5G Radio Access Network Architecture E-Book

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

Seitenzahl: 830

Veröffentlichungsjahr: 2020

Beschreibung

Discover how the NG-RAN architecture is, and isn't, ready for the challenges introduced by 5G 5G Radio Access Network Architecture: The Dark Side of 5G explores foundational and advanced topics in Radio Access Network (RAN) architecture and why a re-thinking of that architecture is necessary to support new 5G requirements. The distinguished engineer and editor Sasha Sirotkin has included numerous works written by industry insiders with state of the art research at their disposal. The book explains the relevant standards and technologies from an academic perspective, but also explains why particular standards decisions were made and how a variety of NG-RAN architecture options could be deployed in real-life networks. All major standards and technologies associated with the NG-RAN architecture are discussed in this book, including 3GPP, O-RAN, Small Cell Forum, IEEE, and IETF. Readers will learn about how a re-design of the RAN architecture would ensure that 5G networks can deliver their promised throughput and low latency KPIs consistently and sustainably. The book is structured as follows: * An overview of the market drivers of the NG-RAN architecture, like spectrum models, 5G-relevant regulatory considerations, and 5G radio interface technical requirements * An overview of the 5G System, from the core network, to the RAN, to the radio interface protocols and physical layer, with emphasis on how these are different compared to 4G * Release-15 RAN architectures defined in 3GPP, O-RAN, and Small Cell Forum * RAN architecture evolution in Release-16 and Release-17 * Enabling technologies, like virtualization, open source technologies, multi-access edge (MEC) computing, and operations, administration, and management (OAM) * NG-RAN deployment considerations, objectives, and challenges, like costs, spectrum and radio propagation considerations, and coverage Perfect for network designers and operators who require a solid understanding of the NG-RAN architecture, 5G Radio Access Network Architecture also belongs on the bookshelves of network engineers who aim to increase their understanding of the standards and technologies relevant to the NG-RAN architecture.

Leseprobe

Table of Contents

Cover

Title Page

Copyright

Dedication

Preface

Acknowledgments

List of Contributors

Contributors

Acronyms and Abbreviations

1 Introduction

2 Market Drivers

2.1 Introduction

2.2 Key Ideas

2.3 Spectrum

2.4 New Spectrum Models

2.5 Regulations Facilitating 5G Applications

2.6 Network Deployment Models

2.7 Technical Requirements of 5G Radio Interfaces

2.8 Business Drivers

2.9 Role of Standards

2.10 Role of Open Source

2.11 Competition

2.12 Challenges

2.13 Summary

References

Notes

3 5G System Overview

3.1 Introduction

3.2 5G Core Network

References

3.3 NG Radio Access Network

References

3.4 NR Protocol Stack

References

3.5 NR Physical Layer

References

Notes

4 NG‐RAN Architecture

4.1 Introduction

References

4.2 High‐Level gNB‐CU/DU Split

References

4.3 Multi‐Radio Dual Connectivity

References

4.4 Control–User Plane Separation

References

4.5 Lower‐Layer Split

References

4.6 Small Cells

References

4.7 Summary

Notes

5 NG‐RAN Evolution

5.1 Introduction

5.2 Wireless Relaying in 5G

References

5.3 Non‐terrestrial Networks

References

Notes

6 Enabling Technologies

6.1 Introduction

6.2 Virtualization

References

6.3 Open Source

References

6.4 Multi‐Access Edge Computing

References

6.5 Operations, Administration, and Management

References

6.6 Transport Network

References

Notes

7 NG‐RAN Deployment Considerations

7.1 Introduction

7.2 Key Ideas

7.3 Deployment Objectives and Challenges

7.4 Deployment Considerations

7.5 Conclusions

References

Notes

Index

End User License Agreement

List of Tables

Chapter 2

Table 2.1 IMT‐2020 spectrum needs based on TPRs.

Table 2.2 LSA vs. CBRS.

Table 2.3 Summary of IMT‐2020 requirements.

Chapter 3

Table 3.4.1 Downlink channel mapping.

Table 3.5.1 Scalable numerology supported by NR.

Table 3.5.2 Supported bandwidth sizes in Release‐15 NR for different subcarri...

Table 3.5.3 Supported PRACH preambles.

Table 3.5.4 DCI formats supported in NR (Release‐15).

Table 3.5.5 Supported PUCCH formats in 5G NR.

Chapter 4

Table 4.1.1 Common Public Radio Interface (CPRI) Radio Equipment Control (REC...

Table 4.5.1 Front haul transport downlink bandwidth comparison.

Table 4.2.1 Uplink transmit and receive window.

Table 4.6.1 Pros and cons of disaggregation points.

Table 4.6.1 Typical cell dimensioning.

Chapter 5

Table 5.3.1 Typical performances of NTN for considered usage scenarios.

Table 5.3.2 NR impacts to support the NTN reference scenarios.

Table 5.3.3 Objectives of non‐terrestrial network (NTN) channel modeling.

Chapter 6

Table 6.4.1 MEC hosts divided into proximity zones according to a certain cri...

Table 6.5.1 Operations and notifications for the provisioning MnSs for the NS...

Table 6.5.2 IOCs for the RAN components.

Table 6.5.3 IOCs for the DU components.

Table 6.5.4 Endpoints IOCs.

Table 6.5.5 Example RRM policy configuration.

Table 6.5.6 Legacy SON functionality.

Table 6.6.1 Head‐of‐line blocking time versus line rate.

Chapter 7

Table 7.1 Typical bandwidths and coverage ranges for different 5G frequency r...

Table 7.2 Fronthaul bandwidth for low‐, mid‐, and high‐band scenarios.

Table 7.3 Latency requirements for various split options.

List of Illustrations

Chapter 1

Figure 1.1 Radio Access Network (RAN).

Chapter 2

Figure 2.1 Cisco VNI IP traffic forecast (Source: SISCO VNI Global IP traffi...

Figure 2.2 Ericsson Mobility Report, global mobile data traffic (EB per mont...

Figure 2.3 United States Frequency Allocations Chart 2016.

Figure 2.4 Comparison of traffic estimates in 2005 with actual data.

Figure 2.5 IMT‐Advanced spectrum estimation, 2013.

Figure 2.6 Spectrum sharing.

Figure 2.7 RAN sharing.

Figure 2.8 Neutral host network deployment.

Figure 2.9 IMT‐2020 usage scenarios.

Figure 2.10 IMT‐2020 requirements.

Figure 2.11 5G is likely to require massive small cell deployments.

Figure 2.12 3GPP meeting attendance.

Figure 2.13 Number of CRs per year.

Figure 2.14 Tux the penguin, mascot of Linux open source operating system.

Chapter 3

Figure 3.2.1 EPS non‐roaming architecture.

Figure 3.2.2 5GS non‐roaming architecture.

Figure 3.2.3 Separation of user plane and control plane in EPS.

Figure 3.2.4 5GC user‐plane configuration with concurrent access to a local ...

Figure 3.2.5 N3IWF hides specifics of non‐3GPP access networks (e.g. WLAN) f...

Figure 3.2.6 W‐AGF hides specifics of wireline access networks from 5GC.

Figure 3.2.7

Uplink classifier

(

ULCL

) functionality in a UPF is used to dive...

Figure 3.2.8 A multi‐homed IPv6 PDU session provides access to both a local ...

Figure 3.2.9 SSC mode 3 – PDU Sessions to the previous and new local data ne...

Figure 3.2.10 Release‐13 DECOR enables redirection to a target MME in the ri...

Figure 3.2.11 Release‐14 eDECOR reduces the need for redirections by enablin...

Figure 3.2.12 Release‐15 enables UEs to concurrently access multiple network...

Figure 3.2.13

Stand‐alone non‐public network

(

SNPN

).

