Fig. 1. Principle block diagram of CDR algorithm

Fig. 2. Data selection principle

Fig. 3. Sampling error

Fig. 4. Loop filter structure

Fig. 5. LDPC encoder structure

Fig. 6. Flow chart of algorithms. (a) Flow chart of CDR algorithm; (b) flow chart of LDPC algorithm

Fig. 7. Experimental platform and algorithm flow. (a) Experimental setup of the real-time transmission over a free space optical link; (b) physical setup; (c) flow chart of algorithm processing

Fig. 8. Comparison of offline and real-time algorithms using the same input data. (a) Input data for ADCs; (b) output of offline Matlab; (c) output of real-time FPGA

Fig. 9. Signal constellation and error curve when VCO is 0000. (a) Output without CDR; (b) output of offline Matlab; (c) output of real-time FPGA; (d) error curve in Vivado ILA

Fig. 10. Signal constellation and error curve when VCO is FFFF. (a) Output without CDR; (b) output of offline Matlab; (c) output of real-time FPGA; (d) error curve in Vivado ILA

Fig. 11. BER versus number of iteration times

Fig. 12. Comparison of quantitative methods and their performance. (a) Block diagram of different quantization methods; (b) performance comparison

Fig. 13. FER performance of non-uniformly quantization LDPC

Fig. 14. Chip planning. (a) Chip planning of CDR; (b) chip planning of LDPC