5G NR and Enhancements: From R15 to R16

5G NR and Enhancements: From R15 to R16 introduces 5G standards, along with the 5G standardization procedure. The pros and cons of this technical option are reviewed, with the reason why the solution selected explained. The book's authors are 3GPP delegates who have been working on 4G/5G standardization for over 10 years. Their experience with the 5G standardization process will help readers understand the technology. Thousands of 3GPP papers and dozens of meeting minutes are also included to help explain how the 5G stand came into form.

• Provides a complete introduction to 5G standards, including Release 15 and 16, the essential vertical features URLLC, V2X and unlicensed spectrum access
• Introduces the 5G standardization procedure, along with the pros, cons and technical options
• Explains the “balance system design principle from the 5G standardization procedure
• Presents a vision of 5G R17 and 6G

• Language: English
• Publisher: Elsevier Science
• Release date: Oct 24, 2021
• ISBN: 9780323911191

Book preview

5G NR and Enhancements

From R15 to R16

Edited by

Jia Shen

Standard Research Department, OPPO Research Institute, Shenzhen, China

Zhongda Du

Standard Research Department, OPPO Research Institute, Shenzhen, China

Zhi Zhang

Standard Research Department, OPPO Research Institute, Shenzhen, China

Ning Yang

Standard Research Department, OPPO Research Institute, Shenzhen, China

Hai Tang

Vice president of OPPO Research Institute, Shenzhen, China

Table of Contents

Cover image

Title page

Copyright

List of contributors

Preface

Chapter 1. Overview

Abstract

1.1 Introduction

1.2 Enhanced evolution of new radio over LTE

1.3 New radio’s choice of new technology

1.4 Maturity of 5G technology, devices, and equipment

1.5 R16 enhancement technology

1.6 Summary

References

Chapter 2. Requirements and scenarios of 5G system

Abstract

2.1 Current needs and requirements in the 5G era

2.2 Typical scenarios

2.3 Key indicators of 5G systems

2.4 Summary

References

Chapter 3. 5G system architecture

Abstract

3.1 5G system architecture

3.2 The 5G RAN architecture and deployment options

3.3 Summary

References

Further reading

Chapter 4. Bandwidth part

Abstract

4.1 Basic concept of bandwidth part

4.2 Bandwidth part configuration

4.3 Bandwidth part switching

4.4 Bandwidth part in initial access

4.5 Impact of bandwidth part on other physical layer designs

4.6 Summary

References

Chapter 5. 5G flexible scheduling

Abstract

5.1 Principle of flexible scheduling

5.2 5G resource allocation

5.3 Code Block Group

5.4 Design of NR PDCCH

5.5 Design of NR PUCCH

5.6 Flexible TDD

5.7 PDSCH rate matching

5.8 Summary

References

Chapter 6. NR initial access

Abstract

6.1 Cell search

6.2 Common control channel during initial access

6.3 NR random access

6.4 RRM measurement

6.5 Radio link monitoring

6.6 Summary

References

Chapter 7. Channel coding

Abstract

7.1 Overview of NR channel coding scheme

7.2 Design of polar code

7.3 Design of low-density parity-check codes

7.4 Summary

References

Chapter 8. Multiple-input multiple-output enhancement and beam management

Abstract

8.1 CSI feedback for NR MIMO enhancement

8.2 R16 codebook enhancement

8.3 Beam management

8.4 Beam failure recovery on primary cell(s)

8.5 Beam failure recovery on secondary cell(s)

8.6 Multi-TRP cooperative transmission

8.7 Summary

References

Further reading

Chapter 9. 5G radio-frequency design

Abstract

9.1 New frequency and new bands

9.2 FR1 UE radio-frequency

9.3 FR2 radio-frequency and antenna technology

9.4 New radio test technology

9.5 New radio RF design and challenges

9.6 Summary

References

Chapter 10. User plane protocol design

Abstract

10.1 Overview

10.2 Service data adaptation protocol

10.3 Packet data convergence protocol

10.4 Radio link control

10.5 Medium access control

10.6 Summary

References

Chapter 11. Control plan design

Abstract

11.1 System information broadcast

11.2 Paging

11.3 RRC connection control

11.4 RRM measurement and mobility management

11.5 Summary

References

Chapter 12. 5G network slicing

Abstract

12.1 General descriptions

12.2 Network slicing as a service in the 5G system

12.3 Network slice congestion control

12.4 Network slice in roaming case

12.5 Network slice specific authentication and authorization

12.6 Summary

References

Chapter 13. Quality of service control

Abstract

13.1 5G quality of service model

13.2 End-to-end quality of service control

13.3 Quality of service parameters

13.4 Reflective quality of service

13.5 Quality of service notification control

13.6 Summary

References

Further reading

Chapter 14. 5G voice

Abstract

14.1 IP multimedia subsystem (IMS)

14.2 5G voice solutions and usage scenarios

14.3 Emergency call

14.4 Summary

References

Chapter 15. 5G Ultra-reliable and low-latency communication: PHY layer

Abstract

15.1 Physical downlink control channel enhancement

15.2 UCI enhancements

15.3 UE processing capability enhancements

15.4 Data transmission enhancements

15.5 Configured grant transmission

15.6 Semipersistent transmission

15.7 Inter-UE multiplexing

15.8 Summary

References

Chapter 16. Ultra reliability and low latency communication in high layers

Abstract

16.1 Timing synchronization for industrial ethernet

16.2 Dynamic authorization versus configured grant and configured grant versus configured grant

16.3 Dynamic authorization versus dynamic authorization

16.4 Enhancements to the semipersistent scheduling

16.5 Enhancement to packet data convergence protocol data packet duplication

16.6 Ethernet header compression

16.7 Summary

References

Chapter 17. 5G V2X

Abstract

17.1 NR–V2X slot structure and physical channel

17.2 Sidelink resource allocation

17.3 Sidelink physical layer procedure

References

Chapter 18. 5G NR in the unlicensed spectrum

Abstract

18.1 Introduction

18.2 Channel sensing

18.3 Initial access procedure

18.4 Wideband operation and physical channel enhancements

18.5 Hybrid automatic repeat request and scheduling

18.6 NR–unlicensed with configured grant physical uplink shared channel

18.7 Summary

References

Chapter 19. 5G terminal power-saving

Abstract

19.1 Requirements and evaluation of power-saving techniques for 5G

19.2 Power-saving signal design and its impact on DRX

19.3 Cross-slot scheduling

19.4 MIMO layer restriction

19.5 SCell dormancy

19.6 RRM measurement relaxation

19.7 Terminal assistance information for power-saving

19.8 Summary

References

Further reading

Chapter 20. Prospect of R17 and B5G/6G

Abstract

20.1 Introduction to Release 17

20.2 Technologies targeting high data rate

20.3 Coverage extension technology

20.4 Vertical application enabling technology

20.5 Summary

References

Index

Copyright

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List of contributors

Wenhong Chen,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Shengjiang Cui,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Yi Ding,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Zhongda Du,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Yun Fang,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Zhe Fu,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Li Guo,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Yali Guo,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Chuanfeng He,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Rongyi Hu,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Yi Hu,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Yingpei Huang,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Haitao Li,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Xue Lin,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Bin Liang,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Hao Lin,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Kevin Lin,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Yanan Lin,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Jianhua Liu,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Qifei Liu,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Wendong