A complete, end-to-end system for land mobile communications has been field-tested for the first time by researchers from NASA's Jet Propulsion Laboratory.
The field tests were made possible through the cooperation of AUSSAT Pty. Ltd., the Australian national satellite system, which provided local facilities used in the experiments.
The experiments, conducted in July and August 1989, involved communications between fixed base station at AUSSAT's downtown Sydney, Australia, facility and mobile unit mounted in van.
The system evaluated in the tests uses vehicle antennas, voice encoders and other hardware developed by JPL under its Mobile Satellite Experiment (MSAT-X) program for NASA.
"Our conclusion was that the system really will work," said Dr. William Rafferty, manager of JPL's Communications Section. Both voice and data calls, he noted, were tested during the experiments.
During the tests the mobile unit ranged as far away as the city of Brisbane, more than 450 miles north of Sydney. That is approximately the distance between Los Angeles and San Francisco, or between New York City and Detroit.
According to Rafferty, routes followed by the mobile unit took it behind trees, under bridges and around other obstructions, with no loss of synchronization during calls lasting more than two hours each.
Calls were relayed over Japan's Experimental Technology Satellite-V (ETS-V). When they are fully operational, mobile communications systems would use special dedicated Earth-orbiting satellites.
Under the MSAT-X program, JPL has been developing technologies that would be useful in mobile satellite systems. Areas of research include mechanically and electronically steered vehicle antennas, modulation encoding and networking methods.
fully developed mobile system would use satellites to extend mobile telephone services to remote ground users and to users in the air and on the sea who cannot be served by cellular telephone systems.
In addition to planes in flight and ships at sea, such system could also serve such users as private drivers, cross-country trucks, forestry personnel and law-enforcement agents.
The summer 1989 test in Australia included secure calls in which digital voice transmission was encrypted. This technique would be important to user agencies participating in the U.S. National Communications System such as the FBI and the Drug Enforcement Agency, Rafferty said.
JPL's role is strictly to develop new technologies required for mobile satellite system. NASA plans to seek cooperative agreements with the commercial operator of first-generation satellite system whereby the space agency will launch the first satellite. In exchange, NASA would be able to conduct technology validation experiments using small percentage of the satellite's capacity for the first two years of operation.
Now that prototype system has been demonstrated, Rafferty said, MSAT-X work at JPL will shift to more "applications-oriented" issues.
MSAT-X is funded by the Communications and Information Systems Division of NASA's Office of Space Science and Applications.
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