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- Sprache: Englisch
Self-contained resource on fundamental concepts and the planning, provisionining, design, and operations of 3GPP-based NTNs
3GPP-based Non-Terrestrial Networks in 5G and 6G: Expanding the Frontiers of Wireless Communications provides an overview of Non-Terrestrial Networks (NTNs) in the context of 3GPP systems such as 4G LTE and 5G NR. Unique challenges of NTNs such as long and variable propagation delays, large and time-varying Doppler shifts, different types of beams including Earth-fixed beams, quasi-Earth-fixed beams, and Earth-moving beams and transparent and regenerative payloads are discussed. The mechanisms that 3GPP foresees to tackle these NTN-specific challenges are described and, furthermore, the planning, provisioning, design, and operations of the radio and core networks for NTNs are illustrated.
NTN considerations in the book range from physical-layer aspects (e.g., synchronization, random access, and uplink and downlink data transmission), to mobility management including handover and cell reselection, and to network architecture. Fundamentals of the associated concepts of NR, eMTC (i.e., LTE_M), and NB-IoT are described so that their customizations for NTNs become clear in NTN-specific discussions. NTN features in 3GPP Release 17, 18, and 19 are described andhe role of NTN in 6G is also summarized.
A companion website provides exercises to help learners to reinforce concepts, along with software utilities (e.g., Excel spreadsheets) that provide templates to investigate the impact of various factors (e.g., carrier frequency and channel bandwidth) on the performance of NTNs (e.g., coverage and capacity/throughput).
3GPP-based Non-Terrestrial Networks in 5G and 6G includes information on:
- Earth-fixed beams, Earth-moving beams, and quasi-Earth-fixed beams, as well as characteristics of Geo Synchronous Orbit (GSO) and Non-GSO (NGSO) satellites such as Low Earth Orbit (LEO) satellites
- Challenges unique to NTNs including large coverage areas, mobility of cells, and different types of payloads (e.g., transparent and regenerative)
- Issues surrounding data transfer in NTNs such as time and frequency pre-compensation, timers for different radio protocol stack layers, and HARQ enabling/disabling
- Random access, RRC connection setup, registration/attach, and PDU session/EPS bearer setup for LTE-M, NB-IoT, and 5G NR
3GPP-based Non-Terrestrial Networks in 5G and 6G is an essential resource for wireless communications and satellite industry engineers and professionals seeking to facilitate the design, provisioning, deployment, operations, maintenance, and optimization of 5G-based NTNs and identify R&D areas for 5G-advanced-based and 6G-based NTNs.
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Table of Contents
Cover
Table of Contents
Series Page
Title Page
Copyright Page
Dedication Page
About the Authors
Preface
Acknowledgments
Acronyms
About the Companion Website
1 Introduction to a Non‐Terrestrial Network
1.1 Non‐Terrestrial Networks: The Definition
1.2 Simplified 3GPP NTN Architecture
1.3 Motivation for the NTN
1.4 An Overview of NTN Use Cases
1.5 3GPP NTN Roadmap
1.6 Role of the NTN in 6G
1.7 Major Takeaways
References
2 Types of NTN Platforms
2.1 Types of NTN Platforms
2.2 Characteristics of Satellites
2.3 Characteristics of UASs of the NTN
2.4 Types of Beams
2.5 An Overview of Pre‐5G Satellite Systems
2.6 Types of NTN Devices for the NTN
2.7 Trends in NTN Deployments
2.8 Major Takeaways
References
3 Radio Interfaces of LTE‐M, NB‐IoT, and NR: A Concise Introduction
3.1 3GPP‐Defined Wireless IoT Technologies and 5G New Radio: A Concise Introduction
3.2 LTE‐M: A 3GPP‐Defined Wireless IoT Technology
3.3 NB‐IoT: A 3GPP‐Defined Wireless IoT Technology
3.4 5G: A 3GPP‐Defined Transformational Technology
3.5 LTE‐M and NB‐IoT Enhancements Beyond Release 13
3.6 Major Takeaways
References
4 Challenges of an NTN
4.1 An Overview of NTN‐Specific Challenges
4.2 Long and Variable Propagation Delays
4.3 High and Variable Doppler Shifts
4.4 NTN Cell Size
4.5 NTN Cell Mobility
4.6 Type of Beams
4.7 Types of NTN Payloads
4.8 Propagation Path Loss
4.9 Long‐Term Signal Strength Characteristics
4.10 Special Atmospheric Effects
4.11 Feeder Link Switch
4.12 Noncontiguous/Noncontinuous Coverage
4.13 3GPP Solutions to the NTN Challenges: A High‐Level Overview
4.14 Major Takeaways
References
5 NTN Architectures
5.1 NTN Network Architectures in a Nutshell
5.2 An NTN with a Transparent Payload
5.3 An NTN Network Architecture with Regenerative Payloads
5.4 Multi‐connectivity NTNs
5.5 An NTN with a Transparent Payload: A Closer Look
5.6 Enhanced Tracking Area Management for an NTN
5.7 Enhanced QoS for an NTN
5.8 Optical Communication for an NTN
5.9 Major Takeaways
References
6 RF Planning and Design Considerations for an NTN
6.1 RF Planning and Design for an NTN: An Overview
6.2 NTN Spectrum
6.3 NTN Devices
6.4 RF Propagation Models
6.5 Framework for NTN Link Budgets
6.6 NTN Capacity Planning
6.7 3GPP‐Estimated Link Budgets and Throughput for an NTN
6.8 Major Takeaways
References
7 Pre‐Data Transfer Operations in an NTN
7.1 Overview of Pre‐Data Transfer NTN Operations
7.2 Pre‐Data Transfer Operations in NR‐NTN: A Closer Look
7.3 Selected Operations in IoT‐NTN: A Closer Look
7.4 Major Takeaways
References
8 Downlink and Uplink Data Transfer in an NTN
8.1 Characteristics of Data Transfer in an NTN: An Overview
8.2 Data Transfer in the NR‐NTN
8.3 Data Transfer in the LTE‐M NTN
8.4 Data Transfer in the NB‐IoT NTN
8.5 Major Takeaways
References
9 Mobility Management in an NTN
9.1 RRC States and Mobility Management in a TN and an NTN
9.2 Mobility Challenges in the NTN and Associated Solutions
9.3 Mobility Management in the NR‐NTN
9.4 Mobility Management in the LTE‐M NTN
9.5 Mobility Management in the NB‐IoT NTN
9.6 Feeder Link Switchover in the NTN
9.7 Discontinuous Coverage in the NR‐NTN or IoT‐NTN
9.8 Major Takeaways
References
10 Evolution of the NTN in 5G‐Advanced and 6G
10.1 Evolution of the NTN
10.2 NTN Enhancements in Release 19
10.3 NTN and 6G
10.4 O‐RAN‐Based NTN Deployments
10.5 NTN Research Directions
10.6 Major Takeaways
References
Index
End User License Agreement
List of Tables
Chapter 1
Table 1.1 Examples of NTN Use Cases.
Chapter 2
Table 2.1 Characteristics of GEO, MEO, and LEO Satellites.
Table 2.2 Characteristics of HAPS‐Based UAS.
Chapter 4
Table 4.1 Example Propagation Delays in the NTN.
Table 4.2 Doppler Shifts in the NTN.
Chapter 6
Table 6.1 Example Frequency Ranges for the 3GPP NTN Analysis.
Table 6.2 3GPP Operating Bands for the NTN.
Table 6.3 3GPP E‐UTRA Operating Bands for the IoT‐NTN (Satellite Ac...