Liu,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Yang Liu,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Qianxi Lu,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Shuai Shao,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Jia Shen,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Cong Shi,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Yongsheng Shi,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Zhihua Shi,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Tricci So,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Jinxi Su,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Jiejiao Tian,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Wenqiang Tian,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Shukun Wang,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Zuomin Wu,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Han Xiao,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Jinqiang Xing,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Jing Xu,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Weijie Xu,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Yang Xu,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Haorui Yang,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Ning Yang,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Xin You,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Wenhao Zhan,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Shichang Zhang,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Zhi Zhang,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Nande Zhao,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Zhenshan Zhao,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Zhisong Zuo,     Standard Research Department, OPPO Research Institute, Shenzhen, China

Preface

From 1G to 4G, mobile communication systems have gone through four stages: analog, digital, data, and broadband. These systems have brought unprecedented experiences to billions of users all over the world. In particular, 4G technology has opened the era of mobile internet and profoundly changed people’s way of life. While users have enjoyed the rich mobile internet applications enabled by 4G such as social media networking, e-meetings, mobile shopping/payments, and mobile gaming, the mobile communication industry has been shifting its focus from 2C to 2B, trying to promote the vertical industries’ digitalization and automation with 5G new radio (NR) technology. Therefore compared with 4G, 5G has gained more attention in a wider scope due to its emphasis on increasing support for a mobile Internet of Things.

What is the core of 5G technology? What innovations has 5G introduced? What’s the difference between 5G and 4G? What kind of technical capability can 5G achieve? We believe these issues are of great interest to readers. From our perspective, 5G is not a magic and omnipotent technology. It inherits the system design concepts of 3G and 4G to a large extent, introduces a series of necessary innovative technologies, and makes a series of special optimizations for various vertical applications. Most of these innovations and optimizations are not big concepts that can be explained in a few words or sentences but are composed of many detailed engineering improvements. The purpose of this book is to analyze the innovation and optimization points of 5G and explain them to readers.

Some may think that 5G copies the core technology of 4G and is a broadband 4G. It is true that, theoretically, 5G follows the core technology of 4G long-term evolution (LTE), namely, OFDMA (orthogonal frequency division multiple access)+MIMO (multiple input multiple output). However, compared with the simplified version OFDMA in LTE, the 5G system design achieves greater flexibility in both time and frequency domains. It can give full play to the technical potential of the OFDMA system and effectively support rich 5G application scenarios such as eMBB (enhanced mobile broadband), URLLC (ultrareliable and low-delay communication), and mMTC (a large scale Internet of Things). At the same time, the 5G system is much more sophisticated and complex than the 4G system. Based on LTE design, many modifications, enhancements, and extensions have been made. Therefore this book is based on the LTE standard, with the assumption that readers already have basic knowledge of LTE, and focuses on introducing the new and enhanced system design adopted in 5G NR, and interpreting the incremental changes of 5G NR relative to 4G LTE.

Unlike most 5G books, this book uses a method of analyzing the 5G standardization process. The book features not only the 5G NR standard but also the 5G system design and standard drafting process. The experience of writing our 4G book showed us recognition of this writing method by the majority of readers. The authors of this book are the 3rd Generation Partnership Project (3GPP) delegates from the OPPO company who participated in 5G NR standardization and promoted the formation of most 5G technology design details. Many of the technical schemes they proposed were accepted and have become part of 5G standards. The standardization delegates will introduced the process of technology selection and system design of 5G NR standards. The standardization delegates will introduced the process of technology selection and system design of 5G NR standards. 5G is a complex system, in which the technical scheme selection in each part is not isolated. The optimal scheme for a single point is not necessarily the one that contributes the most to the performance of the whole system. The goal of system design is to select the technology combination achieving the overall optimization of the system. In most chapters, this book reviews the various technical options in 5G standardization, introduces the advantages and disadvantages of various options, and tries to interpret the reasons and considerations the 3GPP used to choose the final solution, which included not only the performance factors, but also the complexity of the device implementation, the simplicity of signaling design, and the impacts on the existing standards. If the target is only to interpret the final version of the technical specifications, it is unnecessary to make such a thorough explanation. But the authors hope to help readers "not only know what it is but also why it is," through the process of reasoning and selection, and to explore the principles, methods, and means of wireless communication system design.

From another point of view, the technical solutions chosen for 5G today are only the best choices made at the specific moment, for specific service requirements, and considering current product R&D capabilities. In the future, when service requirements change and equipment capabilities become stronger, the rejected suboptimal options today may become optimal and become our new choices. The 3GPP standard is only a tool document to guide product development, and does not have the function of interpreting technical principles and design ideas. If only the final results of standardization were shown to readers, they may mistakenly think that these designs are the only reasonable choice, as if the comparison of advantages and disadvantages, the difficult technical trade-offs have never occurred, giving readers only a one-sided 5G. Readers would find it difficult to understand in many cases why a certain design choice was made. Was there no other choice? What’s the advantage of this design? On the contrary, if readers are allowed to take a critical and objective view of 5G standards through these technology selection processes, fully learn from the experience and lessons of 5G standardization when they design the next-generation system (such as 6G), and have the opportunity to conceive better designs, the authors’ review, analysis, and summary in this book will be meaningful and helpful. Because of this feature, I believe this book can not only be used as a reference book for 5G R&D engineers, but also as a reference book for college students majoring in wireless communications to learn 5G.

