Clipping Distortion Analysis for DFT-Precoded Visible Light Communication OFDM Systems With Dimming Control

Visible light communication (VLC) plays a vital role in enabling the Internet of Things (IoT), providing both high-speed, secure communication and illumination through the use of existing lighting devices. However, there is often a conflict between the communication and illumination requirements of systems, particularly regarding the power of the transmitted optical signal when employing orthogonal frequency division multiplexing (OFDM) for communication due to its higher peak-to-average power ratio (PAPR). The discrete Fourier transform (DFT) precoding method has been effective in reducing the PAPR in optical OFDM systems. Nevertheless, the combined communication and illumination performance of OFDM systems after DFT precoding has not been thoroughly analyzed, including aspects, such as the optimal selection of the dimension of the DFT precoding matrix. This study focuses on developing an analytical model for the clipping noise in communication signals and illumination within DFT-precoded VLC systems, specifically within the context of asymmetrically clipped optical OFDM (ACO-OFDM) in systems constrained by bandwidth and power limitations. We introduce a new analytical tool, the weighted Bussgang theorem, to analyze the clipping noise in non-Gaussian DFT-precoded OFDM signals. Furthermore, we identify a tradeoff between clipping effects resulting from power constraints and the performance of illumination, providing insights into selecting the appropriate dimension for the DFT-precoding matrix based on varying illumination requirements. Additionally, we suggest utilizing a power index within the OFDM system to adjust signal strength, thereby balancing clipping distortion and illumination performance. Simulation results validate the efficacy of our analytical approach, demonstrating improved bit rates in adjustable illumination DFT-ACO-OFDM systems compared to non-DFT-precoded alternatives.