Impact of atmospheric turbulence on OOK and BPSK modulations for satcom optical uplink

Abstract

The constant growth in the demand for communication services has implied an increase the transmitted data rate and bandwidth. Optical satellite communications have provided a solution to this problem, allowing to increase exponentially the transfer rate between the ground station and an in-orbit satellite. However, although this technology offers numerous advantages, such as higher bandwidth, lower power consumption, narrower beam width, as well as greater simplicity of development, when the transmitted light signal passes through the atmosphere it experiences attenuation and fluctuations due to atmospheric turbulence. In this work, optical power fluctuations are modelled by means of a Gamma-Gamma optical turbulence model, so strong turbulence conditions are established according to Rytov’s turbulence theory, considering a measure of the intensity of the optical turbulence when extended to strong fluctuation conditions, depending on the zenith angle variations from 0\(^\circ \) to 60\(^\circ \). Finally, the performance evaluation of BPSK and OOK modulation schemes for conditions with variations of pointing angle, based on atmospheric attenuation, signal scattering and absorption is given. The results show better performance of the modulation schemes at low zenith pointing angles and wavelengths of 1550 nm, over 850 nm and 1064 nm. Moreover, BPSK modulation shows to be able to provide lower bit error (BER) values for a given signal-to-noise ratio, outperforming OOK modulation scheme in this sense.