This book is divided into 20 chapters. In addition to the overview in Chapter 1, Chapters 2–14 are the introduction to 5G core features, which are mainly defined in 3GPP Release 15. The core of Release 15 5G NR is for the eMBB use cases and provides a scalable technical basis for Internet of Things services. From Chapter 15 to Chapter 19, we introduce the technical features of 5G enhancement defined in Release 16, including URLLC, NR V2X, unlicensed spectrum communication, terminal power saving, etc., which are indispensable parts of a complete 5G technology. In Chapter 20, we also briefly introduce the further 5G enhancement in Release 17, and our preliminary view on the trend of 5G-Advanced and 6G.

The authors listed at the beginning of each chapter are all our colleagues in the standard research department of OPPO. They are 5G standard experts in various fields, and many of them have participated in the standardization of 4G LTE. We thank them for their contributions to 5G international standardization. When readers use 5G mobile phones, a part of the hardware or software design (though it may be only a small part) is based on their innovation and effort. At the same time, we would like to thank Zheng Qin and Ying Ge of the OPPO external cooperation team for their contributions to the publication of this book. Finally, I would like to thank Tsinghua University Press and Elsevier for their support and efficient work in getting this book to readers as soon as possible. Questions or comments about this book should be sent to the authors via [e-mail].

Authors

Chapter 1

Overview

Jinxi Su, Jia Shen, Wendong Liu and Li Guo

Abstract

As the overview of the book, this first chapter focuses on the main enhancement and evolution of fifth-generation mobile communication (5G) new radio (NR) technology and standards compared to LTE. At the same time, it also summarizes and analyzes the choices of new technologies in the standardization process of NR. Then the maturity of 5G key devices and equipment is introduced, which is an important factor in promoting the process of 5G standardization. Finally, this chapter summarizes the main functional features of the R16 version that has been just standardized by 3GPP.

Keywords

NR technology; R16 enhancement technology

1.1 Introduction

Mobile communication basically follows the law that a new generation of technology emerges every decade. Since the successful deployment of the first generation of the analog cellular mobile phone system in 1979, mobile communication has evolved through four generations and has entered the fifth generation. Each generation of mobile communication system has its own specific application requirements, and continues to adopt innovative system designs and technical solutions to promote the rapid improvement of the overall performance of mobile communication.

First generation mobile communication technology (1G) was deployed in the 1980s and that was the first time cellular networking was adopted. It provides analog voice services to users. However, its service capacity and system capacity were very limited, and the price for the service was expensive.

About 10 years later, second-generation mobile communication technology (2G) was born. 2G system adopted narrowband digital mobile communication technology for the first time, which not only provided high-quality mobile calls, but also supported short message services as well as low-speed data services at the same time. The cost of mobile communication was greatly reduced, which enabled large-scale commercial use of the 2G systems all over the world. At the end of the 1990s, driven by the tide of the Internet, third-generation mobile communication (3G) came into being. 3G systems finally produced three different communication standards: the European-led WCDMA technology scheme, the American-led CDMA2000 technology scheme, and the TD-SCDMA technology scheme independently proposed by China. The data transmission capacity of 3G can reach dozens of Mbps, which enhances the system capacity of voice services and can also support mobile multimedia services. However, the pace of the development of mobile communication technology did not slow down. With the explosive growth of mobile Internet and intelligent terminals, the transmission capacity of 3G system is increasingly unable to satisfy service requirements. Fourth-generation mobile communication (4G) technology appeared around 2010. The key air interface technologies adopted in 4G systems include orthogonal frequency division multiplexing [Orthogonal Frequency Division Multiplexing (OFDM)] and multiantenna, multiinput and multioutput [Multiple Input Multiple Output (MIMO)]. The transmission rate in 4G systems can reach from 100 Mbps to 1 Gbps, and it can support a variety of mobile broadband data services, which well meet the needs of the current development of mobile Internet.

In summary, after nearly 40 years of rapid development, mobile communication has entered into every corner of social life and has profoundly changed the manner of communication between people and even the normal life. However, new requirements for communication keep emerging, and the communication technologies keep evolving with new innovations. In 2020, the world ushered in the deployment of large-scale of fifth-generation mobile communication (5G) commercial networks. A 5G system can support large bandwidth, low latency, wide connectivity, and the Internet of everything. In the following chapters of this book, we will provide detailed description and discussion on what a 5G system exactly looks like, what problems have been solved, what businesses and requirements are supported, and what technology enhancements and evolution have been made.

At the beginning of the commercial use of the fourth-generation mobile communication technology, the global mainstream telecom enterprises and research institutions have begun to actively invest in the research on the fifth-generation mobile communication (5G) technology. There are many forces driving the emergence of 5G technology, including the emergence of new application scenarios, technological innovation, standards competition, business drive, industrial upgrading, and other factors.

Of course, in addition to the driving force of national strategy and industrial competition, the evolution and development of 5G technology is also the inevitable result of the continuous optimization and enhancement of the technology itself and the evolution toward higher and stronger technical indicators and system performance targets. 5G technology adopts the new radio (NR) design [1–12] based on the fundamental air interface technology framework of LTE OFDM + MIMO. 5G technology also includes numerous technical enhancements and improvements in comparison with LTE from the perspective of system scheme design, including the support of higher frequency band and larger carrier bandwidth, flexible frame structure, diversified numerology, optimized reference signal design, new coding, symbol-level resource scheduling, MIMO enhancement, delay reduction, coverage enhancement, mobility enhancement, terminal energy saving, signaling design optimization, new network architecture, quality of service (QoS) guarantee enhancement, network slicing, vehicle to everything (V2X), industry Internet of things (IIoT), new radio-unlicensed (NR–U) spectrum design, good support for a variety of vertical industries, etc. These advanced technical solutions enable 5G to fully meet the 5G vision requirements of ubiquitous connection and intelligent interconnection between people, between things as well as between people and things in future product development and commercial deployment.

