Innovation for a Sustainable Future

Sustainability > Innovation for a Sustainable Future


Communications infrastructure unites the world and keeps our economies running. In the future, communications will be ubiquitous as the air and will provide a lifeline of equal or even greater importance than what we rely on today. New network technology aims to provide the maximum possible service area to extend coverage areas where terrestrial cellular services have not been provided.

NTT is testing a proof of concept that retransmits radio waves from the ground and delivers them to another location – whether from the sky, sea or space. Working with partners, we collaborate to trial a solar-powered High Altitude Platform Station (HAPS) for evaluation of wireless connectivity. The trial tests and demonstrates how transmitting radio waves could lead to stratospheric communications to devices such as smartphones. It also offers a reliable solution for expanding coverage for 5G and 6G networks.

We investigate wireless networks and HAPS connectivity to identify practical applications, develop the necessary technologies, and launch space-based wireless communications.

The collaboration model for developing and testing HAPS technologies will bring commercial connectivity to all users for direct-to-device and backhaul use cases. This proof of concept can bridge the connectivity gap by providing access to remote industries and additional capacity when needed.

Beyond these benefits, preparing for the 5G and 6G coverage expansion will extend communication networks to any location, including air and sea, with non-terrestrial networks also playing a role.

The simulation sees the HAPS fly about 20 km above the earth, alongside NTN technologies that use geostationary-orbit (GEO) satellites and low Earth-orbit (LEO) satellites. The radio wave experiment from the stratosphere was set to this altitude to connect to a receiving antenna on the ground. Tests involved a direct connection between the radio equipment onboard a HAPS flying in the stratosphere and the ground antenna under ever-changing altitudes and day/night variable conditions.

The trial tested the stability of the connection between the HAPS and the ground antenna to see how it was affected by factors such as weather conditions or differences with 2 GHz. In addition, radio propagation tests using 450 MHz were also successfully evaluated up to a distance of 140 kilometres.


The provision of space-based radio access network services using NTN technologies, collectively called Space RAN (radio access network), is expected to support worldwide mobile communications with ultra-wide coverage and improved disaster resistance and enhanced 5G and 6G. In addition, HAPS platforms can also interconnect to the terrestrial network gateway and extend the reach of existing mobile services directly to end-user devices, providing service options including rural, emergency and maritime connectivity.

The research team will create the commercialization of NTN technology for extreme coverage extension that creates new economic and accessibility opportunities.

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