Guo Q, Song P, Zhang Z Q, et al. Research on the key technology of turbulence suppression for atmospheric optical laser communication based on OFDM[J]. Opto-Electron Eng, 2020, 47(3): 190619. doi: 10.12086/oee.2020.190619
Citation: Guo Q, Song P, Zhang Z Q, et al. Research on the key technology of turbulence suppression for atmospheric optical laser communication based on OFDM[J]. Opto-Electron Eng, 2020, 47(3): 190619. doi: 10.12086/oee.2020.190619

Research on the key technology of turbulence suppression for atmospheric optical laser communication based on OFDM

    Fund Project: Supported by National Natural Science Foundation of China (61701384), Scientific Research Program Fund of Education Department of Shaanxi Province (18JK0341), and Xi′an Science and Technology Bureau Science and Technology Innovation Fund (201805030YD8CG14 (12))
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  • Based on the analysis of the two main problems of atmospheric channel in free space optics (FSO), aiming at the problem of laser atmospheric channel especially the problems of frequency selective fading and multipath effect in complex turbulent environment, the suppression method is proposed based on OFDM turbulence effect, the FSO-OFDM system is built, the baseband model of this system and the signal of multi-carrier modulation and demodulation method are studied. First of all, this article systematically analyzes the mechanism of turbulence effect of atmospheric channel, and discusses the model of plane wave laser communication system under the influence of atmospheric turbulence, the space optical communication system model of Gaussian beam of a logarithmic normal turbulent channel is established under the influence of atmospheric turbulence, the probability density function of light intensity is deduced, the methods for analyzing the effects of various atmospheric turbulence effects on system performance using the signal-to-noise ratio probability density function; the OFDM multi-carrier modulation scheme of FSO-OFDM system is designed, the baseband mode model of FSO-OFDM system is constructed, and the modulation and demodulation principle of its signal is studied using this model. Finally, FSO-OFDM system is realized by using MATLAB, and the FSO communication system under the multipath interference is simulated, experiments on bit error rate characteristics under different guard intervals are performed. It is confirmed that the FSO-OFDM system has a strong ability to resist multipath interference and frequency selective fading, as well as good bit error rate (BER) performance. It can effectively solve the problem of intersymbol interference and the reliable link, and has a very broad application prospect and using value.
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  • Overview: In order to support higher information transmission rate, improve the system error characteristics, solve the problems of frequency selective fading and multipath effect of the wireless optical communication system in complex turbulent environment, improve laser atmospheric channel signal transmission problems, based on orthogonal frequency division multiplexing technology, the FSO-OFDM system was built, the multicarrier modulation, modulation and demodulation, etc used this system were studied. Firstly, the turbulence effect, which is a bottleneck problem restricting the application of atmospheric laser communication, was discussed in detail. Then, on the basis of Kolmogorov spectrum model, the plane wave model was studied. By using the modified Rytov method, the spatial optical communication system model of Gaussian beam under log-normal turbulence channel was established, and the probability density function of the system light wave intensity was derived. Then, the OFDM multi-carrier modulation scheme of the wireless optical communication system was designed, the baseband mode model of the FSO-OFDM system was constructed, and the modulation and demodulation of the signal were studied using this model. When the signal of the binary signal source was sent out, it was encoded and modulated to the series-and-conversion module for series-and-conversion, followed by IFFT exchange. After digital-to-analog conversion and filtering, electro-optical conversion was carried out, which becomes the signal s(t) modulated by OFDM. After passing through the atmospheric channel, the signal was sent to the receiving module of the FSO-OFDM system, which is photoelectric converted, low-pass filtering, and then converted by mode/number to restore the orthogonality of the subcarrier. After FFT and string/combination conversion, the signal was restored to the signal before OFDM modulation. After demodulation and decoding, the original input signal was restored. Finally, MATLAB programming was adopted to realize the FSO-OFDM system. Simulation experiments were carried out on the FSO communication system under multi-path interference. Under the same bandwidth condition, the average bit error rate performance of the single-carrier wireless optical communication system and the FSO-OFDM communication system were simulated, respectively. Compared with the traditional single-carrier system, the OFDM system improves the atmospheric channel transmission of laser signal and the information transmission rate. FSO-OFDM system has a strong ability to resist multi-path interference and spectrum selective fading, as well as a good BER performance. It provides a technical method to break through the bottleneck of optical communication and has a very wide application prospect and value.

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