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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Comprehensive reference on O-RAN technology, covering its history, architecture, security, ecosystem, and more, with didactic resources included throughout
Discussing both basic and advanced concepts, Fundamentals of O-RAN delivers a comprehensive summary of O-RAN, covering its history, architecture, control loops and microservices (i.e., xApps and rApps), security, ecosystem, R&D initiatives, and challenges and evolution toward 6G. The book not only includes key theoretical principles of O-RAN, but also provides a framework for the reader to carry out guided hands-on exercises through online auxiliary materials. Homework problems and review questions are included in online auxiliary materials to reinforce learning.
The book includes instructions on how to create xApps, which are expected to be one of the most promising aspects of O-RAN; for example, by working with an end-to-end O-RAN system using a network slicing functionality where the rApp provides slicing specified policies to the xApp which then allocates the base station’s spectrum resources based on the slicing policy to each user (belonging to a certain slice).
Readers will also gain an understanding of cellular networks, particularly radio access networks, software virtualization, and software-defined networking concepts, and the knowledge needed to design, build, and test a 5G O-RAN system.
Some of the sample topics explored in Fundamentals of O-RAN include:
- RAN evolution from black box 4G RAN to software-based and virtualized RAN (vRAN)
- Components of the O-RAN architecture including SMO, Non-RT RIC, Near-RT RIC, O-CU-CP, O-CU-UP, O-DU, O-RU, and O-Cloud
- xApp design and prototyping from scratch using open cellular software, srsRAN and O-RAN Software Community (OSC) software.
- Examination of various security dimensions inherent in the O-RAN architecture.
- Testing and integration, covering Open Test and Integration Centers (OTICs), global PlugFests, certification and badging, and end-to-end test specifications
- Work Groups (WGs), including WG1 to WG11, and focus groups, with information on how to obtain WG specifications
Fundamentals of O-RAN is an essential reference for the workforce of tomorrow’s cellular industry, including graduate students, teachers, researchers, faculty members, engineers, and employees involved in the field of wireless networks, especially radio networks.
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Table of Contents
Cover
Table of Contents
Title Page
Copyright
About the Authors
Preface
Acknowledgments
Acronyms
About the Companion Website
1 Introduction to O‐RAN
1.1 Evolution of Cellular Technologies
1.2 Components of Cellular Systems
1.3 Evolution of the RAN
1.4 Introduction to the O‐RAN ALLIANCE and the O‐RAN Architecture
1.5 Driving Forces Behind O‐RAN
1.6 O‐RAN Ecosystem
1.7 O‐RAN Use Cases
1.8 O‐RAN: Accomplishments, Technical Priorities, and Potential Future Work
1.9 Major Takeaways of the Chapter
References
Notes
2 O‐RAN Architecture
2.1 O‐RAN Logical Architecture
2.2 O‐RAN Components: A Closer Look
2.3 O‐RAN Interfaces: A Closer Look
2.4 Functional Split 7.2x
2.5 Inside O‐RAN Domain: Functional Distribution Between O‐RAN and Other SDOs
2.6 O‐RAN Deployment Scenarios
2.7 Major Takeaways of the Chapter
References
Notes
3 O‐RAN Applications: xApps and rApps
3.1 O‐RAN Control Loops
3.2 Near‐RT Control Loop: Near‐RT RIC and xApps
3.3 Near‐RT RIC xApps: Enabling RAN Customization
3.4 E2 Interface: Empowering RAN Control and Data Exchange
3.5 xApp Use Cases
3.6 Machine Learning (ML)‐Based xApps
3.7 xApp Workflow
3.8 xApp Development: A Closer Look
3.9 Non‐RT Closed Loop: Non‐RT RIC and rApps
3.10 Real‐Time RIC Closed Loop: RT RIC and μApps/dApps
3.11 Multi‐time‐scale RIC Framework
3.12 Major Takeaways of the Chapter
References
4 O‐RAN Security
4.1 Motivation for O‐RAN Security
4.2 Methodology of O‐RAN Security Analysis
4.3 Threat Model
4.4 Risk Assessment
4.5 Security Principles, Security Requirements, and Security Controls in O‐RAN
4.6 O‐RAN Security Protocols
4.7 O‐RAN Security Testing
4.8 Major Takeaways of the Chapter
References
5 O‐RAN Ecosystem
5.1 Internal and External O‐RAN Ecosystems
5.2 Internal O‐RAN Ecosystem
5.3 External Ecosystem
5.4 O‐RAN: A Deployment Perspective
5.5 Major Takeaways of the Chapter
References
Note
6 O‐RAN Testing and Integration
6.1 O‐RAN Testing and Integration in a Nutshell
6.2 Test Specifications
6.3 Open Testing and Integration Centers
6.4 Global PlugFests
6.5 Certification and Badging
6.6 Major Takeaways of the Chapter
References
Note
7 O‐RAN Research and Development Initiatives
7.1 Industry‐Led Initiatives
7.2 Government‐Led Initiatives
7.3 Academia‐Led Initiatives
7.4 Major Takeaways of the Chapter
References
8 O‐RAN Challenges and Evolution of O‐RAN Toward 6G
8.1 O‐RAN Challenges and Solutions
8.2 6G: A Concise Introduction
8.3 O‐RAN in 6G
8.4 Major Takeaways of the Chapter
References
Notes
Appendix A: Energy Efficiency in Open Radio Access Networks
A.1 Introduction
A.2 EE Improvement Methods in Traditional RAN Environment
A.3 EE Improvement Methods in O‐RAN
A.4 Summary
References
Index
End User License Agreement
List of Tables
Chapter 1
Table 1.1 Groups in the O‐RAN ALLIANCE.
Table 1.2 Examples of O‐RAN Use Cases.
Chapter 3
Table 3.1 Sample AI/ML Models in O‐RAN Use Cases.
Chapter 4
Table 4.1 Security Controls for Near‐RT RIC APIs.
Table 4.2 Testing and Measurement Tools.
Chapter 5
Table 5.1 Example WG1 Work Products.
Table 5.2 Example WG2 Work Products.
Table 5.3 Example WG3 Work Products.
Table 5.4 Example WG4 Work Products.
Table 5.5 Example WG5 Work Products.
Table 5.6 Example WG6 Work Products.
Table 5.7 Example WG7 Work Products.
Table 5.8 Example WG8 Work Products.
Table 5.9 Example WG9 Work Products.
Table 5.10 Example WG10 Work Products.
Table 5.11 Example WG11 Work Products.
Table 5.12 Example TIFG Work Products.
Table 5.13 Example nGRG Work Products.
Table 5.14 A Snapshot of OSC Software Releases.
Chapter 6
Table 6.1 Specifications for Conformance and Interoperability Testing.
Table 6.2 Test Scenarios for the M‐Plane Test Cases.
Table 6.3 Test and Measurement Equipment and Tools for E2E Testing.
List of Illustrations
Chapter 1
Figure 1.1 Evolutionary Path of Cellular Technologies.
Figure 1.2 5G System: A High‐Level Overview.
Figure 1.3 Evolution of the RAN Architecture.
Figure 1.4 Disaggregation of the Base Station.
Figure 1.5 Disaggregated Base Station with SDN Principles.
Figure 1.6 The Three Focus Streams of the O‐RAN ALLIANCE.
Figure 1.7 Simplified Logical O‐RAN Architecture.
Figure 1.8 Major Driving Forces Behind O‐RAN.
Figure 1.9 Building Blocks of the O‐RAN Ecosystem.
Chapter 2
Figure 2.1 O‐RAN Logical Architecture.
Figure 2.2 SMO Framework: A Closer Look.
Figure 2.3 Reference Architecture for the SMO Framework and the Non‐RT RIC....
Figure 2.4 Non‐RT RIC Functions.
Figure 2.5 Near‐RT RIC Architecture: A Closer Look.
Figure 2.6 Near‐RT RIC APIs: An Overview.
Figure 2.7 O‐CU‐CP: A Closer Look.
Figure 2.8 O‐CU‐UP: A Closer Look.
Figure 2.9 O‐DU: A Closer Look.
Figure 2.10 O‐RU: A Closer Look.
Figure 2.11 O‐eNB: A Closer Look.
