It's a Bird! It's a Plane! It's ... a HAP?
By Dave Mock, Mon Oct 22 00:00:00 GMT 2001

High-Altitude Platform Systems (HAPS) - global communications revolution or pie in the sky?

In the 1990s, a new era of communications was being shopped around the financial markets of the world. Visionaries were stating that Low Earth Orbit (LEO) satellites by the hundreds would fill the free space above the earth, providing fixed and mobile communications to the masses, regardless of locale or economic class. Whether you were a busy professional hopping the globe or a remote farmer secluded in the Andes, a satellite link would open you to the world in real-time.

Many believed that the new LEO systems would be more cost-effective than GEO satellites, which are much farther out in space and suffer many physical limitations to providing broadband services. Some were even bold enough to predict the rapid demise of terrestrial communications systems, especially the costly and obtrusive cellular networks. As envisioned, the only essential terrestrial components would be a relatively few, strategically located backhaul links.

A mere 5 years has changed the picture substantially. With the bankruptcy of Iridium and financial struggles of Globalstar and others, the industry has taken a hard second look at the feasibility - both economically and technically - of such ambitious undertakings. While many are still plugging away to make LEO satellite systems a pervasive medium, a fraction of this group have been quietly working on an alternate path - stratospheric platforms.

It's all in your latitude

High-Altitude Platform Systems (HAPS) basically act more like an 11-mile high wireless base station than an orbiting satellite. The payload that provides communication functions resides onboard either an airplane or airship (blimp-like balloon) hovering around an altitude of 17 to 22 km. By comparison, LEO satellites orbit in space at altitudes around 800 km to 1400 km, some 40-80 times farther out from the earth.

At this height in the atmosphere, stratospheric platforms are above commercial air traffic and in a climatic "sweet spot" where violent air currents are less common. The platform can be manned by pilots, self-guided or controlled remotely. Their task is to remain stationary while providing broadband radio communications to a large area on the ground.

The platform may either circle in a tight loop or hover in place (in the case of an airship) while the payload of communications gear and antenna arrays maintain radio links with subscriber units and backhaul gateways on the ground. Depending upon the altitude and antenna system, some platforms claim to provide coverage over an area from 40 to 400 miles in diameter, supporting hundreds of thousands of simultaneous phone calls or equivalent T1 data lines.

It would take hundreds of well-placed terrestrial towers or thousands of miles of buried fiber to provide similar coverage and capacity.

The best of both worlds

While HAPS may share some of the same functions as satellites, they don't necessarily have the same goals. Because stratospheric platforms operate much closer to the earth, they are more ideally suited for broadband applications in focused areas. This leads to economic benefits that some think will help HAPS succeed where satellites fail.

"Compared to satellites, we would not compete, but complement their deployment by addressing the 'hot spot problem'" says Marc Arnold, CEO of Angel Technologies, a company that's approaching deployment of a HAP using piloted aircraft. "They [satellites] can not deliver sufficient tele-density to adequately meet concentrated demand."

With capacity for voice and data services that is thousands of times higher than LEO satellites, HAPS are ideally suited to provide economical high-bandwidth services in concentrated areas. "They [satellites] will do a great job serving remote subscribers in sparsely populated areas. We do a great job for the top 200 cities which encompass 35% of the world's GDP", adds Arnold.

This is why most HAPS providers see broadband data services as their ideal market. For a vast majority of businesses, the cost of installing a high-capacity feed via fiber or T1 lines is beyond reason. HAPS could economically provide the necessary bandwidth to businesses and residential customers who have no easy access to a fiber point, DSL line, or cable connection.

HAPS for mobile 3G

While mobile wireless services may not be the primary market for HAPS, the skyrocketing costs of realizing terrestrial 3G networks is making the case of deploying HAPS in this market much more compelling. Most platform vehicles can provide either fixed broadband or mobile services simply with a different payload.

The ITU has already set aside large swaths of spectrum for HAPS telecommunications, reserving 2x300MHz of bandwidth around 48GHz for fixed applications. In addition to this primary allocation, some other bands are used in different regions as well, such as 28GHz in Japan and the United States.

The ITU has also approved HAPS as a delivery vehicle for IMT-2000 services in the specified mobile bands. Depending upon the application, cellular service providers could employ HAPS to complement, augment or even launch (literally) new services.

Many of the payloads being built into platforms are set up to mimic the cellular structure of mobile networks through sophisticated antenna design. This allows them to reap the capacity benefits of frequency reuse while avoiding the pains of locating and erecting vast arrays of towers.

