5G Backhaul and Fronthaul E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 555

Veröffentlichungsjahr: 2023

Beschreibung

5G BACKHAUL AND FRONTHAUL In-depth coverage of all technologies required for deployment and further evolution of 5G mobile network backhaul and fronthaul In this book, a team of communications technology experts deliver an up-to-date and technical discussion of 5G backhaul and fronthaul, preparing readers for the deployment of 5G technologies, covering the technologies essentials, and offering views of further 5G backhaul and fronthaul evolution. 5G Backhaul and Fronthaul serves both advanced-level experts with senior roles in organizations who are already proficient in these technologies, and general interest readers seeking a primer on what these technologies can provide. Readers will also find: * Thorough introductions to 5G backhaul and fronthaul, as well as selected industry forums and activities * Analysis of high-level requirements for 5G backhaul and fronthaul and 5G network architecture * In-depth explorations of wireless backhaul and fronthaul access technologies, including fiber optic and wireless technologies, network security, network slicing, IP VPNs, Ethernet services, time sensitive networks and shared transport * Practical treatments of the functions and services provided by backhaul and fronthaul * Coverage of new 5G enterprise, industrial and smart city deployments Perfect for mobile network industry professionals, 5G Backhaul and Fronthaul will also earn a place in the libraries of people with an interest in 5G technologies, fiber technologies, IP and security, Ethernet, mobile network synchronization and mobile network performance.

Leseprobe

5G Backhaul and Fronthaul

Edited by

Esa Markus Metsälä Nokia Networks, Finland

Juha T. T. Salmelin Nokia Networks, Finland

This edition first published 2023

© 2023 John Wiley & Sons Ltd

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The right of Esa Markus Metsälä and Juha T. T. Salmelin to be identified as the authors of the editorial material in this work has been asserted in accordance with law.

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Library of Congress Cataloging-in-Publication Data

Names: Metsälä, Esa, editor. | Salmelin, Juha, editor.

Title: 5G backhaul and fronthaul / Esa Markus Metsälä, Juha T. T. Salmelin.

Description: Hoboken, NJ: John Wiley & Sons, 2023. | Includes bibliographical references and index.

Identifiers: LCCN 2022054499 (print) | LCCN 2022054500 (ebook) | ISBN 9781119275640 (hardback) | ISBN 9781119275664 (pdf) | ISBN 9781119275572 (epub) | ISBN 9781119275671 (ebook)

Subjects: LCSH: 5G mobile communication systems.

Classification: LCC TK5103.25 .A115 2023 (print) | LCC TK5103.25 (ebook) | DDC 621.3845/6–dc23/eng/20230111

LC record available at https://lccn.loc.gov/2022054499

LC ebook record available at https://lccn.loc.gov/2022054500

Cover Design: Wiley

Cover Image: © metamorworks/Shutterstock

Set in 9.5/12.5pt STIXTwoText by Integra Software Services Pvt. Ltd, Pondicherry, India