Table 6.4 Salient Characteristics of NTN Devices.
Table 6.5 Clutter Loss for Different Environments.
Table 6.6 Probability of LOS RF Propagation.
Table 6.7 Shadow Fading Standard Deviation for Different Environmen...
Table 6.8 Propagation Model Coefficients for the Building Penetrati...
Table 6.9 Key Components of the NTN Link Budget.
Table 6.10 Example Link Budget Parameter Settings for the Uplink....
Table 6.11 Example Link Budget Parameter Settings for the Downlink...
Table 6.12 Satellite Parameters for the NTN Analysis.
Table 6.13 NTN UE Parameters for the NTN Analysis.
Table 6.14 CNR for Selected 3GPP Study Cases for an NTN (3GPP 2023...
Table 6.15 UE Throughput for Selected 3GPP Study Cases for an NTN ...
Chapter 7
Table 7.1 System Information Enhancements for the NR‐NTN.
Table 7.2 SIB 19 in NR‐NTN: A Closer Look.
Table 7.3 NTN‐Config in SIB 19 in NR‐NTN: A Closer Look.
Table 7.4 SIB 25 in NR‐NTN: A Closer Look.
Table 7.5 Key System Information Enhancements for the LTE‐M NTN.
Table 7.6 SIB 31 in LTE‐M NTN: A Closer Look.
Table 7.7 SIB 32 in LTE‐M NTN: A Closer Look.
Table 7.8 SIB 33 in LTE‐M NTN: A Closer Look.
Table 7.9 Key System Information Enhancements for the NB‐IoT NTN.
Table 7.10 IoT‐NTN‐Related Capabilities of an LTE‐M NTN UE in Rele...
Table 7.11 IoT‐NTN‐Related Capabilities of an LTE‐M NTN UE in Rele...
Table 7.12 IoT‐NTN‐Related Capabilities of an NB‐IoT NTN UE in Rel...
Table 7.13 IoT‐NTN‐Related Capabilities of an NB‐IoT NTN UE in Rel...
Chapter 8
Table 8.1 Characteristics of CQI Tables.
Chapter 10
Table 10.1 Required Capabilities for 6G Usage Scenarios.
List of Illustrations
Chapter 1
Figure 1.1 Simplified NTN Architecture.
Figure 1.2 NTN Use Case Categories.
Figure 1.3 3GPP NTN Roadmap.
Chapter 2
Figure 2.1 Types of NTN Platforms.
Figure 2.2 Earth‐Fixed Beams in an NTN.
Figure 2.3 Quasi‐Earth‐Fixed Beams in an NTN.
Figure 2.4 Earth‐Moving Beams in an NTN.
Figure 2.5 Examples of Pre‐5G Satellite Constellations.
Figure 2.6 Example Types of NTN Devices.
Chapter 3
Figure 3.1 LTE, LTE‐M, and NB‐IoT: A Quick Comparison.
Figure 3.2 Traditional EPC Architecture.
Figure 3.3 Methods for IoT Traffic Transfer.
Figure 3.4 IoT‐Centric Enhanced EPC Architecture.
Figure 3.5 5G System Architecture.
Figure 3.6 LTE‐M Features.
Figure 3.7 Radio Interface Protocol Stack for LTE, LTE‐M, and NB‐I...
Figure 3.8 LTE Frame Structure.
Figure 3.9 Narrowbands and Subframes in LTE‐M.
Figure 3.10 Initial Attach and EPS Bearer Setup in LTE‐M.
Figure 3.11 Random‐Access Procedure in LTE‐M.
Figure 3.12 RRC Connection Setup in LTE‐M.
Figure 3.13 Downlink Data Transfer in LTE‐M.
Figure 3.14 Uplink Data Transfer in LTE‐M.
Figure 3.15 Handover in LTE‐M.
Figure 3.16 Cell Reselection and Tracking Area Update in LTE‐M.
Figure 3.17 NB‐IoT Features.
Figure 3.18 Initial Attach and EPS Bearer Setup in NB‐IoT.
Figure 3.19 Random‐Access Procedure in NB‐IoT.
Figure 3.20 RRC Connection Setup in NB‐IoT.
Figure 3.21 Downlink Physical Signals and Channels in NB‐IoT.
Figure 3.22 Downlink Data Transfer in NB‐IoT.
Figure 3.23 Example Uplink Data Transfer in NB‐IoT.
Figure 3.24 Key Features of 5G NR.
Figure 3.25 Initial Registration in 5GS.
Figure 3.26 PDU Session Setup in 5GS.
Figure 3.27 Random‐Access Procedure in 5G NR.
Figure 3.28 RRC Connection Setup in 5G NR.
Figure 3.29 Downlink Data Transfer in 5G NR.
Figure 3.30 Uplink Data Transfer in 5G NR.
Figure 3.31 Handover in 5G NR.
Figure 3.32 Cell Reselection and Tracking Area Update in 5G NR.
Figure 3.33 Post‐Release 13 LTE‐M and NB‐IoT Enhancements.
Chapter 4
Figure 4.1 Major Challenges of the NTN.
Figure 4.2 Propagation Delays for Different NTN Platforms.
Figure 4.3 Propagation Delay Variations in an NTN.
Figure 4.4 Doppler Shifts in an NTN.
Figure 4.5 Cell Sizes in an NTN.
Figure 4.6 Impact of NTN Cell Mobility on Registration Updates.
Figure 4.7 Transparent and Regenerative Payloads in an NTN.
Figure 4.8 Long‐Term Signal Strength Characteristics in an NTN.
Figure 4.9 Feeder Link Switch in an NTN.
Chapter 5
Figure 5.1 NTN Architecture Options.
Figure 5.2 An NTN with a Transparent NTN Payload.
Figure 5.3 An NTN with a Regenerative NTN Payload Containing a gNB...
Figure 5.4 An NTN with a Regenerative NTN Payload Containing a gNB...
Figure 5.5 A Multi‐connectivity NTN with a Transparent NTN and a T...
Figure 5.6 A Multi‐connectivity NTN with a gNB‐Based Regenerative ...
Figure 5.7 A Multi‐connectivity NTN with a gNB‐DU‐Based Regenerati...
Figure 5.8 A Multi‐connectivity NTN with Two Regenerative NTNs.
Figure 5.9 An NTN with Non‐terrestrial Core/Service Networks.
Figure 5.10 Example Implementation of an NTN with a Transparent P...
Figure 5.11 Enhanced Tracking Area Management in an NTN.
Chapter 6
Figure 6.1 RF Planning and Design in an NTN.
Figure 6.2 RF Propagation Modeling in an NTN.
Figure 6.3 Capacity Planning in a Cellular Network.
Figure 6.4 Capacity Planning in a Cellular Network.
Figure 6.5 Consideration of Large Cells for NTN Capacity Planning....
Figure 6.6 Consideration of Cell Mobility for NTN Capacity Plannin...
Figure 6.7 Consideration of a Variable Cell Size for NTN Capacity ...
Figure 6.8 Consideration of Variable Device—NTN Payload Distances ...
Figure 6.9 Consideration of Unique Interfaces for NTN Capacity Pla...
Chapter 7
Figure 7.1 Pre‐Data Transfer Operations upon NTN UE Power‐Up in an...
Figure 7.2 Key NR‐NTN Enhancements in Pre‐Data Transfer Operations...
Figure 7.3 Cell Selection and SI Acquisition in an NTN.
Figure 7.4 Timing Relationship in an NR‐NTN.
Figure 7.5 Simplified 4‐Step Random‐Access Procedure in NR‐NTN....