1.2 Enhanced evolution of new radio over LTE

Mobile communication has profoundly changed the life of people, and is infiltrating into every aspect of human society. Fourth-generation mobile communication (4G) is a very successful mobile communication system [13]. It well meets the needs of the development of the mobile Internet and brings great convenience to communication between people. The world as a whole and most industries can enjoy the rewards of the developments of the mobile communication industry. However, the LTE technology adopted by 4G still has some technical shortcomings and some unresolved problems are also seen during the commercial network deployment of LTE. Any technological evolution and industrial upgrade are driven by the strong driving force of business and application requirements to achieve rapid maturity and development. As the two major driving forces of 5G development, mobile Internet and mobile Internet of things provide broad prospects for the development of mobile communications in the future. 5G defines three major application scenarios [14,15]: enhanced mobile broadband (eMBB), ultrareliable and low latency communications (URLLC), and massive machine type communications (mMTC). Among them, eMBB is mainly for the application of mobile Internet, while URLLC and mMTC are mainly for the application of mobile Internet of things. The mobile Internet will build an omnidirectional information ecosystem centered on end users. In recent years, ultrahigh definition video, virtual reality (VR), augmented reality (AR), distance education, telecommuting, telemedicine, wireless home entertainment, and other human-centered needs are becoming more and more popular. These booming new service requirements will inevitably put forward higher requirements for the transmission bandwidth and transmission data rate of mobile communication. On the other hand, vertical industries such as mobile Internet of things, industrial Internet, Internet of vehicles, smart grids, and smart cities are also being rapidly informatized and digitized. In addition to smartphones, mobile terminals such as wearable devices, cameras, unmanned aerial vehicles, robots, vehicle-borne ships, and other terminal modules, as well as customized terminals for the industry, etc., also come with more diverse forms. It is difficult for 4G technology to meet the vision of 5G and the emergence of a variety of new business requirements and new application scenarios, and evolution from the 4G to 5G technology and development of 5G technology is an inevitable trend. The major shortcomings of LTE technology and the corresponding enhancements and optimizations made in 5G NR will be introduced in the following sections.

1.2.1 New radio supports a higher band range

The frequency range supported by LTE is mainly in the low-frequency band, and the highest frequency band supported in LTE is TDD Band42 and Band43 in the range of 3400–3800 MHz. The actual commercial deployment networks of the global LTE are basically deployed in a frequency range below 3 GHz. For mobile communication, the spectrum is the most precious and scarce resource. The available bandwidth range in low-frequency band is limited, and that will be occupied by the existing mobile communication system for a long time. With the vigorous development of follow-up mobile communication Internet services, the requirements of wireless communication and transmission data rate are getting higher and higher, and 4G networks have traffic congestion in high-capacity areas. Therefore there is an urgent need to explore more frequency bands to support the development of mobile communications in the future.

In the current global radio spectrum usage, there is still a wide range of unused frequency bands above 6 GHz. Therefore 5G supports the millimeter wave band in the frequency range 2 (FR2) (24.25–52.6 GHz) to better resolve the difficulties of insufficient wireless frequency band. On the other hand, in order to solve the challenges of poor millimeter wave propagation characteristics, large propagation loss, and signal blocking, the NR protocol introduced a series of technical schemes, such as beam scanning, beam management, beam failure recovery, digital + analog hybrid beamforming, and so on, to ensure the quality of millimeter wave transmission. Supporting a wide millimeter wave band is a huge enhancement of 5G NR in comparison with LTE, with great potential for future 5G deployment and business applications.

1.2.2 New radio supports wide bandwidth

In the LTE standard, the maximum single-carrier bandwidth is 20 MHz. If the system bandwidth exceeds that, multicarrier aggregation (CA) has to be implemented. CA brings extra complexity to both protocol and product implementation due to the addition and activation of auxiliary carriers in the empty port, as well as the joint scheduling between multicarriers. Furthermore, a certain guard period (GP) is inserted between carriers in multiCA, which reduces the effective spectrum efficiency. In addition, the effective transmission bandwidth of LTE carrier signal is only about 90% of the carrier bandwidth, and the spectrum efficiency is also lost due to that. With the development of the semiconductor industry and technology in the past decade, the processing capabilities of semiconductor chips and key digital signal processing devices have been greatly enhanced. Together with the application of new semiconductor materials and devices such as radio-frequency power amplifiers (PAs) and filters, they can make it possible for 5G equipment to handle larger carrier bandwidth. At present, the maximum carrier bandwidth of 5G NR is 100 MHz in the frequency bands below 6 GHz, and the maximum carrier bandwidth of millimeter wave band is 400 MHz, which is an order of magnitude larger than that of LTE. That lays a better foundation for the NR system to support large bandwidth and ultrahigh throughput.

Compared with LTE, NR also greatly improves the effective spectrum efficiency of the system bandwidth by applying a digital filter, which increases the effective bandwidth of the carrier from 90% of the LTE to 98%, thus equivalently increasing the system capacity.

1.2.3 New radio supports more flexible frame structure

LTE supports two types of frame structures, FDD and TDD, which are frame structure type 1 and frame structure type 2, respectively. For the TDD frame structure, the uplink and downlink service capacity is determined by the uplink and downlink time slot ratio, which can be configured and adjusted. Seven kinds of fixed uplink and downlink time slot ratios were specified and the frame structure of TDD in a LTE cell was determined in the process of cell establishment. Although the dynamic TDD frame structure was also designed in the subsequent evolution version of LTE, it is not applicable to traditional UE, and the overall scheme is still not flexible enough and therefore has not been applied in practical LTE commercial networks.

From the beginning, NR design considered the flexibility of the frame structure. First, it no longer distinguishes between the FDD and TDD frame structure. The effective FDD is implemented by configuring OFDM symbols as uplink or downlink in the time slots. Secondly, the uplink and downlink configuration periods of the TDD band can be configured flexibly. For example, various cycle lengths such as 0.5 Ms/0.625 Ms/1 Ms/1.25 Ms/2 Ms/2.5 Ms/5 Ms/10 Ms can be configured by signaling. In addition, each symbol in a time slot can be configured not only as an uplink or a downlink symbol, but also as a flexible symbol that can be used as a downlink or an uplink symbol in real time though dynamic indication in the physical layer control channel, so as to flexibly support the diversity of services. It can be seen that 5G NR provides great flexibility for TDD frame structure as well as downlink and uplink resource allocation.