Contents

Cover

Title page

Copyright

Acknowledgments

About the Editors

List of Contributors

1 Introduction

1.1 Introducing 5G in Transport

1.2 Targets of the Book

1.3 Backhaul and Fronthaul Scope within the 5G System

1.4 Arranging Connectivity within the 5G System

1.5 Standardization Environment

1.5.1 3GPP and other organizations

References

2 5G System Design Targets and Main Technologies

2.1 5G System Target

2.2 5G Technology Components

2.3 Network Architecture

2.4 Spectrum and Coverage

2.5 Beamforming

2.6 Capacity

2.6.1 Capacity per Cell

2.6.2 Capacity per Square Kilometre

2.7 Latency and Architecture

2.8 Protocol Optimization

2.8.1 Connectionless RRC

2.8.2 Contention-Based Access

2.8.3 Pipelining

2.9 Network Slicing and QoS

2.10 Integrated Access and Backhaul

2.11 Ultra Reliable and Low Latency

2.12 Open RAN

2.13 3GPP Evolution in Release 16/17

2.14 5G-Advanced

References

3 5G RAN Architecture and Connectivity – A Techno-economic Review

3.1 Introduction

3.2 Multi-RAT Backhaul

3.3 C-RAN and LTE Fronthaul

3.4 5G RAN Architecture

3.5 5G D-RAN Backhaul Architecture and Dimensioning

3.6 Integrating 5G within a Multi-RAT Backhaul Network

3.7 Use Case – BT/EE 5G Network in the UK

3.8 5G C-RAN – F1 Interface and Midhaul

3.9 5G C-RAN – CPRI, eCPRI and Fronthaul

3.10 Connectivity Solutions for Fronthaul

3.11 Small Cells in FR1 and FR2

3.12 Summary

References

4 Key 5G Transport Requirements

4.1 Transport Capacity

4.1.1 5G Radio Impacts to Transport

4.1.2 Backhaul and Midhaul Dimensioning Strategies

4.1.3 Protocol Overheads

4.1.4 Backhaul and Midhaul Capacity

4.1.5 Fronthaul Capacity

4.1.6 Ethernet Link Speeds

4.2 Transport Delay

4.2.1 Contributors to Delay in 5G System

4.2.2 Allowable Transport Delay

4.2.3 User Plane and Control Plane Latency for the Logical Interfaces

4.2.4 Fronthaul (Low-Layer Split Point)

4.2.5 Low-Latency Use Cases

4.3 Transport Bit Errors and Packet Loss

4.3.1 Radio-Layer Performance and Retransmissions

4.3.2 Transport Bit Errors and Packet Loss

4.4 Availability and Reliability

4.4.1 Definitions

4.4.2 Availability Targets

4.4.3 Availability in Backhaul Networks

4.4.4 Recovery Times in Backhaul and Fronthaul

4.4.5 Transport Reliability

4.4.6 Air Interface Retransmissions and Transport Reliability

4.4.7 Packet Duplication in 5G and Transport

4.4.8 Transport Analysis Summary for Availability and Reliability

4.5 Security

4.5.1 Summary of 5G Cryptographic Protection

4.5.2 Network Domain Protection

4.5.3 Security in Fronthaul

4.6 Analysis for 5G Synchronization Requirement

4.6.1 Frequency Error

4.6.2 Time Alignment Error (Due to TDD Timing)

4.6.3 Time Alignment Error (Due to MIMO)

4.6.4 Time Alignment Error (Due to Carrier Aggregation)

4.6.5 Time Alignment Accuracy (Due to Other Advanced Features)

References

5 Further 5G Network Topics

5.1 Transport Network Slicing

5.1.1 5G System-Level Operation

5.1.2 Transport Layers

5.2 Integrated Access and Backhaul

5.2.1 Introduction

5.2.2 IAB Architecture

5.2.3 Deployment Scenarios and Use Cases

5.2.4 IAB Protocol Stacks

5.2.5 IAB User Plane

5.2.6 IAB Signalling Procedures

5.2.7 Backhaul Adaptation Protocol

5.2.8 BH Link Failure Handling

5.2.9 IAB in 3GPP Release 17 and Beyond

5.3 NTN

5.3.1 NTN in 3GPP

5.3.2 Different Access Types

5.3.3 Protocol Stacks

5.3.4 Transparent Architecture

5.3.5 Feeder Link Switchover

5.4 URLLC Services and Transport

5.4.1 Background

5.4.2 Reliability

5.4.3 Latency

5.5 Industry Solutions and Private 5G

5.5.1 Introduction to Private 5G Networking

5.5.2 3GPP Features Supporting Private 5G Use Cases

5.5.3 URLLC and TSC in Private 5G

5.6 Smart Cities

5.6.1 Needs of Cities

5.6.2 Possible Solutions

5.6.3 New Business Models

5.6.4 Implications for BH/FH

References

6 Fibre Backhaul and Fronthaul

6.1 5G Backhaul/Fronthaul Transport Network Requirements

6.1.1 Capacity Challenge

6.1.2 Latency Challenge

6.1.3 Synchronization Challenge

6.1.4 Availability Challenge

6.1.5 Software-Controlled Networking for Slicing Challenge

6.1.6 Programmability and OAM Challenges

6.2 Transport Network Fibre Infrastructure

6.2.1 Availability of Fibre Connectivity

6.2.2 Dedicated vs Shared Fibre Infrastructure

6.2.3 Dedicated Infrastructure

6.2.4 Shared Infrastructure

6.3 New Builds vs Legacy Infrastructure

6.4 Optical Transport Characteristics

6.4.1 Optical Fibre Attenuation

6.4.2 Optical Fibre Dispersion

6.5 TSN Transport Network for the Low-Layer Fronthaul

6.6 TDM-PONs

6.6.1 TDM-PONs as Switched Transport Network for Backhaul and Midhaul

6.6.2 TDM-PONs as Switched Transport Network for Fronthaul

6.7 Wavelength Division Multiplexing Connectivity

6.7.1 Passive WDM Architecture

6.7.2 Active–Active WDM Architecture

6.7.3 Semi-Active WDM Architecture

6.8 Total Cost of Ownership for Fronthaul Transport Networking

References

7 Wireless Backhaul and Fronthaul

7.1 Baseline

7.2 Outlook

7.3 Use Cases Densification and Network Upgrade

7.4 Architecture Evolution – Fronthaul/Midhaul/Backhaul

7.5 Market Trends and Drivers

7.5.1 Data Capacity Increase

7.5.2 Full Outdoor

7.5.3 New Services and Slicing

7.5.4 End-to-End Automation

7.6 Tools for Capacity Boost

7.6.1 mmW Technology (Below 100 GHz)

7.6.2 Carrier Aggregation

7.6.3 New Spectrum Above 100 GHz

7.7 Radio Links Conclusions

7.8 Free-Space Optics

7.8.1 Introduction

7.8.2 Power Budget Calculations

7.8.3 Geometric Loss

7.8.4 Atmospheric Attenuation

7.8.5 Estimating Practical Link Spans

7.8.6 Prospects of FSO

References

8 Networking Services and Technologies

8.1 Cloud Technologies

8.1.1 Data Centre and Cloud Infrastructure

8.1.2 Data Centre Networking

8.1.3 Network Function Virtualization

8.1.4 Virtual Machines and Containers

8.1.5 Accelerators for RAN Functions

8.1.6 O-RAN View on Virtualization and Cloud Infrastructure

8.2 Arranging Connectivity

8.2.1 IP and MPLS for Connectivity Services

8.2.2 Traffic Engineering with MPLS-TE

8.2.3 E-VPN

8.2.4 Segment Routing

8.2.5 IP and Optical

8.2.6 IPv4 and IPv6

8.2.7 Routing Protocols

8.2.8 Loop-Free Alternates

8.2.9 Carrier Ethernet Services

8.2.10 Ethernet Link Aggregation

8.3 Securing the Network

8.3.1 IPsec and IKEv2

8.3.2 Link-Layer Security (MACSEC)

8.3.3 DTLS

8.4 Time-Sensitive Networking and Deterministic Networks

8.4.1 Motivation for TSN

8.4.2 IEEE 802.1CM – TSN for Fronthaul

8.4.3 Frame Pre-emption

8.4.4 Frame Replication and Elimination

8.4.5 Management

8.4.6 Deterministic Networks

8.5 Programmable Network and Operability

8.5.1 Software-Defined Networking Initially

8.5.2 Benefits with Central Controller

8.5.3 Netconf/YANG

References

9 Network Deployment

9.1 NSA and SA Deployments

9.1.1 Shared Transport

9.1.2 NSA 3x Mode

9.1.3 SA Mode

9.2 Cloud RAN Deployments

9.2.1 Motivation for Cloud RAN

9.2.2 Pooling and Scalability in CU

9.2.3 High Availability in CU

9.2.4 Evolving to Real-Time Cloud – vDU

9.2.5 Enterprise/Private Wireless

9.3 Fronthaul Deployment

9.3.1 Site Solutions and Fronthaul

9.3.2 Carrying CPRI over Packet Fronthaul

9.3.3 Statistical Multiplexing Gain

9.3.4 Merged Backhaul and Fronthaul

9.4 Indoor Deployment

9.5 Deploying URLLC and Enterprise Networks

9.5.1 Private 5G Examples

9.5.2 Private 5G RAN Architecture Evolution

9.5.3 IP Backhaul and Midhaul Options for Private 5G

9.5.4 Fronthaul for Private 5G

9.5.5 Other Transport Aspects in Private 5G Networks

9.6 Delivering Synchronization

9.6.1 Network Timing Synchronization Using PTP and SyncE

9.6.2 SyncE

9.6.3 IEEE 1588 (aka PTP)

9.6.4 ITU-T Profiles for Telecom Industry Using SyncE and PTP

9.6.5 Example of Putting All Standards Together in Planning

9.6.6 Resilience Considerations in Network Timing Synchronization

9.6.7 QoS Considerations in Network Timing Synchronization

9.6.8 Special Considerations in Cloud RAN Deployment

9.6.9 Satellite-Based Synchronization

9.6.10 Conclusion for Synchronization

References

10 Conclusions and Path for the Future

10.1 5G Path for the Future

10.2 Summary of Content

10.3 Evolutionary Views for Backhaul and Fronthaul

Index

End User License Agreement

List of Tables

CHAPTER 02

Table 2.1 5G numerology in...

Table 2.2 Traffic density assumptions.

Table 2.3 Round-trip time components.

CHAPTER 03

Table 3.1 Example of backhaul...

CHAPTER 04

Table 4.1 Example RTT target values (ms).

Table 4.2 Bit error and packet...

Table 4.3 Input assumptions and...

Table 4.4 Input assumptions for...

Table 4.5 5G system frequency error...

Table 4.6 Summary of constraint...

Table 4.7 Maximum theoretical distance...

Table 4.8 5G system TAE...

Table 4.9 5G system TAE...

CHAPTER 05

Table 5.1 SST

Table 5.2 Different platforms [10].

CHAPTER 06

Table 6.1 Ethernet OAM.

CHAPTER 08

Table 8.1 Recovery with routing...

CHAPTER 09

Table 9.1 Typical backhaul options.

List of Illustrations

CHAPTER 01

Figure 1.1 Network domain within...

CHAPTER 02

Figure 2.1 5G targets.

Figure 2.2 Summary of 5G technology...

Figure 2.3 Key 5G technology components...

