Overview of global 6G research and development

01Overview

Mobile communication technology has now evolved to the fifth generation (5G). Throughout its development history, 2G/3G has achieved basic mobile connections, while 4G, the most widely deployed, has brought huge data throughput through the popularization of smart terminals and changed users' lifestyles. 5G has attracted much attention even before it is fully commercialized. Its goal is not only to improve the business experience of traditional users, but also to combine mobile communications with vertical industries to greatly expand the field of mobile communications business. Although 5G is still in the initial stage of deployment globally, and cooperation with vertical industries has just begun to advance, in the future, as deployment and services continue to mature, it will surely bring prosperity to the mobile communications market and accelerate the digitalization process of various industries and even the entire society.

Although the system indicators and capabilities of 5G have been greatly improved, and the application scenarios have become increasingly diversified, there are still limitations. Facing the future, there are still huge driving forces to promote the continuous evolution of mobile communication networks. On the one hand, it is driven by emerging technologies, such as artificial intelligence, blockchain, cloud computing and other ICT technologies, as well as new materials, antennas and other processes. On the other hand, due to the continuous evolution of demand, with the development of diversified terminals and the improvement of digitalization levels in various industries, services such as holographic, immersive XR, tactile Internet, and smart factories have been proposed, which not only require improvements in traditional performance indicators such as speed, delay, number of connections, and coverage, but also bring new dimensions of demand for perception, positioning, and security. Therefore, research on the vision, needs and technology of the next generation of mobile communications has been gradually carried out. Due to the huge changes and additional economic value brought by 5G to society, competitive countries and industrial chains around the world attach great importance to mobile communications technology. Not only major standards organizations, academia and even many relevant national institutions and industries have begun pre-research, aiming to have a mature technical system in the next 10 years, that is, 2030, to be able to have a mature technology system to meet new business needs while improving its own competitiveness.

Focusing on the next generation of mobile communications, namely the 6G system, this article sorts out the research background and related progress of major global standards organizations, regional and national organizations, and university research institutions, analyzes the current potential wireless side and network side technology directions and the technical advantages they bring, and finally summarizes the progress of 6G and puts forward thoughts on the 6G vision and overall development direction.

02Global 6G research status

2.1 International and regional organizations

2.1.1 International Telecommunications Union (ITU)

The Telecommunications Standardization Sector Study Group 13 (ITU-T SG13) under the International Telecommunications Union is committed to future network research and established the NET-2030 Network Focus Group in July 2018 to explore network service needs for 2030 and beyond. The focus group has three sub-groups, including application scenarios and requirements, network services and technologies, and architecture and infrastructure. It released two white papers in 2019, focusing on application scenarios and new service capabilities of the 2030 network. It proposed a variety of new scenarios such as holographic and tactile Internet, as well as current network gaps and services that require the most attention in future networks.

In addition, the 5D Working Group of the Radio Communication Sector (ITU-R WP5D) under the ITU launched research work for 2030 and the future (6G) at a meeting held in Geneva, Switzerland, in February 2020. The meeting formed a preliminary 6G research schedule, including future technology trend research reports, future technology vision proposals and other important planning nodes. At this meeting, ITU started the writing of the "Future Technology Trend Report", which is scheduled to be completed in June 2022. The report describes the technological evolution direction of IMT systems after 5G, including IMT evolution technology, high spectral efficiency technology and deployment. In addition, it is also planned to launch the "Future Technology Vision Proposal" in the first half of 2021 and complete it by June 2023. This proposal contains the overall goals of the IMT system for 2030 and the future, such as application scenarios, main system capabilities, etc. At present, the ITU has not yet determined the development plan for the 6G standard.

2.1.2 Institute of Electrical and Electronics Engineers (IEEE)

IEEE launched future network research with the goal of "realizing 5G and beyond" in August 2018. On March 25, 2019, the world's first 6G Wireless Summit sponsored by IEEE was held in Finland. Many participating representatives from industry and academia published the latest insights and innovations on 6G, and discussed the theoretical and practical challenges that need to be addressed to realize the 6G vision. The papers and reports of the conference covered many technologies such as 6G scenario imagination, millimeter waves and terahertz, smart connections, edge AI, machine wireless communications, etc. The second 6G Wireless Summit was also held online in 2020, with keynote speeches, technical meetings and related demonstrations by industry, operators, research institution scholars and stakeholders. The 6G Summit is a global technology event, with the goal of clarifying the vision and development direction of 6G through the collective efforts of various industries.

