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由于OFDM调制技术能有效抵御大气散射效应,提出了频带FSO-OFDM传输的系统方案。在建立大气散射信道模型之后,推导了由散射造成的光强衰减系数及光强起伏方差和系统误符号率(SER)间的关系。以雾天和雨天为例,通过仿真实验验证了其正确性。结果表明:毛毛雨、广延雨和雷暴雨散射造成的光强起伏方差分别为2.4×10-2、3.044 1×10-4和8.776 2×10-5。当误符号率Pe=10-5、子载波N=32时,相对于毛毛雨,广延雨天和雷暴雨天的误符号率分别降低了12 dB、15 dB。虽然平流雾较辐射雾散射造成的光强衰减大,但它们的光强起伏方差均较小。当误符号率Pe=10-3,子载波N=32时,相对于平流雾,辐射雾的误符号率降低了10 dB。因此,在散射信道中系统误符号率主要取决于散射造成的光强起伏方差,其次取决于散射造成的光强度衰减系数。
As OFDM modulation technology can effectively resist the atmospheric scattering effect, the system scheme of frequency band FSO-OFDM transmission is proposed. After establishing the model of atmospheric scattering channel, the relationship between the light intensity attenuation coefficient and the fluctuation of light intensity undulation and the system symbol error rate (SER) is deduced. Taking foggy and rainy days as an example, its correctness is verified through simulation experiments. The results show that the fluctuation of light intensity caused by drizzle, rain and thunderstorm rain are 2.4 × 10-2, 3.044 1 × 10-4 and 8.776 2 × 10-5, respectively. When the symbol error rate Pe = 10-5 and subcarrier N = 32, the symbol error rates of extended rainy days and thunderstorm days decreased by 12 dB and 15 dB, respectively, compared with the drizzle. Although advection fog radiation intensity attenuation caused by radiation fog larger, but their light intensity fluctuations are smaller. When the symbol error rate Pe = 10-3 and subcarrier N = 32, the symbol error rate of the radiation fog is reduced by 10 dB compared to the advection fog. Therefore, the systematic symbol error rate in a scattering channel depends mainly on the fluctuation of light intensity caused by scattering, and secondly on the attenuation coefficient of light intensity caused by scattering.