Efficient Real-Fourier Domain-Based Color Shift Keying OFDM Implemented with Hartley Transform for Visible Light Communication System

Abstract

In visible light communication (VLC) system, the color shift keying (CSK) modulation scheme has been employed and combined with orthogonal frequency division multiplexing (OFDM) to improve the spectrum efficiency. However, the traditional fast Fourier transform (FFT) based OFDM module requires the CSK symbols to be Hermitian symmetric, which induces the waste of the bandwidth. In this paper, we propose a real-Fourier domain-based CSK OFDM scheme using the discrete Hartley transform (DHT), which is capable of transforming the real-valued signal to a real-valued signal and removes the requirement of Hermitian symmetry. Hence the spectrum utilization is approximated doubled thanks to removal of the requirement of Hermitian symmetry in conventional FFT-based OFDM systems. Moreover, the theoretical symbol error rate (SER) is evaluated for the asymmetrically-clipped optical OFDM (ACO-OFDM) and the DC-biased optical OFDM (DCO-OFDM) with CSK scheme. We then simulate the performance of CSK modulated DHT- based OFDM system, and the results show that the presented DHT-CSK-OFDM system can provide higher spectral efficiency while maintaining the same error performance as compared with the counterpart FFT-based OFDM systems.