Abstract :

Abstract — The proposed terrestrial free space optic (FSO) link from Cairo tower to the great Pyramid (distance 11.5 km) with 130 m altitude and 1550 nm wavelength is evaluated with data rate 10Gb/s and transmitted power 500mw.In this proposed, the measured visibility gives the equivalent effects of all weather parameters and so, it is used to calculate the weather attenuation by using Mie scattering law. And the scintillation (C2n) is evaluated using a combatable model of Cairo weather. The effect of turbulence becomes very weak by using the receiver aperture greater than the maximum optical spot size due to divergence and turbulence. During year 2016, the visibility usually greater than 2km, except it equals zero during 90 minutes only, but it becomes 1 km during 56.5 hr. Also weak atmospheric turbulence C2n < 6*10-16 m-2/3 at altitude h=130 m, the scintillation index σ2 ≤ 0.8, except three days, and the air dispersion very small around 0.47 ps km-1 nm-1. The availability dependence not only on the SNR (BER) but also on the value of received power (Pr) to realize the minimum received power (Pr min). With visibility V ≤ 1km, or scintillation index (σ2 >1), the link becomes not available. We consider the availability occurs if the SNR ≥ 36 ≡ 15.56 db (i.e. BER ≤ 10-9 and Q-factor ≥ 6) also, Pr ≥ minimum received power (Pr min). SNR increases with the ratio of the transmitted power (Pt) to the data rate (Br).The effects of all parameters on the performance of FSO are discussed, and the simplified design steps are achieved. The calculations of weather effect are based on the measured data of Cairo weather which published by Egyptian meteorological authority. The required transmitted power must be related to the expected visibility. In year 2016, the availability, becomes 99.983%.