An Abstracted Survey on 6G: Drivers, Requirements, Efforts, and Enablers
AAn Abstracted Survey on 6G:Drivers, Requirements, Efforts, and Enablers
Bin Han ∗ , Wei Jiang † , Mohammad Asif Habibi ∗ , and Hans D. Schotten ∗†∗ Technische Universit¨at Kaiserslautern, † German Research Centre for Artificial Intelligence (DFKI)
Abstract —As of today, 5G mobile systems have been alreadywidely rolled out, it is the right time for academia and industryto explore the next generation mobile communication systembeyond 5G. To this end, this paper provides an abstracted surveyfor the 6G mobile system. We shed light on the key drivingfactors for 6G through predicting the growth trend of mobiletraffic and mobile service subscriptions until the year of 2030,envisioning the potential use cases and applications, as well asderiving the potential use scenarios. Then, a number of keyperformance indicators to support the 6G use cases are identifiedand their target values are estimated in a quantitatively manner,which is compared with those of 5G clearly in a visualizedway. An investigation of the efforts spent on 6G research indifferent countries and institutions until now is summarized,and a potential roadmap in terms of the definition, specification,standardization, and spectrum regulation is given. Finally, anintroduction to potential key 6G technologies is provided. Theprinciple, technical advantages, challenges, and open researchissues for each identified technology are discussed.
Index Terms —B5G, 6G, wireless, communication networks
I. I
NTRODUCTION
The year of 2019 opens a new era of the 5G mobilecommunications. As we are writing the paper, a list of coun-tries such as South Korea, United States, Switzerland, UnitedKingdom, and Spain have launched commercial 5G servicesfor the general public, while this list grows quickly and isenvisioned to become much longer in the near future. As arevolutionary technology, 5G will penetrate into all aspects ofsociety, generating tremendous economic and societal benefits.From the perspective of technology research, however, it isalready the time to start considering what the future beyond-5G (B5G) or 6G mobile networks should be, in order to satisfythe demand on communications and networking in 2030.Since 2018, several pioneering projects have been launchedaiming at the next generation of mobile networks. TheInternational Telecommunication Union TelecommunicationStandardization Sector (ITU-T) Focus Group Technologiesfor Network 2030 (FG NET-2030) was established in July2018, intending to study the capabilities of networks forthe year 2030 and beyond, when it is expected to supportnovel forward-looking scenarios. The European Commissioninitiated to sponsor beyond-5G research activities, such as itsrecent Horizon 2020 call - 5G Long Term Evolution – wherea number of pioneer projects will be kicked off at the earlybeginning of 2020. In Finland, the University of Oulu beganground-breaking 6G research as part of Academy of Finland’sflagship program, 6G-Enabled Wireless Smart Society andEcosystem (6Genesis). Besides, other counties such as the United States, China, Japan, and South Korea already formallystarted the research and development of key 6G technologiesor at least announced their ambition to support the 6G works.During the same time, there has also been a significantliterature conducted for 6G, as listed in Tab. I. Some ofthese works focus on the description of use cases or appli-cations, some list a number of potential key technologies butonly in rough introduction, while some others are providingdetailed technological description to very specific categoriesof technologies. To the best of our knowledge, yet there isno comprehensive survey that can provide a complete viewto link the aforementioned related works into an organicstructure. To fill this gap, in this article we attempt to provide acomplete and through view of the state-of-the-art advances inthe development and research of 6G by providing vision, usecases, use scenarios, requirements, efforts, roadmap, as wellas a introduction to the promising key technologies.The rest of this article is organized as follows: Sec. II dis-cusses the key driving factors for the necessity of developing6G, including the prediction of the explosive growth of mobiletraffic and mobile users by 2030, the envision and use casesand application scenarios. Sec. III analyzes the requirementsfor the 6G systems by quantitatively depicting a number of keyperformance indicators. The efforts of research, regulatory, andstandardization of the main players in the mobile communica-tion industry are summarized and the potential timelines androadmap for development and standardization are estimatedin Sec. V. Sec. IV provides a brief survey of a dozen of keytechnologies that are identified as the key enablers for 6G.Finally, Sec. VI concludes this article.II. D
RIVERS
As of today, the commercial deployment of 5G mobilenetworks has been rolled out for around one year across theworld, and the network scale in some countries is already verylarge. Following the historical tradition in the mobile industry,i.e., a new generation every ten years, it is the right time todiscuss the successor of 5G in the research and standardizationcommunity. The key driving forces for the development ofa next-generation system are not only from the exponentialgrowth of mobile traffic and connectivity demand, but alsofrom new disruptive services and applications on the horizon.
