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Vision, Requirements, and Technology Trend of 6G: How to Tackle the Challenges of System Coverage, Capacity,User Data-Rate and Movement Speed
Shanzhi Chen, Ying-Chang Liang, Shaohui Sun, Shaoli Kang, Wenchi Cheng, Mugen Peng
TL;DR
The paper addresses the lack of a clear 6G description and the coverage, capacity, data-rate, and mobility challenges inherited from 5G. It reviews 5G developments to synthesize 6G visions, requirements, technology trends, challenges, and a proposed standardization roadmap, concluding that 6G should support a Ubiquitous Intelligent Mobile Society.
Problem
6G lacks a clear description while future mobile communications must address terrestrial coverage limits and evolving system requirements.
Method
The paper comprehensively reviews 5G developments and discusses 6G visions, requirements, technology trends, challenges, and standardization.
Results
6G is expected to provide 10 times higher data rate, density, and energy efficiency than 5G, about 3 times higher mobility and spectrum efficiency, and 99% coverage.
Takeaways & Limitations
The proposed 6G vision integrates communication with computing, navigation, perception, and artificial intelligence to support a Ubiquitous Intelligent Mobile Society.
Takeaways & Limitations
Practical deployment remains constrained by unresolved technical challenges, including high-frequency hardware design for THz communications.
Abstract
from arXiv · showhide
Since 5G new radio comes with non-standalone (NSA) and standalone (SA) versions in 3GPP, research on 6G has been on schedule by academics and industries. Though 6G is supposed to have much higher capabilities than 5G, yet there is no clear description about what 6G is. In this article, a comprehensive discussion of 6G is given based on the review of 5G developments, covering visions and requirements, technology trends and challenges, aiming at tackling the challenge of coverage, capacity, the user data rate and movement speed of mobile communication system. The vision of 6G is to fully support the development of a Ubiquitous Intelligent Mobile Society with intelligent life and industries. Finally, the roadmap of the 6G standard is suggested for the future.
I. INTRODUCTION
6G research follows the standardization of 5G NSA and SA, but the paper argues that 5G remains an incomplete realization of interconnection of everything. It reviews 5G development to frame 6G’s broader research agenda, including global coverage and future societal needs.
- 6G research began alongside continuing 5G enhancements after 3GPP finalized NSA in 2017 and SA in 2018.
- The paper reviews 5G development, vision, requirements, technologies, challenges, and a proposed 6G roadmap.
- 5G defines eMBB, URLLC, and mMTC scenarios, but mMTC was not incorporated into 5G NR and eMBB developed faster than the other scenarios.
- 5G advances interconnection of everything, yet unresolved requirements and industry pain points mean it is treated as the starting phase of IoE.
- Terrestrial networks cover about 20% of global land area and less than 6% of Earth’s surface, motivating broader coverage for future mobile communications.
B. The Vision And Requirements of 6G
The paper envisions 6G as a Ubiquitous Intelligent Mobile Society supported by integrated coverage, higher performance, personalization, endogenous security, and converged communications with computation and sensing.
- 6G should address 5G limitations while supporting a Ubiquitous Intelligent Mobile Society for mobile demands in 2030 and beyond.
- 6G is expected to provide ten to hundred times higher data rate, higher capacity and spectrum efficiency, lower delay, broader coverage, and support for higher movement speed.
- An integrated terrestrial, satellite, and short-range device-to-device network should provide global mobile broadband across airspace, land, and sea.
- Higher-frequency bands including mmWave, Terahertz, and visible light are intended to support Tbps peak data rate and 10Gbps user experience data rate.
- Artificial intelligence supports personalized virtualized communication through user-, data-, and content-centralized networking.
- 6G incorporates endogenous security, self-awareness, real-time analysis, adaptive risk evaluation, and merged communications, computation, navigation, and sensing.
- 6G can generate massive Internet-of-Everything data, combine with computing and artificial intelligence, and realize everything intelligence and swarm intelligence.
C. APPLICATION SCENARIOS AND CAPABILITIES OF 6G
6G is expected to extend mobile communication beyond traditional 5G scenarios into applications such as holographic communication, personal monitoring, drone taxis, and robotic systems. Its proposed capabilities substantially improve several 5G KPIs and add broader coverage, reliability, positioning, and sensitivity targets.
- 6G scenarios include traditional eMBB, mMTC, and URLLC alongside holographic communication, personal monitoring, drone taxis, and Internet of Robots.
- 6G is expected to enhance data rate, density, and energy efficiency tenfold, mobility and spectrum efficiency about threefold, and reduce latency below 1 millisecond.
- Coverage percentage is expected to increase from 70% to 99%, while reliability rises from 99.9% to 99.999%.
- Positioning error is expected to improve from meter level to centimeter level, with receiver sensitivity better than -130dBm.
III. TECHNOLOGY TREND AND CHALLENGES
The paper organizes 6G challenges around coverage, capacity, data rate, movement speed, spectrum efficiency, and energy efficiency. It proposes integrated satellite-terrestrial networking, additional and reusable spectrum, heterogeneous access, and computing and AI support, while identifying architectural and mobility-management difficulties.
