Hermitian symmetry (HS) is essential for attaining a real-valued signal for intensity modulation and direct detection of visible light communication (VLC). However, HS results in an increase of the peak-to-average power ratio (PAPR). We propose an HS free direct current optical-universal filtered multicarrier (HSF DCO-UFMC) system for VLC. In this technique, the conventional complex UFMC signal is transformed by juxtaposing the real and imaginary components to attain a real valued signal. Therefore, HSF DCO-UFMC offers a great reduction of the PAPR. We also address the nonlinear companding transforms for further reduction of the PAPR of the HSF DCO-UFMC signal. A new companding transform called two μ-law that reduces the PAPR and provides more design flexibility by employing two optimum companding levels and a threshold value is proposed for the HSF DCO-UFMC system. However, this scheme raises the average power level of the signal. So, to maintain a constant average power level, an enhanced two μ-law is proposed to reduce the PAPR effectively. Simulation outcomes exemplify that the proposed HSF DCO-UFMC provides better PAPR reduction. In addition, the proposed two μ-law and enhanced two μ-law can provide an improved PAPR reduction, suppressed side-lobe levels, and better bit error rate performance than the original HSF DCO-UFMC signal.

中文翻译：

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带压扩技术的埃尔米特对称自由直流光学通用滤波多载波调制/直接检测系统

厄米对称（HS）对于获得用于强度调制和直接检测可见光通信（VLC）的实值信号至关重要。但是，HS导致峰均功率比（PAPR）增大。我们提出了一种用于VLC的无HS直流光学通用滤波多载波（HSF DCO-UFMC）系统。在该技术中，通过将实数分量和虚数分量并置来变换常规复数UFMC信号，以获得实值信号。因此，HSF DCO-UFMC大大降低了PAPR。我们还讨论了非线性压扩变换，以进一步降低HSF DCO-UFMC信号的PAPR。对于HSF DCO-UFMC系统，提出了一种新的压扩变换，称为“两个μ律”，可通过使用两个最佳压扩级别和阈值来降低PAPR并提供更大的设计灵活性。但是，该方案提高了信号的平均功率水平。因此，为了保持恒定的平均功率水平，提出了增强的2μ律以有效降低PAPR。仿真结果表明，提出的HSF DCO-UFMC可以更好地降低PAPR。此外，与原始HSF DCO-UFMC信号相比，建议的2μ律和增强的2μ律可以提供更好的PAPR降低，抑制的旁瓣电平以及更好的误码率性能。提出了增强的2μ律，以有效降低PAPR。仿真结果表明，提出的HSF DCO-UFMC可以更好地降低PAPR。此外，与原始HSF DCO-UFMC信号相比，建议的2μ律和增强的2μ律可以提供更好的PAPR降低，抑制的旁瓣电平以及更好的误码率性能。提出了增强的2μ律，以有效降低PAPR。仿真结果表明，提出的HSF DCO-UFMC可以更好地降低PAPR。此外，与原始HSF DCO-UFMC信号相比，建议的2μ律和增强的2μ律可以提供更好的PAPR降低，抑制的旁瓣电平和更好的误码率性能。