Layered Optical OFDM With Adaptive Bias for Dimming Compatible Visible Light Communications

Abstract

Capable of supporting the dual functionalities of dimming control and high-speed data transmission, dimmable optical orthogonal frequency division multiplexing (O-OFDM) has attracted increasing attentions in visible light communication (VLC). A major design challenge in the dimmable O-OFDM is to realize spectrally efficient VLC link compatible with dimming control while conforming to the low-complexity philosophy of the intensity modulation/direct detection (IM/DD) system. To cope with this challenge, a novel scheme is conceived, named as adaptively biased layered O-OFDM (ABLO-OFDM), which can be well integrated with the industry-preferred pulse width modulation (PWM) dimming technique. Similar to the conventional layered asymmetrically clipped O-OFDM (LACO-OFDM), multiple layers of subcarriers are utilized to transmit information data in ABLO-OFDM, resulting in high spectral efficiency. Only one inverse fast Fourier transform (IFFT) block is required in ABLO-OFDM to generate the layered O-OFDM signal compared to multiple IFFT blocks in LACO-OFDM. Moreover, the demodulation of the dimmable ABLO-OFDM (DABLO-OFDM) signal can straightforwardly rely on standard OFDM receiver, which is immune to the dimming process. Therefore, the proposed scheme achieves high spectral efficiency whilst possessing low-complexity transceiver compared to conventional O-OFDM. It is shown that DABLO-OFDM is superior to its counterparts in terms of the achievable spectral efficiency for intermediate dimming levels.