LED Backhaul Project Engineer Blog
Answers to FAQ (Part 3)
Answers to questions about the current status and prospects of Li-Fi
Last Update: December 21th, 2021
Introduction
The word "Li-Fi" is an "icon" of optical wireless communication, but few people have ever touched the real thing. I've mentioned it many times in this blog, but mainly in "theoretical" explanations, and not so much in "how does Li-Fi work in reality? In this article, which will be the last one for this year, I would like to talk about Li-Fi. In this last article of the year, I'd like to answer some frequently asked questions about Li-Fi and touch on the current and expected position of Li-Fi.
Q. What is the definition of Li-Fi? What's Li-Fi and what's not?
A. Actually, there is no definition.
Wi-Fi has an industry organization called the Wi-Fi Alliance, and only devices that have been certified and confirmed as interoperable can claim to be Wi-Fi enabled. There is a company called pureLiFi, created by Professor Haas of the University of Edinburgh in the UK, who proposed the name Li-Fi, and they are leading the Li-Fi industry, but they do not define the term Li-Fi, nor do they have an organization to do so. There is no organization that does.
Our company defines Li-Fi as a type of optical wireless communication device where a parent device is installed in a high place such as a ceiling and communicates with multiple child devices. It looks like the figure below. However, if we take the definition of Li-Fi strictly, it should be "a communication device that communicates with lighting (=white light)," and in fact, pureLi-Fi, the granddaddy of Li-Fi, has released such a product. However, there are also devices that are attached to the ceiling but communicate with invisible infrared light instead of white light, and if you ask me if I don't call them Li-Fi, that's not true either. So we call all ceiling type devices Li-Fi.
Figure 1: Li-Fi image.
However, there are actually many people who use Li-Fi in a broader sense. For example, our product LED backhaul is an optical wireless communication device that normally communicates horizontally on a one-to-one (point-to-point) basis, so we don't call it Li-Fi according to the internal standards mentioned earlier. However, some people call all optical wireless communication devices that communicate at high speed Li-Fi, and our products are also called Li-Fi by such people.
So, in the end, there is no definition of Li-Fi at all, and the name "Li-Fi" only promises optical communication.
Q. What about Li-Fi standardization?
A. They are working on standardization, but it will be a long time before it is released.
Optical wireless communication itself has existed for a long time, and standards have not been absent. In Japan, the ARIB (Association of Radio Industries and Businesses), a radio industry organization, standardized the optical wireless LAN system under the number STD-T50, and the first edition was published in February 1997. The first edition was published in February 1997, and the current Wi-Fi (802.11b/g) was listed in ARIB in December 1999, so it means that optical has existed before Wi-Fi. Since our company became a full member of ARIB and started working on optical wireless communications much later, I don't know why optical wireless was discussed at ARIB at that time, but I am sure that there was at least some need for it to be standardized. However, that standard is now a "dead" standard that no one uses because it is quite primitive as an optical wireless communication and the communication speed is slow (maybe it was dead from the beginning).
Now, let's get to the point. The standardization of "modern" high-speed optical wireless communication is based on IEEE802.15.13 and [ITU-G.9991(G.vlc)](https://www.itu.int/rec/T-REC -G.9991/en), and some of them are completed. However, this standard is more suitable for backhaul type of optical wireless communication, which is our product. It is not a standard that can cover Li-Fi, which requires functions such as multiple access, advanced accessibility, mobility, and so on. Therefore, in order to achieve these functions, it would make more sense to incorporate Wi-Fi functions instead of the conventional optical communication framework, and Li-Fi is now being standardized under IEEE802.11, which is a Wi-Fi standard. It's called LIGHT COMMUNICATION TASK GROUP(link) and has a branch number of "bb". In other words, Li-Fi is going to be called "IEEE802.11bb", which sounds like a kind of Wi-Fi.
