SoftBank Corp. (“SoftBank”) and its subsidiary HAPSMobile Inc. (“HAPSMobile”) developed a new global model that can estimate radio wave interference at high altitudes and enable the design of network area coverage for High Altitude Platform Station (HAPS) stratospheric-based wireless communication systems. The new model was added as a part of a revision to the International Telecommunication Union Radiocommunication Sector (ITU-R*1)’s “HAPS Radiowave Propagation Prediction Method” and published in Recommendation ITU-R P.1409-2*2. After deliberations in Japan, the method was submitted to ITU-R as a Japanese proposal, and in collaboration with other countries, was made a part of the global standard. In preparation for a HAPS business launch, SoftBank and HAPSMobile have been conducting global standard activities related to HAPS radio wave propagation models. The global standardization of the new model developed by SoftBank and HAPSMobile that was revised and added to the “HAPS Radiowave Propagation Prediction Method” represents a major contribution to operators around the world aiming to deploy HAPS services.
To operate HAPS-based networks as communications infrastructure, the accurate calculation of radio wave 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” and the “HAPS Radiowave Propagation Prediction Method for Design of Systems” (Figure 1). These methods need to factor in radiowave propagation loss caused by environmental factors, including atmospheric attenuation (such as gaseous absorption and rain attenuation), diffraction due to terrain, vegetation loss, building entry loss, clutter loss due to building shielding, and human shielding loss (Figure 2). The “HAPS Radiowave Propagation Prediction Method for Frequency Sharing and Compatibility Studies” is essential for regulating interference to neighboring countries and adjusting frequencies between other wireless communication systems. Radiowave interference can decrease communication speeds and the quality of various wireless communications systems based on the ground, in the sky and in space, making it difficult for existing operators to provide stable connectivity. Operators therefore need to accurately calculate interference levels that could impact other wireless communication systems with a common standard. To study the Agenda Item for ITU-R’s World Radiocommunication Conference 2023 (WRC-23), it was required that “HAPS Radiowave Propagation Prediction Method for Frequency Sharing and Compatibility Studies” be completed by 2021. Furthermore, the “HAPS Radiowave Propagation Prediction Method for Design of Systems” is an important prediction method that can be used for conducting detailed studies on the number of required HAPS and where they should be deployed when designing network coverage for HAPS wireless communication systems.
The previous “HAPS Radiowave Propagation Prediction Method for Frequency Sharing and Compatibility Studies” calculated radiowave propagation loss for only some environments, including atmospheric attenuation (such as gaseous absorption and rain attenuation) and diffraction due to terrain. SoftBank and HAPSMobile, in cooperation with ITU-R participants from other countries, organized calculation methods for these respective environments and clarified application methods. Also, in addition to radiowave propagation loss for atmospheric attenuation (such as gaseous absorption and rain attenuation) and diffraction due to terrain, SoftBank and HAPSMobile proposed the addition of factors for vegetation loss, building entry loss, clutter loss due to building shielding, and other radiowave propagation losses that are caused by environmental factors to the ITU-R’s “HAPS Radiowave Propagation Prediction Method for Frequency Sharing and Compatibility Studies” for application as necessary. As a result, this proposal was added as a part of a revision to the “HAPS Radiowave Propagation Prediction Method” and published in Recommendation ITU-R P.1409-2 to be used for the study of the WRC-23 Agenda Item.
Furthermore, with the revision of the “HAPS Radiowave Propagation Method,” SoftBank and HAPSMobile developed and proposed new models that factor in the various radiowave propagation loss characteristics of different environments that comprise the “HAPS Radiowave Propagation Method,” and some of these models were adopted as global standards (Figure 3).
Specifically, for the “Vegetation loss model,” Japan and Kenya were added as application vegetation environments, and a model that calculates radiowave propagation loss while factoring in seasonal changes was developed and proposed. The model was added to a part of a revision to “Vegetation attenuation” and published in Recommendation ITU-R P.833-10*3. Furthermore, a new “Human shielding loss model” that factors in surrounding building environments and corresponds to radiowaves coming from various angles was developed and proposed, and was added as a part of a revision to the “HAPS Radiowave Propagation Prediction Method for System Design” in Recommendation ITU-R P.1409-2. For the “Building entry loss model,” radiowave propagation measurements were made to ascertain important parameters used to calculate attenuation when radiowaves enter a building, and this was added as a revision to “Compilation of measurement data relating to building entry loss” and published in Report ITU-R P.2346-4*4. Furthermore, SoftBank and HAPSMobile developed and proposed a “Clutter loss model”, and calculation methods were included in ITU-R’s Liaison statement*5 and a notification was issued to related Working Parties*6. These radiowave propagation loss models developed by SoftBank and HAPSMobile could also potentially be applied to other wireless communication services. SoftBank and HAPSMobile contributed to a global standard that took certain environmental characteristics (vegetation loss, human shield loss) into consideration for the “HAPS Radiowave Propagation Prediction Method for Design of Systems.”
Thanks to these global standard achievements, operators around the world looking to offer commercial HAPS services will be able to apply these radiowave propagation prediction methods. As a result, they will be able to study frequency sharing and coexistence with existing wireless communication systems and effectively design HAPS-based wireless communication systems while taking radiowave interference and other factors into account. In preparation for commercial HAPS services, SoftBank and HAPSMobile will continue to promote global standard activities for HAPS and engage regulatory authorities in various countries to help foster a HAPS ecosystem.
Contributing to the Sustainable Development Goals (SDGs) is a top managerial priority for SoftBank, and the company has identified six key initiatives (materiality) to achieve them. “Building high-quality social communication networks” is one such initiative. With the aim of providing communication networks around the globe, SoftBank is promoting the deployment of Non-Terrestrial Network (NTN) solutions. SoftBank’s NTN solutions will encompass the stratospheric telecommunication platforms of HAPSMobile, the Low Earth Orbit (LEO) satellite communication services of OneWeb and the Geosynchronous Earth Orbiting (GEO) satellite NarrowBand IoT (NB-IoT) services of Skylo.
To bridge the digital divide and realize a society where everyone is connected, SoftBank and HAPSMobile will continue advance HAPS business preparations.
*1ITU-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.*2The 2012 “HAPS Radiowave Propagation Prediction Method” global standard was added to and revised, and published in October 2021 as Recommendation ITU-R P.1409-2.*3Added to and revised, and published in October 2021 as Recommendation ITU-R P.833-10.*4Added to and revised, and published in July 2021 as Report ITU-R P.2346-6.*5A Liaison statement is a document used within the ITU for information exchange with other organizations and standardization bodies. SoftBank’s proposed clutter loss model was included in Statement 5D/723: “Reply liaison statement to Working Party 5D (copy to Working Parties 4A, 4C, 5A, 5B, 5C, 6A, 7B, 7C and 7D for information) – WRC-23 agenda item 1.4 – Propagation information requested from Working Party 5D.” The estimation method was issued as a method to be referred to by other WPs (Working Parties) for the study of interference in HAPS and other wireless communication services.*6Working Parties are organizations under Study Groups that make Recommendations or Reports.
