The company said it will use helium-filled blimps that dangle antennas about 100 meters above the ground and provide mobile coverage over a radius of roughly three kilometers in a suburban landscape. Softbank will carry out trials through June of next year to test factors such as the coverage area, data speed and voice quality.

The blimps are equipped with two types of antennas, one to link up with users' cell phones and the other to exchange signals with a truck that carries a portable cell tower and is physically plugged into the company network. The trucks can be over five kilometers away from the blimps if line-of-sight is maintained.

Mobile coverage often goes down during earthquakes and other natural disasters, which cut power and damage fixed cell towers. Portions of Japan's northeast coast were without service for weeks and months after the magnitude 9 earthquake and resulting tsunami that hit last year. DoCoMo, Japan's largest carrier, has invested in a network of large cell towers with long range and smaller truck-based towers to provide emergency coverage.

Softbank developed the blimps together with Hokkaido University. They can be constructed in various sizes but all have the same, flattened-out shape, with their height about 60 percent of their diameter.

The blimps are kept steady with guide wires, and powered via a line that is just 1.3 millimeters and teflon coated to avoid wind effects. They use an onboard fan to keep the inner pressure stable and avoid instability as the outside temperature changes.