- 6G challenges include system coverage and capacity, user data rate and movement speed, spectrum efficiency, and energy efficiency.
- Satellite mobile communication can extend coverage over oceans, forests, and deserts and support mobile terminals moving beyond Mach level.
- Integrating terrestrial, satellite, and short-range direct communication requires new core-network architecture and mobility management.
- Capacity can increase through more bandwidth, higher air-interface spectral efficiency, smaller cells for spectrum reuse, and flexible spectrum sharing.
- Heterogeneous wireless access and integrated computation, navigation, and sensing increase system complexity, requiring AI technology and computing capability.
A. Expending Coverage: The Integration Of Terrestrial And Satellite Mobile Communication
Satellite communication is positioned as an important 6G infrastructure component for extending coverage and supporting high-speed users, while integration with terrestrial systems introduces substantial design challenges.
- Coverage and mobility: Satellite communication can provide wider coverage over seas, forests, and deserts and support mobile terminals moving beyond Mach speed.Its advantages complement terrestrial systems’ coverage and movement-speed limitations.
- System differences: Satellite and terrestrial systems differ in transmission distance, delay, frequency band, path loss, link type, Doppler shift, cell radius, and frequency reuse.The cited table contrasts satellite links above 600 km and tens-to-hundreds-millisecond delay with terrestrial links around 1 km and microsecond-to-millisecond delay.
- Standardization: 3GPP began studying NR support for non-terrestrial networks to integrate satellite mobile communication with terrestrial mobile communication.The study addressed channel modeling, design constraints, and NR impacts, leading to technical report TR38.811 in 2018.
- Satellite architecture: LEO satellites are considered especially prospective because lower orbit height provides shorter transmission delay and smaller path loss than MEO or GEO.LEO systems also benefit from reduced deployment costs enabled by launching multiple satellites together.
- Integration challenges: LEO integration faces large-scale control complexity, strong Doppler variation, higher transmission delay and path loss, and resulting redesign requirements across protocol functions.At 600 km orbit height and 20 GHz Ka-band carrier, Doppler shift can reach 480 KHz and affect synchronization, random access, measurement, and detection.
1) Terahertz And Visible Light Band:
THz and visible-light communications offer ultra-wide spectral resources for high-rate 6G links, but both require major hardware, channel, bandwidth, and signal-processing advances before deployment.
- Opportunities: The THz band from 0.1 THz to 10 THz and visible-light band from 400 THz to 800 THz are identified as ultra-wide spectral bands for 6G communications.These bands are intended to alleviate spectrum scarcity and capacity limitations.
- THz communications: THz communications target applications including holographic video, virtual reality, nanoscale health-monitoring networks, and inter-satellite or near-space communications.The passage describes both solid-state frequency-mixing systems and spatial direct-modulation systems.
- THz communications: THz deployment requires efficient broadband hardware, high-gain fast-scanning antennas, low-noise transceivers, advanced modulators, and accurate channel models.The cited challenges include THz mixers, oscillators, amplifiers, antennas, modulators, and channel estimation.
- Visible-light communications: VLC uses LED intensity modulation and silicon-photodiode direct detection, achieving gigabits-per-second downlink transmission with commercial LEDs.Applications include indoor personal-area links and vehicle-to-vehicle or vehicle-to-infrastructure communication.
- Visible-light communications: Commercial LEDs’ limited modulation bandwidth and slow response directly constrain VLC data rates, motivating transmitter and receiver equalization.Blue filtering, pulse shaping, and subcarrier equalization are cited as bandwidth-enhancement methods.
2) Cognitive Radio And Intelligent Spectrum Sharing:
6G spectrum management must address scarcity and low utilization through cooperative spectrum sharing, while intelligent access remains difficult in complex network environments.
- Spectrum scarcity: Spectrum resources, especially established lower-frequency bands, remain scarce as wireless traffic grows exponentially despite exploration of THz and visible-light bands.Earlier dedicated allocations occupy spectrum fully while producing low utilization rates.
- Symbiotic radio: Symbiotic radio enables heterogeneous subsystems to cooperate for mutually beneficial transmission and efficient resource sharing.The technique uses the same spectrum, signal source, and infrastructure as a primary system for IoT transmission.
- Intelligent access: Intelligent dynamic spectrum access typically requires complete network-state information, but existing protocols do not adapt effectively to complex real-world models.Deep reinforcement learning has been explored for distributed access algorithms, while lower-overhead model-free distributed learning remains desirable.
- Intelligent sharing: 6G spectrum sharing must manage technologies such as device-to-device communication, in-band full-duplex, non-orthogonal multiple access, and unlicensed-spectrum sharing.The passage identifies distributed and efficient interference avoidance as a challenge for massive connections.
C. New Resource For Modulation: OAM
Orbital angular momentum provides orthogonal wave modes that can be multiplexed for additional wireless capacity, but divergence and non-line-of-sight transmission complicate practical deployment.
- Motivation: Non-orthogonal resource exploration is motivated by the need to improve spectrum efficiency, user rate, and capacity beyond conventional frequency, time, code, and space resources.OAM is presented as one candidate new modulation resource.
