In the 1990s and 2000s, several projects were launched to explore the potential application of high-altitude platforms (HAPs) for telecommunication and remote sensing. The US, Japan and South Korea took the lead with several projects.
HAPs are commonly deployed in the stratospheric layer, far higher than the altitude at which commercial aircraft operate, and are capable of covering large surface areas and can be used for maritime and land-based applications such as communication systems, persistent surveillance, and navigation. HAPs can also be used for aerial imaging, environmental monitoring, and internet services. HAPs are often referred to as alternatives to satellite systems due to their capacity for fulfilling similar purposes. A major application for Africa is providing low latency broadband internet access in rural areas.
The stratosphere is the second major layer of Earth’s atmosphere, just above the troposphere and below the mesosphere, and is not subject to the varying weather conditions of the troposphere. HAPs may be aircraft, airships, balloons or even drones.
Remarkably, the ITU at the World Radio Conference in 1997 (WRC97) discussed the concept and even identified possible frequencies for HAPs located at an altitude of between 20 and 50 km. The concept has gone through various names but ultimately HAPs was standardised on.
The first stratospheric flights were undertaken in the 1930s in balloons with pressurise gondolas by Swiss pioneer Auguste Piccard. In the 1950s and 1960s, aircraft with jet propulsion flew in the stratosphere. Nothing much more happened until 2011 when tests were started again using a weather balloon and basic, off-the-shelf radio parts – the first prototype. The next two years were a process of rapid iteration to prove that balloon-powered internet might just work.
On 15 May 2015, Google provided background on the recommendation from the Federal Communications Commission’s WRC advisory committee to the US WRC delegation that the US proposed to study broadband delivered from high-altitude stations. Google and others in the US had been investing unmanned aerial systems (UAS), including for the delivery of broadband communications to underserved communities, and for disaster relief.
While tests of unmanned aircraft at high altitudes for broadband internet service are recent, high-altitude base stations have been studied by the ITU for about two decades. High-altitude platform stations (HAPS) are defined in Article 1.66A of the Radio Regulations as a “ station located on an object at an altitude of 20 to 50 km and at a specified, nominal, fixed point relative to the Earth”.
Google is developing unmanned aircraft that will circle for months to maintain coverage of a constant service area on the ground. Such nominally fixed aircraft, which could be considered HAPS, are one promising model for delivery of broadband.
Google has made several announcements about successful HAPs projects under the Loon name. Currently most have been for disaster relief. Collaborating with the Federal Communications Commission, the Federal Aviation Authority, FEMA, AT&T, T-Mobile, and many others, Project Loon provided basic connectivity to 200 000 people in Puerto Rico after Hurricane Maria. Project Loon launched balloons from Nevada, using machine learning algorithms to direct them over Puerto Rico. Recently, a project in Brazil was able to deliver LTE type connectivity. Loon is part of Google Alphabet, which focuses on the extraordinary (sometimes seen as crazy) ideas that reside inside Google.
With demand for broadband continuing to grow, the identifications for HAPS, now limited, may need to be expanded geographically and spectrally, in order to allow lightweight, nominally fixed-position UAS to deliver broadband at current generation speeds. Global identifications facilitating the delivery of broadband via HAPS would provide the economies of scale necessary to make this technology affordable in underserved areas, especially those with terrain features that make it challenging to deploy services and those that have suffered disasters.
South Africa has an interest in HAPs as was shown in the recent WRC19 Industry Preparatory Group meeting. WRC19 agenda item 1.14 deals with the frequency spectrum for HAPS. Participants agreed that HAPS is a technology that South Africa should consider in meeting its broadband-for-all targets.
Whether the technology is ready for widespread deployment is still an open question. There are many technologies that can be deployed to keep a platform in a stable position, but the important issue is establishing how to produce enough energy from solar panels and store it efficiently for night time position maintenance and continued service delivery.
Using large balloons as demonstrated by Loon is not an option. Currently, the Loon balloons stay up for around 100 days before being replaced. This does not seem an economic solution to provide broadband in difficult to reach rural areas which are also sparsely populated. For now, it seems satellites with several ground stations feeding mesh terrestrial networks are the solution, however HAPs development is continuing.