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
NEXTG Alliance
Snapshots from other sources

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.

NEXTG Alliance

NEXTG Alliance outlines two topics "6G Usage Scenarios and Capabilities" and "6G Requirements & Design Considerations" and the two topics collectively provide a detailed overview of the strategic foundation and operational blueprint for the development of the sixth generation of mobile communications technology, 6G.

"6G Usage Scenarios and Capabilities" outlines the broad usage scenarios and new capabilities that 6G aims to support, illustrating a forward-thinking approach to immersive, massive, and ultra-reliable communication technologies. It emphasizes the enhancements over current 5G technologies and introduces new dimensions such as AI integration and improved environmental sensing capabilities.

"6G Requirements & Design Considerations" delves deeper into the specific requirements and design considerations necessary to implement these advanced 6G capabilities. It segments the core prerequisites into Essential Needs, Use Case Requirements, and Design Considerations, each category meticulously detailing what will be required to effectively develop and deploy a robust 6G network. This includes everything from ensuring digital inclusion and energy efficiency to addressing complex design challenges related to system architecture and reliability.

Together, these tables present a comprehensive vision for 6G, highlighting both the ambitious goals and the practical steps needed to achieve them, thus setting the stage for a transformative impact on global connectivity and technological innovation.

6G Position Statement : An Operator View

Following table provides a structured overview of the strategic framework guiding the development of IMT-2030, the next evolution in telecommunications technology envisioned to succeed 5G. It outlines four key areas: Innovations & Services, Operational Priorities, Guiding Principles, and Spectrum considerations. Each category encapsulates essential objectives and strategies, from enhancing interoperability and integrating advanced network features to emphasizing sustainability through energy reduction and security by design. Additionally, it addresses the importance of global standards and the need for a robust spectrum strategy to accommodate evolving technological demands. This holistic approach ensures that future telecommunications infrastructure will not only support increased connectivity demands but also advance in a manner that is sustainable, secure, and adaptable to future innovations.

Category	Description
Innovations & Services	Supporting IMT-2030 new features
	Interoperability and integration with fixed and satellite systems
	Network API
Operational Priorities	Network simplification
	Absolute energy reduction
	Automated operations and orchestration
	Proactive management
	Quantum-safe infrastructure
Guiding Principles	Global standards
	No forced hardware refresh
	Software-based upgrades
	Backward compatibility
	5G performance guaranteed
	Modular deployment
	Demonstrable customer needs
	Security by design
Spectrum	Sub-7GHz bands remain essential
	6-15GHz bands for 5G and beyond
	sub-THz bands may need a new interface

6G Requirements & Design Considerations

NEXTG Alliance delineates a comprehensive framework essential for shaping the future of telecommunications with the advent of 6G technology. It categorizes the core elements into three main sections: Essential Needs, Use Case Requirements, and Design Considerations. These components collectively outline the critical areas of focus that will drive the development and implementation of 6G networks. The "Essential Needs" segment underscores the fundamental requirements such as digital inclusion and energy efficiency, vital for creating an inclusive and sustainable technological ecosystem. "Use Case Requirements" detail specific operational needs including mobility, connectivity, and AI integration that 6G must address to support advanced applications and services. Lastly, "Design Considerations" focus on the architectural and functional attributes necessary to ensure that the network is capable of meeting the defined requirements with optimal performance, security, and flexibility. This structured approach emphasizes the multifaceted planning required to realize the potential of 6G in meeting future digital demands comprehensively.

Category	Items
Essential Needs	Digital inclusion
	Energy Efficiency
	Environment Impact
	Native Trustworthiness
	Regulated Public Safety
	Automation
	Programmability
	AI & Compute
Use Case Requirements	Mobility requirements
	Connectivity requirements
	AI & Compute requirements
	Trustworthiness requirements
	Cost implications
	Environmental Interaction
	Service composition framework
	Service creation and delivery
Design Considerations	System architecture considerations
	Area capacity
	Peak and experienced data rate
	Reliability and latency
	Coverage
	New capability metrics (sensing, imaging, AI/compute, environmental impact)
	Trade-off analysis

Snapshots from other sources

Here I am compiling snapshots from various other sources including mine. Just take a quick look at the diagram and you can easily make your own stories.

Source : The shift to 6G communications: vision and requirements (Dec 2020)

Following illustrations shows a 6G definition by Huawei. As you see, eMBB, mMTC, URLLC would take evolutionary path into 6G and Network Sensing will become a new pillar in 6G. All the components will be coordinated / controlled by AI in 6G. Source : 6G: The Next Horizon