Figure 2.4 Overall 5G network architecture...

Figure 2.5 5G architecture with key...

Figure 2.6 5G architecture options supported...

Figure 2.7 Different options for user...

Figure 2.8 5G radio protocol stack...

Figure 2.9 5G protocol stack for...

Figure 2.10 5G protocol stack for...

Figure 2.11 5G eCPRI different L1...

Figure 2.12 5G eCPRI protocol stack...

Figure 2.13 Typical 5G spectrum usage...

Figure 2.14 Coverage difference compared to...

Figure 2.15 Mid-band (3.5...

Figure 2.16 Beamforming enhances radio capacity...

Figure 2.17 Massive MIMO principles with...

Figure 2.18 Common channel beamforming in...

Figure 2.19 5G vs 4G capacity...

Figure 2.20 Maximum traffic density per...

Figure 2.21 Round-trip time evolution...

Figure 2.22 Example speedtest measurements in...

Figure 2.23 Network architecture with local...

Figure 2.24 Connectionless 5G solution with...

Figure 2.25 Contention-based access...

Figure 2.26 5G pipelining receiver solution.

Figure 2.27 Network slicing concept...

Figure 2.28 From LTE quality of...

Figure 2.29 From bearer-based QoS...

Figure 2.30 QoS architecture in 5G...

Figure 2.31 IAB operation principle...

Figure 2.32 IAB architecture.

Figure 2.33 TSN operation over 5G...

Figure 2.34 Different fronthaul/midhaul deployment...

Figure 2.35 RIC in O-RAN...

Figure 2.36 3GPP standards schedule...

Figure 2.37 3GPP Release 16 key content.

Figure 2.38 3GPP Release 17 key...

Figure 2.39 Main contents of 5G...

CHAPTER 03

Figure 3.1 Pre-5G mobile backhaul...

Figure 3.2 Backhaul and LTE...

Figure 3.3 5G RAN functional decomposition...

Figure 3.4 5G RAN functional decomposition...

Figure 3.5 5G D-RAN mobile...

Figure 3.6 BT/EE multi-RAT...

Figure 3.7 RAN protocol architecture and...

Figure 3.8 eCPRI and CPRI reference...

Figure 3.9 gNB architectures – options...

CHAPTER 04

Figure 4.1 Multi-user MIMO and...

Figure 4.2 Transport 5G dimensioning...

Figure 4.3 NG and F1 bit...

Figure 4.4 Fronthaul capacity for FR1...

Figure 4.5 Capacity estimate for FR1...

Figure 4.6 Delay requirements impact on...

Figure 4.7 Real-time operations over...

Figure 4.8 Deployment with local UPF...

Figure 4.9 Retransmissions.

Figure 4.10 Availability of optical...

Figure 4.11 Transport reliability example...

Figure 4.12 PDCP duplication with...

Figure 4.13 Reliability block diagram including...

Figure 4.14 Redundant N3 tunnels with...

Figure 4.15 TDD interference aspects...

Figure 4.16 Hex model for cell...

Figure 4.17 BS2BS-DL2UL interference...

Figure 4.18 BS2BS-UL2DL interference.

Figure 4.19 UE2UE-DL2UL interference...

CHAPTER 05

Figure 5.1 S-NSSAI...

Figure 5.2 Session setup signalling...

Figure 5.3 Transport network slicing...

Figure 5.4 IAB architecture and...

Figure 5.5 IAB topologies supported in...

Figure 5.6 IAB deployments: SA (NR...)

Figure 5.7 User plane protocol stacks...

Figure 5.8 Control-plane protocol stacks...

Figure 5.9 Control-plane protocol stacks...

Figure 5.10 IAB-node integration...

Figure 5.11 Different paths can...

Figure 5.12 NTN architecture alternatives [9...

Figure 5.13 Transparent satellite user plane...

Figure 5.14 gNB-DU placed on...

Figure 5.15 gNB placed on the...

Figure 5.16 gNB in transparent architecture...

Figure 5.17 Seamless feeder link switchover...

Figure 5.18 Disjoint paths...

Figure 5.19 Local UPF and server.

Figure 5.20 Standalone non-public network...

Figure 5.21 Public network integrated non...

Figure 5.22 UE registered to standalone...

Figure 5.23 RAN sharing between public...

Figure 5.24 Private 5G as a...

Figure 5.25 Example of city network...

Figure 5.26 Smart pole alternatives...

Figure 5.27 Shared city network.

Figure 5.28 Example of actors in...

Figure 5.29 Infrastructure sharing...

CHAPTER 06

Figure 6.1 Transport network requirements...

Figure 6.2 Data centre latency requirements...

Figure 6.3 Connectivity options...

Figure 6.4 Transport network for FTTH.

Figure 6.5 Wavelength-dependent attenuation...

Figure 6.6 Dispersion characteristics of...

Figure 6.7 Passive WDM.

Figure 6.8 Active–active packetized fronthaul...

Figure 6.9 Active optical packetized WDM...

Figure 6.10 Semi-active WDM...

CHAPTER 07

Figure 7.1 Macro-cell backhaul transport...

Figure 7.2 Spectrum used in wireless...

Figure 7.3 Radio link characteristics by...

Figure 7.4 5G mobile BH transport...

Figure 7.5 Mobile fronthaul (CPRI/eCPRI...

Figure 7.6 E-band spectrum fees...

Figure 7.7 Transport solutions vs geographical...

Figure 7.8 Wireless backhaul installation example...

Figure 7.9 Use cases vs frequency...

Figure 7.10 Wireless transport architecture scenarios...

Figure 7.11 5G requirements and wireless...

Figure 7.12 E/V band radio...

Figure 7.13 Microwave transmission radio TRx...

Figure 7.14 URLLC requirements (3GPP)...

Figure 7.15 Use cases for E-band deployment.

Figure 7.16 E-band success story...

Figure 7.17 Carrier aggregation in radio...

Figure 7.18 Microwave CA deployment example...

Figure 7.19 Carrier aggregation link extension...

Figure 7.20 Carrier aggregation evolution...

Figure 7.21 Microwave deployment connecting...

Figure 7.22 Spectrum evolution...

Figure 7.23 D-band use cases.

Figure 7.24 D-band technology...

Figure 7.25 FSO link beam spreading.

Figure 7.26 The geometric and total...

Figure 7.27 The cumulative time when...

Figure 7.28 Estimated unavailability of two...

CHAPTER 08

Figure 8.1 Data centre and network...

Figure 8.2 Simplified representation of a...

Figure 8.3 Data centre as a...

Figure 8.4 ETSI NFV model...

Figure 8.5 Virtualization options.

Figure 8.6 Networking solution for virtual...

Figure 8.7 Tenant networks with virtual...

Figure 8.8 Networking in Kubernetes...

Figure 8.9 Lookaside and inline accelerators...

Figure 8.10 O-RAN cloud architecture...

Figure 8.11 O-RAN AAL overview...

Figure 8.12 IP MPLS VPN...

Figure 8.13 MPLS TE architecture example.

Figure 8.14 E-VPN with multihoming...

Figure 8.15 Segment routing principle...

Figure 8.16 Connectivity with IP and...

Figure 8.17 Loop-free alternate example...

Figure 8.18 Ethernet services...

