Fig. 1. Schematic diagram of space coherent optical communication

Fig. 2. Receiving end signal constellation under BPSK modulation. (a) ±2 MHz, RSN=20 dB; (b) ±10 MHz, RSN=20 dB; (c) ±20 MHz, RSN=20 dB

Fig. 3. Influence of carrier frequency drift on the BER of BPSK system

Fig. 4. Receiving end signal constellation under QPSK modulation. (a) ±2 MHz, RSN=20 dB; (b) ±10 MHz, RSN=20 dB; (c) ±20 MHz, RSN=20 dB

Fig. 5. Influence of carrier frequency drift on the BER of QPSK system

Fig. 6. Frequency control schematic diagram

Fig. 7. Frequency control flow chart

Fig. 8. (a) Carrier adjustment process diagram; (b) carrier stable process diagram; (c) stable carrier wave; (d) control circuit