What is 6G ?

Simple answer is 'We don't know yet' -:). At least, as of Jul 2019 when I was writing the first note on this topic. But from various presentations and documents that I've gone through, it seems that we may identify a few pillars as we did at the early stages of 5G as shown below. I tried to set the three pillars as in 5G. It seems that the first two pillars Terahertz and AI/ML seems to the ones that are most commonly mentioned in the early discussion but I am not sure whether the third pillar High Data Rate in eMTC/URLLC can be a clear target for 6G or not.

Teraherz/Tera bps : In many of the documents, this goal is described as Terahertz. The literal meaning of Teraherzh implify that the carrier frequency of the signal is in the range of TeraHz(1000 Ghz). But I would interpret this as a Tera bps rather than Tera Hertz since the carrier frequencies being proposed in various documents are not always in the range of Tera Hz. The frequency range being discussed in those documents are in the range of several hundreds of Ghz or in Tera Hz (For the details of 6G the frequency range being actively discussed, refer to 6G Spectrum page). However, it seems to be clear that the final target is to achieve Tera bps range of data transfer (Refer to 6G KPI page for the details of 6G data rate requirement). Now you may have some fundamental questions and stick to it for several years. What kind of electronics would be used to achieve this goal ? Would we call this mmWave ? or Optical wave ? (For the details of the electronics for 6G implementation, refer to 6G Electronics page)

AI(Artifical Intelegence)/ML(Machine Learning) : In 6G, it seems that AI/ML would be a feature that is integrated into the functionality of the radio and core network. It would implie that most of the network component should be virtualizied to apply the flexibility of AI/ML to the network functionality. There are many documents that defines 6G in various different aspects. None of them defines better than others. You would not know of the best definition for a while even after 6G realization. The only thing we can do as of now (May 2021) would be to collect as much diverse opinions as possible and try to get another picture of your own.

Followings are the 6G overview from some important organizations and sources.

ITU
3GPP : 6G Study Items - Overall
3GPP : 6G Study Items - RAN1

ITU

ITU propose/outlines the capabilities and usage scenarios of IMT-2030 represent a comprehensive blueprint for the next generation of wireless communication technologies. The proposal outlines the strategic expansion from the existing 5G standards (IMT-2020) to the advanced features envisioned for 6G. They depict an ambitious set of enhancements and new capabilities aimed at transforming global connectivity, integrating cutting-edge technologies such as AI and advanced sensing, and significantly improving network performance across various metrics such as reliability, latency, and data rates. Together, these diagrams underscore a future where digital communication is more immersive, ubiquitous, and efficient, driven by overarching principles of sustainability, security, and inclusivity in connecting the unconnected.

6G Use Case Scenario

This diagram illustrates the six usage scenarios anticipated for the IMT-2030 (commonly referred to as 6G), which aims to extend and enhance the capabilities established by IMT-2020 (5G). This vision for 6G represents a significant leap forward in connectivity and communication. It promises not only to enhance existing applications but also to unlock entirely new possibilities in areas like immersive experiences, IoT, and AI.

Source : ITU's IMT2030 Usage scenarios

Extension from IMT-2020 (5G)

The Extension from IMT-2020 (5G) to IMT-2030 (6G) represents an ambitious leap in telecommunications technologies, seeking to build upon and expand the capabilities established by 5G networks. This progression aims to transform the landscape of digital communication by enhancing current services like Enhanced Mobile Broadband (eMBB) and introducing next-generation capabilities such as immersive communication. It also seeks to elevate machine type communications and ultra-reliable low-latency operations to meet the burgeoning demands of various emerging technologies and applications.

eMBB to Immersive Communication: Enhanced Mobile Broadband (eMBB) focuses on high data rates and is being expanded to immersive communication, which could include technologies like virtual reality (VR) and augmented reality (AR) to provide a more immersive user experience.
mMTC to Massive Communication: Massive Machine Type Communication (mMTC) is used for large-scale IoT deployments. In 6G, this could evolve into even larger scales, enabling more extensive IoT networks.
URLLC to HRLLC: Ultra-Reliable and Low-Latency Communication (URLLC) is crucial for tasks requiring immediate response, like remote surgeries or autonomous driving. In 6G, this would progress to Hyper Reliable and Low-Latency Communication (HRLLC), emphasizing even more reliability and lower latency.