Figure 2.12 O‐Cloud: A Closer Look.
Figure 2.13 O‐Cloud Planes (O‐RAN ALLIANCE 2024n).
Figure 2.14 O‐RAN OAM Logical Architecture.
Figure 2.15 Management Services of the O1 Interface.
Figure 2.16 Uses of the O2 Reference Point‐Based Interfaces.
Figure 2.17 A1 Services.
Figure 2.18 A1 Protocol Stack.
Figure 2.19 Interworking Between the Near‐RT RIC and E2 Nodes.
Figure 2.20 Categories of E2 Functions (O‐RAN ALLIANCE 2024g.)
Figure 2.21 E2 Interface Protocol Stack.
Figure 2.22 Functional Split with CUS‐Plane and M‐Plane of the Open FH Inter...
Figure 2.23 Protocol Stacks for the M‐Plane of the Open FH Interface.
Figure 2.24 Data Flows on the CUS Planes of the Open FH Interface.
Figure 2.25 Transport Network Encapsulation for the CUS Planes of the Open F...
Figure 2.26 Protocol Stacks for the CUS Planes of the Open FH Interface.
Figure 2.27 CTI Reference Architecture.
Figure 2.28 Interworking of CTI and the Transport Network.
Figure 2.29 3GPP‐Defined Interfaces in O‐RAN.
Figure 2.30 Functional Split 7.2x: A Closer Look.
Figure 2.31 Cell Site, Edge Cloud, and Regional Cloud.
Figure 2.32 O‐RAN Deployment Scenarios.
Figure 2.33 O‐RAN Example Deployment Scenario Mapping.
Chapter 3
Figure 3.1 O‐RAN Control Loops.
Figure 3.2 Near‐RT RIC Architecture.
Figure 3.3 Extended Application (xApp).
Figure 3.4 xApps: Enablers for Implementation of Control Algorithms.
Figure 3.5 Illustration of E2AP Packet.
Figure 3.6 Setup Procedure for E2 Session Between the Near‐RT RIC and an E2 ...
Figure 3.7 Procedures Related to Sending of KPMs from an E2 Node to the Near...
Figure 3.8 Illustration of Services Information Exchange Between the Near‐RT...
Figure 3.9 End‐to‐end Workflow and Signaling Procedure for the Collection of...
Figure 3.10 Total PDCP Bytes Received by the en‐gNB in the Uplink from All U...
Figure 3.11 UE Bandwidth Variation When Associated with Different Slices.
Figure 3.12 AI/ML Workflow Process for the O‐RAN Architecture.
Figure 3.13 xApp Workflow Process.
Figure 3.14 Kubernetes Cluster.
Figure 3.15 Container Attribute of xApp Descriptor.
Figure 3.16 Controls Attribute of xApp Descriptor.
Figure 3.17 Additional Attributes of the xApp Descriptor.
Figure 3.18 An Example of a Docker File.
Figure 3.19 Output of the Docker Image Build and Submission to the xApp Regi...
Figure 3.20 Asserting the nginx Server Can Access the xApp config File.
Figure 3.21 Verifying Successful Deployment of the xApp.
Figure 3.22 Various Commands to Remove xApp and RIC Components.
Figure 3.23 Non‐RT RIC Architecture.
Figure 3.24 Illustration of A1 Interfaces and Other Related Interfaces.
Figure 3.25 Exposure of SMO and Non‐RT RIC Services.
Figure 3.26 RICWorld Concept Architecture, Showing EdgeRIC and O‐RAN Integra...
Figure 3.27 Multi‐Time‐Scale RIC Framework Vision and It's Use Cases.
Figure 3.28 Overview of SPARC usecase.
Figure 3.29 Operational Flow of SPARC System.
Chapter 4
Figure 4.1 Logical Architecture of O‐RAN System.
Figure 4.2 Methodology of O‐RAN Security Analysis.
Figure 4.3 Building Blocks for O‐RAN Threat Model.
Figure 4.4 O‐RAN Security Threats Groups.
Figure 4.5 O‐RAN Threat Agents.
Figure 4.6 Concepts of Risk Assessment.
Figure 4.7 Risk Assessment Matrix.
Figure 4.8 SSH Overview.
Figure 4.9 Key Aspects of O‐RAN Security Testing.
Chapter 5
Figure 5.1 Overall O‐RAN Ecosystem.
Figure 5.2 O‐RAN Work Groups in a Nutshell.
Figure 5.3 OSC Projects.
Figure 5.4 Examples of OSC‐Published xApps.
Figure 5.5 Roles of a University in an External O‐RAN Ecosystem.
Chapter 6
Figure 6.1 O‐RAN Testing and Integration Mechanisms.
Figure 6.2 Network Architectures Supported for Testing.
Figure 6.3 The O‐RAN System as System Under Test.
Figure 6.4 Types of End‐to‐End Tests.
Figure 6.5 O‐RAN Testing and Integration Mechanisms.
Chapter 7
Figure 7.1 Prominent Industry‐Led Initiatives.
Figure 7.2 TIP O‐RAN Liaisons (Telecom Infra Project 2024).
Figure 7.3 Open RAN Subgroups—(1) Component Subgroups and (2) Segment Subgro...
Figure 7.4 ONF's SD‐RAN Platform—An Exemplar Platform for O‐RAN Based on Spe...
Figure 7.5 ONF's SD‐RAN Exemplar Platform (ONF Aether 2024).
Figure 7.6 High‐level μONOS RIC Architecture (ONF SD‐RAN 2020).
Figure 7.7 O‐RAN Reference Architecture on AWS (AWS O‐RAN evolution 2024).
Figure 7.8 Top 28-O‐RAN Telecom Vendors Across Categories (TeckNexus 2021)....
Figure 7.9 Top 5 Virtual RAN Vendors for Open RAN (TeckNexus 2021).
Figure 7.10 Top 18 Radio Unit Vendors for Open RAN (TeckNexus 2021).
Figure 7.11 Top 6 RAN Chip Vendors for Open RAN (TeckNexus 2021).
Figure 7.12 Top 7 System Integrators for Open RAN (TeckNexus 2021).
Figure 7.13 Open RAN Deployments and Trials Across the World (TeckNexus 2021...
Figure 7.14 Overview of VIAVI's O‐RAN End‐to‐End Testing Capability (VIAVI 2...
Figure 7.15 Overview of OAIC Controllers (OAIC‐C) Platform.
Figure 7.16 Overview of OAIC‐T Platform.
Figure 7.17 Colosseum (Colosseum 2024)/Northeastern University.
Figure 7.18 OpenRANGym Architecture (OpenRANGym 2024).
Figure 7.19 ColORAN Platform (ColORAN 2024).
Figure 7.20 CCI xG Testbed (CCI‐xG‐Testbed 2024)/Commonwealth Cyber Initiati...
Figure 7.21 AERPAW Fixed Node Deployments in the Research Triangle Park (AER...
Figure 7.22 AERPAW OTIC O‐RU Conformance Test Setup (AERPAW).
Chapter 8
Figure 8.1 O‐RAN Challenges.
Figure 8.2 IMT‐2030 Usage Scenarios and Overarching Aspects.
Figure 8.3 Performance Targets for IMT‐2030 Capabilities.
Figure 8.4 Potential 6G Technology Enablers.
Figure 8.5 Impact of 6G on O‐RAN.
Appendix A
Figure A.1 BS On/Off Technique.
Figure A.2 Antenna Selection Technique.
Figure A.3 Antenna Selection Technique.
Figure A.4 RF Channel Switching On/Off Technique.
Guide
Cover
Table of Contents
Title Page
Copyright
About the Authors
Preface
Acknowledgments
Acronyms
About the Companion Website
Begin Reading
Appendix A: Energy Efficiency in Open Radio Access Networks
Index
End User License Agreement
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IEEE Press445 Hoes LanePiscataway, NJ 08854
IEEE Press Editorial BoardSarah Spurgeon, Editor-in-Chief
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Tony Q. S. Quek
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Thomas Robertazzi
Diomidis Spinellis
Fundamentals of O-RAN
Nishith D. TripathiVirginia TechParker, TX, USA
Vijay K. ShahNorth Carolina State University and WiSights LabRaleigh, NC, USA
Copyright © 2025 by The Institute of Electrical and Electronics Engineers, Inc. All rights reserved.
