TOKYO -- SoftBank and Google are joining forces to set up an airborne wireless base station 20 km above ground, in a move that promises to expand high-speed mobile access in remote areas.

The base station would be launched into the stratosphere aboard an unmanned aircraft, and would be compatible with 5G services.

Group companies on both sides are to forge a capital tie-up for the project. The involvement of two of the tech world's biggest names is expected to promote the spread of the new technology.

At the heart of the plan is a device known as a high-altitude pseudo-satellite, or HAPS. SoftBank unit HAPSMobile, which deals in the technology, is to enter into the tie-up with Loon, a subsidiary of Google parent Alphabet.

Loon was born out of Google X, an Alphabet division tasked with conducting advanced research and development.

The two units are in talks to take stakes in each other. For starters, HAPSMobile is expected to invest about 10 billion yen ($89.4 million) in Loon.

HAPSMobile is currently developing an unmanned aircraft driven by solar power. The craft is expected to measure about 80 meters long and cost several hundred million yen.

The players aim to commercialize it early in the 2020s.

The stratosphere is the ideal place to put an airborne base station, since there is little wind. The aircraft would stay within a specified zone for months, allowing the base station to cover an area with a diameter of 200 km on the ground.