Researchers Should Take Every Experience as a Positive One to Improve Their Well-being

Effective use and development of radio-wave resources and optical-wireless cooperative control toward IOWN implementation

—Could you tell us about the research you are currently conducting?

To put Extreme Network as a Service (Extreme NaaS) (Fig. 1) into practical use, which will provide network services that link everything and meet the extreme requirements (ultra-high capacity, ultra-high reliability, ultra-low latency, etc.) of diverse users and services in an ever-changing wireless environment, we at NTT Access Network Service Systems Laboratories are researching and developing two themes: (i) advanced wireless-access technology for further expanding the potential of wireless access and (ii) multi-radio proactive control technology (Cradio^®) for providing a network that adapts to the environment to maximize the potential of wireless access.

Fig. 1. Extreme NaaS.

With Extreme NaaS, we aim to create a world in which new value is constantly created through various forms of cooperation by enabling everything to be coordinated. To achieve this, everything needs to be properly connected—anytime, anywhere, and to anything. How to innovate wireless access, which is one element of Extreme NaaS, is the pillar of the above-mentioned research themes. Optical and wireless networks have been evolving individually, which resulted in the two networks having different qualities. In the future, it will be necessary to consider communication quality in a combination of both optical and wireless networks, and this combination is the aim we want to achieve by implementing the Innovative Optical and Wireless Network (IOWN). Extreme NaaS is a means to deliver IOWN and requires a dramatic improvement in both the reliability and speed of wireless communications; thus, we are investigating these research themes.

—Could you explain efforts to develop radio frequencies, including high-frequency bands?

In addition to telecommunications, radio waves have a variety of uses such as broadcasting, radar, and astronomical observation. Under these circumstances, expanding the range of frequencies available for telecommunications has become an important issue. We believe that there are two approaches to address this issue: development and utilization of higher frequencies (high-frequency-band technology) and sharing frequencies among different wireless systems (Fig. 2).

Fig. 2. Development of radio frequencies.

Regarding the high-frequency-band technology, to enable the provision of ultra-high-speed, ultra-high-capacity communications in the sixth-generation mobile communications system (6G) era, the use of frequencies above 100 GHz, which makes it possible to obtain significantly wider bandwidth, is attracting attention. However, as the frequency of radio waves increases, the loss due to reflection and diffraction also increases, and the propagation characteristics become more complex due to the scattering effects of microscopic unevenness of wall surfaces. To use high-frequency bands, it is thus necessary to identify the characteristics of radio-wave propagation by measuring such propagation in field experiments and study how to use those bands. We therefore began to study modeling of radio-wave-propagation characteristics up to 300 GHz by transmitting radio waves—as a world’s first—in an outdoor urban environment (Fig. 3). By accumulating the results of these experiments, we are investigating ways in which high-frequency bands can be practically used. We are also sharing these experimental results with international standardization organizations, such as the International Telecommunication Union - Radiocommunication Sector (ITU-R), and the Beyond 5G Promotion Consortium.

Fig. 3. Development of new frequency bands (> 100-GHz band).

For frequency sharing, we have contributed to the study toward the revision of regulations to allow wireless local area network (LAN) systems to use the 6-GHz band, which is used for satellite communications, fixed microwave communications, and radio relay for television broadcasting, in addition to the 2.4- and 5-GHz frequency bands that have been available. Since 2022, the 5.925-to-6.425-GHz frequency band has been used for wireless LAN systems. We are currently discussing ways to expand the use of wireless LAN in this frequency band. We have also contributed to revising regulations to allow wireless LAN systems to use the so-called “platinum bands” below 1 GHz, which include the 920-MHz band used for low-power wide area (LPWA) networks, for targeting new Internet-of-Things services (Fig. 2).

Designed to promote frequency sharing, a technology called automated frequency coordination (AFC) is currently attracting attention. AFC coordinates frequency usage by enabling a wireless LAN equipment (access point (AP)) to select the appropriate available frequencies according to the location in which it is being operated to prevent harmful interference with other wireless systems operating in the same frequency band. The Ministry of Internal Affairs and Communications (MIC) of Japan and others are currently discussing the introduction of AFC, and we are contributing to the development of a frequency-sharing mechanism.

To bring new wireless technologies into society, establishment of regulations, such as frequency allocation, is quite relevant in addition to widespread use of wireless equipment and creation of wireless services. The allocation of frequencies, including their use, is subject to both international rules determined by ITU-R and the World Radiocommunication Conference and domestic regulations that are discussed in various committees established by MIC for domestic implementation, and we are actively contributing to standardization and institutionalization efforts. The industry as a whole needs to develop a vision for the widespread use of wireless equipment through the standardization activities of the 3GPP (3rd Generation Partnership Project), Wi-Fi Alliance, IEEE (Institute of Electrical and Electronics Engineers), and other organizations. It is also important for us to create services unique to the NTT Group while taking into account such standardization and institutionalization. We are engaged in research and development (R&D), standardization and institutionalization, widespread use of equipment, and creation of services—all in harmony like the four wheels of a car.

—What kind of technology is Cradio^® × low-latency FDN?

It is an optical-wireless cooperative control technology for real-time control of optical and wireless networks via an extended Cooperative Transport Interface (eCTI) for the provision of low-latency, high-stability network services. This technology consists of Cradio^®, a multi-radio proactive control technology, and a low-latency function-dedicated network (FDN), which is a technology that provides services in a sustainable and stable manner by monitoring the transmission time of the network and processing time of edge computing to achieve end-to-end communication quality that has low latency and low jitter in accordance with service requirements (Fig. 4).