1.2.4 New radio supports flexible numerology

The subcarrier spacing (SCS) of the OFDM waveform defined in the LTE standard is fixed at 15 kHz. Based on the basic principle of the OFDM system, the time-domain length of the OFDM symbol is inversely proportional to the SCS, so the air interface parameter of LTE is fixed and has no flexibility. The services supported by LTE are mainly traditional mobile Internet services, and the possibility of supporting other types of services will be limited by the fixed underlying parameters.

In order to better meet the needs of diversified services, NR supports multiple SCSs. The SCS is extended by the integer power of 2 based on 15 KHz, which includes the values of 15 kHz/30 kHz/60 kHz/120 kHz/240 kHz. With the increase of SCS, the corresponding OFDM symbol length is also shortened proportionally. Due to the use of flexible SCS, it can adapt to different service requirements. For example, the low-latency services of URLLC require a larger subcarrier interval to shorten the symbol length for transmission, in order to reduce the transmission air interface delay. On the other hand, the mMTC services of the Internet of things with its large number of connections need to reduce the subcarrier interval and increase the symbol transmission time and power spectral density to extend the coverage distance.

The carrier bandwidth of the millimeter wave band supported by NR is often larger, and the Doppler frequency offset is also relatively large, so larger SCS is suitable for the carrier in the high-frequency band to resist Doppler shift. Similarly, for high-speed scenarios, a larger subcarrier interval is also suitable.

It can be seen that NR has laid a good technical foundation for the flexible deployment and coexistence of multiple various services in the followup 5G through supporting flexible numerology and a unified new air interface framework for both high- and low-frequency bands.

1.2.5 Low-latency enhancements of air interface by new radio

The basic unit of time interval for data scheduling and transmission defined in the LTE protocol is 1 Ms subframe. This is the main reason the air interface data transmission cannot break through the time unit limit of 1 Ms. In addition, due to the design of the timing relationship of at least N+4 for HARQ retransmission in LTE, it is difficult for the air interface delay of LTE to meet the service requirements of low delay. Although LTE introduced the technical scheme of shortening the transmission time interval (TTI) in the subsequent evolution of the protocol, due to the practical factors such as the progress of the whole industry of LTE, the development cost, and the weak deployment demand, the probability of practical application and deployment of shortening TTI technology in an LTE commercial network is very low.

In order to solve the issues of air interface delay, the 5G NR system was designed and optimized in several technical dimensions from the beginning. First, NR supports flexible SCS. For low-delay traffic, large SCS can be used to directly shorten the length of OFDM symbols, and thus the length of a time slot is reduced.

Secondly, NR supports symbol-level resource allocation and scheduling. The time-domain resource allocation granularity of the downlink data channel can support 2/4/7 symbol length, while the uplink can support resource scheduling of any symbol length (1–14). By using symbol-level scheduling, when the data packet arrives at the physical layer, it can be transmitted at any symbol position of the current time slot instead of waiting for the next frame boundary or the next time-slot boundary, which can fully reduce the waiting time of the packet at the air interface.

In addition to increasing the subcarrier interval and symbol-level scheduling mechanism to reduce the air interface delay, NR also reduces the feedback delay of hybrid automatic repeat request (HARQ) by means of a self-contained time slot. In a self-contained time slot all three different direction attributes of symbol, downlink symbol, guard interval, and uplink symbol, are contained in one time slot. The same time slot includes physical downlink shared channel (PDSCH) transmission, GP, and downlink acknowledgement/negative acknowledgement (ACK/NACK) feedback transmission, so that the UE can receive and decode the downlink data and quickly complete the corresponding ACK/NACK feedback in the same time slot. As a result, the feedback delay of HARQ is greatly reduced. Of course, the implementation of self-contained time slots also requires high UE processing capacity, which is very suitable for URLLC scenarios.

1.2.6 Enhancement of reference signals in new radio

The design of reference signal is the most important technical aspect in the design of mobile communication systems, because the wireless channel estimation at the receiver is obtained through the reference signal. The design of the reference signal will directly affect the signal demodulation performance of the receiver. In 4G systems, the cell-specific reference signal (CRS) defined by the LTE protocol can be used for maintaining downlink synchronization and frequency tracking of all users in the cell. The CRS is also used as demodulated reference signals of LTE users in various transmission modes such as space-frequency block code (SFBC) and space division multiplexing (SDM). That is, the channel estimation obtained based on CRS is used for the demodulation and reception of PDSCH data in the downlink traffic channel. The CRS occupies the whole carrier bandwidth in the frequency domain, and the base station sends it steadily after the cell is established. The CRS is transmitted no matter whether there are users and data transmission in the cell or not and it is a type of always-on signal. Due to the transmission of full bandwidth, such an always-on reference signal CRS not only costs large overhead of downlink resources, but also brings cochannel interference in the overlapping areas of the network. Another consequence caused by constant reference signal transmission is that the base station equipment cannot achieve effective energy savings by using technical means such as radio-frequency shutdown when there is no service transmission in the cell.

In view of those issues existing with the CRS, the public reference signal of LTE, 5G NR made fundamental improvements in pilot design to avoid cell-specific public signals as much as possible. For example, in NR system, only synchronization signals are retained as cell-specific public signals, but all the other reference signals in NR are UE-specific. In this way, the system overhead of constant resource occupation of cell-specific public signals can be reduced, and the spectrum efficiency can be improved. For example, when the base station sends data to a UE, the UE-specific demodulation reference signal (DMRS) is only sent within the bandwidth of the scheduled data. In addition, considering that the 5G base station system generally uses the beamforming technology of massive MIMO for data transmission, the same precoding method is applied on both the data symbols and demodulated pilots, and pilot signals are sent only when there is data transmission. The beamformed transmission will also effectively reduce the interference in the system.

Furthermore, NR adopts the design of front-loaded DMRS combined with additional DMRS. The front-loaded DMRS is beneficial for the receiver to estimate channel quickly and reduce the demodulation and decoding delay. The purpose of introducing additional DMRS is to meet the requirement of time-domain DMRS density in high-speed scenarios. For the users moving at different speeds, the base station can configure the number of additional pilots in the time slot to match the user’s mobile speed and provide a guarantee for accurate channel estimation at the user side.

1.2.7 Multiple input multiple output capability enhancement by new radio

The air interface technology of LTE is OFDM+MIMO, and the support for MIMO has been constantly evolving and enhanced. The full-dimensional MIMO (FD–MIMO) introduced in the later version of LTE can achieve spatial narrow beamforming in both horizontal and vertical dimensions, which can better differentiate the users spatially. However, as the most important technical mechanism to improve the air interface spectrum efficiency and system capacity of wireless communication, MIMO technology has always been an important direction for pursuing the ultimate performance.