Figure 7.6 RRC Connection Setup in an NR‐NTN.
Figure 7.7 Initial Registration in the 5GS via NR‐NTN.
Figure 7.8 UE Capability Transfer in NR‐NTN.
Figure 7.9 PDU Session Setup in 5GS via NR‐NTN.
Figure 7.10 Key IoT‐NTN Enhancements in Pre‐Data Transfer Operati...
Figure 7.11 Cell Selection and SI Acquisition in IoT‐NTN.
Figure 7.12 Timing Relationship in IoT‐NTN.
Figure 7.13 Simplified 4‐Step Random‐Access Procedure in IoT‐NTN....
Figure 7.14 RRC Connection Setup in an IoT‐NTN.
Figure 7.15 Initial Attach with EPS Bearer Setup in IoT‐NTN.
Figure 7.16 UE Capability Transfer in IoT‐NTN.
Chapter 8
Figure 8.1 Important Factors for Data Transfer in an NTN.
Figure 8.2 Key Data Transfer Prerequisites for the NR‐NTN.
Figure 8.3 Timing Relationship Between the DL Frame and the UL Fra...
Figure 8.4 Downlink Data Transfer in the NR‐NTN.
Figure 8.5 Uplink Data Transfer in the NR‐NTN.
Figure 8.6 Key Data Transfer Prerequisites for the LTE‐M NTN.
Figure 8.7 Timing Relationship Between the DL Frame and the UL Fra...
Figure 8.8 Downlink Data Transfer in the LTE‐M NTN.
Figure 8.9 Uplink Data Transfer in the LTE‐M NTN.
Figure 8.10 Key Data Transfer Prerequisites for the NB‐IoT NTN.
Figure 8.11 Timing Relationship Between the DL Frame and the UL F...
Figure 8.12 Downlink Data Transfer in the NB‐IoT NTN.
Figure 8.13 Uplink Data Transfer in the NB‐IoT NTN.
Chapter 9
Figure 9.1 Impact of the RRC State on Mobility Management in 5G NR...
Figure 9.2 NTN Mobility: Challenges and Candidate Solutions.
Figure 9.3 Location‐Based Trigger in the NR‐NTN.
Figure 9.4 Time‐Based Trigger in the NR‐NTN.
Figure 9.5 Conditional Handover in the NR‐NTN.
Figure 9.6 NR‐NTN UE Activities in the RRC_IDLE State.
Figure 9.7 Conditional Handover in the LTE‐M NTN.
Figure 9.8 Activities of an LTE‐M NTN UE in the RRC_IDLE State.
Figure 9.9 Feeder Link Switchover in the NTN.
Chapter 10
Figure 10.1 NR‐NTN Enhancements in Release 19.
Figure 10.2 IoT‐NTN Enhancements in Release 19.
Figure 10.3 Key 6G Organizations.
Figure 10.4 IMT‐2030 Usage Scenarios and Overarching Aspects.
Figure 10.5 Performance Targets for IMT‐2030 Capabilities.
Figure 10.6 Potential 6G Technology Enablers.
Figure 10.7 Candidate 6G Radio Technologies.
Figure 10.8 Key Technology Areas for Trustworthiness in 6G.
Figure 10.9 O‐RAN architecture.
Guide
Cover Page
Table of Contents
Series Page
Title Page
Copyright Page
Dedication Page
About the Authors
Preface
Acknowledgments
Acronyms
About the Companion Website
Begin Reading
Index
WILEY END USER LICENSE AGREEMENT
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IEEE Press445 Hoes LanePiscataway, NJ 08854
IEEE Press Editorial BoardSarah Spurgeon, Editor in Chief
Moeness Amin
Ekram Hossain
Desineni Subbaram Naidu
Jón Atli Benediktsson
Brian Johnson
Yi Qian
Adam Drobot
Hai Li
Tony Quek
James Duncan
James Lyke
Behzad Razavi
Hugo Enrique Hernandez Figueroa
Joydeep Mitra
Thomas Robertazzi
Albert Wang
Patrick Chik Yue
3GPP‐based Non‐Terrestrial Networks in 5G and 6G
Expanding the Frontiers of Wireless Communications
Nishith D. Tripathi
Virginia TechBlacksburgh, VA, USA
Jeffrey H. Reed
Virginia TechBlacksburgh, VA, USA
Copyright © 2026 by The Institute of Electrical and Electronics Engineers, Inc. All rights reserved.
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Library of Congress Cataloging‐in‐Publication DataNames: Tripathi, Nishith D. author | Reed, Jeffrey H. author | John Wiley & Sons publisherTitle: 3GPP‐based non‐terrestrial networks in 5G and 6G : expanding the frontiers of wireless communications / Nishith D. Tripathi [and] Jeffrey H. Reed, Virginia Tech, Blacksburg, VA, USA.Description: Hoboken, New Jersey : Wiley, [2026] | Includes index.Identifiers: LCCN 2025025543 (print) | LCCN 2025025544 (ebook) | ISBN 9781394203383 hardback | ISBN 9781394203390 adobe pdf | ISBN 9781394203406 epubSubjects: LCSH: Artificial satellites in telecommunication | 5G mobile communication systems | 6G mobile communication systemsClassification: LCC TK5104 .T75 2025 (print) | LCC TK5104 (ebook)LC record available at https://lccn.loc.gov/2025025543LC ebook record available at https://lccn.loc.gov/2025025544
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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, non‐terrestrial network (NTN)/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 co‐authored 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 thirty contributions toward the development of the 3GPP 5G specifications. As a wireless industry expert, Dr. Tripathi has contributed to organizations such as Federal Communications Commission (FCC), CTIA, Global System for Mobile communications Association (GSMA), Next G Alliance (NGA), NSC, Scientific American, FTC, EE Times University, and CNN. As an Academics Engagement Lead for the Next G Alliance (NGA), he has facilitated identification of 6G vision and requirements and made contributions to several NGA white papers on 6G. He is the founder of Aum Research and Consulting (ARC) that provides research and consulting services.
Dr. Jeffrey H. Reed is the Willis G. Worcester Professor of ECE. Professor Reed’s research interests are wireless communications, wireless security, cognitive radio, software radio, telecommunications policy, and spectrum access. Dr. Reed has co‐authored more than 500 articles and books. In addition, Dr. Reed co‐founded several commercial companies, including Federated Wireless, which commercializes spectrum sharing; PFP Cybersecurity, which provides security solutions for IoT devices; and Cirrus360, which produces tools for rapid prototyping of O‐RAN. He is the Founding Director of Wireless@Virginia Tech, a university research center, and co‐founder of Virginia Tech’s Hume Center for National Security and Technology, where he served as the Interim Director. He also served as the Interim Director of the Commonwealth Cyber Initiative and is currently its CTO. Dr. Reed is a Fellow of the IEEE for contributions to software radio and communications signal processing and for leadership in engineering education. Dr. Reed is a Fellow of the National Academy of Inventors.
Preface
Even with the deployment of five generations of cellular technologies, a significant portion of the planet’s surface area and many people still do not have access to wireless communications. Non‐Terrestrial Networks (NTNs) are becoming increasingly important in providing wireless communication services anywhere on the planet. The cost of sending a payload to space has reduced significantly recently, leading to a rise in the number of satellite launches. The NTN can also provide backhaul connectivity to the terrestrial radio network in remote areas, fallback connectivity when the terrestrial network infrastructure becomes damaged or unavailable, and supplemental connectivity to augment resource availability at the wireless device. This book explains key concepts of 3GPP1‐based NTNs in ten chapters.
