Distinguished Researcher
Wataru Yamada

--Please tell us about the research fields, research projects, and research themes that you are currently engaged in.

The smartphones that we use in our daily lives are equipped with many wireless communication systems including LTE and Wi-Fi, but in actual communications, a smartphone uses the radio waves of those frequency bands allocated to each wireless system. These radio waves are invisible to the naked eye, but we can use radio wave propagation technology to visualize their behavior from an engineering viewpoint in terms of numerical formulas. Clarifying the behavior of radio waves in this way through visualization techniques enables us to uncover frequencies applicable to new wireless systems, design communication areas, and design diverse wireless systems such as by adjusting parameters to achieve a target transmission speed. I myself have been consistently engaged in the research and development of radio wave propagation technology since entering NTT. At present, I am focused on broadening the possibilities of wireless communications even further through the research and development of three-dimensional radio wave propagation technology that targets not only ground level—the usual range of communications up to now—but also the space up to several hundred meters above the ground. We expect this technology to enable stable operation of wireless systems at just about anywhere on earth.

--What was your reason for targeting anywhere on earth -even the sky above- for your technical studies?

Unmanned aerial vehicles in the manner of drones have attracted much attention in recent years and even news articles on the development of flying cars have appeared. At present, trials toward the practical operation of such vehicles are being held mainly in non-residential areas out of safety concerns, but I believe the time is coming when the flying of such futuristic vehicles in an urban environment will be commonplace. Needless to say, onboard wireless communication systems that can exchange information with the outside world will be essential to the stable operation of these vehicles, but radio wave propagation characteristics in that part of the sky where these vehicles will operate has been an unexplored area. In particular, understanding how radio waves propagate from the ground to points above buildings in an urban environment is vitally important from the viewpoint of operating safe services. The way in which radio waves propagate through the air depends on the mutual interaction of a variety of elements such as antenna installation format, frequency, and urban structures. From among these elements, those that have a large effect on radio wave propagation must be appropriately determined and expressed by numerical formulas that are as simple as possible. This is a chance for us radio wave propagation researchers with extensive experience and knowledge to show off our skills! We are already making some progress in the research and development of this area, and this includes the world's first experimental studies on radio wave propagation characteristics in urban skies, which are attracting much interest from researchers both inside and outside Japan.

International standardization activities are essential to the widespread dissemination of technology. In the Radiocommunication Sector (ITU-R) of the International Telecommunication Union (ITU), a specialized agency of the United Nations, the research committee includes ITU-R Study Group 3 (SG3) that addresses radio wave propagation technology. I have been involved in international standardization activities in ITU-R SG3 for more than ten years. At present, I am busy making proposals toward the international standardization of three-dimensional radio wave propagation technology. In addition, I have served as a Working Party (WP) vice-chairman and subgroup chairman as part of these standardization activities, and I believe that serving in these managerial positions was a testimony to the international community of our world-class technical abilities and contributions in this field.
Up to now, we have been studying radio wave propagation technology for various wireless systems including Wi-Fi and 5G, and we have been applying the results of our research including those that have become international standards to the design of a variety of wireless systems at NTT group companies. In relation to this research, we have received a number of best paper awards from academic journals and international conferences. It has been my intention to pursue research and development that has both engineering value that can be applied to business and scientific value that can be recognized by academic societies. By leveraging the experience and knowledge that we have so far accumulated, I believe that we can also make steady progress in our current research theme of three-dimensional radio wave propagation technology.

--In what way will the promotion of your research themes change the world and how would you personally like to change the world?

Through our efforts in researching and developing three-dimensional radio wave propagation technology, I feel that we can contribute to the creation of a future worldview as depicted, for example, in movies and science fiction novels. Radio wave propagation at NTT Laboratories has a very long history, and there is no one in the field of wireless communications that is unaware of the great research results by NTT pioneers based on experiments and measurements such as the Okumura curves. Wishing to follow in the footsteps of these legendary pioneers, our plan is to take up the challenge of developing novel radio wave propagation technology that also incorporates advanced technologies such as deep learning that have not yet been effectively used in the field of radio wave propagation. We hope to announce our results in rapid succession. Finally, we aim to contribute to sustainable development in society through radio wave propagation technology that also relates to the uncovering of frequency bands for new wireless communication systems of the future and to the creation of new use cases for wireless communication systems.