Figure 8.19 MACSEC and IPsec.

Figure 8.20 DTLS-based protocol stacks...

Figure 8.21 Profile A with strict...

Figure 8.22 Frame pre-emption...

Figure 8.23 MAC merge sublayer...

Figure 8.24 FRER application...

Figure 8.25 Distributed model example...

Figure 8.26 Distributed user/centralized network...

Figure 8.27 Fully centralized model example...

Figure 8.28 Cross-domain operation...

CHAPTER 09

Figure 9.1 Shared backhaul...

Figure 9.2 Use of 5G/LTE split bearer.

Figure 9.3 3x mode with CSG...

Figure 9.4 3x control plane architecture...

Figure 9.5 SA mode (disaggregated architecture...

Figure 9.6 Legacy RAN vs centralized...

Figure 9.7 Key protocol layers and...

Figure 9.8 Capacity scaling with or...

Figure 9.9 Failure directions and enablers...

Figure 9.10 Redundancy models and downtime...

Figure 9.11 Geo-redundant CU...

Figure 9.12 Distributed and centralized...

Figure 9.13 Basic server-level pooling...

Figure 9.14 Very basic inter-vDU...

Figure 9.15 Inter-server pooling (within...

Figure 9.16 Fronthaul link redundancy...

Figure 9.17 Example of enterprise RAN

Figure 9.18 Site example...

Figure 9.19 Carrying CPRI over...

Figure 9.20 Statistical multiplexing gain...

Figure 9.21 Traffic flows.

Figure 9.22 Merged network...

Figure 9.23 Technical solutions for...

Figure 9.24 Indoor solution covering multiple...

Figure 9.25 Micro RRH deployment in...

Figure 9.26 All-in-one small...

Figure 9.27

Small/medium campus

...

Figure 9.28

Small/medium campus

...

Figure 9.29

Small/medium campus

...

Figure 9.30

Small/medium campus

...

Figure 9.31

Large enterprise network

...

Figure 9.32 Timing distribution concept...

Figure 9.33 Simplified model.

Guide

Cover

Title page

Copyright

Table of Contents

Acknowledgements

About the Editors

List of Contributors

Begin Reading

Index

End User License Agreement

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Acknowledgments

The editors would first like to acknowledge all of the contributing authors, individually and also as a team: our thanks go to Mika Aalto, Pascal Dom, Akash Dutta, Kenneth Y. Ho, Harri Holma, Lieven Levrau, Raija Lilius, Esa Malkamäki, Antti Pietiläinen, Paolo di Prisco, Derrick Remedios, Andy Sutton and Antti Toskala.

For specific review efforts and large and small suggestions and contributions, we would like to thank our colleagues at Nokia, including Hannu Flinck, Markus Isomäki, Qinglong Qiu, Litao Ru, Olli Salmela, Peter Skov and Jeroen Wigard for specific input, in addition to a number of experts who have contributed during the preparation and review of the material. We are also grateful to the community of radio and networking professionals in the industry, with whom we have had the pleasure of discussing the topics covered in this book.

We thank the excellent team at John Wiley & Sons for very good co-operation and support during the time of writing.

We appreciate the patience and support of our families and our authors’ families during the writing period and are grateful for this.

We welcome comments and suggestions for improvements or changes that could be implemented in forthcoming editions of this book. Feedback is welcome to the editors’ email addresses: [email protected] and [email protected].

Esa Metsälä and Juha Salmelin

Espoo, Finland

About the Editors

Esa Metsälä leads the 5G Radio Access System Specification Team for networking at Nokia. He has extensive experience in leading mobile backhaul and mobile network system-level topics and teams since 2G.

Juha Salmelin manages Smart City initiatives for Nokia Networks. He has over 20 years’ experience in mobile backhaul research as a team leader, department manager and technology head at Nokia.

List of Contributors

Mika AaltoNokia Cloud and Network ServicesEspoo, Finland

Pascal DomNokia Network InfrastructureAntwerp, Belgium

Akash DuttaNokia NetworksBengaluru, India

Kenneth Y. HoNokia Networks (Retired)New Jersey, USA

Harri HolmaNokia Strategy& TechnologyEspoo, Finland

Lieven LevrauNokia Network InfrastructureValbonne, France

Raija LiliusNokia NetworksEspoo, Finland

Esa MalkamäkiNokia Strategy& TechnologyEspoo, Finland

Esa MetsäläNokia NetworksEspoo, Finland

Antti PietiläinenNokia NetworksEspoo, Finland

Paolo di PriscoNokia NetworksMilan, Italy

Derrick RemediosNokia Networks InfrastructureOttawa, Canada

Juha SalmelinNokia NetworksEspoo, Finland

Andy SuttonBritish TelecomWarrington, UK

Antti ToskalaNokia Strategy& TechnologyEspoo, Finland

1 Introduction

Esa Metsälä and Juha Salmelin

1.1 Introducing 5G in Transport

Mobile networks evolve, with new system generations bringing higher speeds and new service capabilities, with improved system architectures and novel radio technologies. With this evolution, 5G mobile backhaul and fronthaul play an increasing role, with new challenges in matching the new 5G system capabilities.

With 5G, higher peak rates are surely an important enhancement, as was the case with 4G. This is just a single item, however. 5G is the most versatile mobile system so far, supporting not only traditional mobile broadband but also new industrial and enterprise use cases with building blocks like network slicing for unique services.

URLLC services extend the 5G capability to applications which were previously not possible in a mobile system. The 5G network is built to serve different use cases and customers, and these impact transport also.

New high-frequency bands mean not only high capacity, but also a potentially huge amount of small cells. Further, radio signals from outdoor sites are heavily attenuated indoors. So, indoor solutions will be required for coverage with related connectivity solutions.

Disaggregation of the 5G radio access and related radio clouds opens up a new type of network implementation, where existing server and computing platforms can be leveraged to support virtualized or containerized network functions. At the same time, opening of the interfaces between network elements allows multi-vendor deployment and operation. With 5G radio energy efficiency is improved and network level optimizations allow further energy savings.

Packet-based fronthaul is a genuine new area, which evolved from previous industry proprietary solutions to use common packet networking technologies, which in turn better allow shared packet infrastructure in fronthaul also, but with special emphasis on the time sensitivity of fronthaul traffic flows and synchronization.

This all shows the range of new tasks there are for 5G mobile backhaul and fronthaul, since there is no longer a single use case or single implementation approach for radio networks.

As transport is all about connecting mobile network elements in an efficient way, there will be many different needs based on the radio cloud and the level of disaggregation targeted, and based on services intended to be delivered over the system, and these all have to be supported on the very same backhaul and fronthaul network.

For example, essential topics like transport latency and capacity requirements all depend on the use cases as well as the type of disaggregation and virtualization deployed.

The focus areas of 5G backhaul and fronthaul are:

Fronthaul, which in 5G is a new packet-based latency critical interface that – with eCPRI and O-RAN – has evolved from previous CPRI-based interfaces.

Radio cloud, which has connectivity needs within and through the data centre to other sites, with related virtualization or containerization of network functions, and needs for scaling and flexible connectivity.

Accurate synchronization support, due to the 5G TDD radio.

Matching the increased 5G system performance targets in transport, with reduced latency and higher reliability and availability.

