Here goes the list of the items in this page, as the techology grows and my knowledge on this subject gets wide and deep enough I will spin out separate pages for more specific topics.
What is It ?
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. However, it seems to be clear that the final target is to achieve Tera bps range of data transfer.
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 ?
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.
Isn't it too early to get into this ?
I asked the same question when I started looking into things about 5G around mid 2013. 5G activities in some pioneering organizations started even earlier. Now I heard some leading company in 5G has started their research back to 2007 or so.
I would say, "Yes it is too early if you are interested only in solid/determined 3GPP specification". I don't think you would see much formal activities in 3GPP until release 18 or later (probably sometime around 2026 or later ?).
However if you are interested in observing the whole process of how a new technology is being formed and evolved and finally turns into operational products, nothing is too learly. To me, it is always enjoyable to follow something from the very early conception through the full developmental process.
Following along Evolutionary Path - Physical Layer/MAC Layer
I will write down some technical progess and my learning process as I am writiing tech diary. This is not necessarily very technical .. just a little memo on my learning process.
[ Jul 2019 ]
- For now (Jul 2019), I am writing comments on this based on the assumption that 6G physical layer will be based on THz(Tera Hertz) technology,
- Roughly two major technology of Thz implementation is being discussed. One is based on Optics and the other is based on electronics, but it is highly likely that electonics based technology would be adopted (at least for communication between mobile station and base station).
- There are many options to implement this, but preferred one would be transistor based on implementation. Then need to check if a source(osciallator), mixer, power amplifiers can be implemented for the selected technology. I am not the expert on this area, so not in the position to share the latest information on this. If you are interested, you may refer to Ref  as a start and follow through the references listed there. It is published in 2011, so I think the technology has been much more matured by now(Jul 2019).
- Once the basic components (e.g, Source, Mixer, Amplifer etc) is developed and commercialized, some pioneering test equipment vendor would come up with signal generator and analyzer. Then the industry or academia would start researching on physical channel properties for the target frequency. This is what had done by 5G several years back (see this as an example).
- The result on this physical channel properties and propagation model would be a critical step to determine whether the selected technology can be adopted for the new communication technology or not. Once it is determined to be feasible to use the technology, you may start hearing on possible concepts of physical layer protocol issues like waveform, modulation scheme, frame structure etc.
- Channel Modeling : As they did for 5G, NYU Wireless is doing pionioring work in this area as well. It seems that they starting researching on this and sharing the research result for a while. Check on NYU Wireless / NYUSIM site.
- MAC for Terahertz Communicaition System : Even if there has been some changes in detail in terms of MAC layer between LTE and 5G, the fundmantel mechanism is almost same in LTE and 5G/NR. But it is likely to be drastic change in Terahertz MAC comparing to conventional cellular technology (e.g, LTE, 5G/NR) since the physical layer properties in Terahertz communication would be drastically different. As of now, I don't see any concrete proposals or specification on this, but I would suggest you to start with this survey paper(Ref ) as a starter. If you are interested in protocol side (rather than physical layer hardware implementation), this can be a good starting reference.
[ Aug 2019 ]
- This month my study has motly focused on reading papers on Machine learning application to this area. At first, I thought the machine learning would mostly for core network optimization, but I learned there has been a lot of research on the application to physical layer process of wireless communication (e.g, detection of modulation scheme, auto encoder etc). See Ref~. I personally recommend you to start with Ref  and pick one of specific direction that you want to follow through.