With the maturity of the key components of Massive MIMO as well as the requirements of engineering application and commercial deployment, from the beginning of 5G requirement scenario definition and system design, Massive MIMO is treated as an important technical component of NR and the mainstream product form of large-scale deployment of 5G commercial network. Therefore 5G NR made a lot of optimizations and enhancements to MIMO technology during the process of standardization.

First of all, NR enhances the DMRS. By the methods of frequency division and code division, DMRS can support up to 12 orthogonal ports, which can better meet the performance requirement of multiuser MIMO than LTE. Secondly, NR introduces a new type 2 codebook with higher performance than that in LTE. The CSI–RS-based type2 codebook can feedback the best matching degree of spatial channels. With the high-precision codebook in UE feedback, the base station can implement higher the spatial beam directivity and shaping accuracy, and thus the performance of multiuser multistream SDM can be greatly improved.

One of the major advantages of NR over LTE is the support of millimeter wave band. Millimeter wave has the characteristics of high-frequency band, short wavelength, large space propagation loss, weak diffraction ability, and large penetration loss. So millimeter wave communication must use extremely narrow beam alignment transmission to ensure the quality of the communication link. In order to defeat those challenges, NR adopts the technology of hybrid digital and analog beamforming. NR supports the narrow beam sweeping mechanism for broadcast channels and public channels for coverage enhancement. For the control channel and traffic channel, NR introduces the beam management mechanism, including multibeam scanning, beam tracking, beam recovery, and other technical means and processes, in order to align the beams of both sides of the communication and adaptively track the movement of users. On the basis of multibeam operation, NR further supports the design of multipanel to improve the reliability and capacity of transmission.

It can be seen that a series of enhancement schemes was introduced by 5G for MIMO technology. Combined with the improved capability of large-scale antenna equipment itself, the massive MIMO will inevitably release huge technical advantages and economic benefits in 5G mobile communication system.

1.2.8 Enhancement of terminal power saving by new radio

LTE has limited consideration on the design of terminal power-saving technology. The major terminal power-saving scheme in LTE is discontinuous reception (DRX) technology. Due to the much wider working bandwidth, larger number of antennas, and much higher data rate of the 5G system, the power consumption of the RF module and baseband signal processing chip in the terminal will increase significantly, and the user experience will be seriously affected by the hot heat or short standby time during the working process of the mobile phone.

Aiming at the terminal power consumption problem, 5G designs a variety of technical schemes. From the perspective of power saving in the time domain, 5G includes a new wakeup signal for users in connected-state when DRX is configured. According to the demand for traffic transmission, the network can determine whether to wake up the UE before the arrival of the DRX activation cycle for data reception monitoring, which can prevent users from entering the DRX activation state for additional service monitoring without data transmission, thus spending unnecessary power consumption for PDCCH detection. In addition, 5G also introduces a cross-slot scheduling mechanism, which can reduce the unnecessary reception and processing of PDSCH by UE before decoding PDCCH in the case of discontinuous and sporadic traffic transmission, and reduce the activation time of RF circuit in the time domain.

From the perspective of power saving in the frequency domain, 5G introduces the function of bandwidth part (BWP). As mentioned earlier, the carrier bandwidth of NR is much larger than that of LTE, and many core bands can support typical 100 MHz carrier bandwidth. The advantage of large bandwidth is that high transmission rate can be supported. However, if the business model is a small amount of data transmission or the service is discontinuous, it is very uneconomical for UE to work in large bandwidth mode. The core of BWP function is to define a bandwidth that is smaller than the carrier bandwidth of the cell and also the bandwidth of the terminal. When the amount of data transmitted by the air interface is relatively low, the terminal works in a smaller bandwidth with the dynamic configuration of the network, so that the RF front-end device, the RF transceiver, and the baseband signal processing module of the terminal can all work with a smaller processing bandwidth and a lower processing clock. Thus the UE can work in a state with lower power consumption.

Another technical mechanism for power saving in the frequency domain is the Scell sleep mechanism introduced for the multi-RAT dual connectivity (MR–DC) and NR CA scenarios. The Scell in the active-state can enter the state of dormant Scell when there is no data transmission. UE only needs to measure channel state information (CSI) without monitoring physical downlink control channel (PDCCH) on dormant Scell, and then quickly switches to the normal state for scheduling information monitoring when there is data transmission. That can reduce the power consumption of UE without deactivating Scell.

From the perspective of power saving in the frequency domain and antenna domain, 5G introduces the self-adaptive function of MIMO layers. The network side combines the demand for terminal data transmission and the configuration of BWP to reduce the number of layers of spatial transmission, so that UE can downgrade the MIMO processing capacity and throughput rate, which would reduce the terminal power consumption equivalently.

In addition to the abovementioned terminal power-saving technologies, 5G also supports mechanisms that can relax the requirements for UE radio resource management (RRM) measurements to reduce power consumption. For example, when UE is still or moves at a low speed, the measurement requirements can be relaxed appropriately by increasing the RRM measurement cycle without affecting the mobility performance of UE to reduce UE power consumption. When UE is in IDLE or INACTIVE state, or when UE is not at the edge of the cell, appropriate RRM measurement relaxation can be carried out to reduce UE power consumption.

1.2.9 Mobility enhancement by new radio

The mobility management in LTE is mainly based on the measurement report of UE. The source base station triggers the handover request and sends it to the target base station. After receiving the confirmation reply from the target base station, the source base station initiates the handover process and sends the configuration information of the target base station to the terminal. After receiving the configuration message, the terminal initiates a random access process to the target base station, and when the random access process is successful, the handover process is completed. It can be seen that in the process of cell handover in LTE system, UE needs to complete random access in the target cell before it can carry out service transmission, and there will inevitably be a short duration of service interruption.

In order to meet the requirement of 0 Ms interruption and improve the robustness of handover, 5G NR makes two main enhancements to mobility: a handover mechanism based on dual active protocol stack (DAPS) and a conditional handover mechanism.