2.1.3 Third Generation Partnership Project (3GPP)

3GPP's current version under development, R17, is still an evolution and enhancement of 5G features, but demand group SA1 has started related projects for future services, including smart grids, tactile communications, etc., which is likely to make a smooth transition to the next generation of mobile communication systems. According to current progress and plans, 3GPP will most likely start work on 6G vision, technology, and requirements in R19 (2023), and start 6G standardization work in R21 or later stages.

2.1.4 6G Flagship

The 6G Flagship, sponsored by a Finnish consortium and led by Oulu University, was established in 2019 and is committed to providing standardized communication technology with "near-instant, unlimited wireless connections". In September 2019, it released a white paper "Key Drivers and Research Challenges for 6G Ubiquitous Wireless Intelligence", which initially answered questions about how 6G will change people's lives, what technical features it has, and what technical difficulties need to be solved. The content includes 6G vision, driving force, applications and services. The wireless research direction focuses on artificial intelligence, new authorization-free access, signal shaping, analog modulation, large-scale intelligent surfaces, etc. The progress and difficulty of wireless hardware are also analyzed. The network research direction focuses on the establishment of trust chain.

2.2 National perspective and layout

2.2.1  欧盟

The European Union launched a consultation on the 6th generation mobile communications (6G) technology research and development project in 2017, aiming to commercialize 6G technology in 2030. At the same time, the European Union has launched a three-year 6G basic technology research project. The main task is to study next-generation forward error correction coding technology, advanced channel coding and channel modulation technology that can be used in 6G communication networks. The EU Horizon 2020 organization will also launch a 6G research project on "intelligent networks and services", which is currently in the preliminary demonstration and pre-research stage.In addition, the EU actively funds universities and research institutions, including the National Technical Research Center of Finland and the University of Oulu, focusing on future application scenarios and technical directions such as terahertz, wireless broadband access, edge intelligence, and codecs.

2.2.2  美国

The U.S. government attaches great importance to 6G technology and continues to make efforts in the fields of terahertz and air-space-ground integration technologies. In March 2019, the FCC promulgated the spectrum allocation in the THz band in the United States: 95 GHz to 3THz. It believes that 6G will move towards the terahertz frequency era. As the network becomes more dense, three major technologies, including dynamic spectrum sharing technology and spatial multiplexing technology based on THz and blockchain, are becoming new technological trends. New York University, University of California, and Virginia Tech in the United States are all conducting pre-research work in terahertz and other 6G directions. In addition, Space-X, OneWeb, Amazon, etc. have launched satellite Internet plans as potential enabling technologies for subsequent 6G.

2.2.3  日本

The Japanese government plans to formulate a comprehensive development strategy for future 6G through public-private cooperation. The Ministry of Economy, Trade and Industry has established a fund totaling 220 billion yuan to establish a key national priority project and launch 6G research and development. It is chaired by the president of the University of Tokyo, and technology giants such as Toshiba provide technical support. Japan currently has a unique advantage in the field of terahertz, and lists terahertz technology as the first among the "Top Ten Key Strategic Objectives of National Pillar Technologies". NTT Group has promoted the development of two B5G and 6G technologies, terahertz and orbital angular momentum. In addition, Japan will also use "optical semiconductors" as the information processing technology to support 6G. NTT said it will cooperate with 65 companies and strive to achieve mass production of optical semiconductors for 6G by 2030.

2.2.4  韩国

South Korea's 6G research is mainly concentrated in enterprises and university research institutions, including Samsung, SK, LG Electronics, Korea Advanced Institute of Science and Technology, etc. Among them, LG Electronics has cooperated with Korea Advanced Institute of Science and Technology to establish a 6G research center; the Institute of Electronics and Telecommunications has signed a memorandum with the University of Oulu in Finland to develop 6G network technology. SK Telecom has signed agreements with Finland's Nokia and Sweden's Ericsson to strengthen cooperation in 6G network research and development. In June 2019, Samsung established an Advanced Communications Research Center and began research on 6G networks. In July 2020, Samsung released a 6G vision white paper "6G: The Next Hyper Connected Experience for All", which covers Samsung's 6G vision, evolution trends, application scenarios, indicator requirements, candidate technologies and expected standardization schedule.

2.2.5  中国

In November 2019, the Ministry of Science and Technology held a kick-off meeting for 6G technology research and development work and announced the establishment of a national 6G technology research and development promotion working group and an overall expert group. Among them, the promotion working group is responsible for promoting the implementation of 6G technology research and development work; the overall expert group is responsible for proposing 6G technology research layout suggestions and technical demonstrations, and providing consultation and suggestions for major decisions. The Ministry of Industry and Information Technology also established a 6G research group in 2019, which was later renamed IMT-2030. It gathered forces from industry and universities, covering demand, wireless and network technologies, and strengthened forward-looking vision requirements and technology research, with the goal of clarifying 6G promotion ideas and key directions.

