Extended‐parity‐based rateless polar codes for HAPS‐to‐ground station communication over free‐space optical links

Abstract This paper presents an extended‐parity‐based rateless polar coding scheme, which is designed to enhance adaptive transmission performance in broadband free‐space optical channels. The proposed rateless polar codes are extended to both blocklength and coding rate variations, enabling finer adaptability to time‐varying channel conditions. The proposed design leverages repetition‐based XOR operations to strengthen the polarization effect and maintain reliable decoding as incremental parity symbols are transmitted. Our scheme is specifically investigated for downlink communication from high‐altitude platform stations to ground stations, where turbulence‐induced fading, pointing loss, and orientation divergence significantly degrade optical link reliability. Simulation results demonstrate that our extended‐parity rateless design achieves notable performance improvements and enhances robustness against turbulence and misalignment effects, confirming its potential for next‐generation, non‐terrestrial optical communication systems.