Fig. 1. Flow chart of the entropy-power loading communication system

Fig. 2. Link structure and experimental link photograph of OFDM-FSO system. (a) Link structure of OFDM-FSO system; (b) photograph of real link in experiment

Fig. 3. Numerical simulation of 256QAM modulation. (a) GMI values corresponding to different SNR and H values; (b) GMI values corresponding to different H values for SNR of 10 dB, 15 dB, and 20 dB

Fig. 4. Maximum GMI of PS-QAM with different orders and GMI of 64QAM

Fig. 5. Experimental results of single phase screen. (a) Pre-estimated SNR; (b) source entropy allocation; (c) normalized power allocation; (d) GMI of entropy-power loading, bit-power loading and fixed-order 64QAM strategies

Fig. 6. GMI values and their average value of bit-power loading, fixed-order 64QAM modulation and entropy-power loading. (a) Strong turbulence; (b) weak turbulence

Fig. 7. Numerical simulation of 256QAM modulation. (a) NGMI values corresponding to different SNR and H values; (b) NGMI values corresponding to different H values for SNR of 10 dB, 15 dB, and 20 dB

Fig. 8. NGMI of entropy-power loading. (a) GMI maximization strategy; (b) joint-parameter strategy

Fig. 9. GMI performance of 256QAM, PS-256QAM with GMI maximization strategy and PS-256QAM with joint-parameter strategy

Fig. 10. GMI values and their average value of bit-power loading, fixed-order 64QAM modulation, and entropy-power loading based on GMI maximization strategy and joint-parameter strategy. (a) Strong turbulence; (b) weak turbulence

Fig. 11. NGMI values and their average value of bit-power loading, fixed-order 64QAM modulation, and entropy-power loading based GMI maximization strategy and joint-parameter. (a) Strong turbulence; (b) weak turbulence