Link budget calculation in optical LEO satellite downlinks with on/off-keying and large signal divergence: A simplified methodology

Direct-to-Earth transmissions with optical on/off-keying are becoming the method of choice to realize telemetry downlinks from low Earth orbit satellites at highest data-rates. Here, we review the calculation procedure for a practical assessment of the mean link budget in this space-ground data communication technology. We present a comprehensive survey of the dynamic orbital and beam-pointing effects as well as the impacts from atmospheric attenuation on the link performance. The paper provides an exhaustive review of the formulas commonly used and propounds a recipe to reliably estimate the received power on ground. An overview of typical data transmitter terminals, transmission channel parameters, and the according optical ground stations is provided. Comparison with measured received powers over transmitter elevation angle and the respective design estimates serves for verification.