Performance estimation of polarization multiplexed DPSK signal transmission over temporally correlated free space optical channel

The performance of polarization division- multiplexing (PDM) and differential phase-shift keying (DPSK) modulated signal transmission over slow, varying turbulence channels is estimated in this paper. The free-space optical channel is simulated using the stochastic differential equation (SDE)-based numerical channel simulator that considers the channel’s temporal correlation effect. The SDE-based channel simulator model may significantly ease the free space optical (FSO) communication system design and enable the simulation of channel states according to predefined first- and second-order statistics, namely channel distribution and auto-covariance. We report the performance comparison of the PDM-DPSK system over an uncorrelated, fast-varying FSO channel and a time-correlated, slow-varying channels. Furthermore, to incorporate the effects of polarization and phase fluctuations in the FSO link, both time-dependent and Gaussian distributed, simulated using SDE methods. The bit error rate (BER) performance obtained from the numerical simulation of the PDM-DPSK system shows that the impact of intensity fluctuations is more severe than polarization and phase fluctuations. The power penalty relative to back-to-back (B2B) is 0.5 dB, 2.5 dB, and 7 dB for a 1 km FSO link to achieve a threshold BER of $$10^{-3}$$ for weak, moderate and strong turbulence conditions, respectively, for a slow-varying turbulence channel. We find that the PDM-DPSK link cannot achieve the threshold BER value for fast-changing turbulent channels, particularly for medium and strong turbulence. For weak turbulence, 2 dB more received power is required to achieve the threshold BER value. Thus, the measured BER performances of the PDM-DPSK systems over a fast-varying turbulent channel are overestimated, which does not provide the actual link performance over the time-correlated turbulent channel.