Figure 3.2.14

Closed Access Group

(

CAG

), an enabler for public‐network‐integ...

Figure 3.3.1 Overall 5G System Architecture.

Figure 3.3.2 Control‐plane protocol stack.

Figure 3.3.3 NG‐U protocol stack.

Figure 3.3.4 IDLE to CONNECTED state transition.

Figure 3.3.5 NG handover.

Figure 3.3.6 NG user‐plane protocol stack.

Figure 3.3.7 Xn handover.

Figure 3.3.8 UE‐triggered transition from inactive to connected state.

Figure 3.3.9 RAN sharing.

Figure 3.3.10 Example of network slicing.

Figure 3.4.1 NG‐RAN architecture.

Figure 3.4.2 User‐plane protocol stack.

Figure 3.4.3 Downlink Layer 2 Structure Protocol.

Figure 3.4.4 Downlink (left) and uplink (right) SDAP Data PDU format with SD...

Figure 3.4.5 RLC AMD PDU with 12 bit Sequence Number with Segment Offset....

Figure 3.4.6 Example of a downlink MAC PDU structure.

Figure 3.4.7 QoS flow mapping in the CN, RAN, and UE.

Figure 3.4.8 An example signaling for a UE configuration of the DRB mapping ...

Figure 3.4.9 RRC states and state transitions.

Figure 3.4.10 An example message flow for initial NAS registration.

Figure 3.4.11 Successful RRC connection reestablishment.

Figure 3.4.12 RRC connection reestablishment with fallback.

Figure 3.4.13 UE AS capability enquiry, network storage, and retrieval.

Figure 3.4.14 Example message flow for state transition from INACTIVE to CON...

Figure 3.5.1 Frame structure supported by NR.

Figure 3.5.2 PRB alignment for different numerologies.

Figure 3.5.3 Examples of slot configurations.

Figure 3.5.4 SSB position indication in frequency domain.

Figure 3.5.5 NR SS/PBCH block structure.

Figure 3.5.6 General structure of the RACH preamble.

Figure 3.5.7 Association of SS/PBCH blocks with PRACH.

Figure 3.5.8 CORESET transmission within a slot.

Figure 3.5.9 Short and long PUCCH structures.

Figure 3.5.10 PUCCH resource sets.

Figure 3.5.11 Modulation sequence for reference signal.

Figure 3.5.12 Basic units for CSI‐RS.

Figure 3.5.13 CSI‐RS for time‐frequency tracking.

Figure 3.5.14 DM‐RS Type I and Type II.

Figure 3.5.15 PT‐RS within PRB for CP‐OFDM.

Figure 3.5.16 Beam measurement and reporting.

Figure 3.5.17 Beam indication for the physical channel.

Figure 3.5.18 Code rate and transport block size scenario for LDPC base grap...

Figure 3.5.19 Illustration of the parity check matrix for LDPC codes.

Figure 3.5.20 Polar coding control information in NR.

Figure 3.5.21 Polar coding chain supported in NR.

Figure 3.5.22 Deployment option for 5G NR.

Figure 3.5.23 Frequency allocation for supplemental uplink.

Chapter 4

Figure 4.1.1 Monolithic gNB architecture.

Figure 4.1.2 gNB architecture with CPRI REC and RE split.

Figure 4.1.3 CPRI protocol stack.

Figure 4.1.4 CPRI chain topology.

Figure 4.1.5 CPRI tree topology.

Figure 4.1.6 CPRI ring topology.

Figure 4.1.7 eCPRI architecture.

Figure 4.1.8 gNB architecture with antenna.

Figure 4.1.9 gNB spit architectures considered in 3GPP study.

Figure 4.1.10 gNB architecture with centralized unit and multiple distribute...

Figure 4.1.11 Generalized gNB functional split architecture with CU, DU, and...

Figure 4.2.1 Overall NG‐RAN architecture.

Figure 4.2.2 gNB‐CU/gNB‐DU protocol stack split.

Figure 4.2.3 F1‐C protocol stack.

Figure 4.2.4 F1 startup and cell activation.

Figure 4.2.5 Inter‐gNB‐DU mobility for intra‐NR.

Figure 4.2.6 RRC inactive to other RRC states transition procedure.

Figure 4.3.1 EN‐DC architecture.

Figure 4.3.2 NGEN‐DC (left) and NE‐DC (right) architectures.

Figure 4.3.3 NR‐DC inter‐gNB (left) and intra‐gNB (right) architectures.

Figure 4.3.4 Control‐plane connectivity for EN‐DC (left) and MR‐DC with 5GC ...

Figure 4.3.5 User‐plane connectivity for EN‐DC (left) and MR‐DC with 5GC (ri...

Figure 4.3.6 MN terminated bearers: MCG bearer (left), SCG bearer (center), ...

Figure 4.3.7 SN terminated bearers: SCG bearer (left), MCG bearer (center), ...

Figure 4.3.8 Radio protocol architecture at the network side for MCG, SCG, a...

Figure 4.3.9 Radio protocol architecture at the network side for MCG, SCG, a...

Figure 4.3.10 Radio protocol architecture for MCG, SCG, and split bearers fr...

Figure 4.3.11 Radio protocol architecture for MCG, SCG, and split bearers fr...

Figure 4.3.12 Secondary Node Addition procedure.

Figure 4.3.13 SN Modification procedure – SN‐initiated with MN involvement....

Figure 4.3.14 SN Modification – SN‐initiated without MN involvement.

Figure 4.3.15 SN Change – SN‐initiated.

Figure 4.4.1 Deployment scenarios for CU/UP separation.

Figure 4.4.2 : Overall architecture for separation of gNB‐CU‐CP and gNB‐CU‐U...

Figure 4.4.3 Interface protocol structure for E1.

Figure 4.4.4 Two options to admit a new UE in a gNB‐CU‐UP.

Figure 4.4.5 NG‐RAN procedure to support VM migration.

Figure 4.4.6 UE initial access procedure involving E1 and F1.

Figure 4.4.7 Mapping of gNB‐CU‐CP and gNB‐CU‐UP to the elements of SDN.

Figure 4.5.1 RAN architecture with CU, DU, and RU.

Figure 4.5.2 Downlink split description, NR, Category “A” Radio.

Figure 4.5.3 Downlink split description, NR, Category “B” Radio.

Figure 4.5.4 Uplink split block diagram.

Figure 4.5.5 Definition of reference points for delay management.

Figure 4.5.6 Control (left), user (center), and synchronization (right) mess...

Figure 4.5.7 O‐RAN transport protocol stack diagram.

Figure 4.5.8 eCPRI header table.

Figure 4.5.9 IEEE1914.3 header table.

Figure 4.5.10 Control plane section type 1 message format.

Figure 4.5.11 Data plane message format.

Figure 4.5.12 Fronthaul transmission procedure.

Figure 4.5.13 Fronthaul timing synchronization configurations.

Figure 4.5.14 Management plane architecture options.

Figure 4.5.15 Management plane protocol stack.

Figure 4.6.1 Small cell disaggregation architectures.

Figure 4.6.2 Small cell platform architectures.

Figure 4.6.3 FAPI architecture.

Figure 4.6.4 FAPI state machine.

Figure 4.6.5 FAPI downlink data procedure.

Figure 4.6.6 FAPI uplink data procedure.

Figure 4.6.7 nFAPI architecture.

Figure 4.6.8 nFAPI state machine.

Figure 4.6.9 Indoor enterprise scenario.

Figure 4.6.10 Outdoor urban scenario.

Figure 4.6.11 Private enterprise scenario.

Chapter 5

Figure 5.2.1 Sub‐6 GHz access can be deployed as HetNets while mmWave access...

Figure 5.2.2 Small‐cell deployment with and without IAB: without IAB, a sepa...

Figure 5.2.3 IAB topology.