New Scenarios Introduced in IMT-2030

IMT-2030 introduces new scenarios that are set to redefine connectivity and technological integration. These include Ubiquitous Connectivity, which aims to provide comprehensive and high-quality network coverage to all areas, and AI and Communication, which seeks to integrate artificial intelligence deeply within network infrastructures to optimize and personalize user experiences. Additionally, the Integrated Sensing and Communication scenario plans to harness the network for environmental sensing, thereby creating smarter and more responsive technology ecosystems.

Ubiquitous Connectivity: This refers to providing high-quality internet access everywhere, not just in densely populated areas, bridging the digital divide.
AI and Communication: Integrating artificial intelligence with communication networks to improve network management, optimization, and user experiences.
Integrated Sensing and Communication: Leveraging the communication infrastructure for sensing the environment, which could be used for applications like smart cities and automated driving.

Overarching Aspects

The Overarching Aspects of IMT-2030 encapsulate the core principles that will guide the development and deployment of 6G technologies. These principles include Sustainability, emphasizing the importance of eco-friendly approaches; Connecting the Unconnected, which aims to expand digital access to underserved areas;

Sustainability: Focusing on eco-friendly technologies and reducing the carbon footprint of networks.
Connecting the Unconnected: Making efforts to provide connectivity in previously unconnected areas.
Ubiquitous Intelligence: Incorporating intelligent functions broadly across the network to make smarter decisions.
Security and Resilience: Enhancing the security and resilience of networks to withstand various threats and ensure stable service.

6G Capabilities

Following diagram outlines the envisioned capabilities for IMT-2030, which is often associated with the future 6G technologies. It categorizes these capabilities into existing enhancements over 5G (shown in green) and entirely new capabilities unique to 6G (shown in blue). This diagram illustrates that the range of values provided for each capability are targets for future research and have equal priority. This means that for any given usage scenario, multiple or single values might be explored and further developed into specific recommendations or standards in future ITU-R publications. This strategic approach ensures a comprehensive development towards realizing the ambitious goals set for the next generation of telecommunications technologies.

Source : Capabilities of IMT 2030

Enhanced Capabilities from IMT-2020 (5G)

Security and resilience: Emphasizing the need for robust security measures and systems that can maintain their operational integrity under adverse conditions.
Reliability: Measured in terms of error rates (1x10^-5 to 1x10^-7), pointing to a very high level of dependability for connections.
Latency: Ranging from 0.1 to 1 millisecond, which would support ultra-responsive network services necessary for applications like autonomous vehicles and remote surgeries.
Mobility: Supporting device speeds from 500 to 1,000 km/h, enabling reliable mobile connections at high speeds, suitable for high-speed trains and other fast-moving vehicles.
Connection density: Handling from 10^6 to 10^8 devices per square kilometer, essential for densely populated urban areas or heavily automated industrial environments.
Area traffic capacity: This refers to the total traffic throughput per area, vital for supporting large numbers of simultaneous users in busy areas.
Peak data rate, user-experienced data rate, and spectrum efficiency: These metrics indicate the speed and efficiency with which data is transmitted over the network, with peak data rates significantly higher than those currently available in 5G networks.

