Research Of The Theory And Method To Improve The Nonlinearity Distortion In OFDM Visible Light Communication

Visible light communication is a novel kind of optical wireless communication. White LED has the characteristics of short response time and high-speed modulation, therefore it is utilized in visible light communication to realize the transmission of wireless signal, allowing the system to function both lighting and communication. In order to achieve high-speed visible light communication, it’s very essential to introduce OFDM to overcome the multi-path interference of wireless channel. However, this will lead visible light communication system to suffer the drawback of nonlinear distortion. The nonlinear distortion in OFDM visible light communication is mainly caused by the nonlinear characteristic of LED and the high peak-to-average power ratio (PAPR) of the OFDM signal. In this paper, above two aspects are studied to explore methods to reduce the nonlinear distortion of the system. Firstly, the influence of LED nonlinear characteristics on the performance of OFDM light communication is analyzed. Combined with the theoretical nonlinear propagation properties and actual working requirements of LED, solid-state amplifier model is introduced to establish the LED nonlinear propagation model of visible light communication. Afterwards, the established model is used to analyze the impact of parameters, including the DC bias point of LED and the OFDM signal power, on the communication performance of the system. The simulation results show that selecting the appropriate DC bias point and controlling the OFMD signal power in an appropriate range can effectively reduce the nonlinear distortion. In addition, the principle of high peak to average power ratio, especially the principle and performance of several existing PAPR reduction methods including pre-distortion, encoding and scrambling are analyzed in this paper. Also a set-off of PAPR reduction technology evaluation criteria is established. Then, a new PAPR reduction method named Amplitude Coding-distortion is proposed. According to the method, the amplitude of OFDM signal is encoded and transformed in accordance with the preset rules, making the high peak signal transformed to the low amplitude signal to achieve the purpose of PAPR reduction. The simulation results show that the proposed method can effectively reduce the PAPR value with a low degree of complexity, while the performance would not decrease with the increasing number of sub-carriers of the system. The number of images, tables and references in this paper are32,3and71.