Satellite-aided land mobile radio experiments,applications and problems

Radio communications between vehicles or individuals and base stations are essential to many public safety, law enforcement and commercial users in urban areas. Present day communications are limited to nearly line-of-sight distances from the vehicle or hand portable units to a base station or repeater. It is probable that many potential users in rural, remote and offshore areas would benefit if the communications were available everywhere on land and territorial waters. Geosynchronous satellites can serve as repeaters for mobile and personal radios, and they appear to be a cost effective means of providing the service.Voice bandwidth communication and automatic position monitoring of an automobile were tested using the VHF transponders of NASAs ATS-3 and ATS-1 satellites. Voice communications were reliable and position fixes were accurate to one fourth mile, with 0.3 mile precision of individual fixes.Demonstrations for potential users have included emergency medical voice and telemetry communications between ambulances and hospitals.While technical feasibility of satellite-aided mobile and personal communications has been demonstrated, and its potential value is appreciated by a small segment of the user community, many problems remain before an operational system could be implemented. Solutions to the problems require an experimental satellite with a multibeam antenna. The satellite or its associated ground terminals should incorporate computer controlled network switching to test demand assignment of channels. Prolonged experience by many users of the experimental satellite in their routine operations would aggregate user needs and define the capital investment that would be justified to implement a commercial operating system.