AN AUSTRALIAN company has beaten its international rivals to the marketplace with the world鈥檚 first satellite-based mobile telephone service. An antenna designed in Queensland has allowed Optus Communications to launch its service more than a year before its American counterparts.
The phone service, called MobileSat, is designed for use in remote areas not reached by cellular mobile phones, which require a string of repeater towers on the ground to send and receive signals. Its uses so far have included helping local and state emergency services maintain communications after Cyclone Bobby hit the Western Australian of Onslow in February.
MobileSat started operating in Australia last August. In September this year, the US company American Mobile Satellite Communications (AMSC) will use the Australian technology when it starts an equivalent service in North America. To relay signals, MobileSat makes use of the company鈥檚 Optus-B satellite which is in geostationary orbit about 32 000 kilometres above Papua New Guinea. With this system, it is possible to telephone anywhere on the Australian continent and 200 kilometres out to sea. The present cellular mobile phone network covers less than 5 per cent of Australia鈥檚 landmass 鈥� a strip running down the east coast to Adelaide and localised such areas as the southwest of Australia and the environs of Darwin.
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But relaying signals using a geostationary satellite so far above the Earth means that antennas have to be powerful enough to receive a weak high frequency signal from space. Conventional mobile phones use an antenna which can receive signals from any direction. But in space telephony, the signals are so faint that this is not possible. It is necessary to point the antenna directly at the satellite in order to maximise the signal strength, which makes it impractical for truly mobile uses such as telephones in cars.
The problem was solved for Optus Communications by microwave engineers at a Brisbane-based company, Mitec, working with the CSIRO Division of Radiophysics in Sydney. They developed a 1-metre long aerial that receives signals along its axis, rather than at right angles to the axis as is usually the case. This antenna will receive signals from the satellite irrespective of the way a vehicle is moving. However, the aerial does need to be nearly vertical. An aerial of this length can also be awkward to manage.
So the Department of Electrical and Computer Engineering at the University of Queensland is working on another design 鈥� an array of smaller antennae which are arranged and controlled to make them behave like one big antenna. The department recently successfully tested a prototype that will sit on the roof of a vehicle 鈥� a cylindrical array of 14 small antenna discs, together measuring about 70 centimetres in diameter. The array is set at 45掳.
MobileSat is not as portable as a cellular phone. Its handset is similar to a conventional mobile phone, but it comes with the 1-metre aerial, a transceiver the size of a large shoebox and the whole instrument weighs about 8 kilograms. The transceivers, which pick up and send the signal, cost about A$8000 to install. Call charges are about A$1.80 a minute. A car battery is needed to power the system. Furthermore, there is a half-second delay between speaking and receiving because of the distance the signal has to travel to and from the satellite.
In seven months, MobileSat has acquired 1000 subscribers. The main users are mining companies, police and emergency services, the fishing industry, long distance road haulage companies, interstate railways, and the Royal Flying Doctor Service. 鈥淭hese are people who work within reach of a vehicle,鈥� says Michael Wagg, managing director of MobileSat.
MobileSat鈥檚 transceivers are being made by NEC in Australia, and by Westinghouse in the US. The agreement with AMSC, says Wagg, not only provides an outlet for Australian technology but also significantly increases the number of potential users to about a million, which provides economies of scale in the production of handsets. This will help lower the cost of the transceivers.
While Optus Communications competes with Australia鈥檚 Telstra and the UK鈥檚 Vodafone in the cellular mobile phone market, it has no competitors in remote areas. But this may change. At least five American consortia are planning to establish global mobile telephone systems using satellites orbiting less than 1000 kilometres overhead to relay signals to and from handsets rather like conventional mobile phones. The idea is to use a procession of small satellites so that there will always be one overhead to carry the signal. The technology will provide cheaper handsets, more capacity, and probably better quality calls than MobileSat.
But being first confers advantages, according to Wagg. The first of the global mobile services 鈥� Motorola鈥檚 Iridium network 鈥� is planned to be up and running by 1998, but Wagg thinks MobileSat has about five years before it runs into serious competition. The big question for Optus is whether the system will become standard equipment in vehicles in the outback within that time. Wagg thinks a fully developed, reliable and cheap service will remain competitive in Australia. 鈥淲e are also looking at developing a system which would switch between the cellular phone network and MobileSat. The phone would go to cellular first, then switch to satellite if it is out of cellular range, he says. Optus is also investigating how it can work in partnership with the global mobile services.
Faster facts
SATELLITES can now transmit data as quickly and accurately as optical fibre, as a result of new equipment developed by an Adelaide research group.
A team from the Institute of Telecommuncations Research at the University of South Australia has built a new codec 鈥� the heart of a modem 鈥� which enables satellites to transmit data at a rate of 155 megabits a second, a speed that is competitive with optical fibre.
A codec transforms or encodes data so that it can be sent at high speed without error. The secret behind this product is the use of a new class of mathematical transformation particularly suited to the conditioned encountered in satellite transmission.
The research team, led by Steven Pietrobon, won a contract against worldwide competition to develop the codec for the international communications company, Intelsat, which operates more than 20 satellites. It was the first R&D contract to be awardeed to an Australian institution in the 20 years that Intelsat has been in operation.