Figure 5.2.4 Examples for layer 2 and layer 3 IAB architectures. 3GPP decide...

Figure 5.2.5 Various options to integrate IAB with EPC and/or 5GC.

Figure 5.2.6 Protocol stacks for UE‐access with two‐hop backhaul. Top: User‐...

Figure 5.2.7 1 : 1 and N : 1 mapping between UE bearers and backhaul RLC cha...

Figure 5.2.8 Motivation for scheduler weighting on backhaul links to provide...

Figure 5.2.9 BAP routing with address and path identifier.

Figure 5.2.10 Resource allocation across spanning tree: (a) resources config...

Figure 5.2.11 Time alignment of IAB node transmission and reception.

Figure 5.2.12 IAB node integration into network (a) IAB node MT operating in...

Figure 5.2.13 Procedures for establishment of redundant route underneath sam...

Figure 5.2.14 Notification of RLF to downstream IAB nodes.

Figure 5.3.1 Access network based on NTN platform with transparent payload....

Figure 5.3.2 Access network based on NTN platform with regenerative payload....

Figure 5.3.3 Satellite backhauling configuration.

Figure 5.3.4 Protocol stack for regenerative architecture, all of gNB functi...

Figure 5.3.5 Protocol stack for transparent architecture, all of gNB functio...

Figure 5.3.6 Protocol stack for split architecture, parts of gNB functionali...

Figure 5.3.7 Four‐step RACH versus two‐step RACH procedure.

Figure 5.3.8 Moving satellites with moving beams with earth fixed tracking a...

Figure 5.3.9 Transmission of HARQ RVs to the gNB via satellite backhauling o...

Figure 5.3.10 Combined satellite and terrestrial channel model methodology....

Chapter 6

Figure 6.2.1 Network evolution toward virtualized RAN.

Figure 6.2.2 Virtual machines versus containers.

Figure 6.2.3 Migrating to microservice‐based architectures.

Figure 6.2.4 Orchestration layer ().

Figure 6.2.5 ONAP framework ().

Figure 6.2.6 RAN virtualization platform.

Figure 6.2.7 Container‐based RAN platform.

Figure 6.2.8 DU container platform.

Figure 6.2.9 CU container platform (assumes CU‐CP and UP are co‐located).

Figure 6.2.10 O‐RAN cloudification and orchestration work ().

Figure 6.2.11 Accelerator models for containers.

Figure 6.2.12 Timing and synchronization ().

Figure 6.3.1 Ideal SDR receiver and transmitter.

Figure 6.3.2 OAI RAN architecture.

Figure 6.4.1 Standalone variant of the ETSI MEC reference architecture (...

Figure 6.4.2 MEC reference architecture: variant for MEC in NFV ().

Figure 6.4.3 UE location lookup procedure ().

Figure 6.4.4 UE location subscribe procedure ().

Figure 6.4.5 NG‐RAN architecture ().

Figure 6.4.6 Example of MEC mapping to the 5G system architecture.

Figure 6.4.7 3GPP‐based 5G system architecture and example of the mapping of...

Figure 6.4.8 A V2X communication setup involving two different mobile operat...

Figure 6.4.9 Graphical representation of the layered/hierarchical approach f...

Figure 6.4.10 A 5G system with MEC, where a MEC application attempts to cons...

Figure 6.4.11 Exemplary topology of a MEC system consisting of four MEC host...

Figure 6.4.12 Visualization of MEC host proximity zones (as seen by the MEC ...

Figure 6.4.13 Potential signaling protocol among functional entities of a ME...

Figure 6.4.14 Cooperative decision making for SOTA/FOTA updates with MEC.

Figure 6.5.1 3G and 4G network management model ().

Figure 6.5.2 Subscribe‐notify communication paradigm ().

Figure 6.5.3 The concept of exposure of network management services.

Figure 6.5.4 gNB (en‐gNB) NRM for all deployment scenarios ().

Figure 6.5.5 An example of deployment scenario for management of a mobile ne...

Figure 6.5.6 Slicing support in RAN: radio resources management policy.

Figure 6.5.7 Centralized SON solution ().

Figure 6.5.8 End‐to‐end SON.

Figure 6.5.9 Hybrid SON solution ().

Figure 6.6.1 Backhaul, midhaul, and fronthaul (xHaul) transport networks.

Figure 6.6.2 Evolution of the backhaul transport network.

Figure 6.6.3 Decomposition of the 5G base station and the resulting xHaul in...

Figure 6.6.4 Summary of mechanisms for upgrading the xHaul physical layer.

Figure 6.6.5 Transport network topologies.

Figure 6.6.6 RAN network segments and their interconnection to the 5GC.

Chapter 7

Figure 7.1 Possible NG‐RAN functional splits ().

Figure 7.2 Estimate number of CUs as a function of transport network round‐t...

Figure 7.3 Two‐level split NG‐RAN architecture suitable for sub‐6 GHz freque...

Figure 7.4 Single‐level split NG‐RAN architecture suitable for mmWave freque...

Guide

Cover Page

Title Page

Copyright

Dedication

Preface

Acknowledgments

List of Contributors

Acronyms and Abbreviations

Table of Contents

Begin Reading

Index

WILEY END USER LICENSE AGREEMENT

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5G Radio Access Network Architecture

The Dark Side of 5G

Edited by

Sasha Sirotkin

Copyright

This edition first published 2021

© 2021 John Wiley & Sons Ltd.

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Library of Congress Cataloging‐in‐Publication Data

Names: Sirotkin, Alexander, 1975- editor.

Title: 5G radio access network architecture : the dark side of 5G /

 Alexander Sirotkin, editor.

Description: Hoboken, NJ, USA : Wiley-IEEE Press, 2021. | Includes

 bibliographical references and index.

Identifiers: LCCN 2020020729 (print) | LCCN 2020020730 (ebook) | ISBN

 9781119550884 (hardback) | ISBN 9781119550891 (Adobe PDF) | ISBN

 9781119550914 (ePub)

Subjects: LCSH: 5G mobile communication systems. | Computer network

 architectures.

Classification: LCC TK5103.25 .A148 2021 (print) | LCC TK5103.25 (ebook)

 | DDC 621.39/81–dc23

LC record available at https://lccn.loc.gov/2020020729

LC ebook record available at https://lccn.loc.gov/2020020730

Cover Design: Wiley

Cover Image: © Paul Cooklin/Getty Images

To my parents, Natalia and Arkadiy, for, among the many things you've given me, the best gifts of all – aspiration for knowledge and critical thinking – which to a very large extent define who I am.

To my children, Jonathan, Maya, Ron, and Tom – given the pace of the world we live in, in a few years when you are old enough to read this book, 5G is likely to become a thing of the past. Don't get discouraged by this in your aspirations to undertake any project you may think of, but do remember – time flies, so use it wisely.

To my wife Tatyana, for the understanding that, despite not saying this as often as I should, I love you dearly, respect you deeply, and value everything that you do.

Preface

This is a different kind of book about 5G.

Most books on this subject (5G in particular, or wireless technologies in general) focus on the physical layer. While the physical layer (together with the access stratum protocol stack) is extremely important and is arguably the key aspect of any wireless technology responsible for most of its performance characteristics, curiously enough it is not necessarily the most important factor when determining how successful a certain wireless technology would be in the market.

The second largest category of books on wireless technologies typically focus on the core network, as it is often the core network features and design that determine the kind of services that a given technology would provide to operators and users. Without questioning the importance of the core network, we note that when it comes to the deployment of a new wireless technology by an operator, the core network is perhaps the most critical component as failures in the core may (and often do) affect the whole network and all the users. Nevertheless, in terms of deployment complexity and ultimately cost, the core network is in no way the biggest contributor to operator's efforts when deploying a network.