A. Explosive Mobile Traffic
We are in an unprecedented era where a massive number ofsmart products, services, and applications emerge and evolve a r X i v : . [ c s . N I] J a n ABLE IA
SUMMARY OF RELATED WORKS IN THE FIELD OF NETWORKS
Ref. Time Topics Contributions [1] Sept. 2018 Vision Review the key services and innovations from 1G to 5G, and provide a vision for 6G.[2] April 2019 ML Review the state-of-the-art advances in machine learning and quantum computing, and propose a quantum computing-assisted ML framework for 6G networks.[3] June 2019 Terahertz Describe the technical challenges and potentials for wireless communications and sensing above , and presentsdiscoveries, approaches, and recent results that will aid in the development and implementation of the 6G networks.[4] July 2019 Vision Outline a number of key technological challenges and the potential solutions associated with 6G.[5] Aug. 2019 AI Discuss potential technologies for 6G to enable ubiquitous AI applications and AI-enabled approaches for the designand optimization of 6G.[6] Sept. 2019 Photonics, hologra-phy, AI Proposes two candidate system architectures for 6G and identifies several 6G technologies including photonics-definedradio, holography, and AI.[7] Sept. 2019 Survey A survey aiming to identify requirements, network architecture, key technologies, and new applications.[8] Sept. 2019 Technologicalenablers Five technology enablers for 6G, including pervasive AI at network edge, 3D coverage consisting of terrestrial networks,aerial platforms, and satellite constellation, a new physical layer incorporating sub-Thz and VLC, distributed securitymechanisms, and a new architecture.[9] Dec. 2019 Green 6G A survey on new architectural changes associated with 6G networks and potential technologies, such as ubiquitous 3Dcoverage, pervasive AI, terahertz, visible light communication, and blockchain.[10] Dec. 2019 AI A special issue provides a comprehensive and highly coherent treatment on all the technology aspects related to ML forwireless communications and networks such as multi-path fading channel, channel coding, and physical-layer design.[11] Jan. 2020 Vision Argue that 6G should be human-centric, and therefore security, secrecy, and privacy are key features. To support thisvision, a systematic framework, required technologies, and challenges are outlined.[12] Feb. 2020 Vehicular, ML A survey on various machine learning technologies that are promising for communication, networking, and securityaspects of vehicular networks, and a envision of the ways toward an intelligent 6G vehicular network, including intelligentradio, network intelligentization, and self-learning.[13] Mar. 2020 Use cases Foresee several possible use cases and presents technologies that are considered as the enablers for these 6G use cases.[14] Mar. 2020 Survey New themes including new human-machine interface, ubiquitous computing, multi-sensory data fusion, and precisesensing and actuation, major technology transformations such as new spectrum, new architecture, and new security arepresented, and the potential of AI is emphasized.[15] April 2020 Survey A comprehensive discussion of 6G based on the review of 5G developments, covering visions, requirements, technologytrends, and challenges, aiming at clarifying the ways to tackle the challenges of coverage, capacity, data rate, andmobility of 6G communication systems.[16] May 2020 Survey A vision on 6G in terms of applications, technological trends, service classes, and requirements, and an identificationon enabling technologies and open research problems.[17] June 2020 ML Discuss possible challenges and potential research directions of advancing machine learning technologies into the future6G network in terms of communication, networking, and computing perspective.[18] June 2020 AI Outline the core concepts of explainable AI for 6G, including public and legal motivations, definitions, trade-off betweenexplainability and performance, and explainable methods, and propose an explainable AI framework for future wirelesssystems. quickly, imposing a huge demand on mobile traffic. It canbe foreseen that the 5G system designed before 2020 cannotwell satisfy such a demand in 2030 and beyond. Due to theproliferation of rich-video applications, enhanced screen reso-lution, Machine-to-Machine (M2M) communications, mobilecloud services, etc., the global mobile traffic will continuouslyincrease in an explosive manner, up to per month inthe year of 2030 compared with
62 EB per month in 2020,according to the estimation of ITU-R made in 2015 [19]. A re-port by Ericsson [20] revealed that the global mobile traffic hadreached around
33 EB per month by the end of 2019, whichpartially proves the correctness of ITU-R’s estimation. Thenumber of smartphones and tablets will further increase, whileother devices such as wearable electronics will grow in a fasterpace, amounting to a total of . billion mobile subscriptionsin 2030. In addition to the human-centric communications,the M2M terminals will experience a more-rapid growth andwill become saturated no earlier than 2030. It is envisionedthat the number of M2M subscriptions will reach billion,as shown in Fig.1, around times over that of 2020. Thetraffic from mobile video services already dominated, account for two-thirds of all mobile traffic. However, the usage ofvideo services keeps growing, such as the boom of Tik-Tokrecently, and the resolution of video continuously improves. Insome developed countries, strong traffic growth before 2025is driven by rich-video services and long-term growth wavewill continue due to the penetration of Augmented/VirtualReality (AR/VR) applications. The average data consumptionfor every mobile user per month, as illustrated in Fig.1, willincrease from around in 2020 to over
