Softbank completes nullforming trial for HAPS spectrum sharing

04 July 2024

In April 2024, Softbank successfully conducted a field trial using its cylindrical antenna for High Altitude Platform Station (HAPS) stratospheric-based wireless communication systems at Hokkaido Spaceport, Taiki Town, in Hokkaido, Japan.

The trial successfully demonstrated the use of nullforming technology to achieve spectrum sharing between HAPS and a terrestrial base station.

The field trial was conducted as part of Softbank’s R&D initiatives to enhance communication technologies used with HAPS. The company is conducting R&D on spectrum sharing to enable the deployment of communication services that use the same frequency for both HAPS and terrestrial base stations.

To effectively use finite spectrum resources, SoftBank is considering the use of cylindrical antennas as antennas for ‘service links,’ which handle data transmission and reception between HAPS and communication devices. The company is also developing nullforming technology, which significantly suppresses radiowave emissions in specified directions to reduce interference. By preventing interference, it is possible to achieve spectrum sharing between HAPS and terrestrial base stations, thereby utilising the spectrum effectively.

In the field trial, SoftBank placed a terrestrial base station within the communication area of a high-altitude tethered aerostat equipped with a cylindrical antenna (airborne base station). Mobile Device A was placed within the communication area of the airborne base station while Mobile Device B was positioned in a geographically close location within the communication area of the terrestrial base station. The same frequency was used for both the airborne base station and the terrestrial base station, and the communication speeds of Mobile Device A and Mobile Device B were measured based on whether nullforming technology was applied.

Through this field trial, it was observed that the application of nullforming technology improved the communication speeds of Mobile Device B without significantly degrading the communication speed of Mobile Device A. Furthermore, by applying nullforming technology, interference between both base stations was reduced, confirming that Mobile Device B achieved communication speeds equal to those in an environment without radio interference when the radiowaves from the airborne base station were halted to prevent interference.

According to the company, the field trial confirmed the feasibility and effectiveness of spectrum sharing between airborne base stations and terrestrial base stations using nullforming technology in actual outdoor environments.