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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.

 

 

 

6G Enabler Techologies

 

Like every new technology, 6G also will require many component technologies that would make it possible. There is nothing we can say for sure about the component technology as of yet (Feb 2021), but following illustration can be a good summary of possible candidates. This is based on Scoring the Terabit/s Goal: Broadband Connectivity in 6G and I think it is one of the best summary with focus on low layer implementation. Try to get familiar with the keywords shown here and it will be much easier for me to read other technical documents once you get familiar with these keywords. I strongly recommend you to read through the paper.

 

Image Source : (Modified from) N. Rajatheva et al.: Scoring the Terabit/s Goal: Broadband Connectivity in 6G

 

 

 

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 up from the very early conception through the full developmental process.

 

 

 

Big Questions

 

As of now (Feb 2021), nothing is fixed about 6G. It may not make much sense of having questions about something that is not clearly defined. But at least there is one thing that seems to be relatively clear. It would be that 6G would be based on Thz (from a few hundreds Ghz to a few Ghz) and my question is based on this assumption.

 

Do we have enough time ?

 

Assuming that 6G is targeted to be deployed in 2030, we have roughly 10 years as of now (Feb 2021). It implies that most of critical component of technology (especially the technologies related to physical layer implementation) should be ready a few years before the deployment target. It means that we have only around 5 years or so until those PHY related technology is ready. Would this be enough time ? I think it would be very challenging.

Looking backwards to the process of conceptualization to realization for 5G which also took almost 10 years, there wasn't much difference in terms of physics between 4G and 5G. You may say that regular radio frequency (mostly under 2Ghz) to mmWave transition is a big difference in terms of physics, but I think the technology gap is small enough that most of 4G technology (semiconductor, OFDM, Antenna Technology etc) can be reutilized. How much of 5G technology can be reutilized in Thz technology ? I don't think there would be much of overlap between 5G and 6G physical layer implementation and a lot of technology need to be reinvented.

A way to shorten the time line for the technical readiness would be to redefine the definition of 6G PHY. For example, instead of targetting 300 Ghz and above as the first target, setting D(110Ghz-170Ghz)  or G(110-300Ghz) band as the first target and try to extend it to higher frequency as 6G evolution. In this case, there would be disputes over whether we can call the D band as Thz technology or not... but this kind of approach has been employed very often. Even in 5G case, under 40 Ghz was set as the first mmWave target and 50~70 Ghz as 5G evolution target.

 

NOTE : As far as I recall, there was proof of concept implementation / demonstration for 5G around early 2013. With the similar time frame, can we have something like this for 6G around 2023 ? To be honest, I think the chance is high. However, if we set D band as the first target as the first target I don't think it is impossible to come up with something to show in a few years.

 

 

How to generate Thz Signal ?

 

I think the first step for PHY implementation is to develop signal (like CW or pulse) for the targeted frequency. In this case, we need to develop a device that can generate the signal at Thz range. There has been a few conventional approach for this. One is to downconvert the optical signal to Thz range and the other one is to upconvert high frequency mmWave to Thz range signal. Recently some researches has been done to develop devices to generate Thz signal directly in Thz range.

Once this type of device is developed, next step would be to reduce the size enough to fit for the communication device (especially size reduction for mobile device would be the most challenging) and develop the process for mass production.

 

 

How to modulate Thz Signal ?

 

Can we use the OFDM which is good for wideband implementation ?  or do we need to turn to single carrier modulation ? If we need to turn to single carrier technology, how can we implement ultra wideband ?   

 

 

Do we have proper antenna technology for Thz ?

 

One of the hot topics when we were talking about 5G technology in comparison to 4G. Now experts are talking about ultra massive mimo. Applying the logic explained here, it would be understandable that we would need to put a lot of more antenna elements to work in such a high frequency like Thz, but there would be a lot of challenges to integrate very high number of elements. In addition, it would be critical to develop analog and digital solutions required for beam foraming (e.g, phase shift and amplification control) that can work in this high frequency region.

 

 

Do we know about the characteristics of Thz Channel and do we have any good model for it ?

 

 

 

How to handle the issue of estimating channel  and reporting channel state information ?

 

 

 

How to handle such a high sampling rate requirement of ADC for ultra-wide bandwidth ?

 

I think this has always been a serious challenges for every new technology. Evolving from 4G to 5G, we needed to revolutionize the ADC handling 20 Mhz BW to 400 Mhz BW. As of writing (Feb 2021), it seems that ADC handling 200 Mhz BW seems to be ready with reasonal cost even for the mobile device, but not sure of the one that can handle 400 Mhz. In 6G, we are talking about 100 Ghz Bandwidth and we can easily guess how hard it would be.

 

 

Do we have such a high performance of DSP or revolutionaly channel coding algorithm  ?

 

Achieving such a high data rate like 1 Tbs implies that we would need to perform such a wide baseband processing. Among these process, channel coding would be the most performance demanding. So we may need to completely redesign the channel coding algorith to be more efficient or to be possible for parallel processing.

 

 

 

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 [11] 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 [15]) 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[19]~[26]. I personally recommend you to start with Ref [26] and pick one of specific direction that you want to follow through.