250 GB in 2030.
B. Use cases
With the advent and evolution of cutting-edge fields, suchas displaying, robotics, edge computing, AI, unmanned aerialvehicle (UAV), and space technology, in combination withthe mobile system, many unprecedented use cases can befostered. Here, we envision several cases with high potential,as summarized in Tab. II.
C. Use scenarios
In the 5G systems, three usage scenarios have been firstlydefined by ITU-R recommendation M.2083 in 2015 [21].More specifically: the enhanced Mobile Broad-band (eMBB)
ABLE IIS
OME USE CASES WITH HIGH POTENTIAL
Use Case Typical Applications Key Requirements
Extended reality (ER) immersive gaming, remote surgery, remote industrial control high data rate ( (cid:62) . /device), low latency, high reliabilityHolographic telepresence online education, collaborative working, deep-immersive gaming ultra high data rate (terabits per second)Multi-sense experience remote surgery, tactile Internet, remote controlling and reparing stringently low latencyTactile Internet for Industry 4.0 industrial automation, smart energy consumption (cid:54) E2E latencyIntell. transport & logistics Automated road speed enforcement, real-time parking management stringently high reliability and low latencyUbiquitous global roaming World-wide roaming services for UE, portable devices, industrial apps. low-cost fully global coveragePervasive intelligence computer vision, SLAM, speech recognition, NLP, motion control high decision accuracy and transparency, complex data privacy M BB U s e r s [ B illi on ] Estimation of global mobile subscriptions
MBBM2M O v e r a ll t r a ff i c [ EB ] Estimation of global mobile traffic
OverallUser M M U s e r s [ B illi on ] T r a ff i c / U s e r [ G B ] Fig. 1. The estimated global mobile subscriptions and traffic from 2020 to2030. Source: ITU-R Report M.2370-0 [19].
URLLCeMBB mMTCULBCuMBBeMBB mULC
Fig. 2. The envisioned use scenarios for 6G systems. addresses the human-centric applications for a high-data-rateaccess to mobile services, multi-media content and data; theUltra-Reliable Low-Latency Communications (URLLC) fo-cuses on enabling mission-critical connectivity for new appli-cations with stringent requirements on reliability, latency, andavailability; while the massive Machine-Type Communications(mMTC) aims at support to dense connectivity with a verylarge number of connected devices that are low-cost, low-power consumption but typically transmitting a low volumeof delay-tolerate data [22].Being customized for highly specialized applications, all5G use scenarios achieve extreme performance in some as-pect by sacrificing in others, and cannot fully satisfy therequirements of envisioned 6G use cases. For instance, an user wearing a lightweight VR glass playing interactive immersivegames requires not only ultra-high data throughput but alsovery low latency connectivity. Autonomous vehicles on theroad or flying drones demand both high data rate and high-reliability low-latency connectivity. Through extending thescope of current 5G use scenarios, as shown in Fig.2, weenvision four extra scenarios to cover their overlapping areas.To accommodate the increasing capacity requirement fromcommercial passenger planes, helicopters, ships, high-speedtrains and the demand of connectivity in remote areas, aubiquitous coverage of MBB service for the whole planet isexpected in 6G, which we named ubiquitous Mobile Broad-Band (uMBB) as an use scenario for 6G. Another key aspectof uMBB is the capacity improvement for hot spots so as tosupport the proliferation of new services, e.g., VR with a datarate of up to /user. Ultra-reliable Low-latency Broad-band Communication (ULBC) supports the services with low-latency high-reliability connectivity and high data throughput,such as moving robots and Automatic Guided Vehicle (AGV)in industrial sites. The scenarios of massive Ultra-reliableLow-latency Communication (mULC) combines the featuresof mMTC and URLLC, facilitating the deployment of massivesensors and actuators in verticals.III. K EY P ERFORMANCE I NDICATOR R EQUIREMENTS
