Probabilistic Link Budget Analysis for Low Earth Orbit Satellites in the Optical Regime
Dhruv Shivkant, Shreyaans Jain, Rohit K Ramakrishnan
TL;DR
This work develops a probabilistic link-budget framework for LEO optical downlinks that integrates static factors (free-space loss, telescope optics, and atmospheric absorption) with dynamic atmospheric effects (scintillation, jitter, beam spread, and wavefront distortion) through stochastic models of $C_n^2(h)$ and the Fried parameter $r_0$. The model expresses the link budget in dB as $P_{Rx}^{dB} = P_{Tx}^{dB} + L_{path}^{dB} + L_{Rx}^{dB} + L_{Tx}^{dB} + G_{Rx}^{dB} + G_{Tx}^{dB} + {L_{atm}^{static}}^{dB} + {L_{atm}^{dynamic}}^{dB}$, enabling dynamic, location-specific performance estimation. The authors derive explicit expressions for free-space loss, optical efficiencies, atmospheric transmittance, and turbulence-induced losses (scintillation, jitter, beam spread, Strehl) while incorporating uncertainty through distributions for key parameters. Case studies on NODE, HANLE, and a balloon-based link demonstrate the model’s ability to match observed trends and reveal where deterministic budgets may be overly conservative or optimistic. Overall, the framework provides a robust tool for designing and optimizing LEO optical networks with realistic probabilistic margins and clear paths for extension to uplink and strong-turbulence regimes.
Abstract
Low Earth Orbit (LEO) optical satellite communication systems face performance challenges due to atmospheric effects such as scintillation, turbulence, wavefront distortion, beam spread, and jitter. This paper presents a comprehensive mathematical model to characterize these effects and their impact on signal propagation. We develop a methodology for dynamically calculating link budgets at any location and time by integrating these models into a probabilistic framework. The approach accounts for spatial and temporal variations in atmospheric conditions, enabling accurate estimation of link loss probabilities. Simulations validate the model's accuracy and applicability to real-world LEO satellite systems. This work offers a robust tool for optimizing link performance and enhancing the reliability of satellite networks, providing valuable insights for system designers and operators.