In terms of deployment and development complexity and cost, the biggest component of a network is actually the one that is often overlooked in literature – that is the Radio Access Network (RAN). The RAN is a collection of base stations, interconnected by a transport network, which also connects it to the core. That collection of base stations, if deployed and configured properly, is ultimately responsible for providing coverage and capacity to the network users. As the number of base stations deployed by an operator is huge (and is expected to grow substantially in 5G), the RAN is (together with spectrum acquisition) by far the biggest contributor to the cost of deploying and running a cellular network.

Unlike the other network components, design of the RAN is more art than science. That is because it is not feasible to analyze or simulate the RAN in its entirety and, therefore, there are very few objective measures of what constitutes a good RAN design. This inevitably leads to a multitude of different designs (or architectures) – some competing, some complementing each other. In this book we try to lead the reader through this maze of different RAN architectures, technical and business considerations that led to their design, and practical considerations affecting the choice of the proper architecture and deploying it successfully and in a cost‐efficient manner.

Welcome to the “dark side” of 5G – one of the most important 5G aspects, which is not in the spotlight as much as it should be.

This book is accompanied by the website: www.darksideof5g.com

Acknowledgments

This book is the result of the joint work of many contributors who used the vast domain expertise in their respective areas to make it possible. I would like to thank them all.

Furthermore, special thanks go to all the reviewers for helping to ensure correctness and consistency of the material presented in the book: Apostolos Papathanassiou, Intel Corporation; Jaemin Han, Intel Corporation; Krzysztof Kordybach, Nokia; and Markus Dominik Mueck, Intel Corporation.

List of Contributors

Alexander (Sasha) Sirotkin is a senior engineer with 20 years of experience in telecommunications, international standardization, intellectual property, machine learning, real‐time systems, and open source.

Currently his primary focus areas are 4G/LTE and 5G/NR Radio Access Network (RAN) Architecture, and licensed and unlicensed spectrum integration and co‐existence. In standards, Sasha contributed to 3GPP RAN2, RAN3, and RAN plenary, where he served as rapporteur for multiple specifications, as well as work and study items. Currently Sasha serves as the 3GPP RAN3 vice chairman and leads the Intel's RAN3 delegation.

In addition to 3GPP, Sasha has contributed to various other standards development organizations and industry fora, such as IEEE, O‐RAN, WFA, WBA, ETSI, and 5G Americas.

Prior to working in the field of wireless (802.11/Wi‐Fi and cellular) communications, Sasha was actively involved in the open source, primarily the Linux operating system. Having been an open source enthusiast since 1993, Sasha was one of the first to realize that the potential of Linux lies not so much in the desktop, but in embedded and real‐time systems, which he worked to promote long before the first version of Android was conceived.

Sasha received an MSc in machine learning and BSc degrees in computer science and physics from Tel‐Aviv University.

Sasha lives with his wife and children in Hod HaSharon, Israel. In his spare time, which his kids make sure he doesn't have too much of, he occasionally goes scuba diving and alpine skiing (usually not on the same day, even though that is sometimes technically possible in Israel), and practices Kyokushin Karate.

