| Summary: | 碩士 === 國立雲林科技大學 === 資訊工程系 === 104 === Abstract
In a VLC system using LED as transmitter to send signals, the nonlinearity of LED V-I relation may cause serious nonlinear distortion. Orthogonal frequency division multiplexing (OFDM) is a multi-carrier technology used to increase the data rate. However, OFDM signals are susceptible to suffer nonlinear distortion because of its high peak-to-average power ratio (PAPR). In the existing literatures, the post-distortion technique was proposed to compensate for the LED's nonlinearity at receiver in OFDM-based VLC systems. However, the computational complexity is the major drawback. This paper proposes a simple but effective way to improve this problem. First, using Zadoff-Chu sequence to reduce the high PAPR of optical OFDM signals. Then use the pre-distortion technique to compensate for LED's nonlinear characteristics. Simulation results show that the proposed method can obtain the better performance in terms of bit-error-ratio (BER) and error vector magnitude (EVM) than the post-distortion technique.
Keyword: OFDM, VLC, LED nonlinearity, Zadoff-Chu, pre-distortion
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