It would be great if 11bb could be standardized soon, but I expect it to take a long time to complete. First of all, Li-Fi standardization needs to cover a much wider range of technologies and it needs to be more tightly defined than backhaul. There is a difference in difficulty between one-to-one communication between devices of the same manufacturer and communication between user devices of various manufacturers. Moreover, the current mobile wireless communication technology has become too complex. For example, both 5GNR and Wi-Fi 6 are a mass of various technologies, and the number, size, and technical scope of the related standards are beyond the scope of individual understanding. The number, size, and technical scope of these standards are beyond the scope of an individual's comprehension. Naturally, the writers of the standards are also numerous, and come from a variety of companies (including Ericsson, Nokia, Huawei, Qualcomm, and Cisco). In other words, the recent telecom standards are the combination of all the world's knowledge.
On the other hand, there are only two companies participating in 11bb: pureLiFi, the flagship of Li-Fi, and the German Fraunhofer HHI Institute, which provides us with optical wireless technology. Neither of them is a large organization, and the number of people involved in standardization is probably not large. Even with such a small organization, they might have been able to manage the technology 20 years ago, when Wi-Fi was first introduced, but when it comes to standardization of communication nowadays, they seem to be lacking in resources. So, unless there is an increase in the number of friends (and huge manufacturers), I expect it will take a long time to finish the standardization of Li-Fi.
Q. When will Li-Fi be available? When will it become practical?
A. A. Actually, it's already on the market.
If it takes so much time for standardization, doesn't it also mean that it will take more time for practical application and sales? In fact, products are already on the market without waiting for standardization. However, since there is no "standardization" in place, there is no consideration for product compatibility, so the basic rule is to purchase a set of a parent device and a child device.
As of the end of 2021, the most readily available, high quality, affordable, and reasonably priced product is probably the French company OLEDCOMM(OLEDCOMM). Since our company is the distributor of their products, you may think that we are just advertising, but I think you will understand if you compare them. Of course, as an engineer, I can honestly say that compared to Wi-Fi 6, the maximum speed is still slower, the communication range is narrower, and the product is not as complete as it should be for end users, but I think you can still experience the benefits of Li-Fi that is not a radio wave. If you are interested in a Li-Fi device that can be purchased and used at a realistic price, please contact us at here. Below is a product introduction image (taken from a brochure) of one of our main products, LiFiMax.
Figure: OLEDCOMM LiFiMax
Q. It says something like "Li-Fi will be able to communicate at more than XX Gbps in the future", but when will such a product come out?
A. I have no proof of this, but I personally expect it to be within 5 years.
If you are a reader of this blog, you may have seen Li-Fi manufacturers claiming that they have achieved 10 Gbps or more at the experimental level, or that they plan to achieve xx Gbps or more in the future. You may have also seen similar statements in the media when Li-Fi is mentioned (although rarely). At present, for example, the aforementioned OLEDCOMM's LiFiMAX has a maximum speed of 100Mbps, but is it realistic to expect a speed of 10Gbps in the near future? You might think so. However, 10 Gbps, or even a few Gbps, is not that difficult to achieve technically. As I have written many times in this blog, this is only possible if laser diodes (LDs) that can withstand the use of Li-Fi become available.
In order for Li-Fi to achieve faster communication speed than Wi-Fi, it is necessary to improve the LD device. With LEDs as the light source, the best we can hope for is a little over 1 Gbps, but with LDs, 10 Gbps is quite possible. Lasers blink quickly, and their amplification characteristics are extremely linear, making them ideal for communication devices. However, they are outperformed by LEDs in almost every aspect except output power, durability, lifetime, ease of use, and price. With the current performance, we can't offer them to end users. I don't have any reason to believe that it will be within 5 years, but I am sure that we will see such LDs in the near future. Please come out, LD manufacturers, please develop!
Q. Will Li-Fi (optical wireless communication) be used in 6G (Beyond5G)?
A. We are expecting it, and it may be possible.
When I listen to the lectures on 6G and Beyond5G (B5G), VLC, or optical wireless communication, is sometimes mentioned as a candidate as a communication method. In fact, Google (Alphabet) is conducting laser transmission experiments, and Softbank is working with Nikon on joint research on optical wireless communication(jp) for 6G. .jp/corp/news/press/sbkk/2021/20210318_01/) for 6G, there is a growing momentum that optical wireless communication may be used for part of 6G. As mentioned above, high power LDs are used in many applications. As mentioned above, if high-power LDs are available, it is possible that the communication speed will be usable.
