# Design of Indoor Visible Light Communication PAM4 System
## 6 Conclusions  
This paper completes the FPGA design and simulation implementation of PAM4 encoding and decoding based on the analysis of theoretical knowledge. At the same time, the lead-lag bit synchronization method and Barker code correlator are designed for bit synchronization signal recovery and frame header detection. Gray coding and 8b/10b  
Figure 21: The BER test results at different communication distances. Figure 20: The experimental system diagram. coding are added before PAM4 coding to reduce the error rate of symbols. The FPGA serial port communication based on PAM4 encoding and decoding is realized through simulation, thereby verifying the feasibility of the PAM4 encoding and decoding scheme. The specific conclusions are as follows:  
1. According to the analysis and research of the three-channel noise models, the BER performance of the PAM4 signal under the additive noise model is the best. The BER under the multiplicative noise model is much larger than that under the additive noise model, and the BER performance under the mixed noise model is almost the same as that under the multiplicative noise model, indicating that in the actual communication system, the influence of the multiplicative noise on the signal is the main factor determining the communication performance. 2. The BER performance of PAM4 in the additive noise model mainly depends on the noise variance. The analysis result shows that the noise variance of Set 2 and Set 10 is large, resulting in worse BER performance. Under the multiplicative noise model, the BER of foggy days and snowy days is higher than that of rainy days, the BER of thick fog is higher than that of mist, the BER of dry snow is higher than that of wet snow, and the BER of light rain is higher than that of moderate rain and heavy rain. 3. The software simulation of the PAM4 encoding and decoding scheme shows that the designed scheme can successfully encode and decode. Two NRZ codes output PAM4 encoded signals, which is the most commonly used method, and the decoding is judged by designing three deciders. Conceptualization, J.L. ; methodology, J.L. and S.L. ; software, S.L. ; validation, J.L., S.L. and X.K. ; formal analysis, X.K. ; investigation, J.L. ; resources, J.L. ; data curation, S.L., J.L. and X.K. ; writing--original draft preparation, S.L. ; writing--review and editing, X.K., S.L. and J.L. ; supervision, X.K. ; project administration, S.L. All authors have read and agreed to the published version of the manuscript. The Key Industrial Innovation Chain Project of Shaanxi Province [grant number 2017 ZD CXLGY-06-01]; the General Project of National Natural Science Foundation of China [grant number 61370780]; the Xi'an Science and Technology Planning Project [grant number 2020 KJRC0083]; and the Xi'an Science and Technology Plan (22 GXFW0115). [PERSON]; [PERSON]; [PERSON] Single lane 150 Gb/s, 100 Gb/s and 70 Gb/s 4 PAM transmission over 100 m, 300 m and 500 m MMF using 25G class 850 nm VCSEL. In Proceedings of the 42 nd European Conference on Optical Communication, Dusseldorf, Germany, 18-22 September 2016. * [PERSON] et al. (2017) [PERSON]; [PERSON]; [PERSON] Error-free 100 Gbps PAM4 transmission over 100m wideband fiber using 850 nm VCSELs. In Proceedings of the European Conference on Optical Communication (ECOC), Gothenburg, Sweden, 17-21 September 2017. * [PERSON] et al. (2019) [PERSON]; [PERSON]; [PERSON] SVM-based equalization algorithm modified by feature vector construction enabled 50-Gb/s PAM4 modulation NG-PON system. _J. Optoelectron. Laser_**2019**, _30_, 1257-1264. * [PERSON] et al. (2019) [PERSON]; [PERSON]; [PERSON] [PERSON] A 16/32 Gb/s NRZ/PAM4 receiver with Dual-Loop CDR and threshold voltage calibration. In Proceedings of the 2019 IEEE 13 th International Conference on ASIC (ASICON), Chongqing, China, 29 October 2019-1 November 2019. * [PERSON] et al. (2021) [PERSON]; [PERSON]; [PERSON] Design and implementation of indoor visible light communication system based on high-order PAM. _J. Nanjing Univ. Posts Telecommun._**2021**, _41_, 53-58.