Asymmetrical and direct current biased optical OFDM for visible light communication with dimming control

Abstract

In visible light communication (VLC) systems, optical orthogonal frequency division multiplexing (O-OFDM) is an appealing modulation. Among many proposed O-OFDM schemes, both direct current biased O-OFDM (DCO-OFDM) and asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) are widely used. Since VLC needs to take the dual requirements of illumination and communication into account, different dimming levels are often required. For high and low dimming level scenarios, system with ACO-OFDM normally has a better spectral efficiency performance than system with DCO-OFDM due to the smaller clipping noise. However, regarding the middle dimming level scenarios, the DCO-OFDM generally outperforms the ACO-OFDM. In order to improve system spectral efficiency within the wide dimming range, an asymmetrical and direct current biased optical orthogonal frequency division multiplexing (AAD-OFDM) is proposed in this paper. In AAD-OFDM based system, the modulation scheme is switched between ACO-OFDM and DCO-OFDM according to the required dimming level. Therefore, by adopting the proposed AAD-OFDM, the VLC system can fully utilize the dynamic range of LED at any dimming levels thus improving the performance. Simulation results show that the proposed scheme has high spectral efficiency within a wide dimming range.