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针对可见光通信中不均匀限幅光正交频分复用(ACO-OFDM)系统发光二极管(LED)非线性限幅失真严重的问题,提出了一种降低LED非线性限幅失真的最优功率分配方法。基于原信号直接叠加非线性限幅失真成分的限幅处理模型,分析了ACO-OFDM系统中的LED非线性限幅失真;利用有效信噪比来衡量限幅失真,将限幅失真转化为有效信噪比分析;基于有效信噪比最优的原则给出了光功率约束下降低限幅失真的最优偏置信号和ACO-OFDM信号功率分配。仿真结果表明,当信道的信噪比较低时,信道噪声起主导作用;当信道的信噪比较高时,限幅失真起主导作用。在光功率约束下若不考虑偏置信号的影响而直接取其值为LED最小输出功率限制,则系统误码率(BER)在信道信噪比大于40dB的情况下也始终大于10-2,而采用最优功率分配时可以保证系统具有较好的误码率性能,当光功率约束为200mW和250mW时,分别需要24dB和27dB的信道信噪比即可使得系统的误码率低于10-3。
In order to solve the problem of non-linear amplitude limiting distortion of non-uniform limiting Orthogonal Frequency Division Multiplexing (ACO-OFDM) system LED in visible light communication, an optimal power reduction method to reduce non-linear LED amplitude limiting distortion Distribution method. Based on the limiting signal processing model which directly superimposes non-linear amplitude-limited distortion components on the original signal, the non-linear LED amplitude-limiting distortion in ACO-OFDM system is analyzed. The effective SNR is used to measure the limiting distortion, Signal-to-noise ratio analysis. Based on the principle of optimal signal-to-noise ratio (SNR), the optimal bias signal and ACO-OFDM signal power allocation under the optical power constraint are given. The simulation results show that the channel noise plays a leading role when the signal-to-noise ratio of the channel is low, and the clipping distortion plays a leading role when the signal-to-noise ratio of the channel is high. Without considering the effect of bias signal under the optical power constraint, the value of the minimum output power of the LED is taken as the limit, and the system BER is always greater than 10-2 when the channel SNR is greater than 40dB. When the optimal power allocation is adopted, the system can ensure good BER performance. When the optical power is limited to 200mW and 250mW, respectively, the channel SNR of 24dB and 27dB respectively can make the system error rate lower than 10 -3.