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Erschienen in:
2013 | OriginalPaper | Buchkapitel
Satellite Radio Communications Fundamentals and Link Budgets
verfasst von : Dr. Daniel R. Glover
Erschienen in: Handbook of Satellite Applications
Verlag: Springer New York
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Abstract
Satellite communications makes use of radiofrequency links. Particular frequencies are allocated for satellite communications through international regulatory registration and coordination processes which prevents interference between systems. In typical operation, a satellite’s transponder receives an uplinked signal from Earth, changes its frequency slightly to avoid self-interference, and retransmits it on a downlink to Earth. Antennas provide gain by focusing the transmitted energy. Path loss describes a natural spreading out of the transmitted wave front as it travels through space. A link budget is an accounting of gains and losses throughout a system that is used as a design tool to provide sufficient power (or gain) to allow a satellite connection to be established. The link margin is the excess amount of received signal power above what is required. Shannon’s Law implies that there are trade-offs possible in a communications system design between power, bandwidth, and complexity.