Performance limitation of laser satellite communication due to vibrations and atmospheric turbulence: Down-link scenario

In this paper, we analyse the effects of vibrations and the atmosphere on the performance of a broadband laser inter-satellite link (BLISL) which was studied within the framework of the BLISL joint Israeli-German applied research project. The use of optical radiation as a carrier between satellites and in satellite-to-ground links enables transmission using very narrow beam divergence angles. Due to the narrow beam divergence angle and the large distance between the satellite and the ground station or airplane the pointing is a complicated process. Further complication results from vibration of the pointing system caused by two fundamental mechanisms of a stochastic nature: (1) tracking noise created by the electro-optic tracker and (2) vibrations caused by internal satellite mechanical mechanisms. Additionally an inhomogeneity in the temperature and pressure of the atmosphere leads to variations of the refractive index along the transmission path. These variations of refractive index as well as pointing vibrations can cause fluctuations in the intensity and the phase of the received signal leading to an increase in link error probability. In this paper, we develop a bit error probability (BEP) model that takes into account both pointing vibrations and turbulence-induced log amplitude fluctuations (i.e. signal intensity fading) in a regime in which the receiver aperture D₀ is smaller than the turbulence coherence diameter d₀. Our results indicate that BLISL can achieve a BEP of 10^-9 and data rate of 1Gbps with normalized pointing vibration of G_T* σ₀² = 0.05 and turbulence of σ_X = 0.3.