Spectrum for stratosphere-based communications is extended

At the close of 2023, as a result of agreements made during the World Radio Conference 2023 (WRC-23) held in December in Dubai, the expansion of the use of spectrum associated with High Altitude Platform Stations (HAPS) for wireless communication systems based in the stratosphere was established.

Unlike satellites, HAPS systems are unmanned aerial artifacts that fly or float in the stratosphere, usually at altitudes of around 20 km. They can be balloons, airships or fixed-wing aircraft that use solar energy or an on-board power source. HAPS solution providers can be strong competitors to broadband providers using satellite technologies. The GSMA table below shows the application characteristics of satellite and HAPS communication technologies in terms of deployment and operational complexity, overall system capacity and latency performance.

HAPS is considered an alternative to complement terrestrial connectivity, providing fixed broadband connectivity resources as well as transmission links between mobile networks and backhaul. In both cases, HAPS applications can be made to serve remote areas, including mountainous, coastal and desert regions.

Mobile communication via HAPS platforms has been discussed for decades, with recent advances in both technological and regulatory terms. Technological innovations have emerged in the areas of antennas, solar panels and high-density batteries. In regulatory terms, a further step was taken during the recent WRC-23. Three mobile spectrum bands were added – 700-900 MHz, 1.7 GHz and 2.5 GHz. As a result of the deliberations at WRC-23, operators in different countries and regions will be able to choose spectrum more flexibly when introducing HAPS-based mobile broadband communication services.

According to previous regulations stipulated by the ITU-R, it was possible to operate HAPS mobile base stations using the 2 GHz mobile spectrum band, but the use of other frequencies (700-900 MHz, 1.7 GHz and 2.5 GHz) was prohibited.

In Japan

On Japanese soil, or rather in Japanese air, a major investor in HAPS technology is Softbank. The Japanese investment holding began work on an unmanned aircraft system project for HAPS in April 2017 and founded HAPSMobile in the same year. After a period of just over three years, in September 2020, the Sunglider aircraft, the result of the efforts, reached the stratosphere during a test flight, and a test of internet connectivity was successfully carried out.

Three more years later, in September 2023, a new field test was successfully conducted using a 5G-ready HAPS cylindrical antenna on the aircraft, also developed by SoftBank. The test successfully verified the optimization technology that maximizes communication capacity throughout the area covered by HAPS. The test was carried out perfectly at a maximum altitude of 16.9 km under challenging atmospheric conditions, according to Softbank, making a video call between a 5G smartphone in Rwanda and members of the SoftBank team in Japan.

Representing Japan, SoftBank led the discussions at WRC-23 to add bands to the HAPS spectrum as an international standard, paving the way for the technology to be implemented worldwide in a standardized way.

Meanwhile, on the other hand, SpaceHYPERLINK Compass, a joint venture between Japanese telecommunications company NTT and satellite broadcaster Sky Perfect JSAT, intends to offer commercial HAPS services to isolated islands and similar areas in the fiscal year starting in April 2025. More details about the project will be presented at the Docomo Open House ’24, which will be held in Tokyo from January 17, 2024.