PROBABILISTIC TREATMENT OF DOWNLINK MARGIN FOR MULTI‐BEAM PAYLOAD

This chapter presents a link‐level analysis of a multi‐beam, bent‐pipe, geostationary‐orbit payload that shows lower equivalent isotropically radiated powers (EIRPs) to be necessary than a traditional, overly conservative analysis would dictate. Even relatively more EIRP can be saved if the downlinks are subject to rain loss and the traditional EIRP requirements are replaced with a link‐availability requirement. A probabilistic characterization more fully and accurately portrays the on‐orbit payload performance. There are different kinds of multi‐beam‐downlink payloads and ways to specify them. The basic specification is either EIRP or link availability. The chapter discusses the payload antenna‐caused variation and fold it into the repeater‐caused variation of C and C/I
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and similarly for the nominal values. It combines a statistical model of atmospheric attenuation with the probabilistic model of payload performance. The chapter develops a multi‐beam‐downlink payload that has been specified by a minimum long‐term link availability.