Error‐Control Strategies for Space‐Ground Optical Links: A Comparative Study of ARQ, FEC, and Interleaving

ABSTRACT This paper presents a comparative performance study of fading mitigation techniques for a free‐space optical (FSO) low Earth orbit (LEO) satellite‐to‐Earth downlink employing intensity modulation with direct detection, on‐off keying and avalanche photodiode reception. The impact of time‐correlated fading is evaluated using realistic time series of received optical power gains that capture the proper marginal distribution and covariance structure of atmospheric scintillation and beam pointing jitter. Three mitigation strategies are investigated: (i) rate‐1/2 (30720, 15360) low‐density parity‐check (LDPC) channel coding with optional block interleaving; (ii) the configuration from (i), combined with outer Reed‐Solomon (RS) packet coding and optional packet interleaving; and (iii) type‐1 hybrid ARQ (HARQ) based on selective‐repeat ARQ combined with LDPC channel coding. In contrast to prior work, both thermal noise and signal‐dependent shot noise are included in the receiver model, and the influence of the channel interleaver symbol size is explicitly analyzed. Furthermore, we assess the combined use of channel and packet interleaving. The schemes are compared in terms of packet error rate, goodput, delay, and memory requirements. The results quantify the trade‐offs between interleaving, packet‐level coding, and retransmission‐based strategies under realistic fading dynamics. In particular, we show how interleaving depth and HARQ retransmissions mitigate burst errors at the cost of increased delay and memory requirements, providing design guidelines for robust and efficient LEO‐to‐ground FSO downlinks.