5G Radio Access Network Architecture: The Dark Side of 5G

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.

Table of Contents:
Preface xv Acknowledgments xvii List of Contributors xix Acronyms and Abbreviations xxi 1 Introduction 1 2 Market Drivers 5 Reza Arefi and Sasha Sirotkin 2.1 Introduction 5 2.2 Key Ideas 7 2.3 Spectrum 9 2.3.1 Spectrum Needs 9 2.3.2 Target Spectrum 12 2.3.3 Spectrum Implications 13 2.4 New Spectrum Models 14 2.4.1 New Ways of Sharing Spectrum 15 2.4.2 Localized Licensing 17 2.5 Regulations Facilitating 5G Applications 18 2.6 Network Deployment Models 19 2.7 Technical Requirements of 5G Radio Interfaces 20 2.8 Business Drivers 23 2.9 Role of Standards 25 2.10 Role of Open Source 29 2.11 Competition 31 2.12 Challenges 32 2.13 Summary 34 References 35 3 5G System Overview 37 3.1 Introduction 37 3.2 5G Core Network 37 Sebastian Speicher 3.2.1 Introduction 37 3.2.2 Service-Based Architecture 39 3.2.2.1 Fostering Functional Reuse 39 3.2.2.2 Overview of 5GC Control-Plane Functions 41 3.2.3 Control-User Plane Separation (CUPS) 43 3.2.4 Common Access-Agnostic Core Network 44 3.2.5 Enablers for Concurrent and Efficient Access to Local and Centralized Services 46 3.2.5.1 Overview 46 3.2.5.2 Single PDU Session-Based Access to Local Services 47 3.2.5.3 Multiple PDU Session-Based Access to Local Services 48 3.2.6 Network Slicing 50 3.2.7 Private Networks 53 3.2.7.1 Overview 53 3.2.7.2 Stand-Alone Non-public Networks 54 3.2.7.3 Public-Network-Integrated Non-public Network 55 References 57 3.3 NG Radio Access Network 59 Sasha Sirotkin 3.3.1 Introduction 59 3.3.2 Network Protocol Stacks 62 3.3.2.1 Control-Plane Protocol Stack 62 3.3.2.2 User-Plane Protocol Stack 62 3.3.2.3 Standards 63 3.3.3 NG Interface 63 3.3.3.1 NG-C Interface 64 3.3.3.2 NG-U Interface 69 3.3.4 Xn Interface 70 3.3.4.1 Xn Control Plane (Xn-C) Interface 70 3.3.4.2 Xn User Plane (Xn-U) Interface 75 3.3.5 Additional NG-RAN Features 76 3.3.5.1 RAN Sharing 76 3.3.5.2 Slicing 77 3.3.5.3 Virtualization 78 3.3.5.4 Non-3GPP Access 78 References 79 3.4 NR Protocol Stack 80 Sudeep Palat 3.4.1 Introduction 80 3.4.2 NG-RAN Architecture 81 3.4.3 NR User Plane 81 3.4.4 Supporting QoS with 5GC 86 3.4.5 NR Control Plane 88 3.4.5.1 RRC States 88 3.4.5.2 RRC Procedures and Functions 89 3.4.6 Summary 97 References 98 3.5 NR Physical Layer 99 Alexei Davydov 3.5.1 Introduction 99 3.5.2 Waveform and Numerology 100 3.5.3 Frame Structure 101 3.5.4 Synchronization and Initial Access 104 3.5.4.1 Downlink Synchronization Signals 104 3.5.4.2 Random Access Channel 106 3.5.5 Downlink Control Channel 107 3.5.6 Uplink Control Channel 109 3.5.7 Reference Signals 112 3.5.7.1 CSI-RS 112 3.5.7.2 DM-RS 114 3.5.7.3 PT-RS 115 3.5.7.4 SRS 116 3.5.8 Beam Management 116 3.5.9 Channel Coding and Modulation 118 3.5.10 Co-Existence with LTE, Forward Compatibility and Uplink Coverage Enhancement 121 References 122 4 NG-RAN Architecture 123 Colby Harper and Sasha Sirotkin 4.1 Introduction 123 4.1.1 Monolithic gNB Architecture 124 4.1.2 Common Public Radio Interface (CPRI) 125 4.1.3 Antenna Interface 129 4.1.3.1 Before 5G: WhereWe Have Been 130 4.1.3.2 New 5G Era: WhereWe Are 131 4.1.3.3 Release-17 and Beyond: WhereWe Are Going 132 4.1.4 gNB Functional Split(s) 133 4.1.5 Conclusions 138 4.1.6 Further Reading 138 References 138 4.2 High-Level gNB-CU/DU Split 140 4.2.1 Key Ideas 140 4.2.2 Market Drivers 141 4.2.3 Functional Description 143 4.2.3.1 F1 Control-Plane Protocol 144 4.2.3.2 User-Plane Protocol 154 4.2.3.3 OAM Aspects 154 4.2.4 Further Reading 154 References 155 4.3 Multi-Radio Dual Connectivity 