NTT Docomo Inc. said it has developed a prototype for Japan’s first underground manhole-type base station for mobile phones.

The telecommunications giant will test the new technology around Japan with an eye on putting it into practical use by March 2019 at densely populated locations, such as stadiums, where it is difficult to set up conventional above-ground base stations.

A manhole base station requires about a hole in the ground about 70 square centimeters and 70 cm deep, where antennas and other components can be placed. The manhole cover for the base station is made of resin instead of iron to prevent interference with the transmission.

Crowds walking over the manhole will cause no problems, the company said.

The signal range is about 90 meters, equivalent to a small base station on the ground.

Base stations have usually been mounted on rooftops. However, it has been a challenge to install such stations without spoiling the landscape of popular tourist destinations and scenic spots.