Clipping-Enhanced Optical OFDM for Visible Light Communication Systems

Visible light communications (VLC), a new optical wireless communication technology that uses illumination light-emitting diodes as transmitters, requires a modulation scheme that is well suited to these devices' nonlinear response. Optical orthogonal frequency division multiplexing (OFDM) is a promising technique to provide high-speed data transmission for VLC. However, the peak transmitted power limitation and nonnegative transmitted signal constraint of the lighting sources can result in nonlinear signal distortion from clipping. In this paper, we propose a novel optical OFDM scheme for VLC systems called clipping-enhanced optical OFDM (CEO-OFDM) that transmits via extra time slots the information clipped by the peak power constraint. CEO-OFDM sacrifices bandwidth to allow a higher modulation index to improve the signal to noise ratio and reduce the clipping distortion caused by the peak power limitation. From analytical and numerical results, the proposed CEO-OFDM provides better bit error rate performance and higher data rate than DC-biased optical OFDM, unipolar OFDM, and asymmetrically clipped optical OFDM. Furthermore, CEO-OFDM can provide a better illumination performance that supports light dimming.