Scintillation characterization of multiple transmitters for ground-to-satellite laser communication

Abstract

Using high data optical transmitters for satellite communication channels has generated an interest in laser communication systems ground-to-satellite data links. The atmospheric turbulence causes laser intensity fluctuations that can seriously degrade the reliability and performance of such laser communication links. In the ground-to-satellite link, the atmospheric turbulent's thickness is much less than the path length. Taking into account the large size of the beam at a satellite in orbit, the spatial coherence radius at the satellite is many times larger than the probable receiving aperture of the satellite's optical antenna. Thus the aperture behave of uplink essentially like a point detector without aperture averaging. An analysis of multiple beams compensation for atmospheric turbulence induced scintillation is carried out in this paper. Using multiple incoherent beams transmit synchronically optical signal from dividable apertures, separated by a distance larger than the atmospheric coherence diameter. The convolution integration to determine what happens for two independent random variable, we generalized this method to multiple independent random variables. According to probability theorem, the multiple beams distribution of the irradiance is given with different scintillation index. For this analysis we assume that the single-beam probability distribution function model of the irradiance is the gamma-gamma distribution. In our analysis of this simulation model, it shows that the adverse effect of scintillation on the communication lasers can be minimized with multiple transmitters under weak, moderate, and strong turbulence conditions. The scintillation index was reduced as the number of laser transmitters was increased. So, fluctuation on the uplink/downlink communication beams can effective reduced by multiple transmitters.