Published by John Wiley & Sons, Inc., Hoboken, New Jersey.Published simultaneously in Canada.
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Library of Congress Cataloging‐in‐Publication Data:
Names: Tripathi, Nishith D., author. | Shah, Vijay K., author.Title: Fundamentals of O-RAN / Nishith D. Tripathi, Vijay K. Shah.Description: Hoboken, New Jersey : Wiley, [2025] | Includes index.Identifiers: LCCN 2024037419 (print) | LCCN 2024037420 (ebook) | ISBN 9781394206803 (hardback) | ISBN 9781394206810 (adobe pdf) | ISBN 9781394206827 (epub)Subjects: LCSH: Open Radio Access Network.Classification: LCC TK5103.2 .T733 2025 (print) | LCC TK5103.2 (ebook) | DDC 621.382 – dc23/eng/20240925LC record available at https://lccn.loc.gov/2024037419LC ebook record available at https://lccn.loc.gov/2024037420
Cover Design: WileyCover Image: © K illustrator Photo/Shutterstock
About the Authors
Dr. Nishith D. Tripathi is a Research Associate Professor at Virginia Tech. Dr. Tripathi has 24 years of hands‐on industry experience and is an expert on various aspects of commercial 3G, 4G, and 5G wireless networks including design, operations, testing, and optimization. At Virginia Tech, he has led several sponsored research projects on 5G, 5G‐Advanced, and 6G in the areas such as 5G O‐RAN testbeds, SpaceNet testbed, O‐RAN xApps, O‐RAN testing, enhanced security for 5G and 6G, NTN, V2X communications, geofencing, positioning, UAV/UAS, and smart warehouses. He has coauthored five books including the world's first multimedia book on 5G, a comprehensive textbook on cellular communications, a pioneering monograph on the RRM using AI, and two books on NTN and O‐RAN. He has made more than 30 contributions toward the development of the 3GPP 5G specifications. As a wireless industry expert, Dr. Tripathi has contributed to organizations such as FCC, CTIA, GSMA, NGA, NSC, Scientific American, FTC, EE Times University, and CNN. He is the founder of Aum Research and Consulting (ARC) that provides research and consulting services.
Dr. Vijay K. Shah is an Assistant Professor in the Electrical and Computer Engineering Department at North Carolina State University. He heads the NextG Wireless Lab@NC State, a leading research group specializing in cutting‐edge exploration of next‐generation wireless communications and networking. His research spans various critical areas including 5G/NextG cellular networks, O‐RAN, dynamic spectrum sharing, and AI/ML applications in wireless technologies. He also serves as the co-founder of WiSights Lab, a startup focused on developing secure and efficient GenAI/LLM solutions for telecom and enterprise networks. He obtained his PhD in Computer Science from University of Kentucky and B. Tech in Computer Science and Engineering from National Institute of Technology, Durgapur, in 2019 and 2013, respectively. After PhD, he served as a Research Assistant Professor in the Bradley Department of Electrical and Computer Engineering at Virginia Tech until 2021, and as a tenure‐track Assistant Professor at George Mason University until 2024. Dr. Shah's research on next‐generation wireless communication networks has been generously supported by federal agencies, such as NSF, NIST, and NTIA.
Preface
Open Radio Access Network (O‐RAN), often referred to as Open RAN, is a revolutionary technology transforming the cellular communications landscape. O‐RAN is an open, programmable, interoperable, and virtualized RAN architecture. O‐RAN provides significant flexibility to cellular service providers to mix and match hardware and software components from different vendors. This book provides a comprehensive view of O‐RAN by addressing various aspects of O‐RAN including the driving forces behind O‐RAN architecture, applications such as xApps and rApps, O‐RAN security considerations, internal and external ecosystems, testing and integration, R&D initiatives, O‐RAN challenges, and evolution of O‐RAN toward the sixth‐generation (6G) cellular technology.
Chapter 1 provides a concise introduction to O‐RAN. This chapter first builds a foundation for O‐RAN by illustrating the evolution of cellular technologies, reviewing components of a cellular system, and describing the evolution of RAN architectures. Then, a brief introduction to the O‐RAN ALLIANCE (which is in charge of defining O‐RAN specifications) is given, followed by illustration of a simplified O‐RAN architecture defined by the O‐RAN ALLIANCE. Deployments of O‐RAN use standards and frameworks developed by the O‐RAN ALLIANCE and several other organizations. Roles of such non‐O‐RAN ALLIANCE organizations in the O‐RAN ecosystem are discussed. Driving forces behind O‐RAN's rising importance are explained. Numerous uses cases of O‐RAN that help optimize various RAN operations are described. Finally, the overall accomplishments of O‐RAN are summarized along with O‐RAN's technical priorities and potential future work.
Chapter 2 provides a detailed look at the O‐RAN architecture. The O‐RAN ALLIANCE has defined a logical O‐RAN architecture that utilizes the 3GPP‐defined 5G and 4G Radio Access Network (RAN) as a baseline and introduces new nodes and interfaces in support of openness and intelligence. Key components of O‐RAN are Service Management and Orchestration (which includes Non‐Real‐Time RAN Intelligent Controller [Non‐RT RIC]), Near‐Real‐Time RAN Intelligent Controller (Near‐RT RIC), O‐RAN Central Unit – Control Plane (O‐CU‐CP), O‐RAN Central Unit – User Plane (O‐CU‐UP), O‐RAN Distributed Unit (O‐DU), O‐RAN Radio Unit (O‐RU), O‐RAN eNodeB (O‐eNB), and O‐RAN Cloud (O‐Cloud). These O‐RAN components are extensively discussed. The interfaces that connect O‐RAN components with each other and external non‐O‐RAN systems are also discussed. These interfaces include O1, O2, A1, E2, Open Fronthaul (Open FH), O‐Cloud Notification, and Cooperative Transport Interface (CTI). While the 3GPP has defined disaggregated Base Stations in the radio network, the O‐RAN architecture further disaggregates the Base Station using the functional split 7.2x, which is described in detail. Functional distribution between O‐RAN and other Standards Developing Organizations (SDOs) is explained. For O‐RAN deployments, an overview of O‐RAN cloudification, hierarchical cloud architecture, and deployment scenarios is also given.
Chapter 3 describes three key control loops within the O‐RAN architecture. These control loops play a crucial role in dynamically optimizing network performance at different time scales. Details of each O‐RAN control loop, its essential components, and associated microservices such as xApps and rApps are discussed. These microservices enable the decomposition of complex RAN functionalities into modular and independently deployable units. The control loop and microservices framework empowers network operators to adapt the network swiftly to evolving demands and promotes a cost‐effective and adaptive approach to building and maintaining telecommunications infrastructure. O‐RAN‐defined RICs such as the Non‐RT RIC and the Near‐RT RIC are also elaborated. Potential enhancements to the O‐RAN architecture such as the Real‐Time RIC (RT RIC) and its microservices, commonly referred to as μApps or dApps, are also summarized.
Chapter 4 focuses on O‐RAN security. In contrast to conventional cellular networks, O‐RAN represents a paradigm shift with its open, programmable, interoperable, and virtualized RAN architecture. This innovative approach empowers network operators to seamlessly integrate hardware and software components from diverse vendors, fostering enhanced flexibility, scalability, and cost efficiency. Furthermore, this approach fosters competition among vendors. However, these O‐RAN characteristics result in critical security implications. This chapter comprehensively examines various security dimensions inherent in the O‐RAN architecture, shedding light on the intricate interplay between openness and safeguarding network integrity.
Chapter 5 discusses the overall ecosystem of O‐RAN from two perspectives—an internal ecosystem and an external ecosystem. Design, development, integration, testing, deployment, maintenance, optimization, and promotion of O‐RAN require a comprehensive internal and external ecosystem. The internal ecosystem of O‐RAN carries out work within the scope of the O‐RAN ALLIANCE focus streams. The external ecosystem includes SDOs, industry alliances, and government entities. Some constituents of the external ecosystem such as SDOs are of existential importance to O‐RAN; without these components, O‐RAN simply cannot exist. In contrast, some constituents of the external ecosystem such as government entities help make the overall ecosystem vibrant to promote the deployment of O‐RAN, realizing the benefits of O‐RAN for consumers, enterprises, and government entities.
