connectiv-
ity services to beyond 5G networks.
1.3 Scope and Structure of the Book
This book highlights the related research work of the contributing 5G PPP Phase 3
projects and presents all the key elements and key architecture enablers and solu-
tions of future 6G network design – a design that is deeply rooted in real needs
and can profoundly benefit humanity in the mid-to-long term. Specifically, a high-
level view of the 6G End-to-End (E2E) architecture as well as a functional view
of the 6G reference architecture are introduced, taking into consideration the new
stakeholders in the mobile network ecosystem and how the architectural work is
taking into account their requirements in all the domains of the network. The key
architecture enablers, which will form the backbone of future sustainable and trust-
worthy 6G network architecture, include all the related technological solutions for
building intelligent, flexible, energy efficient, secure, programmable networks and
enabling versatile radio technologies, localization, and sensing in the 6G networks.
As 5G PPP Phase 3 consists of the last calls of the Horizon 2020 programme, this
book is aimed to lay the architectural foundation for the next European programme
towards 6G, i.e., smart networks and services (SNS) joint undertaking (JU).
The rest of this book is structured into the following eight chapters.
Chapter 2 – Architecture Landscape draws the envisioned system view of the
overall 6G architecture associated with a functional view. The presented architec-
ture is built up considering the key design principles that are populated based on
the envisioned use cases, requirements, and trends as highlighted in Section 2.1.
The discussions on the management and orchestration (M&O) as well as security
and privacy architecture complete the big picture. A brief overview of the architec-
tural enablers is also captured, which sets the guidance for the following detailed
chapters enumerated from three to eight.
Chapter 3 – Towards Versatile Access Networks presents the envisioned enhance-
ments for the wireless networks, including the efficient utilization of 3GPP and
non-3GPP access networks. Such enhancements include the distributed multiple-
input multiple-output (D-MIMO) implementation, integrated access and back-
haul (IAB) deployments, RIS, multi-access connectivity, and sub-THz access. It
is argued that for the limitless connectivity requirement of 6G, D-MIMO can
provide expected macro diversity, design flexibility, and interference management;
IAB can offer cost-efficient densification without the need of fibre to connect the
8 Introduction
small cell sites; and RIS can provide means to fine-tune the wireless configuration
environments. Multi-access multi-connectivity will remain an important feature
for 6G to enhance the wireless link’s throughput, reliability, or even latency. In
addition, sub-THz bands can help fulfil the requirements of the high data rate
applications in short distances or can offer wireless connectivity for the backhaul.
Chapter 4 – Towards Joint Communications and Sensing presents the incor-
poration of sensing capabilities into the mobile networks. These capabilities can
be separated into three different categories. First, the 6G network can efficiently
collect, store, and analyse sensing data from various different sensors, and pro-
vide localization, sensing, and mapping information to applications and users to
enhance different 6G services. Second, the localization, sensing, and mapping infor-
mation can be provided to the radio network itself to improve the communication,
e.g., through location or environment-aware beamforming or pre-emptive han-
dover if an impending obstacle is detected. Finally, the purpose of the radio interface
itself is reimagined, where the radio signals are used for both communication and
sensing, either simultaneously or only using common hardware, potentially provid-
ing access to a plethora of transmitters and receivers in a more densified network
that can sense and map the environment in a radar-like fashion without the need
for dedicated hardware deployment.
Chapter 5 – Towards Natively Intelligent Networks presents the recent efforts
in the design of an architecture that is natively capable of incorporating all the
elements required by network functions empowered by Artificial Intelligence (e.g.,
data gathering, representation, decision enforcement), as well as some examples of
such Network Intelligence Functions and their application in different domains of
the network, such as the radio access and the orchestration.
Chapter 6 – Towards Sustainable Networks presents targeted metrics as well
as the main technological enablers towards ensuring high sustainability in next-
generation networks. The chapter focuses on two main principles, “sustainable
6G,” i.e., how to make the 6G networks sustainable, and “6G for sustainability,”
i.e., how 6G can be leveraged so as to ensure sustainability in other markets and
value chains. In this context, a broad analysis of the key network sustainability
enablers is provided spanning across different levels, i.e., from enablers that include
architectural or hardware innovations, and enablers at management/orchestration
level or at service/application level that target at network operation efficiency max-
imization to cross-layer sustainability enablers, which include innovations in more
than two layers.
Chapter 7 – Towards Continuously Programmable Networks presents design
principles and technology enablers towards realizing programmability frameworks,
References 9
i.e., frameworks that abstract the underlay network infrastructure and capabilities
so that the network is dynamically controlled and configured. Standardized solu-
tions and research enablers for such abstraction are indicated, organized in three
levels, namely, service/application provisioning level, network and resource man-
agement level, as well as network deployment and connectivity level. Indicative
approaches include the deployment of common Application Programming Inter-
face (API) managers, the exploitation of P4-programmable switches, the usage of
open interfaces of Open-RAN (O-RAN), and the design of Software Development
Kits (SDKs) for providing network slices as a service.
Chapter 8 – Secure, Privacy-Preserving, and Trustworthy Networks presents
aspects related to network privacy and security for information sharing among dif-
ferent tenants and cloud-stored data, as well as end-users’ network security. More-
over, it investigates the application of blockchain-based platforms for network slic-
ing by using smart contracts, as well as for industrial Internet of Things networks.
Finally, it focuses on trusted execution, trust-as-a-service, as well as trustworthy
ML/AI.
Chapter 9 – 6G Outlook and Timeline presents the most recent picture about
European perspectives on the current status of 6G in terms of standardization,
research and regulation initiatives. This final chapter presents also concluding
remarks of the book.
References
[1] P. Marsch, Ö. Bulakci, O. Queseth, M. Boldi, Eds. 5G System Design –
Architectural and Functional Considerations and Long Term Research, Wiley
2018.
[2] 3GPP, “Release 18 Overview,” 2022. Accessed: April 6, 2023. [Online].
Available: https://www.3gpp.org/specifications-technologies/releases/relea
se-18.
[3] 5G PPP, “5G PPP Phase 3 Research Projects,” 2022. Accessed: April 6, 2023.
[Online]. Available: https://5g-ppp.eu/5g-ppp-phase-3-projects/.
[4] 5G PPP Phase 3 ICT 20 Call,” 2022. Accessed: April 6, 2023. [Online]. Avail-
able: https://5g-ppp.eu/5g-ppp-phase-3-4-projects/.
[5] 5G PPP, “5G PPP Phase 3 ICT 52 Call,” 2022. Accessed: April 6, 2023.
[Online]. Available: https://5g-ppp.eu/5g-ppp-phase-3-6-projects/.
[6] Hexa-X, “A flagship for B5G/6G vision and intelligent fabric of technology
enablers connecting human, physical, and digital worlds,” 2021. Accessed:
April 6, 2023. [Online]. Available: https://cordis.europa.eu/project/id/10
1015956.
10 Introduction
[7] 5G PPP white papers, 2023. Accessed: April 6, 2023. [Online]. Available: https:
//5g-ppp.eu/white-papers/.
[8] 5G PPP Architecture WG, “The 6G Architecture Landscape: European Per-
spective,” White paper v6.0, 2023. Accessed: April 6, 2023. [Online]. Avail-
able: https://5g-ppp.eu/wp-content/uploads/2023/02/Whitepaper-final-versi
on-rev1.pdf .