Making the backhaul and fronthaul secure and robust against both intended and unintended anomalies with cryptographic protection.

Introducing new 5G services through backhaul and fronthaul with ultra reliability and low latency and supporting new use cases – like industrial and enterprises – over backhaul and fronthaul.

Future proofness and adaptability for different deployments and support for the cloud-native 5G network.

The trend for more openness in network management, in object modelling and in related interfaces, driven by O-RAN and other forums.

Making the network programmable to speed up service creation and enable managing a network that encompasses huge amounts of RUs as well as new millimetre-wave small cells.

Close cooperation with LTE for dual connectivity, NSA mode, reuse of sites and transport network, with continued support for legacy protocols and technologies.

Transport links are to be upgraded for 5G. Physical media are fibre complemented, with new high-bandwidth wireless links that offer 10G and more capacity.

Network connectivity services focus on resiliency, flexibility, security and future proofness for network expansion and new services. All network resources have to be protected against unauthorized use and communications in the network domain have to be secure.

Synchronization is of high importance since the TDD mode of the 5G system requires phase and time synchronization. Many cases rely on the transport network to deliver synchronization.

In transport networks, major planning cycles occur once in a while – around every 10 years – and at these moments, physical network topologies and physical media usage are also modified. Connectivity layer upgrade is a slightly smaller task once the physical media is in place, since network equipment on existing sites can be changed more easily and with less effort than laying new fibre, even though equipment changes involve not only capex costs but also (more importantly) related training and competence development costs for the new technologies.

For mobile backhaul and fronthaul, the introduction of the 5G system is a trigger for an upgrade cycle – at minimum, capacity additions in links and nodes, and possibly including enhancements and modernization of the network in a wider scope which can include in addition to new networking functionality also retiring links and nodes that are poorly performing in terms of bit errors, packet loss, latency, energy efficiency or security.

1.2 Targets of the Book

While there are multiple challenges identified above for 5G backhaul and fronthaul, there are also new technologies and improvements that address such challenges.

This book aims to cover the key requirements for 5G mobile backhaul and fronthaul and also open up some of the inner workings of the 5G system, especially the 5G radio access network, in order to find the transport services that are most feasible.

Once the drivers for the networking layers are covered, the book concentrates on different technologies that address the needs 5G brings. Some specific use cases and configurations are discussed, with the intent of summarizing the technical aspects covered.

Chapter 2 introduces the 5G system and Chapter 3 follows on in analysing key technical and economic considerations of 5G backhaul and fronthaul, from an operator viewpoint. Next, Chapter 4 discusses the requirements for 5G backhaul and fronthaul performance and other drivers.

Chapter 5 focuses on essential new 5G items related to transport, like network slicing, IAB (Integrated Access and Backhaul), NTNs (Non-Terrestrial Networks) and private networks for industry solutions and shared networks for smart cities.

Chapter 6 covers physical layer technologies in the optical domain. The optical domain covers a wide range of technologies, from passive to active WDM and also PONs (Passive Optical Networks). Fibre is the medium that provides ample capacity for 5G backhaul and fronthaul.

Optical, while often the preferred choice, needs to be complemented with wireless links – especially in access. Going from traditional microwave bands to E- and D-bands gives capacities of 10G, 25G and more, which means that wireless continues to remain a feasible option for many sites and can bridge the gap in those areas where fibre deployment is not economical. This is the topic of Chapter 7. In rare cases, optical wireless links can also be considered. These FSOs (Free Space Optics) are presented at the end of the chapter.

Chapter 8 continues with key cloud and networking technologies. Cloud nativeness, when applied to 5G radio, is not a trivial topic itself and for networking it introduces new concepts and requirements. New technologies – like segment routing – can help for a light version of traffic engineering, while fronthaul requires time-sensitive networking solutions.

In Chapter 9, example deployment cases are presented, covering – in addition to traditional macro deployment for 5G – also cloud, fronthaul, industrial, indoor and synchronization cases. The book concludes with a summary in Chapter 10.

1.3 Backhaul and Fronthaul Scope within the 5G System

In 5G service delivery, transport on the backhaul and fronthaul is an integral and important part of the 5G system infrastructure.

The 5G mobile network elements in both the 5G core and 5G radio include IP endpoints for communication with peer(s); then they interface the backhaul or fronthaul networks, which operate as their own networking domain, with physical layer facilities like fibre cabling and networking devices that are separate from the mobile network elements, with their own network management.

Figure 1.1 shows the gNB communicating with a peer element, which could be another 5G RAN element or a 5G core network element. Networking devices and physical transport media provide the required connectivity, which in many cases is useful to abstract as a connectivity service.

Figure 1.1 Network domain within the 5G system.

The IP endpoints of gNB, related processing and IP interfaces are somewhat in a grey area between radio and the network domain: they are part of the radio domain in the sense that they form part of the base station. They are also part of the network domain since the protocols processed are networking protocols not radio protocols.

Often, the 5G radio elements (including IP endpoints) are administered by the radio team and the external networking devices by the transport team. In the network domain, devices may further be operated by dedicated teams based on competence (e.g. the optical layer is managed by one competence pool, wireless transmission by another and the IP layer by yet another expert team).

In this book, ‘transport’ is used interchangeably with ‘networking’ to cover protocols from the transport physical layer and media up to the IP layer but touching also protocols on top of the IP layer, like UDP and SCTP. The 5G layer protocols include, for example, GTP-U and application protocols like NG-AP and all 5G RAN internal radio protocols like PDCP, RLC, MAC and radio L1.

Backhaul refers to the RAN–core network interface (NG2, NG3), midhaul to the RAN internal F1 interface (which is the high-level fronthaul split point defined by 3GPP) and fronthaul to the RAN internal low-level split point (which is defined by O-RAN).

1.4 Arranging Connectivity within the 5G System

The connectivity service is supplied in-house by a transport team or a third-party connectivity service is used. Often, a combination of the two – some network tiers or geographical areas are served by own transport assets, while others rely on external service providers.

Service Level Agreements (SLAs) describe essential characteristics of the service at the User-to-Network Interface (UNI). MEF (Metro Ethernet Forum) is an organization focusing on standardized service definitions that are useful for 5G backhaul and fronthaul.

The connectivity service concept includes CE (Customer Equipment) and PE (Provider Edge) – CE meaning equipment on the customer side and PE the peer element on the service provider side. This terminology is used, for example, with IP VPNs.

When the service is abstracted, the user of the service is agnostic to how the actual network is implemented and what is the current operating state of the underlying individual network links and nodes. This simplifies many topics for the user as there is no need to worry about the details in implementation.

The implementation aspects sometimes become visible, e.g. when the underlying network path changes, causing change in the experienced latency, or when there are network anomalies like bit errors. As long as these are within the SLA of the service, the user should not be concerned. What is of importance is the possibility to monitor that the actual obtained service level matches the agreed SLA which the user is paying for.

With packet-level service, there are many possible service-impacting topics to be considered. Ultimately, a complete fibre can be leased, in which case the user has a hard guarantee and can decide to use full bandwidth without interference from other traffic sources, but this is not feasible for all cases and fibre bandwidth can be shared by wavelengths or by packet (IP) nodes.

