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自由空间光通信(FSO)的信道是随机的,会受到灰尘、雨滴、雾等粒子散射的影响,正交频分复用(OFDM)调制方式可以很好地抵御大气散射的影响,但简单地将OFDM与FSO结合的系统复杂度较高。为了降低传统FSO-OFDM系统的复杂度及改善系统性能,借鉴Alamouti空时编码理念,设计了一种新的时频码。依据大气信道的特点,建立了信道模型。在介绍了系统模型之后,详细地陈述了时频码的编译码方法,分析了系统误码率(BER)与信道特性关系。最后通过Monte Carlo仿真实验进一步证明了该时频码的有效性。结果表明,以雨天为例,采用该时频编码不仅可以降低FSO-OFDM系统的复杂度,而且误码性能得到了显著的提高。
Free-space optical communications (FSO) channels are random and subject to scattering of particles, such as dust, raindrops and fog. Orthogonal frequency division multiplexing (OFDM) modulations are well suited to the effects of atmospheric scattering, but simply The system combining OFDM and FSO is more complex. In order to reduce the complexity of the traditional FSO-OFDM system and improve the system performance, a new time-frequency code is designed based on the Alamouti space-time coding concept. Based on the characteristics of the atmosphere channel, a channel model is established. After introducing the system model, the method of coding and decoding the time-frequency codes is stated in detail, and the relationship between system BER and channel characteristics is analyzed. Finally, Monte Carlo simulation experiments further prove the effectiveness of the time code. The results show that using rainy days as an example, using the time-frequency coding can not only reduce the complexity of the FSO-OFDM system, but also improve the error performance significantly.