This ability to practically eliminate the need for terrestrial towers and wired infrastructure is probably the strongest selling point for HAPS. Most systems require only a few land-based gateways for each platform, so the cost for siting and maintenance is only a fraction of what a full terrestrial system would run. With operators already indebted for more than $100 billion just for 3G licenses, a more cost-effective means of deploying a network is guaranteed to get more attention.

"The capital cost to deploy a single SkyTower station over a city, covering a region ranging from 40 to 400+ miles in diameter, is projected to be approximately $20 million, including both operating and backup aircraft/network systems" says Stuart Hindle, Vice President of Strategy and Business Development for SkyTower Inc.

With estimates showing that about half-dozen platforms would cover the entirety of a country like the United Kingdom, a nationwide 3G network could theoretically be deployed for a little over $100 million. Compare that to the billions projected by operators to get decent but spotty coverage in most populated regions and you begin to see why HAPS have captivated operators.

To sweeten the pot though, HAPS have some other strong attributes. The ability to launch a network within days rather than months offers keen advantages as well. New markets could theoretically "go live" within days from licensing spectrum from the government. No more long waits to recoup investment.

From the labs to the skies

Even with all the promise of HAPS, there's still a lot of work ahead and some are cautious about their eventual use. The operational plans for various platforms are under scrutiny for their safety and reliability from regulatory agencies. While the concept is great when all goes as planned, they want to make sure systems are developed to operate safely even when everything goes wrong.

The different types of platforms - airplane or airship - and different modes of operation - manned, self-guided or remote control - all approach safety and reliability issues differently. They also demonstrate different levels of economic feasibility for services. There are trade offs at each level, so no single business model for HAPS has a clear lead. Here are some of the major projects underway around the world:

  • SkyNet - One of the larger airship programs, SkyNet has been underway in Japan since 1998. Like many of the other projects engaged in HAPS research, it is funded primarily by the local government and assisted through a number of research organizations. Their expectations are to realize a commercial broadband platform around 2005.

  • Platforms Wireless - A publicly traded corporation, their Airborne Relay Communications (ARC) system has received substantial press during recent trials in the U.S. and Brazil. Their HAPS solution involves a tethered airship that is anchored by a 15,000-foot cable. The system aims to deliver a range of cellular services to over 125 000 subscribers in Brazil with operator Americel if testing continues to show good results.

  • SkyTower - Based in the United States, SkyTower is testing a high altitude, solar powered aircraft to deliver communications services. They are teamed with AeroVironment, the designers of the Helios solar plane. Helios recently set a world record for altitude and has shown a lot of promise for an unmanned communications platform. Development of efficient fuel cells to keep Helios flying longer and receiving FAA certification of the aircraft are a few of the remaining hurdles. They hope to be able to launch commercial services within the next 2 to 3 years.

  • HeliNet - This project also includes a solar-powered craft called HeliPlat. Funded by the European Commission, a team at the University of York is leading the research in broadband communications applications with HAPS. In addition to communications, HeliNet is looking at commercial possibilities in environmental monitoring and vehicle localization as well.

  • HALO - Angel Technologies is the most likely candidate to deploy a HAP for communications in the near future. Their HALO Network is based upon a manned aircraft with pilots operating on 8-hour shifts, making it a much lower risk than other concepts. The HALO-Proteus aircraft have been flying since 1998, so they have a well-proven platform that has been tested extensively.

  • Challenges ahead

    Obviously, some doubt about HAPS' commercial viability exists. Otherwise the various projects would be commanding billions of dollars of funding as LEO projects did in the early 1990s. Still reeling from the consequences of poor LEO network business models, many in the industry are taking a wait and see approach to commercial HAPS. But some contrast is now emerging between the economic models for various solutions.

    "Our studies over the years, both internally and externally funded, continue to point to an unmanned, solar-electric aircraft as being the most economically and technically viable aerial platform for providing telecom services" says SkyTower's Hindle.

    But others note it is important to factor in risk and time to market as well. "We believe piloted aircraft represent the most business-like approach and entails more manageable risks for the foreseeable future" says Arnold of Angel Technologies. "Using conventional technology, Angel believes the business model can be proven and deployed long before more novel solutions are fully developed", he adds.

    But whether HAPS solutions take a less risky, conventional route or more advanced, novel path, the mobile wireless industry will be watching closely. With the specter of 3G infrastructure buildout looming in the coming years, HAPS could fit the bill.

    One thing is for sure though, getting investors to back another pie in the sky venture - no matter how compelling - is bound to be a little tougher this time around.

    Dave Mock is a freelance writer covering mobile technologies and markets. He's published papers to educate investors in wireless markets that are available through and He also speaks at seminars and provides training to corporate clients. His first hardcover book on investing in wireless will be published with McGraw-Hill in Spring 2002.