Contributors

Reza Arefi, Intel Corporation – Washington DC, USA

Nicolas Chuberre, Thales Alenia Space – Pibrac, France

Stefano Cioni, European Space Agency – Noordwijk, the Netherlands

Alexei Davydov, Intel Corporation – Nizhny Novgorod, Russia

Thibault Deleu, Thales Alenia Space – Toulouse, France

Miltiadis Filippou, Intel Deutschland GmbH – Neubiberg, Germany

Yuri Gittik, RAD Data Communications, Ltd. – Tel Aviv, Israel

Georg Hampel, Qualcomm Incorporated – Hoboken, NJ, USA

Colby Harper, Pivotal Commware Inc. – Seattle, WA, USA

Thomas Heyn, Fraunhofer IIS – Erlangen, Germany

Ron Insler, RAD Data Communications, Ltd. – Petah Tikva, Israel

Sudeep Palat, Intel Corporation – Cheltenham, UK

Sergio Parolari, ZTE Corporation – Milan, Italy

Sridhar Rajagopal, Mavenir – Dallas, TX, USA

Leszek Raschkowski, Fraunhofer HHI – Berlin, Germany

Dario Sabella, Intel Corporation – Munich, Germany

Eiko Seidel, Nomor Research GmbH – Munich, Germany

Clare Somerville, Intel Corporation – Maidenhead, UK

Sebastian Speicher, Qualcomm Wireless LLC – Zürich, Switzerland

Yaakov (J.) Stein, RAD Data Communications, Ltd. – Jerusalem, Israel

Jianli Sun, Intel Corporation – Hillsboro, OR, USA

Feng Yang, Intel Corporation – Beijing, People's Republic of China

Vladimir Yanover, Cisco Systems, Inc. – Kfar‐Saba, Israel

Andreas Neubacher, Deutsche Telekom – Korneuburg, Austria

Vishwanath Ramamurthi, Verizon Wireless – Walnut Creek, CA, USA

Acronyms and Abbreviations

3GPP

3rd Generation Partnership Project

5G ACIA

5G Alliance for Connected Industries and Automation

5G AKA

5G Authentication and Key Agreement

5G MOCN

5G Multi‐Operator Core Network

5G‐PPP

5G Infrastructure Public Private Partnership

5GAA

5G Automotive Association

5GC

5G Core

5GS

5G System

5QI

5G QoS Class Identifier

A/D

Analog to digital

AAS

Active Antenna System

ACK/NACK

acknowledgement/negative acknowledgement

ACM

Adaptive Coding and Modulation

ADSL

Asymmetric digital subscriber line

AECC

Automotive Edge Computing Consortium

AF

Application Function

AI

artificial intelligence

AISG

Antenna Interface Standards Group

AM

Acknowledged Mode

AMC

adaptive modulation and coding

AMF

Access and Mobility Management Function

AN

Access Network

AN

Access Node

ANDSP

Access Network Discovery and Selection Policy

ANR

Automatic Neighbor Relation

API

Application Programming Interface

APN

Access Point Name

APS

Automatic Protection Switching

AR

Augmented Reality

ARIB

Association of Radio Industries and Businesses

ARQ

Automatic Repeat Request

AS

Access stratum

ASF

Apache Software Foundation

ASG

aggregation site gateway

ASIC

application‐specific integrated circuit

ATIS

Alliance for Telecommunications Industry Solutions

ATM

asynchronous transfer mode

AUSF

Authentication Server Function

B2B2C

business to business to consumer

BAP

Backhaul Adaptation Protocol

BBF

Broadband Forum

BBU

Baseband Unit

BC

Boundary Clock

BE

Best Effort

BFD

Bidirectional Forwarding Detection

BFRP

Beam Failure Recovery Response

BFRQ

Beam Failure Recovery Request

BGP

Border Gateway Protocol

BiDi

bidirectional traffic on a single fiber

BIOS

basic input/output system

BLER

Block Error Rate

BNetzA

Bundesnetzagentur

BSD

Berkeley Software Distribution

BSR

Buffer Status Report

BSS

Broadcast Satellite Services

BWP

Bandwidth Part

C‐RNTI

Cell Radio Network Temporary Identifier

C‐SON

centralized SON

CA

Carrier Aggregation

CAC

Connection Admission Control

CAG

Closed Access Group

CAPEX

Capital Expenditure

CB

code block

CBG

Code block group

CBRS

Citizens Broadband Radio System

CC

continuity check

CCCH

Common Control Channel

CCE

Control Channel Element

CCSA

China Communications Standards Association

CDM

code division multiplexing

CDR

Charging Data Record

CEPT

European Conference of Postal and Telecommunications Administrations

CGI

Cell Global Identifier

CGS

computer‐generated Quadrature Phase Shift Keying (QPSK) sequence

CLI

Cross‐Link Interference

CM

Configuration Management

CN

Core Network

CNF

container network function

CNI

container network interface

CoMP

Coordinated Multi‐Point

CORESET

control resource set

COTS

Commercial Off‐The‐Shelf

CP

control plane

CP

Cyclic Prefix

CPA

Coverage Per area

CPP

Coverage Per Population

CPRI

Common Public Radio Interface

CPU

central processing units

CQI

channel quality indicator

CR

Change Request

cRAN

cloud RAN

CRC

Cyclic Redundancy Check

CRS

Cell‐Specific Reference Signal

CSG

cell site gateway

CSG

Closed Subscriber Group

CSI

Channel State Information

CSR

cell site router

CTC

Convolution Turbo Codes

CU

central unit

CU

Centralized Unit

CU/DU

central unit/distributed unit

CU/DU

centralized unit/distributed unit

CUPS

Control‐ and user‐plane separation

CUS

control, user, and synchronization

CV

connectivity verification

D‐SON

distributed SON

D/A

Digital to analog

D/C

Data or Control

DA

destination address

DAG

Directed Acyclic Graph

DAS

Distributed Antenna Systems

DC

Dual Connectivity

DCCH

Dedicated Control Channel

DCI

Downlink Control Information

DCI/UCI

downlink and uplink control information

DCN

Dedicated Core Network

DDDS

Downlink Data Delivery Status

DDoS

Distributed Denial‐of‐Service

DECOR

dedicated core network

DEI

discard eligibility indicator

dEPC

distributed EPC

DetNet

deterministic networking

DGM

distributed GM

DL/UL

downlink/uplink

DM

domain manager

DM‐RS

demodulation reference signals

DMRS

Demodulation Reference Symbols

DN

Data Network

DNCP

Dynamic Host Configuration Protocol

DNS

Domain Name System

DOCSIS

Data Over Cable Service Interface Specification

DoS

denial of service

DPDK

Data Plane Development Kit

DRB

Data Radio Bearers

DRX

Discontinuous Reception

DSCP

Differentiated Services Code Point

DSCP

DiffServ code point

DSL

digital subscriber line

DSP

digital signal processor

DTCH

Dedicated Traffic Channel

DU

Distributed Unit

DVFS

Dynamic Voltage and Frequency Scaling

DWDM

Dense Wavelength Division Multiplexing

E‐RAB

E‐UTRAN Radio Access Bearer

E‐UTRA

Evolved Universal Mobile Telecommunications System Terrestrial Radio Access

E‐UTRAN

Evolved Universal Terrestrial Radio Access Network

E2E

end‐to‐end

EAP

Extensible Authentication Protocol

EB

Exabytes

ECOMP

Enhanced Control, Orchestration, Management and Policy

EDR

Event Data Record

EIRP

Effective Isotropic Radiated Power

EM

Element Managers

eMBB

enhanced mobile broadband

EN‐DC

E‐UTRA‐NR Dual Connectivity

ENG

Electronic New Gathering

EPC

Evolved Packet Core

EPL

Ethernet private line

EPON

Ethernet passive optical network

ePRC

enhanced PRC

EPS

Evolved Packet System

eRE

eCPRI Radio Equipment

eREC

eCPRI Radio Equipment Control

ESMC

Ethernet Synchronization Messaging Channel

ETSI

European Telecommunications Standards Institute

EVM

error vector magnitude

EVPL

Ethernet Virtual Private Line Service

F1‐C

control‐plane part of the F1 interface

F1‐U

F1 User‐Plane

F1AP

F1 Application Protocol

FCS

frame check sequence

FDD

Frequency Division Duplexing

FEC

Forward Error Correction

FFT

Fast Fourier Transform

FHBW

fronthaul bandwidth

FIB

Forwarding Information Base

FM

Fault Management

FOMA

Freedom of Mobile Multimedia Access

FOSS

free and open source software

FPGA

field programmable gate array

FRER

Frame Replication and Elimination for Reliability

FRR

fast reroute

FSF

Free Software Foundation

FSPF

free space propagation formula

FSS

Fixed Satellite Services

GAA

General Authorized Access

GEO

geostationary orbit

GGSN

Gateway GPRS Support Node

gNB‐CU

gNB central unit

gNB‐CU‐UP

centralized user‐plane node

gNB‐DU

gNB distributed unit

GNSS

Global Navigation Satellite System

GoS

Grade of Service

GP

Guard Period

GPL

General Public License

GPL

GNU General Public License

GPON

gigabit passive optical network

GPP

general purpose compute

GPRS

General Packet Radio System

GPU

graphic processing unit

GSA

Global mobile Suppliers Association

GSMA

GSM Association

GTP

GPRS Tunneling Protocol

GTP‐U

GPRS Tunneling Protocol User Plane

GUAMI

Globally Unique AMF ID

HAPS

High Altitude Platforms

HARQ

Hybrid ARQ

HEO

high elliptical orbit

HetNet

heterogeneous network

HFN

Hyper Frame Number

HPLMN

Home Public Land Mobile Network

HSS

Home Subscriber Server

I/Q

In‐phase & Quadrature

IAB

Integrated Access‐Backhaul

IE

Information Element

IEEE

Institute of Electrical and Electronics Engineers

IET

interspersing express traffic

IETF

Internet Engineering Task Force

iFFT

inverse FFT

IIOT

Industrial Internet of Things

IMS

IP multimedia subsystem

IMT‐2020

International Mobile Telecommunications‐2020

IOC

Information Object Class

IoT

Internet of Things

IPR

intellectual property rights

ISG