Chapter 6 narrates testing and integration aspects of O‐RAN. O‐RAN is characterized by openness and intelligence. Openness of O‐RAN is evident by the support for multiple open interfaces. Open interfaces enable a service provider to make use of products and O‐RAN components from different vendors. Openness provides significant flexibility to a service provider to select vendors to meet its business objectives. However, integration of different O‐RAN components is a nontrivial matter. Testing of integrated products is especially important to ensure proper operations of O‐RAN in commercial deployments. A brief overview of Open Testing and Integration Centers is given. The O‐RAN certification and badging program is also described. Global PlugFests that bring companies and institutions from multiple continents together are discussed. An overview of testing‐related O‐RAN specifications is given. Finally, examples of best practices and recommendations for O‐RAN testing and integration are given.
Chapter 7 provides a glimpse of O‐RAN R&D initiatives. In the last few years, O‐RAN has received significant attention from governments, industry, and academia. This chapter outlines key O‐RAN R&D initiatives led by industry, academia, as well as governments in the United States and across the world to propel the development and adoption of O‐RAN technology for 5G and upcoming 6G networks.
Chapter 8 provides an overview of O‐RAN challenges and implications of 6G on O‐RAN. O‐RAN is expected to be one of the prominent ways of designing and deploying a 5G Radio Access Network. However, with any new technologies, there are challenges to overcome. This chapter provides a glimpse of O‐RAN challenges. Examples of potential O‐RAN enhancements to address these challenges are also given. While O‐RAN currently supports 5G and 4G radio interfaces at the time of this writing, it is expected to support 6G in future. A brief overview of 6G is given, followed by areas of focus in O‐RAN to support 6G.
In our wireless communications industry, we cannot escape acronyms! To help you navigate through the maze of acronyms, we have included a list of acronyms in the front matter of the book. If you like to go into more details, the list of references mentioned at the end of each chapter is a good starting place. Online exercises to help you reinforce key O‐RAN concepts are available at https://www.wiley.com/go/tripathioran.
We hope that this book will significantly increase your O‐RAN knowledge and facilitate your professional growth. Please consider this book as the beginning of our teacher–student relationship; feel free to connect to us via social media.
November 2024
Happy O‐RAN learning!Dr. Nishith D. Tripathi and Dr. Vijay K. Shah
Acknowledgments
We are thankful to our families for their patience and sacrifice of time while we worked on the book in the evenings and weekends and during holidays. We appreciate the support and encouragement from Prof. Jeffrey H. Reed (Virginia Tech) for this endeavor.
We thank the O‐RAN ALLIANCE for defining O‐RAN specifications, without which this book would not exist!
We thank our employers, Virginia Tech, George Mason University, and North Carolina State University, where we got opportunities to perform Open Radio Access Network (O‐RAN) research. Our research facilitated the development of this book.
We appreciate the support from National Telecommunications and Information Administration (NTIA). This book is partially based upon work supported by the NTIA's Public Wireless Supply Chain Innovation Fund (PWSCIF) under the award number (51‐60‐IF007). We thank National Science Foundation (NSF) for partially supporting this book through the “Open AI Cellular” project (NSF Award # 2120411).
We thank our students who contributed directly or indirectly to this book. We thank Pratheek Upadhyaya (Virginia Tech) for his early work on building 5G O‐RAN testbeds at Virginia Tech and providing relevant documents. We thank Kumar Sai Bondada (Virginia Tech) for helping build a hands‐on O‐RAN workshop and developing some of the diagrams that are part of this book. We also thank Zac Martin (Virginia Tech) for developing nice diagrams for this book.
We extend our gratitude to our PhD students, postdocs, and colleagues at NextG Wireless Lab (NextG Lab) at North Carolina State University. Specifically, we acknowledge Abiodun Ganiyu (NextG Lab) for his contributions to the O‐RAN security chapter and for his insightful feedback on a few other chapters of this book. We also appreciate Nathan Stephenson (George Mason University) for developing the xApp design and development workflow, which contributed to Chapter 3 on xApps and rApps. We thank Pranshav Gajjar for his contributions with indices and chapter exercises. Lastly, we thank Dr. Sayanta Seth (NextG Lab) for providing essential documents on O‐RAN energy efficiency. We thank the reviewers of this book whose feedback helped enhance the book.
Finally, we deeply appreciate the flexibility and guidance of our publisher, IEEE Press/Wiley.
November 2024
Dr. Nishith D. Tripathi and Dr. Vijay K. Shah
Acronyms
1PPS
1 Pulse Per Second
3GPP
Third Generation Partnership Project
4G
Fourth Generation
5G
Fifth Generation
6G
Sixth Generation
6G‐IA
6G Smart Networks and Services Industry Association
5GC
5G Core (Network)
5GCN
5G Core Network
AAL
Acceleration Abstraction Layer
AERPAW
Aerial Experimentation and Research Platform for Advanced Wireless
AF
Application Function
AH
Authentication Header
AI
Artificial Intelligence
AI/ML
Artificial Intelligence/Machine Learning
ALM
Application Life Cycle Management
AMF
Access and Mobility Management Function
AMPS
Advanced Mobile Phone System
AN
Access Network
AnLF
Analytics Logical Function
ANR
Automatic Neighbor Relation
API
Application Programming Interface
ARA
Agriculture and Rural Communities
AS
Access Stratum
AS
Application Server
ASN
Abstract Syntax Notation
ATIS
Alliance for Telecommunications Industry Solutions
AWS
Amazon Web Services
BBU
Baseband Unit
BLER
Block Error Rate
BS
Base Station
BSC
Base Station Controller
BSS
Business Support Systems
CA
Carrier Aggregation
CapEx
Capital Expenditure
CAPTCHA
Completely Automated Public Turing Test to Tell Computers and Humans Apart
CAS
Cloud Access Switch
CCC
Cell Configuration and Control
CCI
Commonwealth Cyber Initiative
CCO
Coverage and Capacity Optimization
CD
Continuous Development
CDMA
Code Division Multiple Access
CHIPS
Creating Helpful Incentives to Produce Semiconductors for America
CI
Continuous Integration
CIA
Confidentiality, Integrity, and Availability
CIA
Confidentiality, Integrity, and Authenticity
CMP
Certificate Management Protocol
CMTS
Cable Modem Termination System
CNCF
Cloud Native Computing Foundation
CNF
Cloud‐Native Network Function
CNF
Containerized Network Function
CNN
Convolutional Neural Network
COTS
Commercial‐Off‐The‐Shelf
CP
Cyclic Prefix
CP
Control Plane
C‐Plane
Control Plane
CPM
Congestion Prediction and Management
CPRI
Common Public Radio Interface
CPU
Central Processing Unit
CQI
Channel Quality Indicator
CR
Cognitive Radio
CTI
Cooperative Transport Interface
C‐RAN
Centralized Radio Access Network
C‐RAN
Cloud RAN
CUS‐plane
Control User Synchronization Plane
CUSM
Control User Synchronization Management
CU
Central Unit
CVE
Common Vulnerabilities and Exposures
DC
Dual Connectivity
DCCF
Data Collection Coordination Function
DDoS
Distributed Denial of Service
DEC
Digital Equipment Corporation
DHCP
Dynamic Host Configuration Protocol
DIX
DEC‐Intel‐Xerox
DL
Downlink
DMS
Deployment Management Service
DNS
Domain Name System
DOCSIS
