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HAPS – High-altitude platform systems

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Challenges and solutions: building 5G networks for the future

The technological innovations and the growing urgency to expand the availability of broadband led to the development of high-altitude platform station (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 around 1996. Nevertheless, HAPS have become more viable due to the evolution of technology through 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.

Nevertheless, HAPS systems face challenges to becoming a commercially available option to drive global broadband delivery, especially in countries with limited infrastructure.

The current ITU-R studies estimate that the total spectrum needs for HAPS systems is 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 needs to cover specific applications (e.g. disaster relief missions) and for connectivity applications (e.g. commercial broadband).

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.

The ITU-R studies on spectrum needs for HAPS demonstrate that spectrum requirements for broadband HAPS applications may not be fully accommodated within current HAPS identifications. In addition, some of the current HAPS frequency bands have geographical limitations, while common worldwide identifications for HAPS are desirable to improve and harmonize their utilization.

Therefore, additional spectrum is being considered to be identified for HAPS systems, taking into account that HAPS will need to ensure the protection of existing and future services, such as mobile and satellite services.

The revision of the regulatory provisions for HAPS may include global or regional designations for HAPS, limitations regarding link directions, and inclusion of technical conditions of operation of HAPS systems for the protection of other services. Further conditions could be imposed on the operation of HAPS, such as mandatory coordination with potentially affected countries and notification of the stations to ITU.​

ITU’s contribution

In 1997, the first frequency bands where use for HAPS is permissible were globally designated in the Radio Regulations (RR). Since then, the Radio Regulations have been modified to designate additional frequency bands regionally and in specific countries where HAPS may operate. At that time, determining bands for HAPS considered mainly the concerns about rain fade, i.e. loss of signal power due to the rain, in the upper frequency bands.  These HAPS identifications were established without envisioning that they would need to support today's broadband applications.  

Although the frequency resources for HAPS systems were established in the Radio Regulations a long time ago, they were not used due to the above constraints and immaturity of technical solutions. 

More recently, the technological advances that improved HAPS viability and the pressing need to facilitate access to global broadband applications have led to the review of the current regulatory provisions.

HAPS is an item on the agenda of the World Radiocommunication Conference 2019 (WRC-19) taking place in Sharm el-Sheikh, Egypt, from 28 October to 22 November 2019. As a result of the sharing and compatibility studies conducted by ITU-R, the following existing and new frequency bands allocated to the fixed service are being considered for identification for use by HAPS under various regulatory and technical conditions:

The results of ITU-R compatibility studies between HAPS and other applications operating in these bands, and examples of regulatory solutions have been consolidated in the Report of the Conference Preparatory Meeting to WRC-19.

HAPS trials have been taking place in some countries to demonstrate their ability for providing broadband connectivity, backhaul links and for disaster recovery communications. Possible global and regionally harmonized designations for HAPS at WRC-19 may facilitate the development of these applications and allow trials to move towards commercial deployments.

*The band 24.25-27.5 GHz (in Region 2) is also being considered for International Mobile Telecommunication (IMT) identification (IMT-2020/5G) ) and the band 38-39.5 GHz is being considered for both IMT and non-geostationary satellite orbit systems operating in the fixed-satellite service (NGSO FSS)​. Studies have been carried out to address mutual compatibility and sharing feasibility among the applications of the services to which allocation and identification of this spectrum are being considered.

Last update: June 2019 ​