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HAPS – High-altitude platform systems

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Challenges and solutions: building 5G networks for the future

Technological innovations and the growing urgency to expand the availability of broadband has led to the development of HAPS systems. These easily deployable stations operating in the stratosphere (layer of the Earth's atmosphere starting at 20 kilometres) are high enough to provide service to a large area or to augment the capacity of other broadband service providers.

HAPS is not a new concept and ITU studies of HAPS began in the mid-1990s. Nevertheless, HAPS have become more viable due to technological advances in solar panel efficiency, battery energy density, lightweight composite materials, autonomous avionics, and antennas.

Recent test deployments delivering broadband Internet access using stations approximately 20 km above ground have demonstrated their ability to provide connectivity to remote or underserved communities. HAPS trials have been taking place in some countries to demonstrate the potential of HAPS for providing broadband connectivity, backhaul links and disaster recovery communications, as well as the move toward commercial deployments. Nevertheless, HAPS systems face some challenges in becoming a commercially viable option for driving global broadband delivery.

ITU’s contribution

Some ITU-R studies estimated that the total spectrum needs for HAPS systems lie in the range from 396 MHz to 2 969 MHz for the ground-to-HAPS platform links and in the range from 324 MHz to 1 505 MHz for the HAPS-platform-to-ground links. These ranges include the spectrum needed to cover specific applications (e.g. disaster relief missions) and for connectivity applications (e.g. commercial broadband).

In 1997, the first frequency bands authorized for HAPS were globally designated in the Radio Regulations (RR). Since then, the Radio Regulations have been modified to designate additional frequency bands regionally, as well as in specific countries where HAPS may operate. Determining bands for HAPS mainly took into account concerns about rain fade, i.e. loss of signal power in certain frequency bands due to its attenuation through the rain.  These HAPS identifications were established without envisioning that they would need to support today's broadband applications.  

Three world radiocommunication conferences (WRC-97, WRC-2000, and WRC-12) designated spectrum for HAPS in the frequency bands 47/48 GHz, 2 GHz, 27/31 GHz, and 6 GHz respectively. Although the frequency resources for HAPS systems were initially established in the RR some time ago, they were not used due to the above constraints and immaturity of technical solutions. 

Before WRC-19, ITU-R studies on the spectrum needs for HAPS had demonstrated that spectrum requirements for broadband HAPS applications may not have been fully accommodated within bands where use for HAPS had been authorized. In addition, some of those frequency bands where use for HAPS was authorized had geographical limitations.  Additionally, studies suggested that worldwide identifications of frequency bands where HAPS could be authorized would be desirable to improve and harmonize their utilization. 

Therefore, at WRC-19, ITU Member States identified additional radio-frequency bands where HAPS systems could operate under specified technical conditions. 

WRC-19 agreed that the frequency bands 31-31.3 GHz, and 38-39.5 GHz also be identified as being allowed for use by HAPS worldwide. It was also confirmed the bands 47.2 – 47.5 GHz and 47.9 – 48.2 GHz, which were already identified before WRC-19, are available for use worldwide by administrations wishing to implement HAPS. The Conference agreed that the frequency bands 21.4-22 GHz and 24.25-27.5 GHz could be used by HAPS in the fixed service in Region 2.

WRC-19 also agreed to limitations regarding link directions and to the inclusion of technical conditions of operation of HAPS systems for the protection of other services.

By approving the use of spectrum for HAPS, the ITU Membership has enabled one more communication platform to connect the unconnected.

Concerning future HAPS developments, ITU-R is currently conducting studies on sharing and compatibility for the possible identification of bands below 2.7 GHz for HAPS to be used as IMT base stations under WRC-23 agenda item 1.4.


Last update: April 2022​