Data Over Cable Service Interface Specification
DoD
Department of Defense
DRB
Data Radio Bearer
DRL
Deep Reinforcement Learning
DRX
Discontinuous Reception
DSS
Dynamic Spectrum Sharing
DT
Digital Twin
DTLS
Datagram Transport Layer Security
DU
Distributed Unit
DUT
Device Under Test
E1AP
E1 Application Protocol
E2AP
E2 Application Protocol
E2E
End‐to‐End
E2SM
E2 Service Model
EAP
Extensible Authentication Protocol
EC
Event Consumer
eCPRI
enhanced Common Public Radio Interface
EDGE
Enhanced Data Rates for GSM Evolution
EE
Energy Efficiency
EHC
EtHernet Header Compression
EI
Enrichment Information
eMBB
enhanced Mobile Broadband
EMS
Element Management System
eNB
evolved Node B
EN‐DC
E‐UTRA‐NR Dual Connectivity
en‐gNB
EN‐DC gNB
EP
Event Producer
EPC
Evolved Packet Core
EPS AKA
Evolved Packet System Authentication and Key Agreement
ES
Energy Savings
ESP
Encapsulating Security Payload
ETACS
European Total Access Communication System
ETSI
European Telecommunication Standards Institute
E‐UTRA
Evolved Universal Terrestrial Radio Access
E‐UTRAN
Evolved Universal Terrestrial Radio Access Network
F1AP
F1 Application Protocol
FCAPS
Fault, Configuration, Accounting, Performance, and Security
FDD
Frequency Division Duplex
FFT
Fast Fourier Transform
FH
Fronthaul
FHM
Fronthaul Multiplexer
FOCOM
Federated O‐Cloud Orchestration and Management
FOCOM
Fault and Configuration Management
FPGA
Field Programmable Gate Array
FTP
File Transfer Protocol
FTPES
File Transfer Protocol Explicit‐mode Secure
FTPS
File Transfer Protocol Secure
GBR
Guaranteed Bit Rate
GCP
Google Cloud Platform
GDPR
General Data Protection Regulation
gNB
next‐generation Node B
gNB‐CU
next‐generation Node B‐Central Unit
gNB‐CU‐CP
gNB‐CU‐Control Plane
gNB‐CU‐UP
gNB‐CU‐User Plane
gNB‐DU
next‐generation Node B‐Distributed Unit
GNSS
Global Navigation Satellite System
GPRS
General Packet Radio Service
GRPC
Google Remote Procedure Call
GSM
Global System for Mobile Communication
GSMA
GSM Association
GTP
GPRS Tunneling Protocol
GUTI
Globally Unique Temporary Identifier
HARQ
Hybrid Automatic Repeat reQuest
HRLLC
Hyper Reliable and Low‐Latency Communication
HTC
Holographic‐Type Communications
HTTP
Hyper Text Transfer Protocol
HTTPS
Hyper Text Transfer Protocol Secure
HW
Hardware
IAB
Integrated Access and Backhaul
IANA
Internet Assigned Numbers Authority
ICMP
Internet Control Message Protocol
IEFG
Industry Engagement Focus Group
IETF
Internet Engineering Task Force
IFFT
Inverse Fast Fourier Transform
IIoT
Industrial Internet of Thing
IKE
Internet Key Exchange
IMI
Internal Messaging Infrastructure
IMS
Infrastructure Management Services
IMT
International Mobile Telecommunication
ION
Intelligent Operation Network
IoT
Internet of Things
IOT
Interoperability Testing
IP
Internet Protocol
IPR
Intellectual Property Right
IPSec
Internet Protocol Security
IPT
Internet Para Todos
IQ
In‐phase Quadrature
ITU
International Telecommunication Union
i‐ZTA
intelligent Zero Trust Architecture
JSON
JavaScript Object Notation
JTAG
Joint Test Action Group
JWT
JSON Web Token
K8s
Kubernetes
KORA
Keysight Open RAN Architect
KPI
Key Performance Indicator
KPIMON
KPI Monitoring
KPM
Key Performance Measurement
KPM
Key Performance Metric
LAA
Licensed Assisted Access
LBT
Listen Before Talk
LCM
Life Cycle Management
LEO
Low‐Earth‐Orbit
LLS
Lower Layer Split
LMF
Location Management Function
LTE
Long‐Term Evolution
MAC
Medium Access Control
MANO
Management and Orchestration
MCHEM
Massive Digital Channel Emulator
MCOT
Maximum Channel Occupancy Time
MCS
Modulation and Coding Scheme
ME
Managed Element
MEC
Multi‐access Edge Computing
MeNB
Master evolved Node B
MFAF
Messaging Framework Adaptor Function
MIB
Master Information Block
MIMO
Multiple Input Multiple Output
MITM
Man‐In‐The‐Middle
mIoT
massive Internet of Things
ML
Machine Learning
MLB
Mobility Load Balancing
MME
Mobility Management Entity
mMTC
massive Machine‐Type Communications
MNO
Mobile Network Operator
MnS
Management Service
MORAN
Multi‐Operator Radio Access Network
MPLS
Multiprotocol Label Switching
MR
Measurement Report
MRO
Mobility Robustness Optimization
mMIMO
massive MIMO
M‐MIMO
Massive MIMO
MU‐MIMO
Multi‐User MIMO
M‐plane
Management‐plane
MS
Microsoft
mTLS
mutual TLS
MTI
Microelectronics Technology
MWC
Mobile World Congress
NACM
Network Configuration Access Control Model
NAS
Non‐Access Stratum
NCC
Network and Computing Convergence
NDAA
National Defense Authorization Act
Near‐RT RIC
Near‐Real‐Time RAN Intelligent Controller
NESAS
Network Equipment Security Assurance Scheme
NETCONF
Network Configuration Protocol
NF
Network Function
NFO
Network Function Orchestrator
NFV
Network Functions Virtualization
NG
Next Generation
NGA
Next G Alliance
NGAP
Next‐Generation Application Protocol
NGC
Next‐Generation Core
NGMN
Next‐Generation Mobile Network
NG‐RAN
Next‐Generation RAN
NI
National Instruments
NI
Network Interface
NIB
Network Information Base
NMEA
National Marine Electronics Association
NMS
Network Management System
Non‐RT RIC
Non‐Real‐Time RAN Intelligent Controller
NPN
Non‐Public Network
NR
New Radio
NRF
Network Repository Function
NS
Network Service
NSA
Non‐Stand‐Alone
NSC
National Spectrum Consortium
NSF
National Science Foundation
NSSI
Network Slice Subnet Instance
NTIA
National Telecommunications and Information Administration
NTN
Non‐Terrestrial Network
NVD
National Vulnerability Database
NWDAF
Network Data Analytics Function
O‐CU
O‐RAN Central Unit
O‐CU‐CP
O-CU Control Plane
O‐CU‐UP
O-CU User Plane
O‐DU
O‐RAN Distributed Unit
O‐eNB
O‐RAN eNB
OAI
Open Air Interface
OAIC
Open AI Cellular
OAIC‐C
OAIC‐Controllers
OAIC‐T
OAIC‐Testing
OAM
Operation, Administration, and Maintenance
OFDMA
Orthogonal Frequency Division Multiple Access
OLT
Optical Line Termination
ONAP
Open Network Automation Protocol
ONF
Open Networking Foundation
ONOS
Open Network Operating System
ONU
Optical Networking Unit
OpEx
Operating Expenditure
O‐RAN
Open Radio Access Network
O‐RU
O‐RAN Radio Unit
OS
Operating System
OSC
O‐RAN Software Community
OSS
Operations Support System
OTA
Over‐The‐Air
OTIC
O‐RAN Testing and Integration Center
OUSD
Office of the Under Secretary of Defense
PAWR
Platform for Advanced Wireless Research
PBCH
Physical Broadcast Channel
PCI
Physical Cell Identifier
PCP
Priority Code Point
PDCP
Packet Data Convergence Protocol
PDSCH
Physical Downlink Shared Channel
PDU
Protocol Data Unit
PHY
Physical (layer)
PKI
Public Key Infrastructure
PLMN
Public Land Mobile Network
PNF
Physical Network Function
PON
Passive Optical Network
POWDER
Platform for Open Wireless Data‐driven Experimental Research
PRACH
Physical Random Access Channel
PRB
Physical Resource Block
PRTC
Primary Reference Time Clock
PSK
Pre‐Shared Key
PTP
Precision Time Protocol
PUCCH
Physical Uplink Control Channel
PUSCH
Physical Uplink Shared Channel
QCI
Quality of Service Class Identifier
QoS
Quality of Service
QP
QoS Prediction
QUIC
Quick UDP Internet Connection
R‐NIB
Radio‐Network Information Base
RACH
Random Access Channel
RADIUS
Remote Authentication Dial‐In User Service
RAN
Radio Access Network
rApp
remote Application
RAT
Radio Access Technology
RC
Radio Control
REST
REpresentational State Transfer
RF
Radio Frequency
RFC
Request For Comments
RIA
RAN Intelligence and Automation
RIC
RAN Intelligent Controller
RIS
Reflective Intelligent Surface
RL
Reinforcement Learning
RLC
Radio Link Control
RMR
RIC Message Router
RNC
Radio Network Controller
ROI
Return On Investment
ROMA
RAN Orchestration and Management Automation
RPC
Remote Procedure Call
RRC
Radio Resource Control
RRM
Radio Resource Management
RS
Reference Signal
RS
Rohde & Schwarz
RSRP
Reference Signal Received Power
RSRQ
Reference Signal Received Quality
