Fade budgets of PAT link in satellite-to-ground optical communications

To achieve enough fade budgets for reliable link in satellite-to-ground optical communications, the expressions for the total probability density functions of signal intensity fluctuation are derived at large zenith angles and small zenith angles considering atmospheric scintillation, static pointing error and pointing jitter and relation of the lost-tracking probability variable with fade budgets is given. Finally, the total probability density function and lost-tracking probability are simulated. Experimental results show that the ratio of the optimal beam divergent angle to the square root of the variance of the pointing jitter for uplink and downlink is 4 and 6; the required fade budget at a lost-tracking probability of 10^-3 is 10 dB and 3 dB for uplink and downlink.