Fig. 4. Cradio^® × low-latency FDN for a continuously connected network.

To evaluate the feasibility of this technology, we conducted the following two demonstration experiments in May 2024 by constructing an environment—assuming a wireless environment in a factory—in which Wi-Fi APs and an IOWN All-Photonics Network (APN) line are connected to establish communication between a wireless user terminal under the Wi-Fi APs and cloud servers and by linking a wireless controller equipped with a Cradio^® function for understanding the wireless usage state with an optical controller for real-time optical-path switching of the IOWN APN line via eCTI (Fig. 5).

Fig. 5. Operation sequence of optical-wireless cooperative control in the demonstration experiments.

This optical-wireless cooperative control technology can be applied to private wireless systems, such as Wi-Fi and private 5G, as well as cellular systems such as Beyond 5G/6G. We will continue to conduct demonstration experiments to verify the cooperative operation of various wireless systems with the IOWN APN and study usage scenarios to contribute to the development of a network-solution business that combines the IOWN APN with private wireless systems.

Bringing research results into a society while harmonizing activities involving R&D, standardization and institutionalization, widespread use of equipment, and creation of services

—Could you tell us what you keep in mind as a researcher?

Since our research is focused on practical application, I think it is important to always think about how to make sure that the research results are made available to society as a whole. In this sense, as I mentioned above, we are engaged in R&D, standardization and institutionalization, widespread use of equipment, and creation of services in a coordinated manner like the four wheels of a car.

During standardization activities in the past, we developed a mechanism that enables multiple wireless LAN APs to be linked together to reduce interference when communicating and proposed implementing this mechanism. However, when we tried to implement technology for this mechanism in products, we did not receive sufficient support from vendors, and the proposal was unfortunately rejected. Regarding the standardization of next-generation wireless LAN currently underway, multi-AP coordination, a technology that enables multiple wireless-LAN APs to be coordinated, has been designated as a key technical area and is currently under discussion. I realized that a technology can be fully implemented, not when the technology is simply developed but when its development coincides with the momentum of each company accumulating the necessary skills to commercialize it, including the expertise to develop equipment. With this experience in mind, I currently serve as vice chairman of the 802.11ah Promotion Council, which is an organization consisting of 187 companies and organizations (as of September 18, 2024) including telecommunications carriers, manufacturers, system integrators, academic organizations, and others. In the Council, we have built cross-industry alliances to implement IEEE802.11ah in Japan and have successfully led the institutionalization and standardization of the IEEE802.11ah standard. If we try to do something only within the scope of what we can see, it will be difficult to create something new, so I feel that it is important to create new value within a larger framework while borrowing wisdom from—and making connections with—various people.

You can’t get such experience just by investigating technologies in the laboratory, and, especially in the case of radio waves, effects such as antenna placement and the actual environment must be considered. Many matters can only be understood in the field, so it is difficult to find a breakthrough without experiencing the real world. Based on these thoughts and experiences, my approaches to R&D, which I use to set research themes and conduct R&D activities, are explained as follows.

One approach is the setting up of a “new frontier” of wireless resources. Wireless technology has been researched and developed as a means to use three resources, time, space, and frequency. However, when designing a highly reliable wireless system, various margins for uncertain variables are built into the design to avoid interference and fluctuations of radio waves in the wireless environment. If we could accurately predict the probability of radio-wave fluctuations in the wireless environment, we would be able to reduce the margin to the bare minimum and efficiently accommodate much more wireless traffic. I am thus promoting an approach that transforms the margin—currently set as an excessively large variable—into a new “fourth resource.” I believe that if we can improve the accuracy of radio-quality prediction and enable resource management that dynamically applies the prediction results to radio-wave control, we can significantly improve frequency-utilization efficiency.

Another approach is collaboration between R&D in wireless access and R&D in other fields. I believe that it is necessary to step outside the framework of wireless technology and challenge ourselves to combine it with other fields and create new technologies in conjunction with people outside the wireless field. In addition to exploring new technological fields, I also see linking with various applications other than wireless systems as another approach. Only optimizing wireless-transmission quality between the radio transmitter and receiver will not meet the quality requirements of the application. In the IOWN era, various databases and computing resources will be linked in real time. I believe that linking of wireless systems with applications will raise the value of wireless systems to a new level.

—What is your message to younger researchers?

I have recently been interested in the well-being of researchers. It has been about 30 years since I joined NTT laboratories, and while pursuing my R&D, I have experienced both times when things were going well and when things were going badly. Sometimes I felt as if things were going wrong all the time. However, I have used those challenging experiences to lead to greater success. I believe it is important to think positively, and even when you are faced with a situation that is not going well, accept it as an experience that will surely lead to significant value someday and proceed with your R&D in a manner that ultimately enables you to accomplish even greater results. Although it is difficult for all researchers to think in this way in every situation, if all members of our R&D team can support each other to have this positive mindset, I think we can create an R&D team that is highly motivated to challenge ourselves.

On a different note, when I was watching news about an overseas large-scale science-and-technology project, I was surprised to see that even though the project was not successful, the project managers and members spoke in a very positive manner, stating that the failure was an opportunity to gain knowledge and skills for the next step. I think it would be quite difficult for researchers involved in an R&D project in Japan to react in such a positive way.

It is important to accept every experience, including bad ones, in a positive manner and to think of—not only by the researchers in charge but also with fellow researchers—how to connect those experiences to the next success and create a new path forward. I believe that this mindset will help improve the well-being of researchers.