03Potential research directions

Research on next-generation mobile communications is inseparable from the discussion of new technologies and new network architectures. This chapter sorts out the current research priorities of major organizations, universities, and research institutions, and divides them into three categories: new spectrum, new wireless side technology, and new networking architecture and network capabilities. It mainly introduces the technical characteristics and the necessity of oriented 6G systems, and provides a basic reference for subsequent more abundant and systematic research work.

3.1 New spectrum
In the future, business types and users will become more diversified, and network performance requirements will become higher and higher. At present, low-frequency frequency resources have gradually been fully occupied, so extending the spectrum to higher bands will become the research direction of 6G. The spectrum that currently attracts more attention from the industry includes terahertz and visible light frequency bands.

Terahertz refers to the frequency band from 100 GHz to 10 THz, with a wavelength range of 0.03~3 mm. It is electromagnetic radiation between radio waves and light waves. It has the characteristics of carrying rich information, sub-picosecond pulse width, high spatiotemporal coherence, low photon energy, strong penetration, high safety in use, good directionality, and high bandwidth. Terahertz communication applications can be divided into two categories based on coverage distance. Long-distance coverage applications include large-capacity wireless fronthaul/backhaul, wireless data centers, space applications, etc. The coverage distance is on the order of hundreds of meters to kilometers. Applications of short-distance coverage include short-range point-to-point communication, chip communication, health monitoring and nanoscale Internet of Things, etc., with coverage ranging from millimeters to meters. The key issues in current terahertz research are the development of core devices and flexible and dynamic air interface design.

The spectrum of the visible light band is 420~780 THz, and the wavelength range is 380~780 nm. It can be used without authorization. Visible light communication has the advantages of combining lighting and communication, no electromagnetic interference, and being green and environmentally friendly. Therefore, VLC is an important means to solve the problem of close home intervention and is considered to be an optional technology for future communication systems. The main application scenarios of VLC include indoor wireless access, indoor positioning, indoor navigation, intelligent transportation, applications in the aviation field, data sharing between devices, high-rate information transmission, underwater communications, information security, etc. However, the current visible light communication industry chain is not mature enough, and the bottleneck lies in the visible light transceiver devices of mobile terminals.

3.2 New wireless side technology

3.2.1 Large smart surfaces

In previous mobile systems, many wireless individual technologies were dedicated to better adapting to the changing wireless channel environment and using optimized transceiver designs (such as waveform schemes, coding schemes, time-frequency and space transmission mechanisms, etc.) to improve system capacity. In the past, the control of electromagnetic waves was limited to transmitters and receivers. However, in recent years, the emergence of smart metasurfaces has enabled the electromagnetic characteristics of the channel environment to be flexibly controlled, which has attracted widespread attention from academia and industry. Smart metasurface is an artificial electromagnetic surface structure with programmable electromagnetic properties, usually composed of new programmable metamaterials. Smart metasurfaces can actively and intelligently regulate electromagnetic waves through digital coding, forming an electromagnetic field with controllable amplitude, phase, polarization and frequency. This mechanism provides an interface between the physical electromagnetic world of smart metasurfaces and the digital world of information science. The advantages of smart metasurface technology also include low energy consumption, low hardware cost, no self-interference, flexible configuration, and wide application. It can control electromagnetic beams in real time through reflection, transmission, scattering, etc. according to different application scenarios, change the wireless environment, enhance useful signal quality, and thereby achieve the purpose of enhancing coverage, improving system capacity, and simplifying design. It is particularly attractive for the development of future mobile communications.

3.2.2 New coding and waveforms

In the previous evolution of mobile systems, from 4G to 5G, the peak rate increased by more than 10 times. It can be predicted that in the next generation of mobile systems, the rate growth trend will still be maintained or even accelerated. The decoding throughput requirement reaches more than 100 Gbps, and the decoding algorithm and error correction code need to be redesigned to improve decoding parallelism. At the same time, reliability requirements are gradually increasing, requiring coding to have a lower error level and optimizing related designs. Coding technologies that are currently being studied more include Spinal coding technology, index modulation technology, and nonlinear precoding. At the same time, artificial intelligence is also gradually attracting attention in coding. In addition, in 5G systems, waveform design can be flexibly adapted to different application scenarios. In the future, 6G will support more complex scenarios and services, and performance indicators will also be greatly improved. The design and introduction of new waveforms is imperative. Current research includes design based on non-orthogonal waveforms, transform domain waveform design, etc. New coding and waveforms will play an important role in future systems and are technical directions that need to be explored.

