Progressively Attenuated Multi-Branch Reception for Inter-HAPS Optical Links

Abstract

Inter HAPS optical links can experience receiver saturation at short separations and become signal to noise ratio (SNR) limited at longer distances. This work proposes a saturation aware spatial multi branch intensity modulation direct detection receiver using nonoverlapping apertures with progressive attenuation and selection of the nonsaturated branch with the highest instantaneous SNR. A Gaussian beam model with finite aperture pointing loss and common two dimensional pointing jitter yields closed form branch level expressions for saturation, insufficient SNR, usability, and outage probabilities. Results show that additional branches suppress short range saturation outage, shift the minimum outage point toward shorter separations, and enable progressive attenuation to control the saturation SNR tradeoff. Monte Carlo simulations closely match the analytical results. Overall, the proposed architecture provides a low complexity approach to extending the usable dynamic range of inter HAPS optical receivers.