PWM-based Dimmable Hybrid Optical OFDM for Visible Light Communications

In visible-light communication (VLC) system, hybrid asymmetrically clipped optical orthogonal frequency division multiplexing (HACO-OFDM) is an attractive multi-carrier modulation to achieve high power and spectrum efficiency. Dimming control is deemed to be an essential technique in VLC since it can meet diverse luminance demands. However, severe non-linear distortion occurs when dimming the HACO-OFDM VLC system, especially with the pulse-width modulation (PWM) dimming technique. In this work, a novel PWM-based dimmable hybrid optical OFDM (DHO-OFDM) scheme is proposed to simultaneously support different illumination requirements and realise a spectral-efficient VLC link. The transmitted symbols in the authors' proposed DHO-OFDM can be readily estimated by the standard HACO-OFDM receiver without requiring the additional detecting the PWM signal, thus reducing the receiver complexity compared to the other PWM-based dimmable schemes. Moreover, the proposed DHO-OFDM scheme can support a broad dimming range with a relatively stable communication performance, which makes it more suitable for broadband data transmission. Numerical results have verified the superiorities of DHO-OFDM over the conventional OFDM schemes in terms of achievable spectral efficiency and bit-error rate.