发光二极管(LED)的非线性特性会使可见光通信(VLC)系统的误差矢量幅度(EVM)和误码率(BER)恶化,介绍了基于非线性LED的光正交频分复用(O-OFDM)VLC系统原理,并推导了系统的BER表达式。提出了将LED非线性失真分为工作区内的非线性失真和工作区外的限幅失真。对于限幅失真,根据Bussgang理论,计算载荷信息的子载波衰减因子,进而得到叠加在子载波上的限幅噪声方差。将工作区内的非线性失真,等效为驱动信号加上非线性失真噪声,用非线性LED输出信号偏离理想线性信号的总平均功率减去直流功率作为噪声方差。用蒙特卡罗法仿真分析了非线性失真对星座图、EVM和BER的影响。

The error vector magnitude (EVM) and bit error rate (BER) performance of visible light communication (VLC) system will be deteriorated by the nonlinear characteristic of light emitting diode (LED). In this paper, the principle of optical orthogonal frequency division multiplexing (O-OFDM) VLC system based on nonlinear LED is introduced, and the BER expression of the system is derived. It is proposed to divide the LED nonlinear distortion into nonlinear distortion in the working area and clipping distortion outside the working area. For the clipping distortion, the subcarrier attenuation factor of the load information is calculated according to Bussgang theory, and then the clipping noise variance superimposed on the subcarrier is obtained. The nonlinear distortion in the working area is the equivalent to the driving signal plus the nonlinear distortion noise, and use the total average power of the nonlinear LED output deviates from the ideal linear signal minus direct current power as the noise variance. The influence of nonlinear distortion on constellation, EVM, and BER is analyzed by Monte Carlo simulation.