Background: In this paper, the impact of the dispersion effect, due to atmospheric pressure and temperature, on NRZ-OOK terrestrial free-space optical transmission system is investigated. An expression for the dispersion parameter in FSO atmospheric channel is derived. Results: The results show that the variation of the refractive index along the transmission path induces fluctuations of group velocity dispersion of the optical pulse resulting in broadening of the pulse duration. Simulation results show that at a propagation distance of 7.5 km, the broadening ratio for input pulse duration of 300 fs is approximately 2.39. Further, at a propagation distance of 7.5 km, the remaining fraction of energy is approximately 40 % for a 300 fs input pulse duration. However, by increasing the transmitter input power, the effect of dispersion could be reduced. Namely, for a reference BER of 10 -9 , the maximum distance that it could be achieved is about 1. 461 km for an input power of 1 mW, while it is about 2.694 km for an input power of 4 mW. Conclusions:The results indicate that the effect of dispersion resulting from pressure and temperature increases with the propagation distance, which induces a high BER. However, the results show that it is possible to reach longer propagation distances with a lower BER by increasing the input power.

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In this paper, the impact of atmospheric turbulence is investigated and analyzed for the Free Space Optical Mobile Ad Hoc Networks (FSO MANET) using the Network Simulator NS-3. The FSO channel random intensity fluctuations have been modeled using the Exponentiated Weibull (EW) distribution. Further, the FSO module has been implemented and integrated with NS3 using the FSO propagation model and the FSO error models. The computation of the key performance indicators (KPI) mainly the throughput and the packet delivery ratio (PDR) shows that the network density affects the network performance. Its effect was illustrated for the different turbulence regimes, strong and weak. It is found that the throughput and PDR values decrease as the number of mobile nodes becomes larger. For instance, at 150 kbps and in the presence of strong turbulence with 25, 50, and 75 nodes, the PDRs are 77%, 76%, and 73% respectively. Moreover, the throughput and PDR values in the strong turbulence regime are lower than those in the weak turbulence regime for the same date rate. The throughput in the strong turbulence regime with 75 mobile nodes at the data rate 150 kbps is 2100 kbps while it is 2300 kbps in the weak turbulence mode at the same rate.