RU
Radio Unit
RX
Receiver or Receive
S‐GW
Serving Gateway
S1AP
S1 Application Protocol
SA
Standalone
SBA
Service‐Based Architecture
SBOM
Software Bill of Materials
SCAS
Security Assurance Specifications
SCTP
Stream Control Transmission Protocol
SDAP
Service Data Adaptation Protocol
SDFG
Standard Development Focus Group
SDK
Software Development Kit
SDL
Shared Data Layer
SDN
Software‐Defined Networking
SDO
Standard Development Organization
SDR
Software‐Defined Radio
SD‐RAN
Software‐Defined Radio Access Network
sFTP
secure File Transfer Protocol
SI
System Integrator
SIB
System Information Block
SIM
Subscriber Identity Module
SINR
Signal‐to‐Interference‐plus‐Noise Ratio
SM
Service Model
SLA
Service‐Level Agreement
SLS
Service‐Level Specifications
SMO
Service Management and Orchestration
SON
Self‐Organizing Network
SP
Security Principlex
SP‐ACC
Security Principle‐Access Control
SP‐ASSU
Security Principle‐Assurance
SP‐AUTH
Security Principle‐Authentication
SP‐CLD
Security Principle‐Cloud
SP‐CRYPTO
Security Principle‐Cryptographic
SP‐OPNS
Security Principle‐Open Source
SP‐RECO
Security Principle‐Recoverability
SP‐SS
Security Principle‐Secure Storage
SP‐SB
Security Principle‐Secure Boot
SP‐TCOMM
Security Principle‐Trusted Communication
SP‐UPDT
Security Principle‐Secure Update
SP‐ISO
Security Principle‐Isolation
SP‐PRV
Security Principle‐Privacy
SP‐ROB
Security Principle‐Robustness
SP‐SLC
Security Principle‐Security Development, Testing, Logging
SPDX
Software Package Data Exchange
SQL
Structured Query Language
SRN
Standard Radio Node
SRS
Sounding Reference Signal
SSB
Synchronization Signal Block or Synchronization Signal Physical Broadcast Channel Block
SSH
Secure Shell
STC
Software Testing Certification
STIN
Space Terrestrial Integrated Network
SuFG
Sustainability Focus Group
SU‐MIMO
Single‐User MIMO
SUPI
Subscription Permanent Identifier
SUT
System Under Test
SW
Software
SWID
Software Identification Tag
T‐GM
Telecom‐Grandmaster
TCO
Total Cost of Ownership
TCP
Transmission Control Protocol
TDD
Time Division Duplex
TDMA
Time Division Multiple Access
TED
Test Equipment O‐DU
TEM
Test Equipment Fronthaul Multiplexer
TER
Test Equipment O‐RU
TIFG
Testing and Integration Focus Group
TIP
Telecom Infra Project
TIRO
Tactile Internet for Remote Operations
TLS
Transport Layer Security
TN
Transport Network
TNL
Transport Network Layer
ToD
Time of Day
TSC
Technical Steering Committee
TTI
Transmission Time Interval
TX
Transmitter or Transmit
UAS
Unmanned Aerial System
UAS
Unmanned Aircraft System
UAV
Uncrewed/Unmanned Aerial Vehicle
UC
User‐Control
UDP
User Datagram Protocol
UE
User Equipment
UHF
Ultra High Frequency
UL
Uplink
UMTS
Universal Mobile Telecommunication System
UP
User Plane
UPF
User Plane Function
URL
Uniform Resource Locator
URLLC
Ultra‐Reliable and Low‐Latency Communication
US
United States
USRP
Universal Software Radio Peripheral
UTM
UAS Traffic Management
V2X
Vehicle‐to‐Everything
vCU
virtual CU or virtualized CU
vDU
virtual DU or virtualized DU
VLAN
Virtual Local Area Network
VM
Virtual Machine
VNF
Virtualized Network Function
VNFC
Virtualized Network Function Controller
VoIP
Voice over IP
VoLTE
Voice over LTE
VR
Virtual Reality
vRAN
virtualized RAN
WG
Work Group
X2AP
X2 Application Protocol
xApp
extended Application
XML
eXtensible Markup Language
XnAP
Xn Application Protocol
XR
eXtended Reality
XSS
Cross‐Site Scripting
YAML
Yet Another Markup Language
YANG
Yet Another Next Generation
ZTA
Zero Trust Architecture
About the Companion Website
This book is accompanied by a companion website:
www.wiley.com/go/tripathioran
This website includes:
Online Excercises
1Introduction to O‐RAN
Cellular technologies are becoming increasingly complex. For example, fifth generation (5G) is significantly more complex than fourth‐generation (4G) cellular technology Long‐Term Evolution (LTE). Open Radio Access Network (O‐RAN), also referred to as Open RAN, is a revolutionary technology that is transforming the cellular landscape. Unlike traditional cellular networks, O‐RAN is an open, programmable, interoperable, and virtualized Radio Access Network (RAN) architecture that allows network operators to mix and match hardware and software components from different vendors. O‐RAN provides increased flexibility, scalability, and cost savings for network operators. Furthermore, O‐RAN leads to enhanced competition among vendors, which ultimately benefits consumers and enterprises.
This chapter first creates a foundation for O‐RAN by illustrating evolution of cellular technologies, reviewing components of a cellular system, and describing evolution of RAN architectures. Then, a brief introduction to the O‐RAN ALLIANCE is given, followed by illustration of a simplified O‐RAN architecture defined by the O‐RAN ALLIANCE. Deployments of O‐RAN require the use of standards and software frameworks developed by organizations other than the O‐RAN ALLIANCE in addition to the specifications developed by the O‐RAN ALLIANCE. Roles of such non‐O‐RAN ALLIANCE organizations in the O‐RAN ecosystem are discussed. Driving forces behind O‐RAN's rising importance are explained. Numerous use cases of O‐RAN that help optimize various RAN operations are described. Finally, the overall accomplishments of O‐RAN are summarized along with O‐RAN's technical priorities and potential future work.
1.1 Evolution of Cellular Technologies
O‐RAN is a comprehensive framework for implementing the radio access network portion of a cellular network. The O‐RAN specifications are developed by the O‐RAN ALLIANCE and support 4G and 5G cellular communications. As the cellular communication technologies evolve, O‐RAN specifications can be augmented to support evolved cellular technologies.
Figure 1.1 shows the evolutionary path of cellular technologies from the first generation (1G) to the sixth generation (6G).
The concept of cellular communications was developed at Bell Labs in the 1970s. The 1G cellular systems were analog. Diverse types of 1G cellular systems were deployed around the world. Examples of such 1G systems included Advanced Mobile Phone System (AMPS) in the United States and NMT 500 and European Total Access Communication System (ETACS) in Europe. The 1G systems provided voice services and typically used frequency‐division multiple access on the radio interface between the user device and the RAN. The analog 1G systems were replaced by digital second‐generation (2G) systems. Examples of 2G systems include Global System for Mobile Communication (GSM) and Interim Standard‐95 (IS‐95). GSM utilized time‐division multiple access (TDMA) and IS‐95 used code‐division multiple access (CDMA) on the radio interface. The 2G systems provided voice and low‐rate data services. The 2G GSM systems typically transitioned to 2.5G General Packet Radio Service (GPRS) and Enhanced Data rates for GSM Evolution (EDGE) and then to third‐generation (3G) Universal Mobile Telecommunication System (UMTS) and UMTS enhancements such as High‐Speed Downlink Packet Access and High‐Speed Uplink Packet Access. 2G IS‐95 systems evolved to 3G CDMA200 and 1xEV‐DO systems. While 2.5G systems provided higher data rates such as peak data rates of few hundred kilobits per second, 3G systems provided peak data rates of few megabits per seconds. The 3G cellular systems use two types of core networks, a circuit‐switched core network to support circuit‐switched voice services and a packet‐switched core network to support Internet Protocol (IP)‐based services such as web browsing, video streaming, and e‐mail. The competing 3G technologies of CDMA2000 and UMTS evolved to the common 4G LTE.