Chapter 1 illustrates a simplified NTN architecture and explains its key components and interfaces. The motivation for the NTN is discussed from the perspective of the use‐case categories of service ubiquity, service continuity, and service scalability. The 3GPP roadmap on the NTN work is outlined to provide a historical perspective and summarize potential future work. The 3GPP started the NTN‐related specifications work as part of 5G cellular technology and has continued enhancing the NTN in 5G‐Advanced. The NTN is expected to play an even more important role in the sixth‐generation (6G) cellular technology. Chapter 1 also provides a glimpse of the NTN’s role in 6G.
Chapter 2 illustrates different types of NTN platforms. These NTN platforms include different types of satellites such as Geosynchronous Earth Orbit (GEO) satellites, Medium‐Earth Orbit (MEO) satellites, Low‐Earth Orbit (LEO) satellites, and High‐Altitude Platform Stations (HAPSs). Chapter 2 also discusses the distinct characteristics of NTN platforms. The NTN platform, based on its capability and design, illuminates its target coverage area using a specific type of beam. Three types of beams are illustrated in Chapter 2: Earth‐fixed beams, Earth‐moving beams, and Quasi‐Earth‐fixed beams. Satellite systems that existed prior to the deployment of the 3GPP NTN deployments are also briefly described.
Chapter 3 provides a foundation of LTE‐M, NB‐IoT, and NR air interfaces by highlighting their key features and overall operations. The associated core networks, EPC and 5GC, are also briefly discussed. While this chapter provides the foundation of LTE‐M and NB‐IoT based on Release 13, enhancements in LTE‐M and NB‐IoT beyond Release 13 are also briefly summarized. Note that the 3GPP has two parallel work streams related to the NTN: NR‐NTN and IoT‐NTN. The NR‐NTN utilizes an NR‐based air interface. The NR‐NTN utilizes gNBs in the radio network and the 5G Core (5GC) Network. The IoT‐NTN supports LTE‐M and NB‐IoT air interfaces and uses the 4G Evolved Packet Core (EPC). The IoT‐NTN utilizes pre‐Release 17 LTE‐M and NB‐IoT specifications and leverages NTN‐specific enhancements defined by the NR‐NTN to determine NTN‐related enhancements for LTE‐M and NB‐IoT specifications.
Chapter 4 describes NTN challenges and their implications for the design and operations of the NTN. The NTN poses distinct radio environment‐related challenges compared to a Terrestrial Network (TN). For example, the NTN typically has a long propagation delay and often a significantly varying propagation delay, requiring timing synchronization and timer enhancements. A non‐geostationary NTN platform leads to large and varying Doppler shifts, and suitable frequency synchronization adjustments are needed. While a TN cell is fixed, an NTN cell can move, requiring enhanced cell reselection, handover, and registration area management. An NTN may use Earth‐fixed beams, quasi‐Earth‐fixed beams, or Earth‐moving beams, requiring different mobility management approaches. The type of NTN payload, such as the transparent payload or the regenerative payload, affects the architecture, design, and operations of the NTN. Long‐term signal strength characteristics differ between the TN and the NTN, requiring a different mobility management approach in the NTN. Special atmospheric effects such as the Faraday effect and scintillations may also need to be considered for the NTN. Chapter 4 also provides a high‐level overview of the NTN solutions that the 3GPP has developed to address these NTN challenges.
Chapter 5 illustrates various candidate architectures of the NTN. While the 3GPP has defined an NTN architecture with a transparent payload in Release 17 and Release 18 NTN specifications, the 3GPP has also investigated other NTN architectures, such as an NTN with a regenerative payload and multi‐connectivity NTNs. The regenerative payload is within the scope of the 3GPP Release 19 specifications. Furthermore, in the case of a multi‐connectivity NTN, an NTN UE simultaneously communicates with (i) two NTNs (e.g., one GEO satellite‐based NTN and another LEO satellite‐based NTN) or (ii) one TN and one NTN. An example NTN architecture with non‐terrestrial core and services networks is also illustrated. Enhanced Tracking Area management and enhanced QoS for an NTN are also described. A brief overview of optical communication in the context of an NTN is also given.
Chapter 6 aims to provide insights into NTN‐specific aspects of RF Planning and Design (RPD) and RF propagation. An overall RPD framework is summarized. Potential NTN spectrum is discussed. Relevant propagation path loss models are specified, and NTN‐specific propagation effects, such as atmospheric effects including scintillations, Faraday effect, and weather effects, are discussed. Various aspects of the NTN link budget are described, including the implications of different NTN platforms, types of beams, and device types. Capacity planning for an NTN is also discussed. NTN configuration guidelines based on the NTN RPD are outlined. Chapter 6 also summarizes 3GPP‐estimated link budgets and UE throughput.
Chapter 7 explains pre‐data transfer operations in the context of the NTN. Note that certain pre‐data transfer operations occur between the NTN UE and the NTN radio and core networks before an NTN UE can exchange data with the radio and core network of the NTN. These operations include cell search, network acquisition, random access, Radio Resource Control (RRC) connection setup, registration or attach, and protocol data unit (PDU) session or EPS bearer setup. Chapter 7 discusses these operations for three radio access technologies: NR, LTE‐M, and NB‐IoT.
Chapter 8 focuses on data transfer in an NTN. The NTN reuses the TN's data transfer framework and makes enhancements to reflect NTN‐specific radio channel challenges. The chapter illustrates various timing relationships in the NTN along with a new Timing Advance procedure for the NTN. The Key prerequisites for downlink and uplink data transfer in the LTE‐M NTN and the NB‐IoT‐NTN are described. A procedure for managing Global Navigation Satellite System (GNSS) measurement gaps is also summarized.
Chapter 9 addresses mobility management. Mobility management principles for a TN are reused in an NTN along with NTN‐specific enhancements. The NTN UE’s RRC state influences mobility management. This chapter briefly overviews the NTN UE’s RRC states, followed by a summary of major NTN mobility challenges and candidate solutions. Mobility management in the NR‐NTN is addressed by discussing measurements and handover triggers, types of NTN handover, and activities of the NR‐NTN UE in the RRC_IDLE and RRC_INACTIVE states. A detailed signaling flow for the Conditional Handover (CHO) in the NR‐NTN is illustrated. Similarly, mobility management in the LTE‐M NTN is addressed by discussing measurements and handover triggers, a detailed signaling flow for the CHO, and activities of the LTE‐M NTN UE in the RRC_IDLE state. A detailed signaling flow for the CHO. Mobility management in the NB‐IoT NTN is also described. Feeder link switchover, a unique aspect of the NTN, is explained. The issue of discontinuous coverage is also summarized.
Chapter 10 provides a brief overview of target NTN enhancements in Release 19. While the NTN‐related specifications work carried out by the 3GPP is formally part of 5G and 5G‐Advanced, the NTN is expected to play an even more key role in 6G. A brief introduction to the 6G vision and requirements is given, followed by the usage scenarios defined by the International Telecommunication Union (ITU) for 6G. The ITU‐specified performance goals for 6G are also summarized. An overview of 6G technology enablers is also given. The NTN’s role in realizing the vision of 6G is explained. Finally, Chapter 10 gives examples of potential NTN research directions.
Since we cannot escape acronyms in our wireless communications industry, we have included a list of acronyms in the front matter of the book to facilitate reading. References listed at the end of each chapter are quite helpful for digging deeper into NTN concepts. We have designed interactive exercises to reinforce learning of key NTN concepts and made them available at www.wiley.com/go/tripathi5g.