- OAM principle: OAM wave-fronts carry helical phase, and distinct topological-charge modes are orthogonal and can be multiplexed or demultiplexed for capacity enhancement.Different data streams can be modulated onto different OAM modes.
- Propagation: Higher-order OAM modes exhibit increasingly central-hollow radiation patterns and greater divergence with distance.OAM mode 0 corresponds to the traditional plane-electromagnetic wave.
- Practical challenges: Beam divergence limits efficient reception and long-distance propagation, motivating converging schemes using parabolic or lens antennas.After convergence, OAM beams can retain a central hollow structure over relatively long transmission distances.
- Practical challenges: OAM transmission is established mainly for line-of-sight settings, while reflection and refraction make non-line-of-sight fading channels difficult to model.The passage identifies NLoS transmission as a critical problem before practical implementation.
D. Increasing System Capacity: De-Cellular And UUDN
6G capacity strategies combine higher-frequency bandwidth with de-cellular, user-centric ultra-dense networking, while AI and distributed computing support adaptive coordination. These approaches address shrinking cells but introduce substantial architecture, mobility, interference, resource, security, and computing challenges.
- Capacity drivers: 6G is expected to use mmWave, Terahertz, and visible-light bands for wider bandwidth, but higher frequencies make base-station and access-point coverage ranges smaller.Cell splitting cannot continue indefinitely because it approaches the limit of system-capacity improvement.
- De-cellular and UUDN: De-cellular networking dynamically organizes an AP group for each user, allowing the network to follow users without requiring their involvement.User-Centric Ultra-Dense Networks have comparable access-point and user densities and shift the network-serving philosophy toward the user.
- Challenges: De-cellular and UUDN require cooperative AP transmission, dynamic mobility management, AI-based interference control, user-and-AP-group resource allocation, and inter-AP security mechanisms.The cited challenges include continuous communication during movement, dynamic AP grouping, complex interference, and trusted authentication and secure transmission.
- Computing and AI: 6G networks should evolve from function-centralized designs toward user-, content-, and data-centralized architectures, with computing and AI capabilities added to the network.The proposed change is intended to support ultra-wide spectral bands, adaptive architectures, and diverse performance requirements.
- Computing and AI: Deploying computing and AI across cloud, edge, and terminals remains difficult because heterogeneous resources make communication, caching, and computing coordination prohibitively difficult and expensive.Fog-computing radio access networks are cited as one approach for flexibly assigning these functions across entities.
F. New Core Network: A Three-Dimensional Architecture And Intelligent Mobility Management
6G proposes a three-dimensional core network integrating terrestrial, satellite, and direct-communication systems with computing, navigation, and perception. Intelligent mobility management is intended to provide ubiquitous, high-speed connectivity across air, space, land, and sea, but deployment still requires solving major architectural challenges.
- Architecture: 6G will integrate terrestrial, medium- and low-orbit satellite, and short-distance direct communication technologies into one system.It also integrates communication with computing, navigation, perception, and other technologies.
- Architecture: The resulting three-dimensional core network is designed to support global ubiquitous coverage of high-speed mobile communications across air, space, land, and sea.Intelligent mobility management and control methods are identified as enablers of this coverage.
- Intelligent mobility management: The 6G core network will combine terrestrial and satellite nodes, potentially embedding AMF, SMF, and UPF functions in satellites and supporting unified PDU sessions.Resources and user-plane connections are dynamically established according to service requirements, user priority, and a global terrestrial-satellite network view.
- Intelligent mobility management: Terrestrial and satellite topologies can be hidden behind data transmission, enabling transparent access and flexible roaming between terrestrial and satellite technologies.This behavior depends on a service-driven, intelligent, three-dimensional core network with dynamic terrestrial-satellite changes.
IV. ROADMAP SUGGESTION OF 6G STANDARDIZATION
The proposed 6G roadmap places continuing research before standardization, with global convergence expected during 2024–2026 and standard work progressing toward 2030. It also calls for broader cooperation across countries, organizations, vertical industries, and enterprises.
- Standardization roadmap: 3GPP Release 16 for 5G NR was expected in early 2020, with beyond-5G research spanning Releases 17–19 and 6G research potentially following in Release 20.The roadmap links 6G research to the progression of 5G NR releases.
- Standardization roadmap: ITU was expected to issue the 5G standard by the end of 2020, after which 6G vision and technology-trend research could begin in parallel with industry activity.Academics and industries were already discussing 6G technologies, visions, and requirements.
- Standardization roadmap: 6G research was expected to converge during 2024–2026, followed by standard work toward 2030.The paper presents standardization as a later phase after research convergence.
- Collaboration: 6G development should strengthen international cooperation and include vertical-sector contributions from the initial research stage.The roadmap also calls for closer cooperation among enterprises as device and equipment materials approach theoretical limits.
- Conclusions: The paper projects 6G standard work around 2025 and a pre-commercial network around 2030, while defining 6G as an integration of communication, computing, navigation, perception, and AI.Its stated societal vision is a Ubiquitous Intelligent Mobile Society with intelligent life and industries.