Figure 1.1 Evolutionary Path of Cellular Technologies.
4G LTE utilizes orthogonal frequency‐division multiple access (OFDMA) on the radio interface. Furthermore, LTE utilizes a single type of core network, a packet‐switched core network called Evolved Packet Core (EPC). Since there is no circuit‐switched core network in LTE, voice calls are supported using Voice over IP (VoIP), widely known as Voice over LTE (VoLTE). The use of OFDMA and wide radio channel bandwidths enable LTE to support much higher data rates such as tens of megabits per seconds.
5G is a technology with the potential to transform many industries and segments of the economy. While 5G continues to use OFDMA on the radio interface, it significantly increases the flexibility such as large channel bandwidths, variable subcarrier spacing, support for millimeter wave spectrum, and cartier bandwidth parts. A high‐performance and flexible radio interface enables 5G to support a much broader set of use cases. These use cases may belong to one or more ITU usage categories of enhanced mobile broadband (eMBB), ultra‐reliable and low‐latency communication (URLLC), and massive Internet of Things (mIoT). 5G introduces network slicing, where different logical networks are created to meet diverse service and customer requirements using the same physical infrastructure. 5G also introduces a Service‐Based Architecture (SBA) that makes use of virtualization technologies for efficiency, scalability, and flexibility.
6G is the first cellular technology that emphasizes humanity and environment right from the requirements phase instead of focusing primarily on user experience and network performance like previous generations of cellular technologies (NGA 2022). 6G is expected to be even more transformational than 5G. 6G is likely to introduce new technologies such as native artificial intelligence (AI), Reflective Intelligent Surface (RIS), and higher‐frequency spectrum, such as sub‐THz spectrum and THz spectrum.
1.2 Components of Cellular Systems
While wireless communication is one of the most prominent features of a cellular system, the overall cellular system includes both wireless and wired links. Figure 1.2 illustrates a high‐level architecture of a 5G system (Tripathi and Reed 2019).
A 5G system consists of the user equipment (UE), the 5G access network (AN), and the 5G core network (5GC or 5GCN) (3GPP TS23.501 2024). Different types of 5G UEs are supported including smartphones, Internet of Things (IoT) devices, smart watches, and augmented reality/virtual reality headsets. The 5G access network may be a Third Generation Partnership Project (3GPP)‐defined RAN such as next‐generation RAN (NG‐RAN) or a non‐3GPP access network. The NG‐RAN may have next‐generation‐Node Bs (gNBs) or next‐generation‐evolved Node Bs (ng‐eNBs). The gNB communicates with 5G UEs using a New Radio (NR) air interface, while the ng‐eNB communicates with UEs using the 4G LTE air interface. Both the gNB and the ng‐eNB connect to the 5GC, which is also referred to as the next‐generation core (NGC). A 5G RAN can be defined as the RAN that utilizes the 5G NR air interface for communications with UEs. Hence, 5G RAN is a subset of NG‐RAN, because NG‐RAN can encompass both gNBs and ng‐eNBs. An example of a non‐2GPP access network is a Wi‐Fi access network. This book primarily focuses on the 5G NR air interface between the 5G UE and the gNB while discussing the O‐RAN.
Figure 1.2 5G System: A High‐Level Overview.
A 5G UE exchanges Access Stratum (AS) signaling such as Radio Resource Control (RRC) signaling with the gNB in support of various RAN operations such as RRC connection setup, bearer setup for user traffic exchange, and handover. A 5G UE exchanges Non‐Access Stratum (NAS) signaling with the NGC in support of operations such as registration, mutual authentication, security activation, and protocol data unit (PDU) session setup. The gNB transparently transports the NAS signaling messages between the UE and the NGC. A UE can connect to and exchange user traffic with data networks (DNs) such as the internet through the 5G AN and the NGC.
The 5G O‐RAN represents one possible way of designing and deploying a 5G AN. An operator or a service provider may deploy a 5G RAN with or without O‐RAN, although O‐RAN is expected to be a dominant way of deploying 5G RAN. The 5G O‐RAN can be viewed as the realization of the 5G RAN, where gNBs or gNB entities such as gNB‐Central Units (gNB‐CUs) and gNB‐Distributed Units (gNB‐DUs) comply with O‐RAN specifications. The O‐RAN specifications utilize concepts such as disaggregation, openness, AI, and virtualization and cloud technologies. The 5G O‐RAN does not alter the 3GPP‐defined NR air interface between the UE and the 5G RAN in any way. A 5G UE does not need to be aware of the O‐RAN and does not need to do anything differently to be able to work with the 5G O‐RAN. A 5G O‐RAN appears to a 5G UE as a 3GPP‐defined 5G RAN. Similarly, the NGC does not need to be aware of the O‐RAN and does not need to do anything differently to be able to work with the 5G O‐RAN.
1.3 Evolution of the RAN
The 3GPP has defined the architectures for 3G, 4G, and 5G. Such architectures are referred to as logical architectures, where logical links between the network nodes, network elements, or network functions (NFs) are defined. For example, two gNBs can communicate with each other using the Xn interface. Specifically, two gNBs exchange Xn Application Protocol (XnAP) signaling with each other. The user traffic can also traverse on the Xn interface between two gNBs via a GTP1 tunnel in support of packet forwarding during the inter‐gNB handover. The 3GPP does not dictate or mandate any specific physical implementation or realization of the architecture. Hence, the operator has flexibility in deciding how to design, provision, and deploy the network architecture to meet target objectives.
Figure 1.3 illustrates how RAN evolution has occurred through generations of cellular technologies.
The older generations of cellular technologies from 1G to 3G utilize the RAN architecture with centralized RAN controllers called Base Station Controllers (BSCs) or Radio Network Controllers (RNCs). A BSC or RNC typically controls hundreds of base stations (BSs) or Node Bs. Certain radio resource management (RRM) tasks, such as the handover algorithm, are implemented at the BSC/RNC. The RAN thus consists of one or more BSCs and numerous BSs or Node Bs. The BSs are distributed across the cellular service area.
In commercial deployments, it is common to divide a BS into two parts, a baseband unit (BBU) and a radio unit (RU). An RU includes components such as radio frequency (RF) amplifiers and filters and is often situated next to the antenna that transmits and receives RF signals in support of wireless communications. A BBU carries out technology‐specific processing at the baseband. The BBU and the RU can be connected via an RF cable to carry an analog signal. It is also possible to use an optical fiber between the BBUs and the RU, which reduces the overall loss for the link between the mobile device and the BS. Common Public Radio Interface (CPRI) is a widely used protocol between the BBU and the RU.
Figure 1.3 Evolution of the RAN Architecture.
In a distributed RAN, BSs are distributed across the service area and a centralized RAN controller is absent. In such flat or distributed architecture, the BS manages its own radio resources and can communicate with other BSs through an interface. For example, in 4G LTE, the BSs called evolved Node Bs (eNBs or eNodeBs) communicate with each other using the Xn interface. An internal IP network of the service provider is used to implement the Xn interface between two eNBs. Such distributed or flat RAN is quite scalable, and new eNBs can be added to meet capacity and coverage needs in a given service area. Each eNB needs to connect to the core network. In commercial deployments, the eNB can be deployed using the BBU and the RU with relatively short BBU‐RU distance such as few or tens of meters. Several 4G LTE and 5G deployments have used such distributed RAN.
In a centralized RAN (C‐RAN) approach, a set of BBUs is placed in a relatively central data center and remote radio units (RRUs) or remote radio heads (RRHs) are placed at cell sites. Since the distance between the BBU and the RU is quite long (e.g., hundreds of meters or few kilometers), such RUs are called remote radio units. The C‐RAN architecture is commercially deployed in LTE networks. The C‐RAN provides benefits such as energy cost savings due to colocation of multiple BBUs, real estate cost savings due to a smaller footprint at the cell site, and performance enhancement due to enhanced collaboration of radio resources across multiple cells.