To satisfy the technical requirements of use scenarios andapplications in 2030 and beyond, the 6G system will providemore system capacity and network performance. Most of thekey performance indicators (KPIs) applied for quantitativelyor qualitatively evaluating 5G networks are also valid for 6Gnetworks while some new KPIs must be considered for thenew features. We briefly summarize our overview to the KPIcomparison between 5G and 6G in Fig. 3 and Tab. III.IV. R
OADMAP AND E FFORTS
Although a discussion is ongoing within the wireless com-munity about whether counting should be stop at 5, severalpioneering works on the next-generation wireless networkshave been initiated, as summarized in Fig. 4.V. T
ECHNOLOGICAL E NABLERS
To pave the road towards the expected extreme performance,so as to realize the envisioned use cases and use scenarios, adiverse set of technologies are expected to play their roles inthe future evolution of mobile networks. We can generallycategorize them into the following groups:
New Spectrum
ABLE IIIC
OMPARISON BETWEEN AND ON SOME
KPI
REQUIREMENTS
KPI 5G Requirement 6G Requirement
Peak data rate /
10 Gbps (DL/UL)
User-experienced data rate /
50 Mbps (cid:62) (DL/UL, dense urban)Latency UP: / (eMBB/URLLC) UP: µ s to µ s CP:
10 ms (eMBB/URLLC) CP: remarkably improvedE2E: not defined E2E: consideredMobility up to
500 km / h (high-speed trains) up to / h (airlines)Connection density per km (with relaxed QoS) per km Network energy efficiency not defined 10 – 100 times better than that of 5GPeak spectral efficiency /
15 bps / Hz (DL/UL) /
45 bps / Hz (DL/UL)Area traffic capacity
10 Mbps / m / m (e.g. indoor hot spots)Reliability (cid:62) . (URLLC: 32 bytes within , urban macro) (cid:62) . Signal bandwidth (cid:62)
100 MHz (cid:62)
Positioning accuracy (cid:54)
10 m cm levelTimeliness undefined considered
Peak Rate(Tbps) User-experience Rate (Gbps) Air-Interface Latency (ms)ReliabilityMobility (km/h)Position Accuracy (m)Connectivity Density (/km )Area Traffic Capacity(Gbps/m ) Fig. 3. The envisioned KPI requirements for 6G in comparison with 5G. consisting of mmWave, Terahertz communications, VisibleLight Communications, Optical Wireless Communications,and the mechanisms of dynamic spectrum management andsharing,
New Networking covering NFV and SDN, RANslicing, Open and Smart RAN (O-RAN), and Security,
New AirInterface that including massive MIMO, Intelligent ReflectingSurfaces, Coordinated Multi-Point, Cell-Free massive MIMO,and new waveform modulation techniques,
New Architecture providing 3D coverage by means of integrating large-scalesatellite constellation, High-Altitude Platform, and UnmannedAerial Vehicle with traditional terrestrial networks, and
NewParadigm empowered by Artificial Intelligence, blockchain,Digital Twin, and Communication-Computing-Control (Co-CoCo) convergence. A brief but systematic summary to themis given in Tab. IV. VI. C
ONCLUSIONS
In this paper, we provided an abstracted outlook at thedrivers, requirements, efforts, and enablers for the next-generation mobile system beyond 5G. The prediction of thetrends, the envision of the future societal and technological evaluation, and the identification of key research directionsmight be rough, partial and even somehow inaccurate with thelimitation of the knowledge of the authors and the informationwe can collect up to now.R
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018 2020 2022 2024 2026 2028 2030
China 6G Kick-off
ITU-R3GPP
R15 R17R16
6G Study Specification
DeploymentWRC-27 Allocate 6G spectrum
WRC-23 Discuss 6G spectrum
WRC-19 5G spectrum allocation
Vision
Requirements
Evaluation
IMT-2030 EU FP8: Horizon 2020
ICT-20 call ICT-52 call
FP9: Horizon Europe
Japan 1 st
6G Panel
South Korea 6G planFinland 6G flagship South 6G trialUS open Thz
Countries
Fig. 4. The roadmap for main 6G research and developments.TABLE IVC
ATEGORIZED KEY ENABLERS WITH ADVANTAGES AND CHALLENGES
Category Enabler Advantages Challenges
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