156 Sergio Parolari 4.3.1 Key Ideas 157 4.3.2 MR-DC Options 157 4.3.3 Market Drivers 158 4.3.4 Functional Description 160 4.3.4.1 Control Plane 160 4.3.4.2 User Plane 164 4.3.4.3 Procedures 169 4.3.5 Further Reading 174 References 175 4.4 Control–User Plane Separation 176 Feng Yang 4.4.1 Key Ideas 176 4.4.2 Market Drivers 177 4.4.3 Functional Description 179 4.4.3.1 Control Plane 180 4.4.3.2 OAM Aspects 187 4.4.3.3 Relation to SDN 188 4.4.3.4 Relation to 5GC 188 4.4.4 Further Reading 189 References 190 4.5 Lower-Layer Split 191 4.5.1 Key Ideas 191 4.5.2 Market Drivers 192 4.5.3 Functional Split 194 4.5.3.1 Fronthaul Bandwidth Requirements 195 4.5.3.2 Low-Level Functional Split Details 196 4.5.3.3 Latency Management 198 4.5.4 Fronthaul Interface 200 4.5.4.1 Messages 201 4.5.4.2 Scheduling Procedure 207 4.5.4.3 Beamforming Methods 209 4.5.5 Fronthaul Timing Synchronization 209 4.5.6 Operation, Administration and Maintenance (OAM) 210 4.5.7 Further Reading 211 References 212 4.6 Small Cells 213 Clare Somerville 4.6.1 Key Ideas 213 4.6.2 Market Drivers 214 4.6.3 Barriers and Solutions 215 4.6.3.1 Site Locations 215 4.6.3.2 Scaling Up Deployment 215 4.6.3.3 Backhaul 216 4.6.3.4 Edge Compute 216 4.6.4 Small Cell Variants 216 4.6.4.1 Disaggregation Architectures 216 4.6.4.2 Platform Architectures 218 4.6.4.3 Operating Frequency Impacts on Architecture 220 4.6.4.4 Operational Models 221 4.6.5 Key Interfaces for Small Cells 222 4.6.5.1 FAPI 222 4.6.5.2 nFAPI 226 4.6.5.3 Management Plane 228 4.6.6 Worked Examples 229 4.6.6.1 Indoor Enterprise Example 229 4.6.6.2 Outdoor Urban Example 230 4.6.6.3 Private Network Example 231 4.6.7 Further Reading 232 References 232 4.7 Summary 233 5 NG-RAN Evolution 235 5.1 Introduction 235 5.2 Wireless Relaying in 5G 235 Georg Hampel 5.2.1 Key Ideas 236 5.2.2 Market Drivers 237                                                                                                                               5.2.3 Functional Description 239 5.2.3.1 IAB Architecture 239 5.2.3.2 Backhaul Transport and QoS 242 5.2.3.3 Resource Coordination 247 5.2.3.4 Plug-and-Play Network Integration 250 5.2.4 Outlook 255 References 255 5.3 Non-terrestrial Networks 257 Leszek Raschkowski, Eiko Seidel, Nicolas Chuberre, Stefano Cioni, Thibault Deleu, and Thomas Heyn 5.3.1 Key Ideas 258 5.3.2 Market Drivers 260 5.3.3 NTN Based NG-RAN Architecture 261 5.3.3.1 Access Network with Transparent NTN Payload 261 5.3.3.2 Access Network with Regenerative NTN Payload 262 5.3.3.3 Transport network based on NTN 262 5.3.4 NTN radio protocol 262 5.3.4.1 Scheduling and Link Adaptation 264 5.3.4.2 NR Layer 2 Enhancements for NTN 264 5.3.4.3 NR Control-Plane Procedure Adaptations for NTN 265 5.3.4.4 NR Mobility within NTN 266 5.3.5 NR Physical Layer Adaptations for NTN 267 5.3.5.1 Timing and Frequency Acquisition and Tracking 267 5.3.5.2 HARQ 268 5.3.5.3 Timing Advance (TA) 271 5.3.5.4 Physical Layer Control Loops 272 5.3.6 NTN Channel Model 272 5.3.7 Outlook 274 References 274 6 Enabling Technologies 277 6.1 Introduction 277 6.2 Virtualization 277 Sridhar Rajagopal 6.2.1 Key Ideas 278 6.2.2 Market Drivers 279 6.2.3 Architecture Evolution Toward Virtualization 280 6.2.4 Containers and Microservices 280 6.2.5 NFV Evolution 284 6.2.6 RAN Virtualization Platform 285 6.2.6.1 gNB-DU and gNB-CU Virtualization 286 6.2.6.2 Standardization of Orchestration and Cloudification in O-RAN 288 6.2.7 Virtualization Challenges 289 6.2.7.1 Accelerator Integration 289 6.2.7.2 Timing and Synchronization 290 6.2.7.3 RAN Scaling withWorkload 290 6.2.7.4 Inter-Process Communication 