强背景光下可见光大气湍流信道建模及分集接收技术

Turbulence Channel Modeling of Visible Light Communication under Strong Background Noise and Diversity Receiving Technologies

可见光大气传输系统面临的主要问题在于由大气湍流引起的光强闪烁和来自日光及其他照明设备的强背景光干扰,为了克服大气湍流造成的信道衰落效应及强背景光带来的噪声干扰问题,对室外可见光通信(VLC)强背景光大气湍流信道进行了建模。在接收端采用分集接收技术,在相同的发射功率下提高系统误码率(BER)性能。构建了在强背景光大气湍流信道模型下基于强度检测脉冲位置调制(PPM)方式的室外长距离可见光分集接收系统模型,在几十微瓦功率背景光噪声下,实现了800 Mb/s PPM信号的仿真系统传输。基于此系统分别研究对比了最大比合并(MRC)、等增益合并(EGC)、选择性合并(SC)3种分集合并方式的误码率性能。结果表明,在相同的发射功率下,误码率性能提升最大的是MRC,其次是EGC,SC最差。以7%前向纠错码(FEC)误码门限作为参考,MRC能显著降低对LED发射功率的要求,并且随着分集支路个数的增多,分集效果越好。

The scintillation caused by the atmosphere turbulence and strong background noise from sunlight and other lighting equipment are two main problems in visible light communication （VLC） atmosphere transmission system. In order to overcome the channel fading effect caused by the atmosphere turbulence and the noise interference caused by the strong background light, VLC atmosphere channel with strong background noise is modeled. Diversity receiving technologies are utilized to improve the bit error rate （BER） performance of the system at the same transmitting power. According to the channel model, outdoor long-distance VLC system based on intensity detection pulse position modulation （PPM） in turbulence atmosphere channel using diversity receiving technologies is finally set up. In our simulation, the system bandwidth is 400 MHz and bit rate is 800 Mb/s. The BER performances of three diversity receiving technologies： maximal ratio combing （MRC）, equal gain combing （EGC）, selection combing （SC） are also compared. The results show that under the same transmitting power, the improvement of BER performance by MRC is the best, followed by EGC and SC is poor. Taking 7% forward error correction（FEC） as the BER threshold, the required LED transmitting power is greatly decreased with MRC. Furthermore, with the increase of the number of diversity branches, the BER performance is better.