Our hope is that this NTN book will significantly increase your NTN knowledge and help you in your professional development. Please feel free to contact us via social media; we will be happy to strengthen our teacher–student relationship.
Happy NTN learning!Well wishes,Dr. Nishith D. TripathiDr. Jeffrey H. Reed
Note
1
The Third Generation Partnership Project (3GPP) is the standards organization that has defined specifications of 3G, 4G, and 5G cellular communication systems. The 3GPP is also expected to define 6G specifications. See
https://www.3gpp.org/
to learn about 3GPP activities.
Acknowledgments
We sincerely express our gratitude to our families for their patience and sacrifice of time while we worked on the book in the evenings, weekends, and holidays.
We thank our employer, Virginia Tech, where we have opportunities to perform non‐terrestrial network (NTN) research. Our NTN research facilitated the development of this book. We also thank Samsung Research America for enabling Dr. Nishith Tripathi to make numerous contributions to the 3GPP 5G NTN specifications.
This book is supported by the research projects sponsored by the National Science Foundation (NSF) and the National Telecommunications and Information Administration (NTIA). Specifically, the book is partially supported by (i) the NSF’s CCRI award number 2235139, (ii) the NSF’s NeTS award number CNS‐2312447, and (iii) the NTIA’s Public Wireless Supply Chain Innovation Fund (PWSCIF) under the award number (51‐60‐IF007).
We thank our students who contributed directly or indirectly to this book. We thank Rahul Varma Chintalapati (Virginia Tech) for contributions to NTN and spectrum‐sharing challenges. We thank Zac Martin (Virginia Tech) for developing nice diagrams for this book. We also thank Dr. Yash Vasavada of DAIICT (India) for his helpful feedback on the RF planning and design aspects of the NTN.
Finally, we sincerely appreciate the flexibility and guidance of our publisher, IEEE/Wiley.
Acronyms
Acronym
Expansion
16QAM
16‐ary quadrature amplitude modulation
5GC
5G Core
5QI
5G QoS identifier
64QAM
64‐ary quadrature amplitude modulation
AAA
authentication, authorization, and accounting
ACI
adjacent channel interference
ACK
acknowledgment
ADC
analog‐to‐digital converter
AF
application function
AiP
antenna in package
AL
atmospheric loss
AM
acknowledged mode
AMBR
aggregate maximum bit rate
AMF
Access and Mobility Management Function
AN
access network
AoD
antenna on display
API
application programming interface
APN
access point name
AR
augmented reality
ARP
allocation and retention priority
AS
access stratum
ATIS
Alliance of Telecommunications Industry Solutions
ATP
acquisition, tracking, and pointing
AUSF
Authentication Server Function
AWGN
additive white Gaussian noise
BIST
built‐in self‐test
BLER
block error rate
BPSK
binary phase shift keying
BR
bandwidth reduced
BSR
buffer status report
BWP
bandwidth part
CA
carrier aggregation
CAN
controller area network
CAPIF
common API framework
CBG
code block group
CCH
common control channel
CCI
co‐channel interference
CDF
cumulative distribution function
CDMA
code division multiple access
CE
coverage enhancement
CE
control element
CGI
cell global identity
CHO
conditional handover
CI/CD
continuous improvement/continuous development
CIM
compute in memory
CINR
carrier‐to‐interference‐plus‐noise ratio
CL
clutter loss
CMOS
complementary metal‐oxide‐semiconductor
CN
core network
CNN
Cable News Network
CNR
carrier‐to‐noise ratio
CoAP
constrained application protocol
CP
control plane
CP
cyclic prefix
CPU
central processing unit
CQI
channel quality indicator
CRC
cyclic redundancy check
CRI
CSI‐RS resource indicator
C‐RNTI
cell‐radio network temporary identifier
CRS
cell‐specific reference signal
CSI‐IM
channel state information‐interference measurement
CSI‐RS
channel state information‐reference signal
CTIA
Cellular Telecommunications Industry Association
CTO
chief technology officer
CU
central unit
D2D
direct‐to‐device
DAC
digital‐to‐analog converter
DAPS
dual active protocol stack
DCI
downlink control information
DD
delay‐Doppler
DID
decentralized identifier
DL
downlink
DLT
distributed ledger technology
DMRS
demodulation reference signal
DN
data network
DNN
data network name
DNS
domain name system
DPD
digital pre‐/post‐distortion
DPSK
differential phase shift keying
DRB
data radio bearer
DRX
discontinuous reception
DTC
direct‐to‐cell
DU
distributed unit
EAB
enhanced access barring
EARFCN
E‐UTRA absolute radio frequency channel number
EASDF
edge application server discovery function
EC‐GSM
extended coverage‐Global System for Mobile Communication
EDA
electronic design automation
eDRX
extended discontinuous reception
EDT
early data transmission
EE
Electronic Engineering
EFC
earth‐fixed cell
EIRP
effective isotropic radiated power
eMBB
enhanced mobile broadband
EMC
Earth‐moving cell
eMTC
enhanced MTC
EN‐DC
E‐UTRA‐NR dual connectivity
ENISA
European Network and Information Security Agency
ENOB
effective number of bits
EOC
edge of coverage
EPC
Evolved Packet Core
EPS
Evolved Packet System
E‐RAB
E‐UTRAN radio access bearer
ESIM
Earth station in motion
ETL
extract, transform, and load
E‐UTRA
Evolved‐Universal Terrestrial Radio Access
E‐UTRAN
Evolved‐Universal Terrestrial Radio Access Network
EVM
error vector magnitude
FCC
Federal Communications Commission
FDD
frequency division duplex
FFT
fast Fourier transform
FOV
field of view
FPC
flexible printed circuits
FPGA
field programmable gate array
FRF
frequency reuse factor
FSK
frequency shift keying
FSO
free space optical
FSPL
free space path loss
FSS
fixed satellite service
FTC
Federal Trade Commission
FTF
frequency translation factor
GBR
guaranteed bit rate
GDPR
general data protection regulation
GEO
geosynchronous/geostationary Earth orbit
gNB
next generation Node B
GPRS
General Packet Radio Service
GPS
Global Positioning System
GPU
graphics processing unit
GSM
Global System for Mobile Communication
GSMA
Global System for Mobile communications Association
GSO
geosynchronous orbit
GTP
GPRS tunneling protocol
GUAMI
globally unique AMF ID
GUTI
globally unique temporary identifier
GW
gateway
HAPS
high‐altitude platform station
HARQ
hybrid automatic repeat request
HBF
holographic beamforming
HBT
heterojunction bipolar transistor
HEO
highly elliptical orbit
HFT
high frequency trading
HOM
high order modulation
HRLLC
hyper reliable and low‐latency communication
HSS
home subscriber server
HTA
heavier than air
IAB
integrated access and backhaul
IE
information element
IETF
Internet Engineering Task Force
IFC
in‐flight connectivity
IFFT
inverse fast Fourier transform
I‐FSK
Impulsive FSK
IIC
incumbent informing capabilities
IIoT
industrial Internet of things
IMS
IP Multimedia Subsystem
IMSI
international mobile subscriber identity
IoT
Internet of Things
IoT‐NTN
Internet of Things‐Non‐Terrestrial Network
IP
Internet Protocol
IPN
integrated phase noise
IPSM‐GW
IP Short Message Gateway
I‐RNTI
inactive‐radio network temporary identifier
ISAC
integrated sensing and communication
ISL
inter satellite link
ISS
international space station
ITO
indium tin oxide
ITU
International Telecommunication Union
JCAS
joint communications and sensing
L1‐RSRP
layer 1‐RSRP
LAA
licensed assisted access
LBT
listen‐before‐talk
LCG
logical channel group
LCT
laser communication terminal
LDPC
low‐density parity check
LED
light emitting diode
LEO
low Earth orbit
LHCP
left hand circular polarization
LI
layer indicator
LNA
low noise amplifier
LO
local oscillator
LOS
line of sight
LPF
low pass filter
LPWA
low‐power wide‐area
LTA
lighter than air
LTE
Long‐Term Evolution
LTE‐M
Long‐Term Evolution‐MTC
LTM
L1/L2 triggered mobility
LUT
look‐up table
MAC
medium access protocol
MAPL
maximum allowable path loss
MBS
multimedia broadcast service
MCS
modulation and coding scheme
MEF
Metro Ethernet Forum
MEMS
micro‐electromechanical system
