In one of the most ambitious telecommunications projects of recent years, Motorola Inc hopes to build a unique satellite-based cellular network that will enable mobile phone users to communicate anywhere in the most remote, unpopulated parts of the world – Motorola puts the cost of the six-year project at a bare minimum of $2,000m, and is already looking for partners to help it in the venture, which faces an array of financial and regulatory obstacles. The technical side of the operation seems to be the area in which Motorola will encounter least problems – no new technology is being used, instead assistant general manager of satellite communications Bary Bertiger says it is more a matter of using existing technologies as building blocks in a different way.
77 satellites
The so-called Iridium network will be composed of 77 700lb satellites orbiting at a height of 413 nautical miles; they will be arranged into seven circular orbits, with 11 satellites in each plane, and each satellite will project 37 cells on the world’s surface; unlike conventional cellular telephony, these cells will span roughly 350 miles. Calls are then switched and routed from satellite to satellite to provide instant 2,400bps digital links for both voice and data; the low altitude of the satellites – normal geosynchronous satellites orbit at a height of 22,300 miles – is intended to make for much improved connections. With Iridium, the caller’s handset sends a microwave signal carrying a phone number and serial number to a satellite overhead; this information is then sent via a second satellite to a base station in the caller’s home country, which then checks that the call is authorised. If the call is allowed, the base station sends the message back to the second satellite, which then switches the call to a satellite over the country to which the call has been sent; finally, the third satellite relays the signal either directly to the handset of another Iridium user or into the public switched network through another base station – thus, if the service takes off, it will be theoretically possible to make a mobile call from anywhere, to anywhere in the world. But Dave Bartram, senior vice-president of Motorola Europe, stressed that Iridium was not putting itself forward as a competitor to conventional land-based cellular telephony or even the proposed Personal Communications Network: its use is likely to be limited to parts of the world that are not covered by any of these systems, and it is aimed at users such as government officials, business executives and engineers that find themselves in these remote or rural areas; alternatively, Iridium could provide ships and aircraft with positioning information, and could be used in disaster recovery efforts were existing communications facilities have been destroyed.
By Mark John
According to Bartram, it cannot compete with land-based cellular in major cities because it cannot project microcells to increase capacity: if cell size becomes too small, transitions would occur too quickly for the inter-satellite switching system. Eventually, it is hoped that Iridium and other land-based cellular networks will work together to create a seamless, worldwide mobile network. For the multibillion dollar project to be economically viable, Bartram reckons that it must attract only 700,000 subscribers worldwide, although he believes that the potential market for the service will be much greater. Motorola plans to market the Iridium network as part of an international consortium in which it will eventually have a minority stake – its role will be as the supplier of the system itself, including the satellites and communications components, as well as providing system support. Memoranda of understanding have already been signed with the International Maritime Satellite Organisation, Inmarsat, the American Mobile Satellite Corp, and Canada-based Telesat Mobile Inc; the agreements call for the three organisations, each of which hold licences to provide satellite communications, to co-operate in studying the techni
cal and financial aspects of Iridium. Motorola is also in discussions with British Telecommunications Plc and network operators in Australia, Hong Kong and Japan; Iridium is likely to be made available on a country-by-country basis following negotiations with the relevant governments and service providers.
Slight premium
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Both subscription to the service and call charges are, admitted Bartram, to include a slight premium on present-day cellular, and the Iridium handsets – slightly larger than Motorola’s current cellular phones – will be considerably more expensive than other cellular alternatives – US estimates put the price of a handset at around $3,000. But the cost of the service to the user is not seen as one of the major hurdles for Iridium. US analysts are convinced that the investment required to fund the venture will vastly exceed the initial estimate of $2,000m, as happened when IBM tried to offer satellite-based communications between fixed sites; moreover Motorola could face competition from the likes of AT&T Co, which is said to be in discussions with other companies to provide a similar service. Other problems are likely to come as Motorola and its partners attempt to secure licences from international groups such as the Federal Communications Commission to operate a network in the new 1.5GHz to 1.6GHz frequency. And because of the large 350-mile footprint, difficulties may occur when a cell spans two countries, one of which wants the service while the other doesn’t. But as Olof Lundberg, director general of Inmarsat noted, the most pressing requirement if Motorola is to start testing the service in 1992, is the question of spectrum availablity. To run the service, a total spectrum of 10MHz is required, and Motorola and its partners will have to wait until the 1992 meeting of the International Telecommunications Union to see whether they have been allocated this spectrum. Only then will Motorola know if it is able to go ahead with its projected first implementation of the 77 satellite constellation in 1994, which is to lead to a full service by 1996..pl 73