On the implementation side for backhaul and fronthaul, wireless devices, photonic devices and switches, routers and security gateways are seldom all sourced from the same vendor. Multi-vendor interoperation is addressed by devices complying with relevant standards and interoperability testing is needed to guarantee correct operation. Simplification of the solution can lead to significant benefits but is not trivial to achieve. Open interfaces and the approach towards a programmable network are key for network integration, efficient operation and intended performance.

Acquiring sites and rights of way for fibre instalments is costly and time-consuming, and one possibility is that transport – especially physical resources like fibre but possibly also higher-layer operations – is shared in such a way that one entity owns and operates the network. This entity can be a neutral host, meaning a third-party ‘independent entity’ offers services to multiple tenants.

All these aspects impact 5G backhaul and fronthaul, which is in practice multi-technology and multi-vendor, with multiple feasible operating models.

1.5 Standardization Environment

The standardization environment is heterogenous regarding 5G backhaul and fronthaul. Since only key protocol definitions are referred to in 3GPP, there are a wide range of networking-related standard defining organizations and industry forums that define technical areas and individual topics related to 5G backhaul and fronthaul. Some of these are briefly introduced here.

1.5.1 3GPP and other organizations

In 5G as in previous mobile generations, transport is standardized in 3GPP for the logical interface protocol stacks [1–9]. 3GPP reuses and refers to existing, primarily IETF standards, where networking protocols are defined. The layers below IP in 3GPP are referred to as the Data Link Layer and the Physical Layer, so are not defined in the 3GPP protocol stacks. In practice, Ethernet is typically used for L2/L1 over fibre or wireless media.

The borderline between 3GPP and networking standards is UDP/IP in the user plane and SCTP/IP in the control plane. 3GPP defines the user-plane GTP-U tunnelling protocol below which the UDP/IP layer is defined in IETF RFCs. GTP-U tunnelling is defined in Ref. [10]. In the control plane, 5G application protocols such as NG-AP are defined in 3GPP while the lower layer, SCTP, is defined in IETF.

5G system architecture includes network elements like gNB and then logical interfaces between the elements, defining which element needs to have connectivity to which other elements. For the actual backhaul and fronthaul network implementation, 3GPP is agnostic.

Connectivity may be arranged with any technology that enables communication between the IP endpoints of the 5G elements (e.g. between gNB and the UPF). The design of the communication service and its characteristics are left for network implementation.

Security is covered for the network domain and 3GPP mandates the use of cryptographic protection in the network domain, with IP security suite of protocols in 3GPP TS 33.210 [11]. Implementations differ also with IPsec e.g. whether the IPsec endpoints reside on the mobile elements themselves or in a separate security gateway [SEG]. Additionally, DTLS is included in the control plane logical interface definitions of 5G for 38.412 NG Signalling Transport, 38.422 Xn Signalling Transport and 38.472 F1 Signalling Transport [4, 6, 8].

Assigning 5G functions into the network elements, delivery of 5G services at the intended user experience and operation of the 5G radio protocols impose requirements for many backhaul and fronthaul aspects, such as maximum delay or availability of the connectivity service. These requirements are, however, also dependent on the network implementation and mobile network operator’s targets, and so a single, generic value cannot be found.

The synchronization method is likewise an implementation topic – how is accurate timing supplied? The accuracy requirement itself originates from the 5G air interface and 5G features. ITU-T and IEEE have defined profiles for synchronization using the IEEE 1588 protocol, and O-RAN also covers the topic.

Fronthaul, or the low-layer split point, is not defined by 3GPP in detail but by O-RAN, so it is a special case compared to the 3GPP logical interface definitions.

IETF: Internet Engineering Task Force

As 3GPP reuses existing networking standards, the role of IETF is important as the protocols for the IP layer – including IP security – originate from there. All logical interfaces rely on IPv6 or IPv4 and IPsec protocols, with commonly Ethernet L2/L1 beneath the IP protocol layer. The IP protocols are defined by IETF RFCs as well as UDP, SCTP, DTLS and IPsec [12–21].

IETF definitions for services like IP and Ethernet VPNs (RFC 4364 BGP/MPLS IP Virtual Private Networks [VPNs] IP VPN and RFC 7432 BGP/MPLS IP Virtual Private Networks [VPNs] Ethernet VPN) are examples of implementation options for the transport network [22, 23]. With work progressing in IETF for new services and capabilities, they will become available also for implementation in mobile backhaul and fronthaul. Some examples of work in progress in IETF relate to segment routing and deterministic networks [24, 25]. IETF is also source for many Yang data models.

With IP networking, the basic IP networking protocols are relevant, like the companion protocols ARP (RFC 862) and ICMP (RFC 792, RFC 4443) [26–28], for example, routing protocols, monitoring and OAM capabilities, and many other definitions.

IEEE: Institute of Electrical and Electronics Engineers

IEEE is the home for Ethernet standards which are in use in both backhaul and fronthaul as de-facto physical interfaces and additionally in other applications.

IEEE 802.3 works on Ethernet physical layer specifications. For 5G fronthaul and backhaul, application data rates of 10G and more are of most interest, like 25G, 50G and 100G.

10G is standardized as IEEE 802.3ae, including both short-range multimode (-SR) and long-range singlemode (-LR) fibre media. For 25G, 25GBASE-SR is standardized as 802.3by and 25GBASE-LR as 802.3cc. These are included in the 2018 update of 802.3 [29].

The single-lane rate for 50 Gbps is in IEEE 802.3cd [30], using PAM-4 modulation. The standard for single-lane 100 Gbps is ongoing by IEEE 802.3ck [31].

Ethernet bridging is specified in 802.1D-2004. This standard has been amended (e.g. with 802.1Q [VLANs], 802.1ad [Provider Bridges], 802.1ah [Provider Backbone Bridges] and 802.1ag [Connectivity Fault Management]). These and other amendments are included in the 2018 update of IEEE 802.1Q [32].

With the Ethernet, cryptographic protection has been added with 802.1X (802.1X-2010 Port-based Network Access Control), 802.1AE (802.1AE-2006 MAC Security) and 802.1AR (Secure Device Identity) [33–35].

An active working area related to 5G fronthaul is Time-Sensitive Networking (TSN). Multiple TSN amendments to the base standard (802.1Q) – also touching 802.3 – have already been included or are in progress. A separate profile for 5G fronthaul is defined in IEEE 802.1CM [36]. Another fronthaul-related standard is for carrying CPRI over Ethernet, in IEEE P1914.3 [37].

The precision timing protocol (IEEE 1588v2) [38] is used for delivering synchronization for the base stations, including phase and time synchronization for 5G.

O-RAN: Open RAN Alliance

O-RAN [39] defines a fronthaul standard that is derived from the eCPRI, with related protocol stacks and functionality.

The O-RAN fronthaul interface is defined in Ref. [40]. O-RAN also has other standards with networking impacts, related to cloud and disaggregated RAN and definitions for RIC. Another important area is data/object models that are defined using Yang, enabling openness in network management.

ITU-T: International Telecommunications Union

ITU-T [41] covers a wide range of transmission-, system- and synchronization-related standards. Many relevant items include optical and photonics standards and profile definitions of timing distribution using the precision timing protocol (IEEE 1588).

