Modeling Optical Key Distribution over a Satellite-to-Ground Link Under Weak Atmospheric Turbulence

TL;DR

This paper models the secret key capacity of optical satellite-to-ground links under atmospheric turbulence, providing insights for optimizing quantum key distribution protocols in varying weather conditions.

Contribution

It introduces a comprehensive atmospheric channel model for IM/DD OKD over satellite links, analyzing the impact of turbulence and wind on key capacity and protocol performance.

Findings

Secret key capacity varies with turbulence strength and wind conditions.

Reverse reconciliation can outperform direct reconciliation under certain turbulence levels.

Error distribution characteristics depend on protocol optimization and atmospheric conditions.

Abstract

In this study, we analyze the secret key capacity of intensity modulation/direct detection optical key distribution (IM/DD OKD) for a free-space optical (FSO) link between a low-Earth orbit satellite and an optical ground station. Focusing on downlink communication, we account for atmospheric turbulence, which causes random variations in the transmittance of the FSO channel. We implement an atmospheric channel model that accounts for absorption and scattering, geometric losses, pointing errors, and intensity fluctuations. The secret key capacity is quantified under different noise scenarios and reconciliation code efficiencies, assuming a hard decoding scheme. The performance of the IM/DD OKD protocol is compared under direct and reverse reconciliation regimes. Additionally, we examine the impact of weak and strong wind on the strength of atmospheric turbulence, leading to different results of the secret key capacity. Furthermore, we analyze the characteristics of error distributions that arise from protocol optimization. Our results provide insights into optimizing IM/DD OKD protocols for varying atmospheric conditions.