Wireless Entrance Project

--Please tell us about the research area of the wireless entrance project first

Tokuyasu: In our Wireless Entrance Project, we conduct a wide range of R&D on wireless communications. The needs and scenes of using wireless communication as a communication infrastructure are expanding. In particular, with the spread of smartphones and tablet terminals in recent years, wireless communication traffic has continued to increase. In the past, wireless services were mainly voice calls, but the spread of mobile phones and wireless LANs has made wireless services more accessible, and various wireless systems have developed independently. In the future, the era of coordination and fusion will arrive, such as automatically connecting the optimal wireless system according to the user's situation or increasing the transmission speed by connecting multiple wireless systems simultaneously. Will be. NTT Access Service Systems Laboratories is conducting research and development to realize a more convenient world where everything is connected wirelessly and everyone can connect with each other naturally without being aware of the wireless system.
In the meantime, the Wireless Entrance Project has begun examining the rapid increase in traffic in urban areas, in anticipation of the widespread use of wireless systems toward the next generation of versatile systems beyond 5G. We are also working on systems that utilize low-Earth-orbit satellites with a view to future use in communications, such as unprecedented large-capacity high-speed communications and ultra-wide-area IoT. Since the disaster, we have been focusing on research and development for disaster countermeasures to prevent isolation in the affected areas during a disaster and support a safe living.

--You are working on research and development of various wireless communication systems, aren't you? Can you tell us about the consideration for next-generation systems after 5G?

Suga: My group is mainly engaged in research and development of high-speed, wide-band wireless systems for the future, and one of them is using a technology called RoF (Radio over Fiber) that transmits wireless signals using optical fibers. I am engaged in research and development of high frequency band RoF systems that can be shared with equipment.
In order to provide high-capacity wireless communication using radio waves in a high-frequency band such as 5G, it is necessary to install base stations at a high density, for example, every several tens of meters. Then, increasing the cost by preparing many base stations becomes a problem. In contrast, in our technology, of the functions of the base station, the signal processing function that depends on the communication method is separated and placed in an NTT building, etc., and only the functions such as antennas that do not depend on the communication method are used as the overhang base station. , And a configuration (RoF) that connects them with an optical fiber. By doing so, some base station functions can be centralized in NTT buildings and other facilities without preparing all base stations with full specifications, and equipment sharing that can reduce costs becomes possible.
By providing different signal processing functions for each wireless service, it will be possible to provide a variety of high-capacity wireless communications. Service updates and renewals only need to be performed for the signal processing function of the central station, which is advantageous in terms of operation. Currently, for practical use of this RoF system, we are working on the development of the world's first technology that realizes signal control with a simple configuration and high wavelength use efficiency when wireless signals are transmitted over optical fibers over long distances. You.

--Could you tell us about wireless communications using low-Earth orbit satellites? It's a language I'm not used to, but what is it?

Goto: A low-orbit satellite is an artificial satellite that flies below 2,000 km above the Earth's surface. The geostationary orbit satellites that have been used so far are at an altitude of around 36,000 km, which is considerably lower than that. In satellite communications, the transmission delay caused by the physically long distance between the earth and the satellite was one hurdle, but low-orbit satellites with a relatively short distance can solve this hurdle.

My group is conducting R&D on satellite communications used by the NTT Group, and is studying a wide range of future satellite communications systems. My main mission is to create new technologies, and I am working on a wide range of activities from academic activities to implementation development. In this effort, I noticed the low-orbit satellite I mentioned earlier. Now, in collaboration with the Japan Aerospace Exploration Agency (JAXA), toward the demonstration experiment of the world's first low-orbit satellite MIMO (Multiple-Input Multiple Output), which realizes high-speed communication by simultaneously using multiple antennas of the satellite, working every day. MIMO transmission is difficult to apply in satellite communications, and there has been no practical example so far. In this joint research with JAXA, we are examining to demonstrate that in communications between satellites and base stations, multiple antennas of the base station can be remotely located to improve the separation characteristics and perform satellite MIMO transmission.
Satellite communication is important as an important communication infrastructure for disaster countermeasures, but the problem is that the transmission speed is lower than that of terrestrial communication systems. In order for satellite communication to play a part in the communication infrastructure, a capacity that can keep up with the increase in traffic is required. If satellite MIMO technology is established, it will not only be expected to contribute to an increase in mobile traffic in the future, but will be able to be used in various wireless communication systems such as satellite IoT that can accommodate ultra-wide area and ultra-large number of terminals.

--So there are still many possibilities for satellite communications. The word "disaster countermeasures" came out on the way. Could you tell us about the research and development of wireless communications for disaster countermeasures?

Fukuzono: My group is researching and developing wireless systems for terrestrial disaster countermeasures and VHF band wireless systems for mountains and islands. My role is to carry out development work in cooperation with operating companies and manufacturers, while also conducting research on wireless signal processing technology for future systems.
Let me introduce some of the products that I am involved in. One of the products that has been put into practical use is the TZ-403D wireless system for disaster response. This system can provide free special public telephones and Internet connection to evacuation shelters when the communication cable is cut due to an earthquake or other disaster. It has been deployed during recent heavy rain disasters and has been used so that people in the affected areas can use their lifelines without being isolated.

As another product, one of the products currently being developed for practical use is a VHF band wireless system for mountains and islands. NTT has an obligation to provide subscribers and payphones called universal services to customers all over Japan. This wireless system aims to provide universal services to customers even in mountains and islands where it is difficult to lay wired cables. Providing universal services was one of NTT's responsibilities, but conversely speaking, NTT can only engage in R&D to support and support all customers.
This VHF band subscriber wireless system must provide communication over a distance of several tens of kilometers, far more than cellular phones. If there is a long communication distance, there will be a long delay wave that can degrade the signal, and a new processing technology that is not available in the world will be required. Therefore, we invented a long delay wave equalizer that can handle long delay waves, which is unprecedented in the world. As a result, we have successfully conducted communication experiments with locations that are more than 50 km away.
In research and development, we do not only look at wireless communication systems for disaster response. In core research, we are working on wireless communication systems that can be used in various wireless communication systems. For example, we are conducting the world's first research on a new waveform MIMO system based on a single carrier that is assumed to be applied to 5G. Originally, this technology has been working on large-capacity transmission at the low frequency of the 60MHz band for disaster response wireless systems, but we are studying a method that can find advantages even in high frequency bands such as 5G.

--What made you happy and motivated to work?

Fukuzono: I was glad that I was able to implement the technology I conceived in the VHF band wireless system, a product that can be put to practical use. Soon, the development verification product will be completed, and a field experiment to actually emit radio waves will be performed. I am looking forward to seeing good communication characteristics.

Goto: Research work is a work that reminds us of something that has never existed before, so it has a pain of birth, but it is very rewarding to gradually realize the technology we envisioned. I'm also very happy when the technology I've created can be a useful discussion with others, or if I can find a way for the output to be of value to the company. To create something new, I don't think there's going to be much better than sitting at a desk and thinking. I try to listen to literature surveys and academic conferences, actively discuss with researchers in various fields as well as my own field, and try to create flexible ideas.

Suga: I think NTT Laboratories' great appeal is that they can not only commercialize existing technologies but also explore new technologies that never existed before. The RoF system that I am currently involved in cannot be realized simply by utilizing existing technologies, and we are studying new technologies. When I saw the technology I thought was working on the actual machine, I felt a great sense of accomplishment and excitement. Also, I am very pleased to receive words that are expected to be evaluated and realized for my proposals at exhibitions and academic presentations.