Event / Workshop / Forum
- Beyond 5G: The Roadmap to 6G and beyond (Jul 4, 2017)
- With 5G Still in the Works, 6G Is Already Taking Shape (Apr 19,2018)
- Get ready for upcoming 6G wireless, too (Jun 28, 2018)
- What Will 6G Be? (Jun 29, 2918)
- Get ready for 6G mobile networks: 1Tbps speeds, microsecond latency and AI optimisation (Sep 2018)
- Forget 5G, China is working on 6G – but what does it do? (Nov 16. 2018)
- It's Officially Time to Start Talking About 6G (Mar 15, 2019)
- FCC opens up experimental spectrum licenses for 6G (Mar 15, 2019)
- The United States Launched 6G Research And Development. The FCC Announced The 6G Test Frequency Band. (Mar 16,2019)
- THE FCC CLEARS EXPERIMENTAL FREQUENCIES TO PAVE WAY FOR 6G (Mar 17, 2019)
- Why 6G research is starting before we have 5G (Mar 21, 2019)
- Towards 6G Networks: Use Cases and Technologies (Mar 28,2019)
- Ready for 6G? How AI will shape the network of the future (Apr 19,2019)
- Do we need 6G wireless already? 5G engineers debate (Apr 25,2019)
- It’s Never Too Early to Think About 6G (May 22,2019)
- Samsung kicks off 6G research (Jun 5,2019)
- Forget 5G: Samsung Is Already Working on 6G (Jun 5,2019)
- Samsung spurs R&D efforts for 6G before 5G becomes mainstream (Jun 4, 2019)
- Researchers say 6G will stream human brain-caliber AI to wireless devices (Jun 14, 2019)
- 6G: What It Is & When to Expect It (Jun 17, 2019)
- A glimpse into the future? Report predicts 6G features (Jun 17, 2019)
- 6G technology market revealed by Mind Commerce (Jun 18, 2019)
- The race for 6G mobile technology is already on (Jun 18, 2019)
- 6G to Support Micro-second Latency for Better Sensing, Imaging, Presence and Location Capabilities, says Mind Commerce (Jun 19, 2019)
- Setting the Stage for U.S. Leadership in 6G (Aug 13,2019)
- Test and Measurement: Keysight sets sights on 6G(Aug 23, 2019)
- Huawei CEO says it’s working on 6G — but the technology is still some 10 years off (Sep 26,2019)
- Huawei started research on 6G ‘a long time ago’, CEO says (Sep 30, 2019)
- 6G: What It Is & When to Expect It (Oct 1, 2019)
- 6G: Building tomorrow's wireless tech beyond 100 GHz (Oct 4,2019)
- Beyond 5G: Sony, NTT and Intel to form 6G partnership (Oct 31, 2019)
Videos - 6G Summit
- 1st 6G Wireless Summit | Keynote Session
- 1st 6G Wireless Summit | Qi Bi, China Telecom
- 1st 6G Wireless Summit | Tanbir Haque, InterDigital: Air-interfaces for ultra-low power comms
- 1st 6G Wireless Summit | Ian Oppermann, NSW Data Analytics Centre
- 1st 6G Wireless Summit | Fan Chen, ZTE
- 1st 6G Wireless Summit | Eric Hardouin, Orange Labs
- 1st 6G Wireless Summit | Kwon Dong Seung, ETRI: What is beyond hyper-connectivity?
- 1st 6G Wireless Summit | Juho Lee, Samsung Electronics
- 1st 6G Wireless Summit | 6G Flagship Views on 6G Challenges
- 1st 6G Wireless Summit | Zhisheng Niu, Tsinghua University: MEET for 6G
- 1st 6G Wireless Summit | Henning Schulzrinne, Columbia University
- 1st 6G Wireless Summit | Magnus Frodigh, Ericsson
- 1st 6G Wireless Summit | Takehiro Nakamura, NTT DOCOMO
- 1st 6G Wireless Summit | Rahim Tafazolli, University of Surrey: What is Next?
- 1st 6G Wireless Summit | Bernard Barani, EU Commission
Videos - General
 How TeraHertz Technology Will Change The World Of Wireless Communication ?
 An overview of integrated THz electronics for communication applications
 Terahertz Waves for Communications and Sensing
 A Perspective on Terahertz Next-Generation Wireless Communications (2019)
 Tuning to Terahertz Electronics (2015)
 THz Electronics
 Terahertz electronics: The last frontier (2014)
 A New Technology for Terahertz Electronics (2003)
 Joint Lab THz Components & Systems
 Terahertz breakthrough allows for ultrafast wireless communications (2015)
 Last Meter Indoor Terahertz Wireless Access:Performance Insights and Implementation Roadmap (2018)
 Compact Terahertz Reciever for Short-range Wireless Communications of Tens of Gbps (2017)
 Micro- and nano-scale Terahertz Band Communications
 Terahertz (THz) Wireless Systems for Space Applications (2019)
 MAC Protocols for Terahertz Communication: A Comprehensive Survey (2019)
 Advances in THz Wireless Communications (2017)
 How AI is Starting to Influence Wireless Communications
 The 5G Future Will Be Powered By AI (2019)
 DeepSig: Deep Learning for Wireless Communications
 Deep Architectures for Modulation Recognition (2017)
 Physical Layer Communications System Design Over-the-Air Using Adversarial Networks (2018)
 Deep Learning-Based Communication Over the Air (2017)
 Deep Learning-Based Channel Estimation (2019)
 "Machine LLRning": Learning to Softly Demodulate (2019)
 ORACLE: Optimized Radio clAssification through Convolutional neuraL Networks (2019)
 Deep Learning in Mobile and Wireless Networking:A Survey (2019)
 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems (2019)
 A Speculative Study on 6G (2019)
 6G Wireless Communications: Vision and Potential Techniques (2019)
 The Roadmap to 6G – AI Empowered Wireless Networks (2019)