3.3 New networking architecture and network capabilities

3.3.1 Integration of space, ground, air and sea

Satellite communications play a vital role in improving life in today's digital economy. Compared with terrestrial networks, satellite networks have complete earth surface coverage, advanced mobility, high security and reliability, and long-distance transmission delay guarantees. Combining satellites, aircraft and ground networks to achieve three-dimensional and heterogeneous network interconnection can achieve wide-range, large-capacity, and huge-connection information distribution and interaction, meet special scenarios such as limited rural area connections, airspace and sea area connections, and disaster management, achieve global seamless coverage and senseless handover, and provide guarantees for next-generation mobile communication coverage and connection requirements. The technical challenges faced by the current technical system include highly dynamic changes in transmission links, complex spatiotemporal behavior of the network, and large differences in heterogeneous business scales. Technical breakthroughs in simultaneous air, space and ground integrated networking, transmission theory, optimized scheduling, and intelligent collaboration also require great technological breakthroughs.

3.3.2 Deterministic Network

Deterministic Networking (DetNet - Deterministic Networking) was originally a technology that helped realize the transformation of IP networks from "best-effort" to "on-time, accurate, and fast", controlling and reducing end-to-end latency. It was initially targeted at vertical industries such as industry, energy, and Internet of Vehicles that have extremely high requirements for low network latency, reliability, and stability. The current TSN standard developed by IEEE provides the determinism of Ethernet, and the deterministic network working group established by IETF is committed to extending the technology developed in TSN to routers and expanding the scale of the network. In the future, as mobile terminals and the types of services they carry become more diverse, "deterministic" requirements such as high-precision time synchronization, absolute end-to-end upper limit delay, and ultra-reliable zero-loss data packet delivery will become the requirements of the next generation of mobile systems. The wireless side is the key to achieving end-to-end certainty in mobile systems. Wireless transmission is easily affected by the environment, and transmission quality is difficult to guarantee. In the 5G era, 3GPP standards have formulated a plan for the integration of TSN and 5G. The 5G system is used as a TSN bridge and the architecture is integrated in a black box manner. However, the two are still independent systems and it is difficult to fully guarantee the performance of TSN. In the future, in the next generation mobile communication system, the characteristics of the business will be fully considered to make 6G native support deterministic. The relevant technical solutions and architecture system need to be further improved.

3.3.3 Cloud native

Cloud native means that applications are deployed on cloud servers and have the characteristics of containerization, microservices, continuous delivery and DevOps. These technologies can build a loosely coupled system that is fault-tolerant, easy to manage and easy to observe. In the 5G era, the core network is based on a service-oriented architecture, which makes it easier to implement network functions using general-purpose servers and achieve cloudification effects in data centers. However, the current 5G core network deployment still does not have features such as containerization and microservices. In the future, in order to build flexible, scalable, rapid innovation and online network services, cloud native can be a suitable solution. Although traditional wireless devices in mobile networks have always been highly closed, and network functions have extremely high requirements for real-time performance, research and exploration related to cloud-native mobile networks have been advancing. It is believed that as the technology and industry continue to mature, its advantages will be fully utilized in the future to build a flexible and elastic new network architecture.

3.3.4 Ubiquitous intelligence

The continuous prosperity of artificial intelligence is revolutionizing every branch of technology, and combining artificial intelligence with next-generation mobile networks has become an unstoppable trend. At present, most of the ways of combining intelligence in the communication field are to use data collection and artificial intelligence algorithms to optimize the business after the system is deployed, but the degree and scope of its application are low. In the future, with the continuous evolution of network architecture and the development of ubiquitous connections, artificial intelligence can be more closely integrated with every aspect of the network. It will not only be deployed in the cloud, but also penetrate into the edge and terminal sides. It will not only be used for intelligent optimization of specific services, but will also be more widely integrated with system design, including network deployment, algorithm design, and computing power allocation. Intelligence will be more widely embedded in the network to achieve true intelligent ubiquity and comprehensively enhance future mobile network capabilities.