New Capabilities Unique to IMT-2030

Coverage: Aims to ensure network access is ubiquitous, reaching more geographic areas with reliable and high-quality service.
Sensing-related capabilities: This could include the use of the network for environmental sensing, object detection, and other sensory applications that contribute to smarter cities and automated systems.
Applicable AI-related capabilities: Integrating AI deeply within network operations to enhance functionalities like predictive maintenance, traffic management, and personalized user experiences.
Sustainability: Emphasizing environmentally friendly technologies that minimize energy consumption and reduce the carbon footprint of network operations.
Interoperability: Ensuring that new technologies can seamlessly work with existing systems and across different platforms and devices.
Positioning: Offering precise location tracking capabilities (with accuracy from 1 to 10 cm), which could revolutionize industries like logistics, automated manufacturing, and personal mobility.

3GPP : 6G Study Items - Overall

Since August 2025, 3GPP has started officially releasing various TDocs, or Technical Documents, related to 6G study activities. These documents provide a more reliable view of the topics currently being discussed and investigated within 3GPP. Therefore, instead of introducing 6G study items based on external opinions, news articles, or vendor-specific materials, it is better to first look at the study items identified directly by 3GPP. This approach gives us a clearer and more standard-based understanding of the early 6G direction, including which technical areas are being considered, how they are being categorized, and what kinds of problems 3GPP intends to study in the initial phase.

No.	Area	Specification / Study	Title
1	Service Requirements	TR 22.870	Study on 6G Use Cases and Service Requirements
2	RAN Requirements	TR 38.914	Study on 6G Scenarios and Requirements
3	6G Radio	FS_6G_Radio	Study on 6G Radio
4	RAN1 / PHY	TR 38.760-1	Study on 6G Radio RAN1 Aspects
5	RAN2 / Protocol	TR 38.760-2	Study on 6G Radio RAN2 Aspects
6	RAN3 / Architecture	TR 38.760-3	Study on 6G Radio RAN3 Aspects
7	RAN4 / RF	TR 38.760-4	Study on 6G Radio RAN4 Aspects
8	System Architecture	TR 23.801-01	Study on Architecture for 6G System; Stage 2
9	Application Enablement	TR 23.801-02	Study on 6G Application Enablement
10	Mission Critical Services	TR 23.801-03	Study on MC Architecture Evolution and 6G Capabilities for MC Services
11	Security	TR 33.801-01	Study on Security for the 6G System
12	Lawful Interception	TR 33.801-06	Study on Lawful Interception for 6G
13	Management and Orchestration	TR 32.801-01	Study on 6G Management and Orchestration
14	Charging	TR 32.801-02	Study on Charging Aspects of 6G System
15	Media	TR 26.870	Study on Media Aspects for 6G System
16	Core Network Protocol	TR 29.840	Study on Control Plane Protocols in Core Network of the 6G System

3GPP : Study Item - RAN1

In most cases, when a new generation of mobile communication technology is defined, the study tends to begin from the lower-layer radio technologies first. This is because RAN1 covers the physical layer, including waveform, frame structure, channel coding, modulation, reference signals, MIMO, beamforming, and other fundamental radio-interface mechanisms. These technologies form the basis of the whole system, and many higher-layer designs are later influenced by the assumptions and limitations decided at this level.

For this reason, it is useful to start the 6G study by looking closely at RAN1 activities. Once the basic physical-layer direction becomes clearer, the related work usually propagates into other areas such as RAN2, RAN3, RAN4, SA, and CT. For example, a new physical-layer feature may later require new RRC signaling, new RAN architecture support, new RF requirements, or new core-network procedures. Therefore, following RAN1 first gives us an early view of the technical foundation on which many other 6G topics will be built.

Also, from my personal point of view, I am more interested in this field because RAN1 is closely related to radio behavior, signal processing, and the practical implementation of the air interface. So, in this section, I will first focus on the 3GPP 6G study items related to RAN1 and then gradually expand the discussion to other areas as needed.

This is the broad Release 20 study item for the 6G radio interface, and RAN1 is the primary responsible group.

