Study On The Influence Of Atmospheric Turbulence To The BER Of Wireless Optical Communication

On the basis of the Rytov approximation and Markov approximation methods for optical wave propagation through random medium, with considering the inner-scale and outer-scale of turbulence, the characteristics of the scintillation and beam spreading for Gaussian beam are analyzed in turbulence regimes from weak to strong, respectively. The analytic expressions of the scintillation index and long-term optical-beam spreading radius, derived by different methods, are calculated and compared in this paper. Then, the influences of these turbulence effects on the error performance of the wireless optical communication systems employing On-Off Keying (OOK), subcarrier phase-shift keying (PSK) and subcarrier differential phase shift keying (DPSK) modulations are discussed. Finally, according to the incoherent superposition method and the fundamental theory for turbulence scintillation, the scintillation and beam spreading problems for the partially coherent Gaussian-Schell Model (GSM) beam are studied, and the scintillation index and mean squared width of GSM beam in turbulent atmosphere are derived. The technical feasibility of using partially coherent beam source to reduce the impact of atmospheric turbulence and improve the performance of optical communication systems is discussed. The results show that irradiance fluctuations can be significantly reduced by using a partially coherent source beam in the weak fluctuation regime. With taking into account the influence of scintillation effect, the subcarrier DPSK modulation is superior to the OOK and subcarrier PSK modulations in optical communication system applications. Therefore, the optical communication systems performance in atmosphere optical channels can be improved by using a partially coherent laser beam source, a larger system receiving aperture, or appropriate modulation and demodulation means. These studies have great academic significance and practical values in the development and application of wireless optical communication systems.