MEO
medium Earth orbit
mHEMT
metamorphic high‐electron‐mobility‐transistors
MIB
master information block
MIB‐NB
master information block‐narrowband
MICO
mobile initiated connection only
MIMO
multiple input multiple output
MIV
MPEG immersive video
ML
machine learning
MME
Mobility Management Entity
mMTC
massive machine type communications
MN
master node
MPDCCH
MTC PDCCH
MPEG
Moving Picture Experts Group
MQTT‐SN
message queuing telemetry transport‐ sensor network
MR
mixed reality
MR‐DC
multi‐radio dual connectivity
MRSS
multi‐RAT spectrum sharing
MSS
mobile satellite service
MSSA
Mobile Satellite Services Association
MT
mobile‐terminated
MTC
machine type communication
MTC‐IWF
Machine Type Communication‐Inter Working Function
MU‐MIMO
multi‐user‐multiple input multiple output
MV‐HEVC
multiview high efficiency video coding
NACK
negative acknowledgment
NAS
non‐access stratum
NB
narrowband
NBI
narrowband index
NB‐IoT
narrowband IoT
NCGI
NR cell global identity
NDI
new data indicator
Near‐RT RIC
near‐real‐time RAN intelligent controller
NEF
Network Exposure Function
NESAS
network equipment security assurance scheme
NF
Network Function
NF
noise figure
NFC
near‐field communication
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 Radio Access Network
NGSO
non‐geostationary orbit
NIDD
non‐IP data delivery
NIST
National Institute of Standards and Technology
NLOS
non‐line of sight
NOMA
non‐orthogonal frequency division multiple access
Non‐RT RIC
non‐real‐time RAN intelligent controller
NPBCH
narrowband physical broadcast channel
NPCI
narrowband physical cell ID
NPDCCH
narrowband physical dedicated control channel
NPDSCH
narrowband physical downlink shared channel
NPRACH
narrowband physical random access channel
NPSS
narrowband primary synchronization signal
NPUSCH
narrowband physical uplink shared channel
NR
New Radio
NRF
Network Repository Function
NR‐NTN
New Radio‐Non‐Terrestrial Network
NRS
narrowband reference signal
NSA
non‐standalone
NSACF
Network Slice Admission Control Function
NSC
National Spectrum Consortium
NSSAAF
Network Slice‐specific and SNPN Authentication and Authorization Function
NSSAI
network slice selection assistance information
NSSF
Network Slice Selection Function
NSSS
narrowband secondary synchronization signal
NTN
non‐terrestrial network
NTN‐GW
NTN‐Gateway
OAM
orbital angular momentum
OAM/OA&M
operations, administration, and maintenance
OCC
orthogonal cover code
O‐Cloud
O‐RAN Cloud
O‐CU‐CP
O‐RAN‐Central Unit‐Control Plane
O‐CU‐UP
O‐RAN‐Central Unit‐User Plane
O‐DU
O‐RAN Distributed Unit
O‐eNB
O‐RAN eNodeB
OFDM
orthogonal frequency division multiplexing
OFDMA
orthogonal frequency division multiple access
OIA
Office of International Affairs
OLED
organic light emitting diode
OMA
Open Mobile Alliance
OOK
on–off keying
O‐RAN
Open Radio Access Network
O‐RU
O‐RAN Radio Unit
OTA
over‐the‐air
OTDOA
observed time difference of arrival
OTFS
orthogonal time frequency space
PA
power amplifier
PAPR
peak‐to‐average power ratio
PBCH
physical broadcast channel
PCB
printed circuit board
PCC
Policy and Charging Control
PCEF
Policy and Charging Enforcement Function
PCF
Policy Control Function
PCI
physical cell ID
PCO
protocol configuration options
PCRF
Policy and Charging Rules Function
P‐CSCF
Proxy‐Call Session Control Function
PDB
packet delay budget
PDCP
packet data convergence protocol
PDN
packet data network
PDSCH
physical downlink shared channel
PDU
protocol data unit
P‐GW
PDN‐Gateway
PHR
power headroom report
PHY
physical
PLMN
Public Land Mobile Network
PMI
precoding matrix indicator
PQC
post‐quantum cryptography
PRACH
physical random access channel
PRB
physical resource block
PSA
PDU session anchor
PSD
power spectral density
PSM
power saving mode
PSS
primary synchronization signal
PUCCH
physical uplink control channel
PUR
preconfigured uplink resource
PUSCH
physical uplink shared channel
QAM
quadrature amplitude modulation
QFI
QoS flow indicator
QoS
quality of service
QPSK
quadrature phase shift keying
RA
random access
RAB
radio access bearer
RACH
random access channel
RAN
radio access network
rApp
remote App
RAR
random access response
RAT
radio access technology
RBG
resource block group
RE
resource element
RF
radio frequency
RFIC
radio frequency integrated circuit
RHCP
right‐hand circular polarization
RI
rank indicator
RIC
RAN Intelligent Controller
RIS
reflective/reconfigurable intelligence surface
RLC
radio link control
RLF
radio link failure
RNA
RAN notification area
RoHC
robust header compression
RoT
rise over thermal
RP
reference point
RPD
RF planning and design
RRC
radio resource control
RSRP
reference signal received power
RSRQ
reference signal received quality
RTD
round trip delay
RTT
round trip time
RU
resource unit
RV
redundancy version
SA
Service and System Aspects
SAE
System Architecture Evolution
SAN
Satellite Access Node
SBA
service‐based architecture
SCEF
Service Capability Exposure Function
SC‐FDMA
single‐carrier frequency division multiple access
SCP
Service Communication Proxy
SC‐PTM
single cell‐point‐to‐multipoint
SCS
Service Capabilities Server
SCS
subcarrier spacing
SDAP
service data adaptation protocol
SDMA
space division multiple access
SDT
small data transmission
SEN
Societal and Economic Needs
SFBC
space frequency block coding
SFM
shadow fading margin
SFN
system frame number
S‐GW
Serving Gateway
SI
system information
SIB
system information block
SIB1‐BR
SIB1‐bandwidth reduced
SIB1‐NB
system information block 1‐narrowband
SIB2‐NB
system information block 2‐narrowband
SiGe
silicon‐germanium
SINR
signal to interference plus noise ratio
SIP
session initiation protocol
SI‐RNTI
system information‐radio network temporary identifier
SL
scintillation loss
SM
session management
SMF
Session Management Function
SMO
Service Management and Orchestration
SMS
short message service
SMTC
SSB measurement timing configuration
SN
secondary node
SNPN
standalone non‐public network
SNR
signal‐to‐noise ratio
SOI
silicon‐on‐insulator
SON
self‐organizing network
SOS
(Morse code distress signal)
SPI
serial peripheral interface
SPS
semi‐persistent scheduling
SR
scheduling request
SRB
signaling radio bearer
SRS
sounding reference signal
SSB
SS/PBCH block
SSBRI
SSB resource indicator
SSC
session and service continuity
SSI
self‐sovereign identity
SSS
secondary synchronization signal
S‐TMSI
SAE‐temporary mobile subscriber identity
SUCI
subscription concealed identifier
SU‐MIMO
single user‐multiple input multiple output
SUPI
subscription permanent identifier
TA
timing advance
TAC
tracking area code
TAI
tracking area identifier
TAR
timing advance report
TAU
tracking area update
TBS
transport block size
TCI
transmission configuration indication
TDD
time division duplex
TEE
trusted execution environment
TEID
tunnel endpoint ID
TLE
two‐line element
TN
terrestrial network
TPC
transmit power control
TPM
trusted platform module
TPU
tensor processing unit
TTI
transmit time interval
UAS
uncrewed/unmanned aerial system
UAV
uncrewed/unmanned aerial vehicle
UCA
uniform circular array
UDM
Unified Data Management
UDR
Unified Data Repository
UDSF
Unstructured Data Storage Function
UE
User Equipment
UI
user interface
UL
uplink
ULI
user location information
UMTS
Universal Mobile Telecommunication System
UP
user plane
UPF
User Plane Function
URLLC
ultra‐reliable low‐latency communications
UTC
coordinated universal time
VGA
variable gain amplifier
VoNR
voice over NR
VR
virtual reality
VSAT
very small aperture terminal
WSSUS
wide‐sense stationary uncorrelated scattering
WTFC
wideband time frequency coding
xApp
extended App
XR
extended Reality
About the Companion Website
This book is accompanied by a companion website:
www.wiley.com/go/tripathi5g
This website includes interactive exercises to reinforce the key concepts covered in all the chapters. References to the topics associated with exercise questions are given as part of hints.