1.3.1 Horizontal Disaggregation of RAN: A Protocol Perspective
A disaggregated RAN divides the BS into a central unit (CU) and a distributed unit (DU). For example, while 5G gNBs have been deployed using the distributed RAN architecture, the 3GPP allows supports disaggregated gNBs, where a gNB is divided into a gNB‐CU and a gNB‐DU. The NR radio interface protocol stack is implemented partially at the gNB‐CU and partially at the gNB‐DU. Time‐sensitive processing (e.g., acknowledgments for received data and any needed retransmissions) is carried out at the gNB‐DU. Relatively less time‐sensitive processing such as AS signaling is carried out at the gNB‐CU. The gNB‐DUs are placed at cell sites. While gNB‐CUs can be colocated with gNB‐DUs, gNB‐CUs are often located in data centers. A gNB‐CU connects to other gNB‐CUs and the NGC. The 3GPP also allows decomposition of the gNB‐CU into the gNB‐CU‐control plane (gNB‐CU‐CP) and the gNB‐CU‐user plane (gNB‐CU‐UP).
Figure 1.4 Disaggregation of the Base Station.
Figure 1.4 illustrates disaggregation of the BS from the perspectives of the radio interface protocol stack and control plane (CP) and user plane (UP) (Peterson et al. 2023). The UP, responsible for carrying user traffic, utilizes the protocols such as Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC), and Physical (PHY) layer with the RF front end. In Figure 1.4, the CU implements RRC and PDCP protocols; the DU implements RLC, MAC, and selected PHY layer functions; and the RU implements selected PHY layer functions and the RF front end.
Software‐Defined RAN: Figure 1.5 illustrates the implementation of the RAN using software‐defined networking (SDN) principles, which leads to the development of a software‐defined RAN. This approach facilitates the incorporation of a programmatic API that supports software‐based control over the RAN UP pipeline. In the O‐RAN architecture, this programmatic API is commonly known as the RAN Intelligent Controller (RIC). Refer to Chapter 2 for more details on RICs.
The 5G O‐RAN makes use of the 3GPP‐defined disaggregated 5G RAN architecture, carries out further disaggregation of the gNB‐DU, and facilitates management of the RAN using intelligent controllers as described in Section 1.4 and Chapters 2 and 3.
When the RAN components are implemented using suitable RAN component software (e.g., the gNB‐CU software) on generic commercial‐off‐the‐shelf (COTS) hardware, such RAN implementation is termed as virtualized RAN (vRAN). The vRAN implementation no longer requires the RAN software to be coupled with specific or proprietary hardware. Hence, a service provider can purchase COTS hardware such as servers and instantiate suitable RAN software of its network vendors on such COTS servers to create a vRAN. While a vRAN can be deployed on a small scale using in‐house network resources, cloud resources can also be exploited to build a vRAN. When cloud resources are used to build a vRAN, such vRAN is also known as Cloud‐RAN. For example, cloud resources of traditional cloud service providers or cloud vendors, such as Amazon Web Services (AWS), Microsoft Azure, and Google Cloud Platform (GCP), can be used to create Cloud‐RAN.
Figure 1.5 Disaggregated Base Station with SDN Principles.
1.4 Introduction to the O‐RAN ALLIANCE and the O‐RAN Architecture
The O‐RAN ALLIANCE is an operator‐driven industry alliance that has defined the O‐RAN architecture. In this book as well as general public literature, O‐RAN usually refers to the O‐RAN architecture defined the O‐RAN ALLIANCE. Section 1.4.1 provides a brief overview of the O‐RAN ALLIANCE. Section 1.4.2 describes a high‐level O‐RAN architecture. Section 1.4.3 summarizes key focus areas of various groups operating in the O‐RAN ALLIANCE. Further details on the O‐RAN ALLIANCE and its groups can be found in Chapter 5. A comprehensive view of the O‐RAN architecture is given in Chapter 2.
1.4.1 O‐RAN ALLIANCE: A Brief Overview
The O‐RAN ALLIANCE was founded in February 2018 by AT&T, China Mobile, Deutsche Telekom, NTT DOCOMO, and Orange. It was established as a German entity in August 2018. Today's O‐RAN ALLIANCE is a global community of mobile network operators (MNOs), vendors, and research and academic institutions. The mission of the O‐RAN ALLIANCE is to “re‐shape the RAN industry towards more intelligent, open, virtualized and fully interoperable mobile networks” (O‐RAN ALLIANCE 2024a).
The O‐RAN ALLIANCE emphasizes openness and intelligence for the next‐generation wireless networks and beyond (O‐RAN ALLIANCE 2018). Open interfaces enable operators to build cost‐effective and agile RAN through multivendor deployments in a more competitive RAN supplier ecosystem. The use of open‐source software and reference hardware designs can accelerate the pace of RAN innovations. Intelligence is important to manage increasing complex RAN by minimizing human involvement, harnessing the power of AI/machine learning (ML), and automating network operations. Embedded intelligence at the component and the network level facilitates dynamic and efficient RRM, optimizing networkwide efficiency. The development of O‐RAN specifications by the O‐RAN ALLIANCE enables a more competitive and diverse RAN supplier ecosystem and can accelerate the pace of RAN innovations to increase efficiency, reduce costs, and enhance user experience.
Figure 1.6 shows the three focus streams of the O‐RAN ALLIANCE. The specification efforts involve extending RAN specifications such as the 3GPP 5G specifications to achieve openness and intelligence. Several work groups (WGs)2 have been formed to address different aspects of O‐RAN and define the overall O‐RAN specifications. The O‐RAN Software Community (OSC) of the O‐RAN ALLIANCE, in cooperation with the Linux Foundation, is in charge of the release and the development of open‐source software for O‐RAN. The testing and integration efforts facilitate O‐RAN members in testing and integration of O‐RAN implementations to ensure interoperability of products and compliance with O‐RAN specifications.
Figure 1.6 The Three Focus Streams of the O‐RAN ALLIANCE.
There are several governing bodies in the O‐RAN ALLIANCE. The O‐RAN ALLIANCE board consists of up to 15 members with 5 founding members and up to 10 elected members. The elections for the (elected) board members take place every two years. The executive committee (EC) supports the board by proposing agendas, priorities, projects, and releases for the board to consider and approve. The EC consists of representatives of the five O‐RAN founding members and two elected representatives from the board members. The Technical Steering Committee (TSC) decides or gives guidance on O‐RAN technical topics and approves O‐RAN specifications prior to the Board approval and publication. The TSC consists of member representatives and the WG and focus group cochairs.
1.4.2 The O‐RAN Architecture in a Nutshell
Figure 1.7 illustrates a simplified O‐RAN architecture (O‐RAN ALLIANCE 2024c).
Figure 1.7 Simplified Logical O‐RAN Architecture.
The 3GPP‐defined gNB‐CU‐CP and gNB‐CU‐UP are transformed into O‐RAN‐CU‐CP (O‐CU‐CP) and O‐RAN‐CU‐UP (O‐CU‐UP) by the O‐RAN ALLIANCE, respectively. Furthermore, the 3GPP‐defined gNB‐DU is disaggregated and transformed into O‐RAN‐Distributed Unit (O‐DU) and O‐RAN‐Radio Unit (O‐RU) by the O‐RAN ALLIANCE. A new interface called the open fronthaul between the O‐DU and the O‐RU is defined by the O‐RAN ALLIANCE. Such disaggregation of the gNB‐DU is often referred to as functional split 7.2x. The 3GPP had studied numerous functional splits of the NR radio protocol stack and finally standardized functional split Option 2 corresponding to the gNB‐CU and the gNB‐DU. The O‐RAN ALLIANCE, in addition to supporting and augmenting such functional split, utilizes an additional split 7.2x. The O‐DU and the O‐RU interact with each other using two interfaces, open fronthaul control–user plane–synchronization (CUS)‐plane and open fronthaul management (M)‐plane. Details on this functional split 7.2x are given in Chapter 5.