3.3.5 Endogenous security

Future new business visions and network architectures, including immersive XR, holography, air-space-ground integrated ubiquitous connections, AI, etc., will introduce more attack points and bring more challenges to security. The traditional security defense model is a patch type, that is, after the system is built, through isolated security design, stacking, and reinforcement, it is a passive protection model, which is inefficient and uneconomical. Therefore, future mobile networks must explore new security models. Endogenous security is based on attributes such as cohesion, collaboration, and nativeness, making security characterized by native creation and symbiotic evolution. Network security is managed through the aggregation of different security protocols and security mechanisms. At the same time, security protection capabilities have independent driving force to adapt to network changes synchronously or even prospectively, so as to derive the inherent robust defense of the network. It is no longer a passive response to security threats and can play an important role in the future 6G network.

04Summarize

6G network is a network that will be oriented to 2030 and beyond. Although it is currently in the initial stage of research, it can still be initially glimpsed from the evolution trends of business and technology. 6G network needs to support higher bandwidth, stricter certainty, wider and deeper coverage of future services, and at the same time, consider providing smarter, safer, and more flexible network services. This article sorts out the progress and potential technical directions of research institutions for 6G. Although the current 6G route is not clear yet, and the potential directions also have problems in theory, physical implementation, and networking. However, with the continuous investment in scientific research and the continuous advancement of the industry, it is believed that the next generation of mobile communication systems will definitely bring more dimensional changes and deeper subversion!

References

【1】Dang S , Amin O , Shihada B , et al. What should 6G be?[J]. Nature Electronics，2020（3）：20-29.
【2】Klaus D , Hendrik B . 6G Vision and Requirements: Is There Any Need for Beyond 5G?[J]. IEEE Vehicular Technology Magazine, 2018, 13(3):72-80.
【3】Yastrebova A , Kirichek R , Koucheryavy Y , et al. Future Networks 2030: Architecture & Requirements[C]// International Congress on Ultra Modern Telecommunications & Control Systems & Workshops. 2019.
【4】White paper.Key drivers and research challenges for 6G Ubiquitous wireless intelligence.2019
【5】Gao Fang, Li Mengwei. The University of Oulu in Finland released a white paper initially proposing 6G vision and challenges [J]. Science and Technology China, 2019(12).
【6】Liu Junfeng, Liu Shuo, Fu Xiaojian, et al. Terahertz information metamaterials and metasurfaces [J]. Journal of Radar, 2018.
【7】Liu Yang, Peng Mugen. 6G endogenous security: architecture and key technologies [J]. Telecommunications Science, 2020(1):11-20.
【8】Zhang X , Wang J , Poor H V . Interference Modeling and Mutual Information Maximization Over 6G THz Wireless Ad-Hoc Nano-Networks[C]// GLOBECOM 2020 - 2020 IEEE Global Communications Conference. IEEE, 2020.
【9】Xie Sha, Li Haoran, Li Lingxiang, et al. A review of research on terahertz communication technology for 6G networks [J]. Mobile Communications, 2020(6):36-43.
【10】Yu M , Tang A , Wang X , et al. Joint Scheduling and Power Allocation for 6G Terahertz Mesh Networks[C]// 2020 International Conference on Computing, Networking and Communications (ICNC). 2020.
【11】Li Xin, Wang Qiang. Discussion on 6G research progress and application prospects of key candidate technologies [J]. Telecommunications Express, 2020, No.593(11):10-13.
【12】You X , Wang C X , Huang J , et al. Towards 6G wireless communication networks: vision, enabling technologies, and new paradigm shifts[J]. Sciece China. Information Sciences, 2021, 64(1).
【13】Chen S , Liang Y C , Sun S , et al. Vision, Requirements, and Technology Trend of 6G: How to Tackle the Challenges of System Coverage, Capacity,User Data-Rate and Movement Speed[J]. IEEE Wireless Communications, 2020.
【14】Guang Y, Liu Y , Huang N , et al. Vision, Requirements and Network Architecture of 6G Mobile Network beyond 2030[J]. 中国通信, 2020, 17(9):100-112.
【15】Rout S P . 6G Wireless Communication: Its Vision, Viability, Application, Requirement, Technologies, Encounters and Research[C]// 2020 11th International Conference on Computing, Communication and Networking Technologies (ICCCNT). 2020.
【16】Zhang Z , Xiao Y , Ma Z , et al. 6G Wireless Networks: Vision, Requirements, Architecture, and Key Technologies[J]. IEEE Vehicular Technology Magazine, 2019 (99):1-1.
【17】Chowdhury M Z , Shahjalal M , Ahmed S , et al. 6G Wireless Communication Systems: Applications, Requirements, Technologies, Challenges, and Research Directions[J]. IEEE Open Journal of the Communications Society, 2020, PP(99):1-1.