ISO: International Organization for Standardization

ISO, in the networking area, is known for the OSI (Open System Interconnection) model and is the origin of the IS-IS routing protocol definition [42]. IS-IS is included in the IEEE work for TSN, which makes the protocol potentially relevant in the 5G fronthaul area.

MEF: MetroEthernet Forum

MEF is the source for service definitions for Ethernet services, with dedicated definitions for backhaul and fronthaul [43]. Service definitions have been expanded to cover IP services also.

Related to the Ethernet rates and transceivers, multiple industry forums are relevant. The Ethernet Technology Consortium [44] and the Optical Internetworking Forum (OIF) [45] have been active in driving new Ethernet MAC rates. Many of these initiatives have since resulted in an IEEE standard.

The SFF (Small Form Factor) committee is similarly an industry forum (now Storage Networking Industry Association [SNIA] Technology Affiliate Technical Working Group) [46] for optical pluggables.

NGMN Alliance (Next Generation Mobile Networks Alliance) is an open forum created by network operators to help the industry with clear operator requirements and guidance for better mobile networks [47]. Many topics cover or impact also 5G backhaul and fronthaul.

ETSI (European Telecommunications Standards Institute) [48] has worked among many other topics (e.g. for network function virtualization definitions and a virtualization framework covering also management and orchestration).

An industry foundation, CNCF (Cloud Native Computing Foundation) [49], covers topics of cloud native computing, container management and orchestration.

The CPRI forum [50] is an industry cooperation that has defined interfaces between the RE (Radio Equipment) and REC (Radio Equipment Control), including CPRI and eCPRI. Recently, new work on fronthaul has been in progress within O-RAN.

References

1

3GPP TS 36.414 S1 Data Transport.

2

3GPP TS 36.422 X2 Signalling Transport.

3

3GPP TS 36.424 X2 Data Transport.

4

3GPP TS 38.412 NG Signalling Transport.

5

3GPP TS 38.414 NG Data Transport.

6

3GPP TS 38.422 Xn Signalling Transport.

7

3GPP TS 38.424 Xn Data Transport.

8

3GPP TS 38.472 F1 Signalling Transport.

9

3GPP TS 38.474 F1 Data Transport.

10

3GPP TS 29.281 General Packet Radio System (GPRS) Tunnelling Protocol User Plane (GTPv1-U).

11

3GPP TS 33.210 Network Domain Security (NDS); IP network layer security.

12

IETF RFC 768 User Datagram Protocol.

13

IETF RFC 8200 Internet Protocol, Version 6 (IPv6) Specification.

14

IETF RFC 791 Internet Protocol.

15

IETF RFC 2474 Definition of the Differentiated Services Field (DS Field) in the Ipv4 and Ipv6 Headers.

16

IETF RFC 4303 IP Encapsulating Security Payload (ESP).

17

IETF RFC 4301 Security Architecture for the Internet Protocol.

18

IETF RFC 6311 Protocol Support for High Availability of IKEv2/IPsec.

19

IETF RFC 7296 Internet Key Exchange Protocol Version 2 (IKEv2).

20

IETF RFC 4960 Stream Control Transmission Protocol.

21

IETF RFC 6083 Datagram Transport Layer Security (DTLS) for Stream Control Transmission Protocol (SCTP).

22

IETF RFC 4364 BGP/MPLS IP Virtual Private Networks (VPNs) IP VPN.

23

IETF RFC 7432 BGP/MPLS IP Virtual Private Networks (VPNs) Ethernet VPN.

24

https://datatracker.ietf.org/wg/spring/documents

.

25

https://datatracker.ietf.org/wg/detnet/about

.

26

IETF RFC 862 An Ethernet Address Resolution Protocol.

27

IETF RFC 792 Internet Control Message Protocol.

28

IETF RFC 4443 Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification.

29

IEEE 802.3-2018 IEEE Standard for Ethernet.

30

IEEE802.3cd Media Access Control Parameters for 50 Gb/s and Physical Layers and Management Parameters for 50 Gb/s, 100 Gb/s, and 200 Gb/s Operation.

31

IEEE802.3ck Media Access Control Parameters for 50 Gb/s and Physical Layers and Management Parameters for 50 Gb/s, 100 Gb/s, and 200 Gb/s Operation.

32

IEEE 802.1Q - 2018 Bridges and Bridged Networks.

33

IEEE 802.1X-2010 Port-based Network Access Control.

34

IEEE 802.1AE MAC Security.

35

IEEE 802.1AR Secure Device Identity.

36

IEEE802.1CM Time-Sensitive Networking for Fronthaul.

37

IEEE P1914.3. Standard for Radio Over Ethernet Encapsulations and Mappings.

38

IEEE 1588-2019 Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control System.

39

www.o-ran.org

.

40

O-RAN.WG4.CUS.0-v07.00, Control, User and Synchronization Plane Specification.

41

www.itu.int/en/ITU-T/Pages/default.aspx

.

42

www.iso.org/home.html

.

43

www.mef.net

.

44

ethernettechnologyconsortium.org

.

45

www.oiforum.com

.

46

www.snia.org

.

47

https://www.ngmn.org

.

48

www.etsi.org

.

49

www.cncf.io

.

50

http://www.cpri.info

.

2 5G System Design Targets and Main Technologies

Harri Holma and Antti Toskala

2.1 5G System Target

5G radio represents a major step in mobile network capabilities. So far, mobile networks have mainly provided connectivity for smartphones, tablets and laptops. 5G will take traditional mobile broadband to the extreme in terms of data rates, capacity and availability. Additionally, 5G will enable further capabilities including massive Internet of Things (IoT) connectivity and critical communication. 5G targets are illustrated in Figure 2.1. 5G is not only about new radio or new architecture or core, but also about the number of new use cases. It is expected that 5G will fundamentally impact the whole of society in terms of improving efficiency, productivity and safety. 4G networks were designed and developed mainly by telecom operators and vendors for the smartphone use case. There is a lot more interest in 5G networks by other parties, including different industries and cities, to understand 5G capabilities and push 5G availability. 5G is about connecting everything in the future.

Figure 2.1 5G targets.

5G radio can bring major benefits in terms of network performance and efficiency, see summary in Figure 2.2. We expect substantially higher data rates – up to 20 Gbps, clearly lower cost per bit, higher spectral efficiency, higher network energy efficiency and lower latency. The values are based on the following assumptions:

Figure 2.2 Summary of 5G technology capabilities.

The shortest transmission time in the 5G layer is <0.1 ms, which enables a round-trip time of 1 ms.

Energy efficiency assumes a three-sector 100 MHz macro base station busy hour average throughput of 1 Gbps, busy hour share of 7% and base station average power consumption of 2 kW. The efficiency improvement of 10× compared to LTE is obtained with power saving techniques at low load and wideband carrier up to 100 MHz in the 3.5 GHz band.

A peak rate of 1.5 Gbps assumes 100 GHz bandwidth TDD with 4×4MIMO and 256QAM modulation and a peak rate of 5 Gbps assumes 800 MHz bandwidth TDD with 2×2MIMO.

