Satellite spacing and frequency sharing for communication and broadcast services

Satellite relays complicate the problem of sharing a limited frequency spectrum that is in great demand. This paper reviews the problem and outlines a general approach for efficient use of orbits and spectrum. The protection of received signals, the equipment capabilities, and systems considerations pertinent to the problem are reviewed before systematically examining the principal direct and scatter modes of interference. Conclusions derived include the following. The full potential use of orbits and spectrum for satellite systems can provide enormous capacities greatly exceeding any current proposals, but it requires careful coordination of many system parameters. The use of spectrum for microwave or satellite relays to fixed terminals could evolve to intense full sharing by both types of service without seriously limiting either one or requiring unreasonable accommodation. The satellite down links for area coverage to small terminals (e.g., mobile and broadcast services) can share fully and intensively the spectrum above VHF that is used for terrestrial mobile and broadcast services without seriously limiting the potential of any of the services. Although the greatest potential capacity of the spectrum lies above 16 GHz, for most down-link applications propagation factors make it more attractive to share the spectrum below about 16 GHz much more intensively before making extensive use of the higher frequencies. Providing the satellite down-link spectrum for area coverage to small terminals deserves priority consideration. For this purpose the UHF band is most attractive; the merit of the spectrum rapidly diminishes for higher frequencies.