 

 

[ Nov 2019 ]

  • I realized that there are TeraHz physical layer deliverables are defined in Teranova. This seems to be similar activities that we saw from METIS specification at early 5G research. As we saw in the difference between METIS specification and final 3GPP specification, it is not sure how much of this early specification will be adopted by the final industry specification (3GPP), but at least it will be good to shape the overal pictures of Terahertz PHY/MAC.
  • I see more and more papers coming out in 2019 about applying Machine Learning to Wirless PHY layer especially signal detection, modulation detection ([31],[32],[33])

 

 

[ May 2020 ]

  • A few month ago(Mar 17, 2020), 2nd 6G Summit was held and videos for presentations are posted here. Comparing to those from the 1st summit, most presentations shows more on technical aspect of 6G. I think it is worth watching.

 

 

[ Jul 2020 ]

  • SamSung released a good white paper on 6G : 6G The Next Hyper Connected Experience for All. At least to me, this is one of the best white papers on 6G giving huge insights on 6G on technical aspects. For me, the section 4 (Candidate Technologies) is the most interesting and informative. Esepcially those topics on Terahertz Technologies, Novel Antenna Technologies,Comprehensive AI were the most intersting ones to me.

 

 

[ Oct 2020 ]

 

 

[ Nov 2020 ]

  • A good Webinar video is shared in public about PHY and low layer aspect/idea on 6G. Status of Radio Module development for Teraherz and a lot of talks on massive MIMO for 6G etc. See this video on YouTube.

 

 

[ Feb 2021 ]

  • I found a very good paper summarizing the current status of Thz technology and challenges. I think this is the in-depth version of first presentation of this webinar which is also very good.

 

 

[ Apr 2021 ]

  • Here goes an excellent webinar about trend and future of telecommunication from 1G through 6G with focus on 5G/6H.

 

 

 

Institutions/Organizations/Forums

 

 

 

Event / Workshop / Symposium

 

 

 

R&D / Test Solution

 

 

 

Articles/Media

 

Followings are the list of articles mostly for general public. If you think it is too early to talk about 6G when 5G  just start being deployed (as of Jan 2020). See my list of articles on 5G and check how early they started talk about 5G.  Not very technical, but I found it intresting to observe how public opinion is formed and new technology is planned and evolve.

 

 

 

Papers/White Papers

 

 

 

Videos - 1st 6G Summit

 

 

Videos - 2nd 6G Summit

 

 

 

Video - 6G Research Visions Webinar Series (2020)

 

 

 

Videos - Terahertz Technology

 

 

 

Video - D/G band

 

 

 

Videos - General

 

 

 

Further Readings

 

[1] How TeraHertz Technology Will Change The World Of Wireless Communication ?

[2] An overview of integrated THz electronics for communication applications

[3] Terahertz Waves for Communications and Sensing

[4] A Perspective on Terahertz Next-Generation Wireless Communications (2019)

[5] Tuning to Terahertz Electronics (2015)

[6] THz Electronics

[7] Terahertz electronics: The last frontier (2014)

[8] A New Technology for Terahertz Electronics (2003)

[9] Joint Lab THz Components & Systems   

[10] Terahertz breakthrough allows for ultrafast wireless communications  (2015)

[11] Last Meter Indoor Terahertz Wireless Access:Performance Insights and Implementation Roadmap (2018)

[12] Compact Terahertz Reciever for Short-range Wireless Communications of Tens of Gbps  (2017)

[13] Micro- and nano-scale Terahertz Band Communications  

[14] Terahertz (THz) Wireless Systems for Space Applications (2019)

[15] MAC Protocols for Terahertz Communication: A Comprehensive Survey (2019)

[16] Advances in THz Wireless Communications (2017)

[17] How AI is Starting to Influence Wireless Communications

[18] The 5G Future Will Be Powered By AI (2019)

[19] DeepSig: Deep Learning for Wireless Communications

[20] Deep Architectures for Modulation Recognition (2017)

[21] Physical Layer Communications System Design Over-the-Air Using Adversarial Networks (2018)

[22] Deep Learning-Based Communication Over the Air (2017)

[23] Deep Learning-Based Channel Estimation (2019)

[24] "Machine LLRning": Learning to Softly Demodulate (2019)

[25] ORACLE: Optimized Radio clAssification through Convolutional neuraL Networks (2019)

[26] Deep Learning in Mobile and Wireless Networking:A Survey (2019)

[27] Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems (2019)

[28] A Speculative Study on 6G (2019)

[29] 6G Wireless Communications: Vision and Potential Techniques (2019)

[30] The Roadmap to 6G – AI Empowered Wireless Networks (2019)

[31] A Deep Learning Framework for Signal Detection and Modulation Classification (2019)  

[32] Fast Deep Learning for Automatic Modulation Classification (2019)  

[33] Automatic Modulation Recognition Using Deep Learning Architectures

[34] Deep Learning for Physical-Layer 5G Wireless Techniques: Opportunities, Challenges and Solutions (2019) 

[35] 6G Wireless Communication Systems: Applications,Requirements, Technologies, Challenges, and Research Directions (2019)

[36] Towards 6G Networks: Use Cases and Technologies (2020) 

[37] Sixth Generation (6G) Wireless Networks:Vision, Research Activities, Challenges and Potential Solutions (MDPI)

[38] THz Channel Sounding: Design and Validation of a High Performance Channel Sounder at 300 GHz (2020)

[39] Scoring the Terabit/s Goal: Broadband Connectivity in 6G (2021)

[40] Towards 6G wireless communication networks: vision, enabling technologies, and new paradigm shifts (2021)