Research on characteristics of free-space optical communication link in weak atmospheric turbulence

Research on characteristics of atmospheric communication link becomes a subject of current interest, and often mainly focuses on some fading parameters including the probability of fade, the mean fade number and the mean fade time. The contribution of false alarm to bit error rate has been considered, however, the temporal characteristic is rarely mentioned., To make up the deficiency, parameters integrating the influence of false alarm and fading were defined. On one hand, the laser communication link were modeled for Gamma-Gamma distribution of irradiance fluctuation subjected to weak atmospheric turbulence. Accordingly the mathematical expressions of these parameters were deduced. On the other hand, characteristic of the parameters were obtained by numerical simulation with various channel environment parameters, such as mean signal-to-noise ratio (SNR), zenith angle and detection threshold. Compared with other researches on fade characteristic, some different conclusions can be drawn from simulation results. With the same SNR and zenith angle, there is an optimum value of detection threshold corresponding to the minimum mean error number, which deviates obviously from that obtained according to the minimum error probability. Either increasing SNR or decreasing zenith angle can reduce mean error number and the optimum threshold. Different from mean error number, mean error time is slightly influenced with channel environment parameters and constant at the order of milliseconds.