According to Tom's Hardware the June test strapped a six-cell beamforming array to a light aircraft flying at 3,000 metres. The plane linked ground kit to phones with a 26 GHz feeder and a 1.7 GHz service link already supported by most 5G handsets.

Unlike the current crop of low Earth orbit satellite projects, SoftBank is betting on High-Altitude Platform Stations that loiter 20 kilometres up in the stratosphere. The company reckons this cuts latency and avoids many of the Doppler and power headaches that plague orbital connections.

During the trial, the aircraft payload carved six fixed coverage cells on the ground while it looped in circles. The system shifted beams every 60 degrees to mimic what a proper stratospheric platform would do, showing that you can keep coverage steady even as the transmitter moves about.

SoftBank’s radio stack chained a millimetre wave backhaul to the plane and a sub-2 GHz link down to devices, meaning the aircraft behaved like a full-blown base station rather than just a dumb relay. The trial ticked off Doppler correction, automatic power control, and adaptive beam tracking on the to-do list.

Compared with LEO-based satellite-to-phone systems such as AST SpaceMobile’s, which recently showed a 5G call from orbit, SoftBank’s HAPS setup promises lower path loss and better spectrum reuse. Thanks to decisions made at WRC-23, operators can now deploy HAPS in regular terrestrial bands, including 700 MHz, 850 MHz, 1.7 GHz, and 2.5 GHz.

The outfit says this approach could eventually bring coverage to disaster zones, offshore waters, and remote islands. SoftBank is not saying when punters can sign up for service, but the engineering proof-of-concept is now in the bag.