Wi-Wi: Wireless two-Way interferometry
This project aims to develop a new platform for time synchronization with picosecond accuracy, using wireless communication technology that is already in widespread use.
In the age of the "Internet of Things" (IoT), we are headed towards a future where more than a trillion devices and sensors will communicate wirelessly. Against this background, our research started with the question "What if there was a method for highly accurate time synchronization between these wireless devices?" Whether you realize it or not, today's information and communications technology is built around the assumption of mismatched clocks, because agreeing on a time has remained difficult.
We are developing "Wireless two-Way interferometry" (Wi-Wi) as a new technique to synchronize clocks. It is a simplification of the Two-Way Satellite Time and Frequency Transfer (TWSTFT) used for international time transfer. Wi-Wi omits the satellite, and instead applies the same techniques over a direct radio wave connection.
Employing the progress in the development of integrated circuits and crystal oscillators, it is now possible to manufacture a module that can perform time synchronization at the picosecond level for the cost of a normal wireless communication device: A picosecond is 1 in 10¹² parts of a second. As of March 2024, the prototype module of Wi-Wi has achieved time synchronization in approximately 30 ns and phase synchronization (jitter) of about 20 ps. We believe that this level of synchronization will be the key to future improvements of communication infrastructure.
Precise time synchronization also plays an important role in position measurement. In a system like GPS, the positioning accuracy depends on how well the satellite clocks can be synchronized. We are conducting research towards a precision position measurement system that is available even in environments where GPS cannot be used.
References
1) S. Yasuda and N. Shiga, Synergy of Things via Space-Time Synchronization, NICT News 494, 6-7 (2022)
2) Y. Yamasaki et al., Delay-Bounded Wireless Network Based on Precise Time Synchronization Using Wireless Two-Way Interferometry, IEEE Access 9, 85084-85100 (2021)
3) B. Panta, K. Kido, S. Yasuda, Y. Hanado, S. Kawamura, H. Hanado, K. Takizawa, M. Inoue and N. Shiga, Distance Variation Monitoring with Wireless Two-way Interferometry (Wi-Wi), Sens. Mater. 31(7), 2313-2321 (2019)
4) S. Yasuda, R. Ichikawa, Y. Hanado, S. Kawamura, H. Hanado, H. Iwai, K. Namba, Y. Okamoto, K. Fukunaga, T. Iguchi and N. Shiga, Horizontal atmospheric delay measurement using wireless two-way interferometry (Wi-Wi), Radio Science 54, 572-579 (2019)
5) N. Shiga, K. Kido, S. Yasuda, B. Patna, Y. Hanado, S. Kawamura, H. Hanado, K. Takizawa and M. Inoue, Demonstration of wireless two-way interferometry (Wi-Wi), IEICE Communications Express 6(2), 77-82 (2017)
6) N. Shiga and Y. Hashimoto, 新技術説明会資料, Japanese presentation material available at shingi.jst.go.jp/pdf/2016/2016_kisoken1_3.pdf (2016)
7) What is WiWi?, Video playlist available on YouTube