# Optical-OFDM VLC System: Peak-to-Average Power Ratio Enhancement and Performance Evaluation
## 1 Introduction
Conversely, the FLIP-OFDM and unipolar OFDM techniques employ the transmit real output in two sequential frames without relying on DC bias for unipolar conversion. Consequently, these schemes feature a lower data rate but exhibit superior BER performance compared to the DCO-OFDM system [14]. Asymmetrically clipped optical ACO-OFDM utilizes the clipping of negative samples for unipolar conversion, eliminating the need for a DC bias. This approach enables the transmission of real unipolar output samples in a single frame, similar to DCO-OFDM, but with improved BER performance. ACO-OFDM shares the same data rate as FLIP-OFDM and U-OFDM [15]. Asymmetrically clipped DC-biased optical ADO-OFDM can be viewed as a hybrid technique, combining elements from both DCO and ACO-OFDM. While ADO-OFDM maintains the same data rate as DCO-OFDM, it exhibits inferior BER performance compared to previously mentioned approaches [16; 17]. The asymmetrically and symmetrically clipping optical ASCO-OFDM technique is a hybrid approach. This approach can achieve a higher data rate with acceptable BER performance. This approach offers a higher data rate than ACO-OFDM and FLIP-OFDM while maintaining an acceptable BER performance compared to DCO-OFDM [18]. The layered asymmetrically clipped optical LACO-OFDM scheme also presents different data rates depending on its structural configuration, leading to varying BER performance. Specifically, LACO-OFDM with a two-layer structure matches the data rate of ASCO-OFDM, and as the number of layers increases, the output data rate also increases. A comprehensive explanation of these O-OFDM schemes will be provided in this paper [19]. Combining parallel data streams to create the OFDM or O-OFDM signal introduces the challenge of PAPR [3]. Top-of-form high PAPR is an inherent challenge of OFDM, leading to nonlinear and distorted signals as well as increased strength demands for the transmitter amplifier [20]. This issue becomes particularly critical in the context of VLC, where LEDs act as transmitter elements. LEDs can be damaged by high-power signals because they operate within a limited voltage range and possess a non-linear voltage-to-current (V-I) relationship. The nonlinear (V-I) properties of LEDs contribute to distortion in the O-OFDM signal, which is exacerbated by its high PAPR. The intense peaks in the OFDM signal can cause LED chips to overheat. Consequently, prior to sending the O-OFDM signal via the LEDs, it is crucial to mitigate its high PAPR [21]. In this study, a PAPR reduction approach is used to solve the limited dynamic range of LEDs. To optimize the performance of the O-OFDM systems. This paper introduces the utilization of the Vandermonde-Like matrix (VLM) pre-coding technique for various MCM methods previously mentioned. This precoding method minimizes PAPR effectively without sacrificing BER performance and operates without the need for supplementary side details or additional processing [21]. The novelty of this work can be summarized in four key aspects. Firstly, as far as the authors are aware, this is the first comprehensive exposition of various MCM techniques employed in VLC communication systems. This exposition encompasses detailed insights into transmitter and receiver structures, spectral efficiency, symbol arrangement, power efficiency, and computational complexity. Second, in the field of lowering the PAPR for VLC systems, this study is the first to introduce a PAPR reduction approach especially designed for O-OFDM systems. Third, the study conducts a thorough evaluation of PAPR and BER performance for these MCM techniques across different modulation orders. Fourth, it includes a comprehensive description of the PAPR reduction technique, along with the quantification of its efficacy in reducing PAPR for these MCM techniques. Additionally, the research assesses the impact of this reduction technique on BER performance. The arrangement of this paper is as follows: Section 2 delineates the O-OFDM system models and parameters.