Industry Specification Group

ITS

Intelligent Transport Systems

ITU

International Telecommunication Union

ITU‐R

ITU Radiocommunication Sector

ITU‐T

International Telecommunication Union Telecommunication Standardization Sector

IWF

Interworking Function

JSON

JavaScript Object Notation

K8S

Kubernetes

KPI

Key Performance Indicators

KQI

key quality indicator

L1‐RSRP

Layer 1 reference signal received power

L3VPN

Layer 3 VPN

LAA

licensed assisted access

LAG

link aggregation

LBT

Listen‐Before‐Talk

LCM

Life Cycle Management

LDPC

Low Density Parity Check

LEO

low ‐earth orbit

LFA

Loop Free Alternates

LLC

logical link control

LLS

Lower‐Layer Split

LMLC

Low Mobility Large Cell

LPI

Low Power Idle

LPWA

low‐power wide area

LSA

Licensed Shared Access

LSP

label switched path

LSR

label switch router

LTE

Long‐Term Evolution

LWA

LTE‐WLAN Aggregation

MAC

Medium Access Control

MANO

Management and Network Orchestration

MBB

Mobile Broadband

MCC

Mobile Country Code

MCG

Master Cell Group

MCL

maximum coupling loss

MCS

Modulation Coding Scheme

MCS/MPS

mission‐critical and priority services

MDT

Minimization of Drive Tests

MEAO

MEC application orchestrator

MEC

Mobile Edge Compute

MEC

Multi‐access edge computing

MEO

Mobile Edge Orchestrator

MEO

medium earth orbit

MEPM

Mobile Edge Platform Manager

MIB

Master Information Block

MIMO

Multiple‐Input and Multiple‐Output

MIT

Massachusetts Institute of Technology

ML

machine learning

MLB

mobility load balancing

MME

Mobility Management Element

MME

Mobility Management Entity

MN

Master Node

MNC

Mobile Network Code

MnF

management function

MNO

Mobile Network Operators

MnS

management service

MOI

Managed Object Instance

MPLS

multiprotocol label switching

MPLS‐TP

MPLS Transport Profile

MR‐DC

Multi‐Radio Dual Connectivity

MRO

Mobility Robustness Optimization

MSI

Minimum System Information

MSS

Mobile Satellite Services

MT

mobility termination

MTC

Machine Type Communication

MU‐MIMO

multi‐user MIMO

N3IWF

Non‐3GPP Interworking Function

NaaS

Network‐as‐a‐Service

NAS

non‐access stratum

NE

Network Elements

NE‐DC

NR‐E‐UTRA dual connectivity

NEF

Network Exposure Function

NF

network function

nFAPI

Network FAPI

NFMF

Network Function Management Function

NFV

Network Function Virtualization

NFV/SDN

Network Function Virtualization and Software Defined Networks

NFVI

network function virtualization infrastructure

NFVO

network function virtualization orchestrator

NG‐AP

NG Application Protocol

NG‐C

NG control plane

NG‐RAN

5G Radio Access Network

NG‐U

NG user plane

NGAP

NG Application Protocol

NGEN‐DC

E‐UTRA‐NR dual connectivity

NGFI

Next Generation Fronthaul Interface

NGMN

Next Generation Mobile Networks

NHN

Neutral Host Network

NHOP

next hop

NIC

Network Interface Card

NID

network ID

nLOS

non‐line‐of‐sight

NM

network manager

NMM

Network Monitor Mode

NMS

network management system

NNHOP

next next hop

NPN

Non‐public networks

NR

New Radio

NR‐DC

NR‐NR dual connectivity

NR‐U

NR user plane

NRF

Network Repository Function

NRM

Network Resource Model

NRPPa

NR Positioning Protocol A

NSA

Non‐Standalone

NSI

Network Slice Instance

NSMF

Network Slice Management Function

NSSAI

Network Slice Selection Assistance Information

NSSF

Network Slice Selection Function

NSSI

Network Slice Subnet Instance

NSSMF

Network Slice Subnet Management Function

NSSP

network slice selection policies

NTN

Non‐terrestrial network

NTP

network time protocol

NWDAF

network data analytics function

O‐DU

O‐RAN Distribution Unit

O‐RAN

Open Radio Access Network

O‐RU

O‐RAN radio unit

OAI

Open Air Interface

OAM

Operation, Administration and Maintenance

OAM

operations, administration and management

OAM

Operations, Administration, and Maintenance

OBSAI

Open Base Station Architecture Initiative

OC

OpenCellular

OEM

original equipment manufacturer

OFDM

orthogonal frequency division multiplexing

OIF

Optical Internetworking Forum

ONAP

Open Networking Automation Platform

OPEN‐O

OPEN‐Orchestrator Project

OPEX

Operational Expenditure

ORAN FH

O‐RAN Fronthaul

ORI

Open Radio equipment Interface

OSA

OpenAirInterface Software Alliance

OSI

Open Source Initiative

OSI

Other System Information

OSM

Open Source MANO

OSS

Operations Support System

OTA

over‐the‐air

OTN

Optical Transport Network

OVS

Open Virtual Switch

OWAMP

One‐Way Active Measurement Protocol

P

polling bit

P‐GW

Packet Data Network Gateway

PAL

Priority Access License

PAPR

peak to average power ratio

PBBN

Provider Backbone Bridge Network

PBCH

Physical Broadcast Channel

PBR

Prioritized Bit Rate

PCE

Path Computation Element

PCell

Primary Cell

PCF

Policy Control Function

PCI

Physical Cell Identity

PCP

priority code point

PCRF

Policy and Charging Rules Function

PDB

Packet Delay Budget

PDCCH

Physical Downlink Control Channel

PDCP

Packet Data Convergence Protocol

PDCP‐RLC

Packet Data Convergence Protocol–Radio Link Control

PDH

plesiochronous digital hierarchy

PDN

Packet Data Network

PDP

packet data protocol

PDSCH

Physical Downlink Shared Channel

PDU

Protocol Data Unit

PDV

packet delay variation

PE

Provider Edge

PF

Paging Frame

PFD

power flux density

PGW

PDN Gateway

PGW‐C

PGW control‐plane function

PHY

Physical Layer

PLL

Phase Locked Loop

PLMN

Public Land Mobile Network

PLR

Packet Loss Ratio

PM

Performance Monitoring

PMI

precoding matrix indicator

PNF

physical network function

PNI‐NPN

Public‐network‐integrated non‐public network

PO

Paging Occasion

PON

Passive Optical Network

PoP

point of presence

PoPs

Points of Presence

PPI

Paging Policy Indicator

PRACH

Physical Random Access Channel

PRB

Physical Resource Block

PRC

primary (frequency) reference clock

PREOF

Packet Replication, Elimination, and Ordering Functions

PRG

Precoding Resource Group

PRTC

Primary Reference Time Clock

PSCell

Primary Secondary Cell Group Cell

PSS

Primary Synchronization Signal

PT‐RS

phase tracking reference signals

PTP

Precision Time Protocol

PUCCH

Physical Uplink Control Channel

QFI

QoS Flow Identifier

QFI

QoS Flow Indicator

QoE

Quality of Experience

QoS

Quality of Service

QSFP

quad small form‐factor pluggable

RACH

Random Access Channel

RAN

Radio Access Network

RAR

Random Access Response

RAT

Radio Access Technology

RATs

radio access technologies

RDI

reflective QoS flow to DRB mapping Indication

RE

Radio Equipment

REC

Radio Equipment Controller

REG

Resource Element Group

RIC

RAN intelligent controller

RIT

Radio Interface Technology

RLC

Radio Link Control

RLF

Radio Link Failure

RMSI

Remaining Minimum System Information

RNA

RAN Notification Area

RNI

radio network information

RNL

Radio Network Layer

RNTI

Radio Network Temporary Identifier

RoE

Radio over Ethernet

RoHC

Robust Header Compression

ROI

Return on Investment

RQI

Reflective QoS Indicator

RRC

RAN Control protocol

RRH

Remote Radio Head

RRM

Radio Resource Management

RSSI

Received Signal Strength Indicator

RSU

Road Side Unit

RSVP

Resource Reservation Protocol

RTT

Round Trip Time

RU

radio unit

RU

Remote Unit

RV

Redundancy Version

S‐GW

Serving Gateway

S‐NSSAI

Single Network Slice Selection Assistance Information

S1‐AP

S1 Application Protocol

SA

source address

SAS

Spectrum Access System

SBA

Service‐based architecture

SC

Software Community

SCEF

Service Capability and Exposure Function

SCell

Secondary Cell

SCG

Secondary Cell Group

SCS

subcarrier spacing

SCTP

Stream Control Transmission Protocol

SD

Slice Differentiator

SDAP

Service Data Adaptation Protocol

SDH

Synchronous Digital Hierarchy

SDN

Software Defined Networks

SDO

Standards Developing Organization

SDR

software‐defined radio

SDU

Service Data Unit

SEQ

number of sequences

SFI

Slot Format Indicator

SFN

System Frame Number

SGSN

Serving GPRS Support Node

SGW

Serving Gateway

SGW‐C

SGW control‐plane function

SI

Segmentation Information

SI

System information

SIB

System Information Broadcast

SIB1

System Information Block 1

SLA

Service Level Agreement

SLO

service level objective

SmartNIC

smart network interface controller

SMF

Session Management Function

SN

Secondary Node

SN

Sequence Number

SNPN

Stand‐alone non‐public network

SO

Segment Offset

SoC

system on a chip

SON

self‐organizing network

SOTA/FOTA

software over the air/firmware over the air

SpCell

Special Cell

SPS

Semi Persistent Scheduling

SR

Scheduling Request

SR‐IOV

single root input–output virtualization

SRB

Signaling Radio Bearers

SRI

Satellite Radio Interface

SRIT

Set of Component RITs

SRP

Stream Reservation Protocol

SRS

Sounding Reference Signal

SSB

Synchronization Signal Block

SSC

Session and Service Continuity

SSCMSP