1Introduction to a Non‐Terrestrial Network
Even with the deployment of five generations of cellular technologies, a significant portion of the planet's surface area and a large number of people still do not have access to wireless communications. Non‐Terrestrial Networks (NTNs) are becoming increasingly important in providing wireless communications anywhere on the planet. This chapter defines an NTN and introduces different types of NTN platforms that help create an NTN. Since the NTN utilizes non‐terrestrial platforms for radio coverage, a different network architecture is needed compared to a traditional terrestrial network (TN).
This chapter illustrates a simplified NTN architecture and explains its key components and interfaces. The motivation for the NTN is discussed from the perspective of three use‐case categories—service ubiquity, service continuity, and service scalability. The Third‐Generation Partnership Project (3GPP) has studied several NTN use cases, including user mobility between a TN and an NTN, satellite‐based backhaul to support TN deployments in remote areas without the transport infrastructure, support for Internet of Things (IoT) devices, factories in remote areas, and offshore wind farms. The 3GPP roadmap on the NTN work is outlined to provide a historical perspective as well as potential future work. The NTN‐related specifications work carried out by the 3GPP NTN is formally part of the fifth‐generation (5G) and 5G‐advanced cellular technologies. However, the NTN is expected to play an even more important role in the sixth‐generation (6G) cellular technology. A glimpse of the NTN's role in 6G is also provided in this chapter.
1.1 Non‐Terrestrial Networks: The Definition
An NTN is a wireless communication network that utilizes radio network equipment placed on an airborne or spaceborne vehicle. From this general perspective, if some radio network equipment is on an uncrewed aerial vehicle (UAV) or a drone, a network involving UAVs would qualify as an NTN. Indeed, in some literature, UAVs are considered to be part of an NTN. However, 3GPP NTN specifications consist of different types of satellites and high‐altitude platform station (HAPS). A HAPS is an airborne vehicle that operates at an altitude between 8 and 50 km (3GPP 2024e). Examples of uncrewed/unmanned aerial systems (UASs) (3GPP 2021a) include lighter‐than‐air (LTA) UAS and heavier‐than‐air (HTA) UAS. Examples of the satellites include low Earth orbit (LEO), medium Earth orbit (MEO), and geosynchronous/geostationary Earth orbit (GEO) satellites. In general, LEO satellites operate at altitudes between 300 and 1,500 km, MEO satellites operate at altitudes between 7,000 and 25,000 km, and GEO satellites operate at an altitude of 35,786 km.
The 3GPP formally defines the (NR) NTN to be “an NG‐RAN consisting of gNBs, which provide non‐terrestrial NR access to user equipments (UEs) by means of an NTN payload embarked on an airborne or spaceborne NTN vehicle and an NTN Gateway” (3GPP 2024e). The 3GPP‐proposed NTN architecture is illustrated in Section 1.2.
1.2 Simplified 3GPP NTN Architecture
Figure 1.1 illustrates a simplified architecture of an NTN (3GPP 2024d,e). The NTN is one of the prominent 5G features defined by the 3GPP in Release 17. See Tripathi and Reed (2019) for details on 5G. While wireless communication is one of the most prominent features of a cellular system, the overall cellular system includes both wireless and wired links. A more detailed NTN architecture is described in Chapter 5 and 3GPP (2023).
An NTN UE communicates with an NTN payload using the radio interface protocol stack. The communication link between the NTN UE and the NTN payload is called the service link or the access link. A typical NTN UE is a handheld smartphone, an IoT device, or a very small aperture terminal (VSAT) device. The radio interface protocol stack may use technologies such as 5G new radio (NR), narrowband IoT (NB‐IoT), and eMTC/LTE‐M.1 The NTN payload resides on an NTN platform. Examples of NTN platforms include satellites such as GEO satellites, MEO satellites, and LEO satellites and HAPSs such as stationary aircraft in the stratosphere.
The NTN payload communicates with an NTN‐gateway (NTN‐GW) using an implementation‐specific radio interface. The communication link between the NTN payload and the NTN‐GW is called the feeder link.
Figure 1.1 utilizes a transparent NTN payload, where the NTN payload does not carry out technology‐specific baseband processing but performs conversion of signals between the service link and the feeder link. In the downlink from the gNB/eNB to the NTN UE, the NTN payload receives the signal from the NTN‐GW and performs functions such as radio frequency (RF) filtering, frequency conversion, and amplification2 and transmits the RF signals that the NTN UE can process using a suitable 3GPP‐defined radio interface such as 5G NR, NB‐IoT, and eMTC/LTE‐M. In the uplink from the NTN UE to the gNB/eNB, the NTN payload receives the RF signal from the UEs in the cell on a suitable 3GPP‐defined carrier frequency and transmits the RF signal to the NTN‐GW on a different carrier frequency after suitable filtering and amplification.
Figure 1.1 Simplified NTN Architecture.
The interface between the NTN‐GW and the gNB/eNB is undefined in the 3GPP specifications. This interface can be internal to the gNB/eNB, where both the NTN‐GW and the gNB/eNB are integrated into one entity. When this interface is external to the gNB/eNB, it can be a wired or wireless interface.
Similar to a TN, the gNB/eNB connects to the core network using 3GPP‐defined interfaces. In general, the gNB connects to the 5GC in the case of NR‐NTN, and the eNB connects to the EPC in the case of IoT‐NTN. The core network connects to data networks such as the Internet, as in a TN.
1.3 Motivation for the NTN
A TN can provide good quality of service (QoS) to users when the users are in the radio coverage of the TN. Service providers carry out coverage and capacity planning to determine the number and locations of base stations in a target service area to meet the expected traffic demands. These base stations need to connect to other base stations to support features such as handover through a transport network. The base stations also need to connect to the core network via a transport network, because the core network interfaces with data networks such as the Internet.
