ITU-R Adopts Two SoftBank Corp. Recommendations
for HAPS Radiowave Propagation as Global Standards

SoftBank Corp. (President & CEO: Junichi Miyakawa, "SoftBank") announced that two of its recommendations related to radiowave propagation for High Altitude Platform Station (HAPS) stratospheric-based wireless communication systems were adopted as global standards by the International Telecommunication Union Radiocommunication Sector (ITU-R^*1), following meetings held from May to June 2025.

Based on measurement methods and data on radiowave propagation characteristics provided by SoftBank and others to the ITU-R, a new report, Report ITU-R P.2554-0, which summarizes the effects of window glass and other building materials on radiowave penetration, was published by ITU-R in June 2025. Furthermore, SoftBank's "HAPS Radiowave Propagation Prediction Method for Design of Systems"^*2, which is necessary for the design of HAPS-based communication networks, clarified radiowave propagation characteristics on the mobile station side in a high-elevation-angle multipath environment, the environment assumed for HAPS-based networks. These findings were added as part of a revision to the ITU-R's existing Recommendation P.1409-4 and published in September 2025.

Findings on characteristics of radiowave penetration through different building materials (Report ITU-R P.2554-0)

To efficiently design 5G and other types of wireless networks, a highly accurate "Radiowave Propagation Prediction Method" is required. SoftBank has been conducting research focused on radiowave propagation characteristics coming from outdoor sources—such as ground base stations and HAPS—that arrive at indoor mobile stations (such as smartphones). Through this research, SoftBank found that window glass—such as multi-layer glass panes with high levels of thermal insulation found in modern buildings—leads to significant radiowave propagation loss.

To address this issue, SoftBank developed a method for measuring the radiowave propagation characteristics of various types of window glass and provided the measurement data to ITU-R. Based on this, SoftBank proposed the publication of a report that enables the highly precise prediction of radiowave propagation loss caused by indoor penetration. Utilizing this proposal and the measurement results from several other countries, ITU-R published a new report, Report ITU-R P.2554-0, that compiles measurement data showing how building materials affect radiowave propagation. This report includes a variety of measurement data on the effects of building materials, including window glass, wood, drywall and others. As a result, the accuracy of predicting radiowave propagation loss between outdoor and indoor environments will be improved, thereby greatly contributing to network design efficiency in urban environments, and the enhancement of communication service quality across indoor and outdoor areas.

Findings on radiowave propagation characteristics on mobile station side in a high-elevation-angle multipath environment (Recommendation P.1409-4)

To provide HAPS-based communication services, the accurate calculation of radiowave propagation from the stratosphere to the ground in various environments is essential. The HAPS Radiowave Propagation Prediction Method is required to make these calculations, and the method is chiefly comprised of the "HAPS Radiowave Propagation Prediction Method for Frequency Sharing and Compatibility Studies"^*3 and the HAPS Radiowave Propagation Prediction Method for Design of Systems. SoftBank has achieved global standardization for the HAPS Radiowave Propagation Prediction Method for Frequency Sharing and Compatibility Studies, as well as for the HAPS Radiowave Propagation Prediction Method for the Design of Systems, which incorporates a model that estimates factors such as the direction and strength of radiowaves arriving at mobile stations from HAPS.

When a HAPS communicates with a mobile station in urban or suburban environments, radiowave propagation from the HAPS are reflected, diffracted and scattered by buildings, and the mobile station is reached through various paths of different lengths (a multipath environment). SoftBank conducted new radiowave propagation measurements and, by clarifying signal strength characteristics caused by differences in radiowave path lengths reaching mobile stations in high-elevation-angle multipath environments, such as those expected with HAPS, submitted recommendations to the ITU-R. These recommendations were added as part of a revision to the existing HAPS Radiowave Propagation Prediction Method for Design of Systems and published in ITU-R's Recommendation P.1409-4. As a result, all radiowave propagation characteristics of the signals transmitted from the HAPS to the mobile station have been fully clarified, making it possible to achieve global standardization.
In the future, these models will be applied for efficient network and antenna design for HAPS networks that use 5G and other types of wireless communications. In addition, it will also become possible to estimate multipath environments in urban and suburban areas by factoring in the "Human Shielding Loss Model," which is part of the HAPS Radiowave Propagation Prediction Method for Design of Systems.

SoftBank will utilize these results to optimize network design and improve communication quality for 5G and other wireless networks, while also promoting the commercial implementation of non-terrestrial networks (NTN)—including HAPS and satellite-based communications—to provide stable communication environments to people around the world.

[Notes]

1. *1
   ITU-R is the radiocommunication sector of the International Telecommunications Union (ITU), a United Nations agency. ITU-R coordinates radiocommunication global standard and global spectrum management. ITU-R has various Study Groups (SGs) that make Recommendations.
2. *2
   "HAPS Radiowave Propagation Prediction Method for Design of Systems" is a prediction method necessary for HAPS operators when they study HAPS platform deployment numbers and locations, antenna design and other details when designing HAPS-base
3. *3
   "HAPS Radiowave Propagation Prediction Method for Frequency Sharing and Compatibility Studies" is an essential prediction method for regulating interference to neighboring countries and adjusting frequencies between other wireless communication systems.
4. *4
   For more details, please refer to the press release dated October 27, 2021, titled "SoftBank Corp. and HAPSMobile Contribute to ITU-R's 'HAPS Radiowave Propagation Prediction Method' Global Standard".
5. *5
   For more details, please refer to the press release dated October 26, 2023, titled "SoftBank Corp.'s 'HAPS Radiowave Propagation Prediction Method for Design of Systems' Adopted as Global Standard by ITU-R".

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