SSC mode selection policy

SSS

Secondary Synchronization Signal

SST

Slice/Service Type

SU‐MIMO

single‐user MIMO

SUL

Supplementary Uplink

SyncE

synchronous Ethernet

TA

Timing Advance

TA

Tracking Areas

TAC

Tracking Area Code

TB

Transport block

TBS

Transport Block Size

TC

Transparent Clock

TCO

Total Cost of Ownership

TDD

Time Division Duplex

TDD/TDD

time division duplex/time division duplex

TDM

time division multiplexed

TE

Traffic Engineering

TEID

Tunnel Endpoint Identifier

TI‐LFA

topology independent LFA

TI‐LFA

Topology Independent Loop Free Alternates

TIP

Telecom Infrastructure Project

TM

Transparent Mode

TNL

Transport Network Layer

TPR

Technical Performance Requirement

TSDSI

Telecommunications Standards Development Society

TSN

Time‐Sensitive Networking

TTA

Telecommunications Technology Association

TTC

Telecommunication Technology Committee

TTI

Transmission Time Interval

TVWS

TV White Spaces

TWAMP

Two‐Way Active Measurement Protocol

UAS

Unmanned Aircraft Systems

UCI

Uplink Control Information

UDM

Unified Data Management

UDM

unified date management

UDP

User Datagram Protocol

UE

User Equipment

UHD

Ultra High Definition

UL/DL

uplink/downlink

ULCL

Uplink Classifier

UM

Unacknowledged Mode

UMTS

Universal Mobile Telecommunications Service

UMTS

Universal Mobile Telecommunications System

UP

User Plane

UPF

User‐Plane Function

URLLC

Ultra‐Reliable Low‐Latency Communication

URSP

UE Route Selection Policy

UTRAN

Universal Terrestrial Radio Access Network

V2X

Vehicle‐to‐Everything

vDU

virtualized gNB‐DU

VID

VLAN identifier

VIM

Virtualized Infrastructure Manager

VM

Virtual Machine

VNF

virtual network function

VNI

Virtual Network Index

VR

Virtual Reality

VR/AR

Virtual Reality and Augmented Reality

vRAN

virtual RAN

VXLAN

Virtual Extensible LAN

W‐AGF

Wireline Access Gateway Function

WAN

wide area network

WBA

Wireless Broadband Alliance

WDM

wavelength division multiplexing

WG7

Working Group 7

WiMAX

Worldwide Interoperability for Microwave Access

WLAN

wireless local area network

WRC

World Radiocommunication Conference

xDSL

digital subscriber line technologies

Xn‐AP

Xn Application Protocol

Xn‐C

Xn Control Plane

Xn‐U

Xn User Plane

ZTP

Zero Touch Provisioning

1Introduction

As a general rule of thumb, every 10 years the cellular industry introduces a new technology: 3G Universal Mobile Telecommunications Service (UMTS) circa 2000, 4G Long‐Term Evolution (LTE) circa 2010, and now finally 5G in 2020. Within that evolution, every technology cycle comes with advancement in terms of performance and new services, which the technology makes possible. These are typically attributed (and justifiably so) to the air interface, including the physical layer and the protocol stack. What is often overlooked is the Radio Access Network (RAN), which is fundamental to the success of every technology and which also undergoes major changes when a new technology is released.

The RAN is arguably the most important component in a mobile network. At least in terms of deployment and operational complexity and cost it certainly is. The air interface, including the physical layer and the protocol stack, typically draw most of the attention at least in the research community as these determine to a very large extent the performance of any wireless technology. However, when it comes to deployments, RAN is what eventually makes it possible and economically feasible (or not).

RAN is typically defined as a collection of base stations, interconnected with each other and connected to the core network, providing coverage in a certain area through one or more radio access technologies. This is illustrated in the simplified Figure 1.1.

Figure 1.1 Radio Access Network (RAN).

In Figure 1.1 the RAN is depicted as a collection of base stations (shown as a single network node) connected via network interfaces (shown as straight lines). The reality of RAN standards, implementations, and, even more so, practical deployments is significantly more complex:

Not all base stations are equal in terms of the capacity, coverage, and throughputs they provide. These can range from macro base stations serving many hundreds of users and covering a few square kilometers to small cells serving just a handful of users in an office.

Base stations often also differ in terms of the radio access technology they provide over the air interface. Some base stations only provide 5G radio, some may provide 4G and 5G, and in some cases base stations providing different radio access may work in conjunction with each other. In other words, base stations also differ in terms of how tightly they are coupled with base stations providing other radio access.

While it is possible to implement a base station with all the components, from antennas, to radio, to baseband, to protocol stack, and finally applications and management services in a single box (as shown in

Figure 1.1

), that is rarely the case. In practice, most base stations are split into multiple nodes in a variety of architectures, interconnected by sometimes standardized and sometimes proprietary network interfaces in a variety of architectures.

Network interfaces themselves, illustrated as straight lines, in practice are anything but straight. What is often overlooked is that these interfaces run on a transport network, which often consists of various technologies – multiple transport network nodes interconnected in various network topologies.

This book is dedicated to the topic of RAN architectures and technologies. It is structured as follows:

In

Chapter 2

(“Market Drivers”) we describe the technological, regulatory, and business driving forces behind 5G in general and how these diverse requirements, challenges, and marketing considerations affect the RAN.

Before we dive into the details of RAN architectures, in

Chapter 3

(“5G System Overview”) we provide a high‐level overview of all the components of a 5G system: the core network, the air interface protocol stack, and the air interface physical layer. These help put the RAN architectures discussed afterward into a proper context.

Chapter 4

(“NG‐RAN Architectures”) is perhaps the main part of the book, where we describe in detail all the 5G RAN architectures defined in the

3rd Generation Partnership Project

(

3GPP

), O‐RAN Alliance, and Small Cell Forum, specifically: the high‐level gNB CU/

DU

(

central unit

–

distributed unit

) split, the multi‐connectivity architectures, the gNB architecture with control/user separation, the low‐level gNB intra‐PHY split, and the small cell architectures.

Chapter 5

(“NG‐RAN Evolution”) is dedicated to NG‐RAN evolution beyond Release‐15, describing technologies introduced in Release‐16: e.g. relaying, also known as

integrated access and backhaul

(IAB

, and satellite access, also known as non‐terrestrial networks.

Chapter 6

(“Enabling technologies”) is dedicated to various technologies that are not always considered part of RAN architecture but are nevertheless fundamental to RAN deployments. These include implementation‐related aspects, such as virtualization and open source, edge computing,

Operations, Administration, and Maintenance

(

OAM

), and last but not least the transport network technologies.

We finish the book with

Chapter 7

(“NG‐RAN Deployment Considerations”) by discussing the practical implications of selecting the right RAN architecture and deploying it to serve the practical needs of an operator.

A note on terminology: throughout this book, we generally try to use a consistent terminology. However, that is not always possible, or convenient – in particular, because similar technologies may sometimes be commonly referred to by different names in different standards, industries, or literature. As this book crosses multiple domains, it is challenging to use a uniform terminology, which is at the same time consistent with different terminologies used in their respective fields. One such example is the term “5G” itself – while it is used extensively in technical literature, marketing materials, product descriptions, etc. – many (but not all) 3GPP specifications intentionally avoid the term, using terminology such as New Radio (NR) when referring to the air interface and NG‐RAN (which is not an acronym at all, but is considered a “monolithic term”) when referring to the RAN. Another example is the network interface between the NG‐RAN and the core network, which is referred to as the NG interface in RAN specifications and N2/N3 reference points in core network standards.

We therefore took the pragmatic approach of using common terminology where we felt it is appropriate, and otherwise using the terminology from the domain being described in the book, with appropriate definitions and explanations in each chapter.

