Phase fluctuations-generated BER of DPSK optical communication system in the satellite-to-ground downlink with anisotropic tilt angle

Recent experiments have demonstrated that the anisotropy property of turbulence cell is inherently present, and the long axis of turbulence cell possibly is not level with the ground but has an anisotropic tilt angle with it. Phase modulation schemes like differential phase shift keying (DPSK) are sensitive to turbulence-generated phase fluctuations. However, the existing literature about the turbulence-generated phase fluctuations and the bit error rate (BER) of phase modulation free-space optical (FSO) communication systems have been confined exclusively to the isotropic Kolmogorov and non-Kolmogorov turbulence models. We derived the expressions for variance of phase fluctuations and BER of DPSK/FSO communication systems with consideration of phase fluctuations in the anisotropic non-Kolmogorov (ANK) satellite-to-ground downlink with anisotropic tilt angle. The results show that with the change of anisotropic tilt angle and azimuth angle, the BER varies periodically and greatly, which is primarily governed by scintillation index rather than phase fluctuations. And the inclusion of phase fluctuations makes the BER increase significantly. For various transmission directions of optical wave, once the anisotropic factor and angle τ are the same, the curvature radius at the interface of anisotropic turbulence cells and beam is the same, thus the BER of DPSK/FSO systems is the same. • The long axis of turbulence cell may have an anisotropic tilt angle with the ground. • The BER expression of DPSK/FSO systems with anisotropic tilt angle is derived. • The phase fluctuations is incorporated in the ANK satellite-to-ground downlink. • The BER varies periodically and greatly with anisotropic tilt angle and azimuth angle. • The inclusion of phase fluctuations makes the BER increase significantly.