One of the reasons why optical wireless communication is expected is that although the millimeter wave (28 GHz band) currently used for 5GNR is very difficult to use, it is terahertz waves of even higher frequency that are being considered for 6G and B5G (i.e., vacant). The terahertz wave here is named terahertz in the industry, but it actually refers to the order of magnitude before the 100GHz terahertz. In order to have a wider frequency bandwidth, we have to choose such a high frequency, but when the frequency is this high, the attenuation of anything we do becomes large. However, I believe that the reason why optical wireless communication is expected by some people is not so much because of terahertz waves themselves, but rather because millimeter waves are now too difficult to achieve.
More than 10 years ago, when LTE had just been rolled out, it was already an established fact that millimeter waves would be used for 5G, but I remember that there were many people who were skeptical about millimeter waves, and I was one of them. However, there were experimental results and predictions from various researchers and vendors, such as "it is possible to fly 1km using beamforming," "it is not as vulnerable to shielding as imagined because it can use reflected waves," and "millimeter wave base stations will be compact, and the price of base stations will drop to the level of commercial Wi-Fi APs. If everyone says so, will we be able to use millimeter wave as well? If that's the case, then millimeter wave will be available? However, the reality is that it flies only 2 to 300m, not 1km, and if it is shielded, it will be cut off soon. The total cost is "high" including the backhaul line cost, which is higher because of the higher transmission speed, but the area is so small that it is necessary to launch many of them. "That's the reason. For this reason, the only countries that are taking millimeter wave seriously are the US and Japan, where for some reason there are no (or no longer any) global radio vendors. The countries with major radio vendors such as Ericsson and Huawei, i.e., Europe, China, and Korea, are not interested in millimeter wave at all. I want to complain to them.
Nowadays, people and vendors who are doing research on terahertz waves are promoting the advantages of terahertz waves and the fact that they can be used, but with many countries failing or refusing to use even millimeter waves, people are even more skeptical about whether terahertz waves are really usable than they were 10 years ago. However, as the laws of physics dictate, in order to increase the speed of communication, a wide open bandwidth is necessary, and as long as radio waves are used, a high frequency is inevitable. Ten years from now, there is a good chance that terahertz waves will work as expected, but still, it is too risky to use only one of them. Therefore, it is understandable that some people would look forward to optical wireless communication, which is easy for anyone to handle, is certain to achieve a certain level of communication speed at present, and is clear about what it can and cannot do in terms of radio wave propagation.
However, from the standpoint of optical wireless communication, it is obvious that it is not so easy for optical to be integrated with cell phone technology. For example, in today's 5GNR, the technology used for both conventional 800MHz and the new 28GHz is exactly the same. Strictly speaking, there are some differences in FDD/TDD, bandwidth, antennas, etc., but since both use the same modulation, the same coding, and the same channel configuration, the difference in frequency does not make a difference in the technology used. On the other hand, the modulation scheme of optical radio is different from that of radio, and it is not possible to use the same technology as in radio; it is possible to use the same MAC layer as in radio, but only the physical layer is different. Therefore, if there is a possibility, optical wireless communication will exist as a completely different technology (RAT in 3GPP terminology), and it will be used as a substitute for functions that technically exist, such as relays and side links, but are difficult to use due to frequency constraints.
It's a long story, so let me summarize my answer
- People who think there is no way to use terahertz waves when millimeter waves cannot be used are expecting optical.
- However, since it is difficult to incorporate optical into 3GPP as it is, it is possible that it will be adopted as another RAT for niche areas where communication speed is necessary.
Conclusion
What did you think of my last engineering blog of the year? I don't know if my prediction will come true or not, but as a person who is involved in optical wireless communication, I hope it will be a little better (or worse). Well, the next update will be on January 11 next year, and I look forward to working with you in 2022.