The handover mechanism of the DAPS is similar to the LTE handover process, and the terminal determines the type of handover to be performed based on the received handover command. If the handover type is based on the DAPS, the terminal will maintain the data transmission and reception with the source cell until the terminal successfully completes the random access process to the target cell before releasing connection with the source cell. Only after the terminal is successfully connected to the target base station will the terminal release the connection of the source cell and stop the data transmission and reception with the source cell based on the explicit signaling from the network. It can be seen that the terminal will maintain connection and data transmission with the source cell and the target cell simultaneously during the handover process. Through the mechanism of DAPS, NR can meet the performance metric of 0 Ms service interruption latency during the handover process, which greatly improves the service awareness of users in mobility.

The goal of conditional handover is mainly to improve the reliability and robustness of the handover process. It can solve the problem of handover failure caused by too long of a handover preparation time or the sharp decline of channel quality of the source cell in the handover process. The core idea of conditional handover is to preconfigure the contents of handover commands to UE, in advance. When certain conditions are met, UE can independently execute the configuration of handover commands and directly initiate handover to a target cell that meets the preconfigured conditions. Because UE no longer triggers measurement reporting when the switching conditions are met, and UE has obtained the configuration in the switching command in advance, the problem that measurement reporting and switching commands cannot be received correctly is solved. Especially for high-speed cases or cases where the signal experiences fast fading in the switching frequency band, conditional switching can greatly improve the success rate of handover.

1.2.10 Enhancement of quality of service guarantee by new radio

In the LTE system, QoS control is carried out through the concept of evolved packed system (EPS) bearer, which is the smallest granularity of QoS processing. A single UE supports up to 8 radio bearers at the air interface. The differentiated QoS guarantee corresponding to maximum 8 EPS bearers cannot satisfy more refined QoS control requirements. The operation of the radio bearer and the QoS parameters setting at the base station completely follows the instructions of the core network. For the bearer management request from the core network, the base station can only choose to accept or reject, but cannot establish the radio bearer or adjust the parameters by itself. The standardized QoS class identifier (QCI) defined by LTE has only a limited number of values, so it is impossible to provide accurate QoS guarantee for business requirements that are different from the preconfigured QCI or standardized QCI in the current operator network. With the vigorous development of various new services on the Internet, and the emergence of a variety of new services, such as private network, industrial Internet, vehicle networking, machine communication, and so on, the types of services that the 5G network needs to support and the demand for QoS guarantee of services greatly exceed the QoS control capability that can be provided in the 4G network.

In order to provide a more differentiated QoS guarantee for a variety of 5G services, the 5G network has made more refined adjustments to the QoS model and types. The concept of bearer is removed at the core network side and is replaced with QoS flow. Each PDU session can have up to 64 QoS flows, which greatly improves the QoS differentiation and carries out finer QoS management. The base station determines the mapping relationship between the QoS flow and the radio bearer, and is responsible for the establishment, modification, deletion, and QoS parameter setting of the radio bearer, so as to use the wireless resources more flexibly. Dynamic 5QI configuration, Delay-Critical resource types, Reflective QoS, QoS Notification Control, Alternative QoS profile, and other features are also added in the 5G network, which can provide a better differentiated QoS guarantee for a wide variety of services.

1.2.11 Enhancement of core network architecture evolution by new radio

In the LTE network, the adopted network architecture has no separation of the control plane and the user plane, and the session management of the terminal and the mobility management of the terminal are handled by the same network entity, which leads to the inflexibility and nonevolution of the network evolution.

In the 5G era, the goal of 5G mobile communication is to achieve the Internet of everything and support rich services of mobile Internet and Internet of things. 4G network architecture mainly meets the requirements of voice service and traditional mobile broadband (MBB) services, and is not able to efficiently support a variety of services.

In order to better and more efficiently meet the above requirements, and to support operators to achieve rapid service innovation, rapid on-boarding and on-demand deployment, etc., 3GPP adopts a network architecture with completed separation of control plane and user plane. This design is beneficial to the independent expansion, optimization, and technological evolution of different network elements. The user plane can be deployed with a centralized or distributed manner. In a distributed deployment, the user plane can be sunk into a network entity that is closer to the user so as to improve the response speed to user requests. However, the control plane can be managed centrally and deployed in a unified cluster to improve maintainability and reliability.

At the same time, the mobile network needs an open network architecture. The network capability can be expanded through changing the open network architecture and the service can invoke the network capability through the open interface. On the basis of such a design, 3GPP adopts 5G service-based architecture (SBA). Based on the reconstruction of the 5G core network, the network entity is redefined in the way of network function (NF). Each NF provides independent functionalities and services and the NFs can invoke the functionalities and services of each other. Thus it transforms from the traditional rigid network (fixed function, fixed connection between network elements, fixed signaling interaction, etc.) to a service-based flexible network. The SBA solves the problem of tight coupling of point-to-point architecture, realizes the flexible evolution of the network, and meets the requirements of various services.

1.3 New radio’s choice of new technology

As discussed in previous sections, NR has made a lot of enhancements and optimizations compared to LTE technology in the process of standardization. In order to meet the basic goal of large bandwidth, low latency, and high data rate of future mobile communication networks, and to support the diversified services of vertical industry more flexibly, the goal of NR from the beginning of standard research and technical scheme design was to adopt many brand-new key technologies, such as new architecture, new air interface, new numerology, new waveform, new coding, new multiple access, and so on. At the formal standardization discussion stage, a large number of program research reports and technical recommendations were submitted by many companies for each key technology. After many rounds of discussion and evaluation, we reached the final conclusion of standardization based on comprehensive consideration of various factors and certain trade-offs. In the determined final NR standardization, some new technologies, such as new numerology and new coding, were finally formulated as a standardization scheme, but other key technologies that were fully discussed during the standardization process were not finally standardized in the completed versions of R15 and R16, such as new waveform and new multiple access technologies. The following sections presents a high-level discussion and summary of NR’s choice of new technologies in the process of standardization.

1.3.1 New radio’s choice on new numerology

The motivation for NR to design flexible numerology is that NR needs to better support diverse business requirements. The SCS of the OFDM waveform defined in the LTE standard is a fixed value, 15 kHz. This single value of SCS cannot meet the system requirements of 5G. The three typical services of 5G, eMBB, URLLC, and mMTC, have different requirements for transmission rate, air interface delay, and coverage capability, so different services would require different numerologies (SCS, cyclic prefix length, etc.). Compared with the traditional eMBB service, the low-latency service of URLLC needs a larger SCS to shorten the symbol length for transmission in order to reduce the transmission air interface delay. However, the mMTC services of the Internet of things with large connections often need to reduce the SCS and increase the coverage distance by increasing the symbol transmission time and power spectral density. And NR needs to ensure that the services with different numerologies can coexist well in the air interface and do not interfere with each other.

