Fig. 1. Block diagram for PPM-SNSPD deep space optical communication system

Fig. 2. Non-ideal property for optical pulse signal. (a) After pulse; (b) pulse tail

Fig. 3. SNSPD photocount PDF for a single pulse when the dead time is greater than the pulse-width. (a) Idea square pulse; (b) square pulse with tail

Fig. 4. Photon detection state transition graph for SNSPD

Fig. 5. Symbol detection states for SNSPD. （a） 4-PPM detection states examples； （b） state transition graph

Fig. 6. Comparison between photocount PDF analysis and simulation

Fig. 7. PPM-SNSPD channel photocount PDF equivalent block diagram

Fig. 8. GTS algorithm delay prediction offset.(a) Photocount PDF integration results over 4 time slots (n_s=5); (b) estimation error histogram for GTS (n_s=5); (c) MSE comparison for delay estimation (B=16)