Attenuation model for free space optics using latency measurements

Abstract

This study proposes a prediction model for the calculation of rain attenuation for optical wavelengths. Based on latency measurements via 850 nm free space optics transceiver, exponential drop size distribution is derived by method of inference from knowledge of attenuation at the highest rain rate. As an alternative to the inferred exponential distribution, a lognormal drop size distribution that suits the observed measurements is derived from published distribution models. Both distributions are found to be consistent with measured data. Furthermore, a formula relating latency to rain rate is derived by nonlinear regression analysis. The derived formula gives a very good correlation of 0.971 with the measured data. Regression analysis is also performed to attenuation data obtained by graphically converting measured latency data to attenuation. The results are compared to the proposed attenuation model and found to be identical. The attenuation model, using both drop size distributions, is then compared to well established models in the literature and is found to be mathematically consistent and in good agreement with these models and their measured data. While the established models are for rain rates of up to 100 mm/hr, the proposed model with a simpler derived power law is for rain rates up to 250 mm/hr. The power law, ?(R) =1.118R0.614, is derived for economy of calculation and ease of use.