According to the basic principle of the OFDM system, the SCS of the OFDM waveform is inversely proportional to the length of the OFDM symbols. Since the OFDM symbol length can be changed correspondingly by changing the SCS, the time length of a time slot in the air interface can be directly determined. Considering that NR should better support different air interface transmission delays and large carrier bandwidths, NR finally supports multiple SCSs, which are based on 15 kHz and expand with the integral power of 2, including the values of 15 kHz/30 kHz/60 kHz/120 kHz/240 kHz/480 kHz. With the increase of SCS, the corresponding OFDM symbol length decreases proportionally. The purpose of this design is to achieve boundary alignment between OFDM symbols with different subcarrier intervals, so as to facilitate resource scheduling and interference control in frequency division multiplexing of services with different SCSs. Of course, at the beginning of the NR discussion, other SCSs such as 17.5 kHz were also considered. But after evaluation, it was determined that the SCS based on 15 kHz could support the compatible coexistence scenario of LTE and NR and the scenario of spectrum sharing better than other SCSs. Thus the scheme of other SCS numerology was not adopted.

Flexible and variable SCS can adapt to different business requirements. For example, using a larger SCS can shorten the symbol length, thus reducing the air interface transmission delay. On the other hand, the FFT size and SCS of the OFDM modulator jointly determine the channel bandwidth. For a given frequency band, phase noise and Doppler shift determine the minimum SCS. The carrier bandwidth of the high-frequency band is often larger, and the Doppler frequency offset is also relatively large. So, a larger SCS is suitable for the high-frequency band carrier, which not only can meet the limitation of the number of FFT points, but also is able to resist the Doppler frequency shift well. Similarly, in high-speed scenarios, it is also suitable to use a larger SCS to resist the influence of Doppler offset.

Based on the above analysis, we can conclude that with multiple SCSs, the NR has good scalability and the NR with flexible numerology can well meet the needs of various scenarios, such as different service delay, different coverage distance, different carrier bandwidth, different frequency range, different mobile speed, and so on. NR has laid a good technical foundation for the flexible deployment and coexistence of 5G multiservices by supporting flexible numerology and a unified new air interface framework on both high and low frequencies.

1.3.2 New radio’s choice on new waveform

NR’s requirements for new waveforms have the same starting point as the flexible numerology discussed earlier, which is that NR needs to support diverse business requirements. Those different services transmitted with different numerologies [SCS, symbol length, cyclic prefix (CP) length, etc.] at the air interface need to coexist well and not interfere with each other. Therefore the design goal of the new waveform is not only to support higher spectral efficiency, good intercarrier resistance to frequency offset and time synchronize deviation, lower out-of-band radiation interference, and excellent peak-to-average power ratio (PAPR), but also to meet the requirements of asynchronous and nonorthogonal transmission among users.

As is well known, the CP–OFDM waveform used in the downlink transmission of LTE has some inherent advantages, such as good resistance to inter-symbol interference and frequency selective fading, simple frequency-domain equalization receiver, easy to be combined with MIMO technology, and support of flexible resource allocation. But CP–OFDM waveform also has inherent disadvantages, such as high PAPR, spectral efficiency overhead due to CP, being sensitive to time synchronize and frequency deviation, large out-of-band radiation, and performance degradation caused by intercarrier interference. Based on the motivation of NR to support a variety of new services, the goal of air interface new waveform design is to flexibly select and configure appropriate waveform parameters according to business scenarios and business types. For example, the system bandwidth is divided into several subbands to carry different types of services and different waveform parameters can be selected for different subbands. There is only a very low protection band or no need for protection bands between the subbands, and the system can implement a digital filter on each subband to eliminate the related interference between the subbands to realize the waveform decoupling of different subbands, and satisfy the flexible coexistence of different services.

During the standardization discussion on new NR waveforms, a variety of optimized or brand-new waveform schemes based on CP–OFDM waveforms were proposed [16–26]. As shown in Table 1.1, more than a dozen proposals for new waveforms were submitted, which can be divided into three categories: time-domain windowing processing, time-domain filtering processing, and no windowing or filtering processing.

Table 1.1

The candidate new waveforms of multicarrier time-domain windowing are as follows:

1. FB–OFDM: Filter-Bank OFDM

2. FBMC–OQAM: Filter-Bank MultiCarrier offset-QAM

3. GFDM: Generalized Frequency Division Multiplexing

4. FC–OFDM: Flexibly Configured OFDM

5. OTFS: Orthogonal Time Frequency Space.

The candidate new waveforms of multicarrier time-domain filtering are as follows:

1. F–OFDM: Filtered–OFDM

2. UF–OFDM: Universal-Filtered OFDM

3. FCP–OFDM: Flexible CP–OFDM

4. OTFS: Orthogonal Time Frequency Space.

In addition to time-domain windowing and time-domain filtering, the following new waveforms are available for single-carrier waveforms:

1. DFT–S–OFDM: DFT-spread OFDM

2. ZT–S–OFDM: Zero-Tail spread DFT-OFDM

3. UW DFT–S–OFDM: Unique Word DFT–S–OFDM

4. GI DFT–S–OFDM: Guard Interval DFT–s–OFDM.

3GPP evaluates and discusses a variety of candidate new waveform schemes, among which several candidate waveforms were mainly discussed, including F–OFDM, FBMC, UF–OFDM, and so on. The new waveforms do have some advantages in the orthogonality between subbands or subcarriers, spectral efficiency, out-of-band radiation performance, and resistance to time-frequency synchronize errors, but they also have some problems, such as poor performance gain, incompatibility with CP–OFDM waveforms, high implementation complexity of combining with MIMO, underutilization of fragment spectrum, and so on. The final conclusion of the standard is that no new waveform is to be adopted, but only specific performance requirements such as effective carrier bandwidth, adjacent channel leakage, and out-of-band radiation of NR are specified in the standard. In order to meet these technical requirements, the technical schemes that may be used in NR waveform processing,