Time series framework for modelling optical LEO satellite links

In this paper, we present a novel framework for modelling a joint time series of rain and cloud attenuation at optical frequencies (150-375 THz). The proposed time series synthesiser considers temporal correlation across varying elevation angles and is therefore applicable for both geostationary (GSO) and non-geostationary (NGSO) cases. Optical propagation is particularly susceptible to fading from tropospheric impairments and therefore accurate time series modelling of attenuation is needed at these frequencies-possibly even more so than at lower frequencies. However, to the best of our knowledge, there are no publicly available joint rain and cloud attenuation time series synthesisers that are applicable for optical frequencies and NGSO SatCom. In this paper, we build on recommendation ITU-R P.1853-2 by making it applicable to the NGSO case and by adapting it for optical communication. As rain attenuation is often neglected in presence of clouds in optical SatCom, we use our joint attenuation synthesiser to statistically evaluate the impact of rain. The analysis showed that rain becomes statistically significant in presence of clouds at low exceedance probabilities of joint attenuation. However, most practical FSO SatCom systems operate with fade margins associated with higher exceedance probabilities, where rain attenuation is statistically negligible.