2Market Drivers

Reza Arefi1 and Sasha Sirotkin2

1Intel Corporation, USA

2Intel Corporation, Israel

2.1 Introduction

In this chapter we discuss various technological, regulatory, and market drivers that triggered the development of 5G and the problems 5G is expected to solve. We then attempt to derive how these affect the Radio Access Network (RAN) architecture and its evolution in order to support 5G, which is the primary focus of the book.

This is not an easy task, as there is no universally agreed definition of what constitutes 5G. To some, this is the technology that meets the International Telecommunications Union (ITU) IMT‐20201 requirements and therefore will be able to make use of the newly identified spectrum for IMT. To others, this is an expansion of cellular technologies beyond their traditional mobile broadband (MBB) use cases and markets into Internet of Things (IoT), private networks (i.e. networks deployed by entities other than traditional cellular operators), and other markets where cellular technologies have not been commonly used before. Some others view 5G as simply an evolution of 4G (Long‐Term Evolution [LTE]) to support higher throughputs, lower latencies, and better energy efficiency targeting primarily MBB; that is, the same use cases as 4G. Some point out that the primary technological advancement of 5G is the support of mmWave spectrum, while others believe that 5G is the turning point when cellular networks finally fully embrace virtualization (including RAN), driving down operational costs by opening up RAN to bigger competition.

Given such diverse views in the industry it is hard to pinpoint a single major market driver for 5G. Moreover, it is quite clear at the time of writing this book that, while at least some of the driving forces mentioned above (e.g. mmWave) do provide substantial technological improvements, these do not necessarily address an existing market need, but are rather being developed in the hope that market need will “catch up” and eventually materialize to take advantage of these new technical advancements.

In our view, unlike previous generations of cellular technologies, it is better to view 5G not as a single technology, but rather as a flexible system designed to serve many use cases and many markets. Such extreme flexibility comes at a cost of increased network and device complexity and, perhaps even more importantly, greater uncertainty of which features of 5G will be deployed and when. It is quite possible that different market forces in different geographies will drive the deployment of different features. It appears that in Asia the major driving force is the increased throughput for the MBB, while European operators are exploring various options for breaking into new markets (e.g. IoT), whereas in North America one of the key driving forces (at least for the moment) is fixed wireless access to provide better internet service to suburban areas. In summary, 5G may not be a one‐size‐fits‐all technology as it is often presented, but rather a toolbox of different technologies that different operators (and potentially new entities) will use for different purposes.

This is not new, as oftentimes this is historically how computing and networking technologies have been developed. A breakthrough in computing power and/or network throughput comes first; applications that make use of these new capabilities are developed later. The caveat is that it is unclear when exactly these new business cases and applications taking advantages of the progress in speed and power will emerge; it can take a while.

One good example of a similar case is 3G, which was initially deployed in the early 2000s,2 but it was not until the late 2000s that 3G MBB market penetration became significant, in part thanks to the launch of the iPhone.

This is not to say that there is no need for better, faster, and more energy‐efficient wireless networks supporting billions of devices. According to the Cisco Virtual Network Index (VNI) forecast, as shown in Figure 2.1, there will be 396 Exabytes (EB) per month overall IP traffic by 2022. Ericsson estimates in their Mobility Report that 80 EB of these will be consumed by mobile devices, as shown in Figure 2.2.

Figure 2.1 Cisco VNI IP traffic forecast (Source: SISCO VNI Global IP traffic forecast 2017–22).

Figure 2.2 Ericsson Mobility Report, global mobile data traffic (EB per month).

There are similar forecasts indicating growth of connected devices in general and IoT in particular, as well as other indicators pointing to the fact that it is reasonable to expect that network traffic in general and mobile traffic in particular are likely to continue growing exponentially. Therefore, even though it may not be clear yet what applications will be served by 5G networks, the demand for 5G is there and mobile networks, RAN in particular, need to evolve to cope with such traffic in a cost‐ and energy‐efficient manner.

Increased throughputs and new spectrum (e.g. mmWave) are not the only, and maybe not even the primary, 5G driving factors. Additional drivers are cost and energy efficiency considerations, competition (between operators, vendors, and even market sectors and technologies), and even politics, in what is sometimes referred to as the “race to 5G.”

In this chapter we elaborate on the various forces driving 5G technology development and deployment with emphasis on how these impact RAN features, RAN‐related technologies, and RAN architecture, which is the primary focus of the book.

2.2 Key Ideas

Data traffic in general and mobile traffic in particular is expected to continue growing exponentially.

In the past, spectrum needs forecasts significantly underestimated actual data usage. To alleviate this issue, the

ITU Radiocommunication Sector

(

ITU‐R

) used a new approach that forecasts spectrum needs ranging from hundreds of MHz to tens of GHz. The 5G target spectrum consists of lower frequency ranges (below 1 GHz), middle frequency ranges (below 6 GHz), and higher frequency ranges (mmWave) to cater to different applications. As the 5G spectrum is expected to be an order of magnitude larger than 4G, this will have a direct impact on RAN.

Spectrum‐sharing models, such as

Citizens Broadband Radio Service

(

CBRS

) in the USA and

Licensed Shared Access

(

LSA

) in Europe, may further increase available spectrum. Furthermore, they may trigger new RAN deployment options, such as the neutral host operator model. Even though CBRS and LSA are currently based on LTE, we expect that in the future spectrum‐sharing models will become applicable to 5G as well.

In order for a technology to qualify for IMT‐2020, it must fulfill certain technical requirements broadly categorized as:

enhanced mobile broadband

(

eMBB

),

Ultra‐Reliable Low‐Latency Communication

(

URLLC

), and massive

Machine‐Type Communication

(

MTC

). Of these URLLC in particular will have the biggest impact on RAN architecture and design, because most real‐world applications are concerned with end‐to‐end latency, not just over the air, which is addressed by the

New Radio

(

NR

) design. URLLC scenarios and other latency‐sensitive applications such as cloud gaming, require 5G networks to support significantly lower end‐to‐end latency, compared with 4G.

5G creates new business opportunities. It allows cellular operators to expand into new markets (which have been served by non‐cellular technologies in the past or did not exist before), for example, by deploying IoT and

Vehicle‐to‐Everything

(

V2X

). Furthermore, it creates new business models with, for example, slicing, allowing

mobile network operator

s (

MNO

s) to lease network capacity to other companies. On the other hand, 5G also helps new entities that have not used cellular technologies in the past to adopt 5G and in some cases compete with traditional cellular operators, with technologies such as private networks and the adoption of the 5G radio interface for satellite communications. Increased competition is likely to make standardized network interfaces more important and may eventually allow network multi‐vendor interoperability in RAN (which is not quite the case in 4G).

Standards will continue being important in 5G and it appears that the

3rd Generation Partnership Project

(

3GPP

) will continue to have a central role in developing cellular standards. This has the positive effect of ensuring that there is only one major 5G standard, reducing market fragmentation. On the other hand, the increased interest in 3GPP triggers increased participation from many more companies and delegates, making a consensus harder to reach. The end result is that, unlike 4G, 3GPP 5G standard will have many options (sometimes presented as “flexibility”). This flexibility has a cost, as it is increasingly hard to predict which standard options will be deployed in the field. Furthermore, there are still many

Standards Developing Organization

s (

SDO

s) and industry fora working on technologies that may be considered competition (e.g. LoRa and the

Institute of Electrical and Electronics Engineers

[

IEEE

]), or may complement 3GPP standards (e.g.

Broadband Forum

[

BBF

],

Open Radio Access Network

[

O‐RAN

], Small Cell Forum, etc.).

Open source, which was extremely successful in the enterprise and data centers, is increasingly finding its way into telecom networks. There are number of open source LTE

Evolved Packet Core

(

EPC

) implementations available (e.g. Magma), open source

Operations, Administration, and Maintenance

(

OAM

) frameworks (e.g.

Open Networking Automation Platform

[

ONAP

] and

Open Source Mano

[

OSM