291 6.2.7.5 Virtualization Overhead 291 6.2.7.6 SCTP/GTP Interface Support 291 6.2.7.7 High Availability 292 6.2.7.8 Power Consumption 292 6.2.7.9 Distributed Cloud Deployments for RAN Nodes 292 6.2.8 Further Reading 293 References 293 6.3 Open Source 294 Sasha Sirotkin 6.3.1 Key Ideas 295 6.3.2 Market Drivers 296 6.3.3 Open Source License 296 6.3.4 Software-Defined Radio 298 6.3.5 Open Source RAN Projects 299 6.3.5.1 srsLTE 299 6.3.5.2 OpenLTE 300 6.3.5.3 OpenBTS 300 6.3.5.4 Open Air Interface 300 6.3.5.5 TIP 301 6.3.5.6 O-RAN 301 6.3.6 Summary 302 References 302 6.4 Multi-Access Edge Computing 303 Miltiadis Filippou and Dario Sabella 6.4.1 Key Ideas 304 6.4.2 Market Drivers 304 6.4.3 MEC Standard 305 6.4.3.1 ETSI MEC System Architecture 305 6.4.3.2 ETSI MEC APIs 308 6.4.3.3 Location API 308 6.4.4 ETSI MEC Deployment in 3GPP 5G Systems 310 6.4.4.1 MEC Deployment in a 5G Network 311 6.4.5 Inter-MEC System Communication 313 6.4.5.1 Possible Implementation 315 6.4.6 Flexible MEC Service Consumption 316 6.4.6.1 Edge Host Zoning in Multi-Vendor Environments 316 6.4.7 High Mobility Automotive Scenarios 321 6.4.7.1 MEC-Supported Cooperative Information 321 6.4.8 Further Reading 323 References 323 6.5 Operations, Administration, and Management 326 Vladimir Yanover 6.5.1 Introduction 326 6.5.2 Key Ideas 326 6.5.3 Service-Based Management Architecture 327 6.5.3.1 Examples of Management Services 328 6.5.3.2 Management Service Exposure 329 6.5.4 NG-RAN and 5GC Information Models 330 6.5.5 Performance Management 330 6.5.6 Management of Split NG-RAN 332 6.5.6.1 Background 332 6.5.6.2 Information Object Classes 332 6.5.7 O-RAN Alliance Management Architecture 333 6.5.8 Management of Network Slicing 334 6.5.8.1 Basic Concepts of Slicing Management 334 6.5.8.2 Support of Slicing Management in RAN Provisioning Service 336 6.5.8.3 Configuration and LCM of NSSI and NSI 337 6.5.8.4 NSI and NSSI Information Models (NRMs) 338 6.5.9 SON in 5G 338 6.5.9.1 SON Evolution 338 6.5.9.2 “Legacy” SON Use Cases 339 6.5.9.3 Multi-Domain SON with E2E Optimization 340 6.5.9.4 SON Enablers in 5G System 342 6.5.9.5 Distributed SON 342 6.5.9.6 Hybrid SON 343 6.5.10 Further Reading 343 References 345 6.6 Transport Network 346 Yaakov (J.) Stein, Yuri Gittik, and Ron Insler 6.6.1 Key Ideas 346 6.6.2 Market Drivers 347 6.6.3 Defining the Problem 349 6.6.4 The Physical Layer 350 6.6.4.1 Achieving the Required Data Rates 351 6.6.4.2 Achieving the Required Latencies 352 6.6.4.3 Achieving the Required Reliability 355 6.6.4.4 Frequency and Time Synchronization 357 6.6.4.5 Energy Efficiency 360 6.6.5 Higher Layers 360 6.6.5.1 xHaul Network Topology 362 6.6.5.2 Transport Protocols 363 6.6.5.3 Protocol Stacks for User Traffic 366 6.6.5.4 Technology Comparison 367 6.6.6 Conclusions 374 References 374 7 NG-RAN Deployment Considerations 379 Andreas Neubacher and Vishwanath Ramamurthi 7.1 Introduction 379 7.2 Key Ideas 381 7.3 Deployment Objectives and Challenges 381 7.3.1 Where to Provide Coverage 381 7.3.2 Network Capacity and Compute Resource Planning 383 7.3.2.1 Air Interface Capacity 383 7.3.2.2 Compute Resources for Edge Computing Services 384 7.3.2.3 Reliability Considerations 385 7.3.3 Service Fulfillment Criteria 386 7.4 Deployment Considerations 387 7.4.1 Deployment Cost 387 7.4.2 Spectrum and Radio Propagation Considerations 388 7.4.3 5G Frequency Ranges 390 7.4.4 Transport Considerations 391 7.4.5 Baseband Pooling 393 7.4.6 Choice of a NG-RAN Split Architecture 394 7.4.6.1 Sub-6 GHz Case 394 7.4.6.2 High-Band (mmWave) Case 394 7.5 Conclusions 395 References 395 Index 397