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ETH - Eidgenoessische Technische Hochschule Zuerich - Swiss Federal Institute of Technology Zurich
Section: Science Life
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Published: 06.07.2006, 06:00
Modified: 05.07.2006, 22:05
The StratXX Project
Flying mobile phone antenna

Kamal Alavi is a dynamic individual with a resourceful mind. He is now the head of the one-man company StratXX Holding AG and has come up with a new idea that could entirely revolutionise the transmission of digital data, mobile phone telephony or even GPS applications.

Peter Rüegg

Alavi wants to build special balloons that will ascend into the stratosphere to a height of 20 kilometres. A small unmanned aircraft essentially containing a mobile phone antenna is attached to the mother ship. By using an ingenious control system the balloon maintains a geostationary position, i.e. it always remains above the same point on the Earth’s surface. Solar cells on the airship’s surface supply energy to the airship and antenna.

Launching these balloons doesn’t need Baikonur or Cape Canaveral either. They can take off from anywhere. They are filled with the inert gas helium, which is lighter than air. The former aerospace engineer says it is possible to calculate exactly how much helium is needed to bring the airship to the required height.

Repairs on the ground thanks to the unmanned aircraft

If the equipment on board becomes faulty, the small unmanned aircraft can be uncoupled. Like a miniature Space Shuttle it returns to earth where repairs can be carried out. The balloons are designed for a useful lifetime of five years. “The technology will be obsolete by then anyway,” is Alavi’s justification for their rather short lifetime.

This mobile phone antenna in the stratosphere could virtually replace the whole forest of mobile phone antennas on the ground, and according to Carmen Kobe of the Center for Product Development of ETH Zurich it solves the problem of the ‘last mile’ (the local loop, the final link to the user’s equipment). This is expensive to lease and in most cases the bandwidth is insufficient. In fact it is scarcely any longer feasible to erect more mobile phone antennas.

1000 times less radiation

Kamal Alavi adds that there is another advantage: “Transmitting on the Earth’s surface causes high radiation levels because of the need to penetrate through countless buildings.” From above there is a line-of-sight link to every point, and transmission takes place mainly through the air. He says that “This enables the radiation to be reduced by a factor of 1000.” The flying antenna for modern broadband applications would replace “ground-based” antennas. Thanks to what are known as spotbeam antennas developed by EPF Lausanne, the beams can be matched to the demand. The radiation is correspondingly low in areas were there is little traffic via the mobile phone network or where only small amounts of data are being transmitted.

IEEE engineers have developed a new mobile phone protocol known as WiMAX (Worldwide Interoperability for Microwave Access) for mobile phone use across such large distances. This enables transmission over a radius of 30 kilometres. In addition its bandwidth is enormous. A Laptop equipped with WiMAX can receive and send 40 megabits per second. Furthermore, each of the spotbeam antenna’s spots transmits up to eight gigabits per second. This would make mobile phone bottlenecks such as New Year’s Eve, when millions of SMS greetings bring the mobile phone network to the point of collapse, a thing of the past.

More economical than a forest of antennas

Kamal, who was born in Iran, says that “The technology is not only good, it’s economical as well.” A stratosphere balloon costs 30 to 40 million Swiss francs. As a comparison: a single mobile phone antenna sets the operator back 300,000 Swiss francs and a satellite 600 million.


A double-skinned balloon holds a small unmanned aircraft in a geostationary position at a height of 20 kilometres. The mobile phone antennas are housed in the aircraft. large

Switzerland needs about 1000 antennas for full mobile phone coverage of the country. A single balloon station would be enough to supply Switzerland with mobile phones, digital TV and radio and the Internet. In addition satellites can only be brought into their orbit by using rockets, their maintenance is expensive and once they have been shot into space they cannot be brought back to the ground again. They burn up on re-entering the atmosphere. They also have technical limits. For example broadband technology would be totally impossible via a satellite. This is why the Swiss Federal Office for Communications (Bakom) is interested in the StratXX project and has assured its support.

Pressure balancing ensures a stable position

The greatest challenge is to hold the airship in a stable position. Strong winds blow in the stratosphere in winter and could carry the balloon away. The sun also heats the gas up during the day. The helium expands and the airship rises. On the other hand it descends at night because the gas contracts again. Alavi has now found a way to manage the pressure balancing so as to maintain the balloon’s height and position. The system has already been patented worldwide. “This is another challenge in the project, namely to bring the airship onto the market as soon as possible. A patent expires after 20 years,” says the inventor.

Alavi’s idea has also convinced partners at the institutes and in industry. At ETH Zurich the Center for Product Development as well as three other institutes from the Department for Mechanical Engineering are collaborating with him. He can also count on support from the EPF Lausanne, EMPA and the University of Neuenburg. RUAG Aerospace, the former federal armaments company, is also involved in the planning.

First test in July 2007

The engineers are now testing the individual components step by step. The solar cells were tested at a height of 30 kilometres in mid-May. The plan is for a balloon to ascend into the stratosphere for the first time on the first of August this year. The first test with a complete system is to take place in July 2007. Alavi and Kobe see this project as an opportunity for Switzerland. They say it offers the possibility of bringing research and industry together and of manufacturing a new high-tech product in Switzerland. Competition is threatening from the USA and Japan. However StratXX is based on a different concept. Alavi emphasizes that “It’s a race, a real challenge. If we succeed, we’ve won.”

Web site of StratXX:

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