Effects of Atmosphere Dominated Phase Fluctuation and Intensity Scintillation to DPSK System

Free-space-optical (FSO) coherent communication is a cost-effective, license-free, high-sensitivity and wide-bandwidth access technique for high date rates applications, whereas its performance strongly suffers from the turbulent atmosphere for the reason of both intensity scintillation and phase fluctuation. In this paper, the intensity scintillation is modeled as a multiplicative random process following the Gamma-Gamma distribution while the phase fluctuation is proved to satisfy Gaussian distribution. And the slow varying characteristic of the power spectrum destiny of the atmosphere is verified. In our research the Mach-Zehnder-interferometer (MZI) based coherent differential-phase-shift-keying (DPSK) transmission system is employed. And its bit-error-rate (BER) performance is studied with BER expression given by Meijer-G function substitution. Besides, a novel simulation model of the atmosphere channel is established based on which effects of the atmosphere to BER performance of the system are simulated. From the simulation, we know over FSO links, to guarantee the performance of the coherent system, measures should be taken to compensate the intensity of the signal when the Rytov variance is over 1.0, and the statistical standard deviation of the received signal frequency should be compensated to less than 100MHz when the transmission rate is 1Gbit/s. By comparing performances of MZI-DPSK and traditional PSK, the advantages of MZI-DPSK are presented.