Spectral efficiency of 10 bps/Hz/cell assumes the use of massive MIMO (Multiple Input Multiple Output) beamforming and four antenna devices. The typical LTE downlink efficiency is 1.5–2.0 bps/Hz/cell in the live networks and +50% more with 4×4MIMO.

2.2 5G Technology Components

The high targets of 5G networks require a number of new technologies. The main new technology components are shown in Figure 2.3.

Figure 2.3 Key 5G technology components.

New spectrum. The very high data rates (up to 5–10 Gbps) require bandwidth up to 800 MHz, which is available at higher frequency bands. 5G is the first radio technology designed to operate on any frequency bands between 450 MHz and 90 GHz. The low bands are needed for good coverage and the high bands for high data rates and capacity. The frequencies above 30 GHz have wavelength <1 cm and are commonly called millimetre waves (mmWs). Sometimes also lower frequencies (24–28 GHz) are included in the mmW notation. LTE specifications are not defined beyond 6 GHz.

Massive MIMO with beamforming increases spectral efficiency and network coverage substantially. Beamforming becomes more practical at higher frequencies because the antenna size is relative to the wavelength. In practice, massive MIMO can be utilized at frequencies above 2 GHz in the base stations and at mmWs even in the devices. Massive MIMO will be part of 5G from day 1, which will avoid any legacy device problems. User-specific beamforming was not supported in the first LTE release but added only later in 3GPP.

Flexible air interface design and network slicing. Physical and protocol layers in 5G need a flexible design in order to support different use cases, vertical segments, different frequency bands and to maximize the energy and spectral efficiency. Network slicing will create virtual networks for the different use cases within the same 5G network.

Dual connectivity. 5G can be deployed as a standalone system but more typically 5G will be deployed together with LTE. The 5G device can have simultaneous connection to 5G and LTE. Dual connectivity can increase the user data rate and improve the connection reliability.

Distributed architecture with cloud flexibility. The typical architecture in LTE networks is fully distributed in the radio and fully centralized in the core network. Low latency requires bringing the content close to the radio network, which leads to local breakout and Multi-access Edge Computing (MEC). Scalability requires bringing cloud benefits to radio networks with an edge cloud and local cloud architecture.

3GPP completed the first version of 5G specifications in December 2017, with specification freeze and stability of specifications for the NSA (Non-Standalone Architecture) reached by end 2018. We list the main decisions below:

Waveform. The downlink solution is an OFDM (Orthogonal Frequency Division Multiplexing)-based waveform with Cyclic Prefix (CP), which is similar to the LTE waveform. The uplink waveform is also an OFDM with single carrier (SC-FDMA/DFT-S-OFDM) option for coverage extension. The uplink solution is different from that in LTE, where only a single carrier is used in the uplink. Having similar downlink and uplink solutions in 5G simplifies beamforming with reciprocal channel, interference avoidance, device-to-device communication (side-link) and in-band backhauling. There is a 1–2 dB coverage penalty in OFDM compared to single carrier, and therefore a single-carrier option is needed also in the 5G uplink.

Channel coding. Data channels use Low Density Parity Check (LDPC) coding and control channels use Polar coding or Reed–Muller coding depending on the number of bits. Both coding solutions are different than in LTE where data channels use Turbo coding and control channels use convolutional and Reed–Muller coding. The main reason for using LDPC is the decoding complexity: clearly less silicon area is required for the decoding process with LDPC compared to Turbo decoding. LDPC is used also in the latest IEEE Wi-Fi specifications but there are some differences between 3GPP and IEEE usage of LPDC. Control channel coding solution was less critical due to the small data rate of the control channel.

The 3GPP numerology is shown in

Table 2.1

. 5G is designed to support a number of subcarrier spacing and scheduling intervals, depending on the bandwidth and latency requirements. Subcarrier spacings between 15 kHz and 120 kHz are defined in Release 15 for data channels and 240 kHz for Synchronization Signal (SS). The narrow subcarrier spacings are used with narrow 5G bandwidths and are better for extreme coverage. If we consider a typical 5G deployment in the 3.5 GHz band, the bandwidth could be 40–100 MHz and the subcarrier spacing 30 kHz. The corresponding numbers in LTE are 20 MHz bandwidth and 15 kHz subcarrier spacing. 5G subcarrier spacing is designed to be 2^N multiples of 15 kHz. If the slot length is >0.125 ms in the narrowband cases and low latency is required, then a so-called mini-slot can be used where the transmission time is shorter than one slot. It is also possible to combine multiple slots together.

Table 2.1  5G numerology in 3GPP Release 15.

Subcarrier spacing [kHz]

15

30

60

120

240

**

Symbol duration [μs]

66.7

33.3

16.6

8.33

4.17

Nominal CP [μs]

4.7

2.41

1.205

0.60

0.30

Nominal max carrier BW [MHz]

50

100

200

400

—

Max FFT size

4096

4096

4096

4096

—

Min scheduling interval (symbols)

14

14

14

14

—

Min scheduling interval (slots)

*

1

1

1

1

—

Min scheduling interval (ms)

1.0

0.5

0.25

0.125

—

*2/4/7 symbol mini-slot for low-latency scheduling.

**SS block only.

2.3 Network Architecture

The overall 5G system architecture has been reworked in line with the following key principles:

Stateless core network entities

Separate control and data handling

Support for both data-centric and service-based architecture

Support for centralized data storage

Support of local and centralized service provision

Minimized access and core network dependencies

The overall architecture is shown in Figure 2.4, illustrating the separate control and user plane elements as well as separate data storage in the network.

Figure 2.4 Overall 5G network architecture.

The control plane has the following main elements:

Access and Mobility Management Function (AMF), covering mobility management functionality on the core network side as well as being the termination for the RAN control plane interface to the core (NG2 in

Figure 2.5

). Also, authentication and authorization are taken care of by the AMF and, respectively, the NAS terminates in the AMF.

Figure 2.5 5G architecture with key reference points.

Session Management Function (SMF), covering roaming functionality, UE IP address allocation and management, as well as selection and control of the user plane function. The SMF is also the termination point towards policy control and charging functions.

Policy Control Function (PCF), providing policy rules for the control plane functions. The PCF gets subscriber information from the data storage functions.

Local and centralized gateways – the User Plane Functions (UPFs) – which are the connection anchor points in connection with mobility. The UPFs cover packet routing and forwarding and take care of the QoS handling for user data. Possible packet inspection and policy rule enforcements are also covered by the UPFs.

The main reference points in the 5G architecture are shown in Figure 2.5, with Unified Data Management (UDM) taking care of the authentication credential storage and processing. Other subscription information is also stored in UDM.

The following main reference points can be identified, with a full list available in 3GPP TR 23.799.

NG1:

Reference point between the UE and AMF, reflecting basically the NAS signalling between UE and AMF.

NG2:

Reference point between the (R)AN and AMF, corresponding to the signalling from the 5G RAN (in some cases could also be from the LTE RAN) to the AMF.

NG3:

Reference point between the (R)AN and UPF, over which user plane data is carried between the RAN and core. This has similarity to the S1-U interface with LTE, as covered earlier in this chapter.

NG4:

Reference point between the SMF and UPF.

NG5:

Reference point between the PCF and an Application Function (AF).

NG6:

Reference point between the UPF and a Data Network (DN). As shown in

Figure 2.5