Cost‐effective deployment of the base stations and the associated transport network is not feasible in areas with sparse populations and remote and vast areas on land, such as mountains, deserts, and national parks. In cases such as large portions of oceans and remote islands, deployment of a terrestrial cellular network is challenging due to inadequate land infrastructure and the lack of a business case.
An NTN offers an attractive solution in the challenging environments mentioned earlier. Figure 1.2 shows three NTN use case categories identified by the 3GPP (2018b). These use case categories represent one of the key motivations behind the design and deployment of an NTN because TNs cannot adequately address the related use cases. Examples of use cases that belong to one or more of these categories are briefly described in Section 1.4.
Service ubiquity.
An NTN platform can create large beams to provide radio coverage anywhere on the Earth. Remote land areas, homes, and IoT devices (e.g., devices in smart farms and manufacturing plants) in underserved or unserved rural areas with sparse populations, vast mountains, and oceans can all be illuminated by beams from spaceborne vehicles. Furthermore, the infrastructure of TNs may be damaged or destroyed due to natural disasters (e.g., earthquakes and floods) and armed conflicts such as wars. Through a suitable design, NTN platforms can connect to data networks on the Earth's surface via a gateway. Such a design obviates the need for the radio equipment to be near the geographic area that is being served. An NTN thus avoids the constraint a TN faces, where the radio equipment needs to be near or inside the area being served.
Figure 1.2 NTN Use Case Categories.
Service continuity.
There are several cases in which the cellular subscriber moves out of the radio coverage of cellular networks. For example, moving out of a suburban area into a rural area, boarding a cruise ship, or during the takeoff in case of air travel often results in the loss of radio coverage and services. Cellular subscribers and IoT devices may be on moving land platforms (e.g., cars, trains, and trucks), airborne platforms (e.g., commercial or private aircraft), and maritime platforms (e.g., cruise ships and container or cargo ships). An NTN can provide service continuity in such cases by providing radio coverage in the areas that are not covered by a TN.
Service scalability.
Cellular systems aim for high efficiency to optimize the network performance and the user experience while meeting resource constraints such as the available amount of spectrum. When the same service content needs to be sent to a target set of users in a large geographic area, all the base stations in such a geographic area need to consume precious radio resources. An NTN cell covers a much larger area compared to a TN cell, resulting in increased efficiency. Examples of the services that can benefit from large‐area broadcasts include over‐the‐air software updates and selected entertainment programs, such as live games and prescheduled movies and shows.
A word of caution…all the target use cases may not be supported in initial NTN deployments. However, as NTN deployments become more capable and widespread, more use cases would become feasible.
1.4 An Overview of NTN Use Cases
An NTN can play an important role in numerous use cases. Table 1.1 lists the use cases identified by the 3GPP as part of a study on using satellite access in 5G (3GPP 2018b).
Table 1.1 Examples of NTN Use Cases.
Use Case ID
Brief Use Case Description
1
Roaming/movement between terrestrial and satellite networks
2
Broadcast and multicast with a satellite overlay
3
Internet of Things with a satellite network
4
Temporary use of a satellite component
5
Optimal routing or steering over a satellite
6
Satellite transborder service continuity
7
Global satellite overlay
8
Indirect connection through a 5G satellite access network
9
5G fixed backhaul between NR and the 5G core
10
5G moving platform backhaul
11
5G to premises
12
Satellite connection of the remote service center to the offshore wind farm
Roaming/movement between terrestrial and satellite networks
. A device may move out of the TN coverage area. For example, a container ship may have containers with IoT devices to track the locations of the containers. On the land and near the shore, such IoT devices can connect to the TN. However, when the ship is away from the shore, these devices lose connectivity with a server that tracks the device/container locations. An NTN can be used to provide continuous location tracking. When two different operators own the TN and the NTN, a suitable roaming agreement is needed between the operators, just like two different TN operators. If the same operator owns both the TN and the NTN, a roaming agreement is not needed, and the mobility management is relatively simple.
Broadcast and multicast with a satellite overlay
. A variety of digital content, including videos, can be broadcast or multicast to numerous devices simultaneously using a standalone receive‐only mode or as a complement to a two‐way communication mode. Some content may even be free. A TN may be congested, or a subscriber to the TN operator may be temporarily out of coverage of the TN. In such cases, the NTN can provide broadcast/multicast services to UEs. A UE may also receive services simultaneously from both the TN and the NTN.
Internet of Things (IoT) with a satellite network
. IoT devices in a remote area may not have radio coverage from a TN. In such cases, the NTN can provide coverage to the IoT devices. One possible application is location tracking, which is similar to the container ship example discussed above. In smart farms, sensors can be connected to an NTN. GEO satellites or LEO satellites can be used to serve these IoT devices. LEO satellites can be helpful if the transmit power of an IoT device is a challenge. In contrast, a GEO satellite can cover a large area without requiring any significant mobility management‐related processing by IoT devices.
Temporary use of a satellite component
. In case of a crisis, such as an earthquake, flood, or war, the TN infrastructure in a given geographic area may be partially or fully destroyed. An NTN can be used to provide communication services so that people needing help can be contacted and medicines, food, and other supplies can be delivered. Services such as logistics and security can also be facilitated by the NTN.
Optimal routing or steering over a satellite
. Factories in remote areas may not have adequate coverage from a TN. These factories can be connected with each other and a central command or management center via an NTN. A variety of data, including videos and control signaling, can be transported via a satellite. LEO satellites can be used to reduce end‐to‐end delays and support higher data rates.
Satellite transborder service continuity
. This use case involves the use of the NTN for users moving between countries. One TN operator may serve areas in one country, while another TN operator may serve areas in another country. Hence, when a user goes from one country to another on a business or personal travel, an NTN can be used to provide services across countries regardless of which TN operator the user has subscribed to, as long as there are business agreements between TN operators and the NTN operator.
Global satellite overlay
. A multinational company typically has offices in different countries with potentially hundreds or thousands of kilometers between the offices. An NTN can be used to connect such offices with custom QoS in support of target applications. Example applications include high‐frequency trading (HFT), banking, or corporate communications. For low‐latency applications, LEO satellites can be quite attractive.
Indirect connection through a 5G satellite access network
. In areas without radio coverage of a TN, some UEs may not have the capability to communicate with an NTN (e.g., legacy pre‐Release 17 UEs). Such UEs cannot communicate with far‐away UEs or a web server on the Internet. In such cases, an NTN can act as a relay and transport packets between non‐NTN‐capable UEs and the NTN, enabling even non‐NTN UEs to access communication services.
5G fixed backhaul between NR and the 5G core
. It is economically challenging to provide TN coverage in remote areas such as villages due to the lack of a suitable transport network, such as a fiber network, and low population density. In one possible solution, a TN base station can connect to the 5GC using a satellite‐based backhaul. Such an arrangement provides users in remote areas access to the Internet and the desired services.
5G moving platform backhaul
. Trains are an important means of transportation in many countries. A train operator may want to offer entertainment services such as video streaming or other programs or basic Internet access. However, the train may not have coverage throughout its journey, preventing travelers from enjoying a seamless service experience. 5G gNBs can be placed on the train to provide 5G NR access to 5G UEs on the train. The gNBs can connect to the 5GC via a satellite.
5G to premises
. In hard‐to‐reach areas such as remote vacation spots or remote communities, providing TN coverage to homes and businesses is not economically viable. An NTN can provide communications services to such areas without requiring any physical infrastructure in remote areas.
Satellite connection of the remote service center to the offshore wind farm
