From stratosphere to smartphone NTT DOCOMO trials solar-powered HAPS

15 November 2021 | Melanie Mingas

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NTT DOCOMO has collaborated with Airbus to trial solar-powered Zephyr High Altitude Platform Station (HAPS) for wireless connectivity and, based on the results, will assess the application of HAPS "in 5G evolution and 6G".

The trial – which took place in the United States in August – saw the Zephyr S aircraft transmit radio waves to demonstrate the feasibility of stratospheric communications to devices such as smartphones.

The aircraft completed 18 days of stratospheric flights, transmitting data at various speeds up to a distance of 140km. The trials pave the way for NTT DOCOMO and Airbus to provide communication services to mountainous areas, remote islands, and maritime areas where radio waves are difficult to reach. The test data will be used to inform future LTE direct-to-device services that are expected to be provided via the Airbus Zephyr HAPS solution.

"DOCOMO believes that HAPS will be a promising solution for coverage expansion in 5G evolution and 6G," said Takehiro Nakamura, General Manager of DOCOMO's 6G-IOWN Promotion Department.

"In this measurement experiment, we were able to demonstrate the effectiveness of HAPS, especially for direct communication to smartphones, through long-term propagation measurements using actual HAPS equipment. Based on these results, we would like to further study the practical application of HAPS in 5G evolution and 6G with Airbus."

It isn't just about remote and rural connectivity.

As part of efforts to further advance 5G and prepare for 6G, "coverage expansion" is being studied worldwide, DOCOMO said. This allows the extension of communication networks to any location, including air and sea, with Non-terrestrial network (NTN) technology also playing a role.

Stratospheric HAPS networking will also be implemented for disaster preparedness and "many industrial use cases", for example, in event venues and remotely controlling heavy equipment at construction sites.

Rain or shine

The trial (see image) involved a radio propagation experiment from the stratosphere at an altitude of approximately 20 kilometres to a receiving antenna on the ground. Tests involved a direct connection between the radio equipment on board a Zephyr S HAPS aircraft flying in the stratosphere and the ground antenna under conditions of ever-changing altitude and day/night time.

The trial tested the stability of the connection between the Zephyr S HAPS and the ground antenna and how it was affected by factors such as weather conditions, differences in reception distance, and the flight pattern of the HAPS aircraft. As a result, under three specific scenarios: clear, rainy and cloudy conditions, and in a multitude of flight patterns, data transmissions across various speeds were successfully demonstrated, up to a distance of 140 kilometres.

"Billions of people across the world suffer from poor or no connectivity. These tests show us the viability of the stratosphere to bridge this divide and provide direct to device connectivity via Zephyr without the need for base stations or extra infrastructure," Stephane Ginoux, SVP and head of North Asia region for Airbus and president of Airbus Japan K.K.