No.	RAN1 Study Area	Description
1	6G Radio Air Interface	This is the overall study of what the new 6G radio interface should look like. It includes the basic design direction of the physical layer before individual PHY functions are finalized.
2	Evaluation Methodology	RAN1 needs common assumptions for comparing different technical proposals. This includes simulation assumptions, evaluation models, performance metrics, baseline configurations, and comparison methodology.
3	Scalable UE Design	6G is expected to support different types of UEs, from high-end mobile broadband devices to lower-complexity or lower-power devices. RAN1 studies how the PHY design can be scalable for these different UE capabilities.
4	Spectrum, Bandwidth, and Carrier Design	This area studies how 6G should support different carrier bandwidths, channel bandwidths, and frequency ranges. It also includes considerations for very wide bandwidth operation, especially in higher frequency ranges.
5	Waveform and Numerology	This is one of the most fundamental RAN1 topics. It studies whether 6G should continue with an OFDM-like waveform, modify the waveform, or introduce additional waveform options. Numerology, subcarrier spacing, symbol duration, and related time-frequency parameters are also part of this area.
6	Frame Structure	This studies how radio frames, slots, symbols, and resource grids should be organized in 6G. Frame structure affects scheduling, latency, control signaling, duplexing, and reference signal design.
7	Downlink and Uplink Physical Channels	This area studies the design of physical channels for user data and control information. In 5G terms, this corresponds to topics similar to PDSCH, PUSCH, PDCCH, PUCCH, PBCH, and related PHY procedures, although final 6G channel names and structures are not fixed yet.
8	Reference Signals and Synchronization Signals	RAN1 studies what kinds of signals are needed for synchronization, channel estimation, beam management, CSI measurement, positioning, mobility, and possibly sensing. These signals are essential for both initial access and connected-mode operation.
9	Initial Access	Initial access covers how a UE first detects and accesses a 6G cell. This includes synchronization, system information acquisition, initial beam selection, and basic PHY procedures before the UE becomes fully connected.
10	Random Access	This studies how the UE performs uplink access toward the network. It may include PRACH-like design, contention-based access, contention-free access, and possible enhancements for different UE types or deployment scenarios.
11	MIMO, Beamforming, and CSI Feedback	This is expected to be one of the major 6G RAN1 study areas. It includes advanced MIMO, distributed MIMO, multi-panel transmission, beam management, CSI acquisition, CSI feedback, and possibly AI-assisted beam or channel prediction.
12	Mobility Support at PHY Layer	RAN1 may study physical-layer support for mobility, especially in high-frequency, beam-based, or distributed radio deployments. This includes measurement support, beam tracking, and PHY behavior related to mobility robustness.
13	Duplexing and Spectrum Aggregation	This area studies TDD, FDD, flexible duplex operation, and aggregation of multiple carriers or frequency ranges. It is important for efficient spectrum usage and coexistence with existing systems.
14	AI/ML for Air Interface	AI/ML may be studied for selected PHY-layer functions such as beam management, CSI feedback, channel prediction, positioning, receiver optimization, or transmitter optimization. This does not necessarily mean that AI/ML replaces the whole PHY, but it may be used to enhance specific functions.
15	Integrated Sensing and Communication	6G is expected to study communication and sensing together. From the RAN1 point of view, this means studying whether waveform, reference signals, beams, and measurements can support sensing functions such as range, velocity, or angle estimation.
16	Energy Efficiency and Low-Complexity PHY Operation	RAN1 also studies efficient PHY operation for UE power saving, network energy saving, and reduced-complexity operation. This is important because 6G is expected to support a very wide range of device types and deployment scenarios.

The practical topics to follow first are waveform, numerology, frame structure, physical channels, reference signals, initial access, random access, MIMO, beam management, CSI feedback, AI/ML support, integrated sensing and communication, and energy-efficient PHY design.

YouTube

3GPP Release 20: An Update on 3GPP 6G Technology Studies - ATIS (May 2026)