Dimming Compatible Optical OFDM for High Speed Visible Light Communications

In this paper, we study a novel optical orthogonal frequency division multiplexing (OFDM) scheme, fractional reversed polarity optical OFDM (FRPO- OFDM), which enables dimmable visible light communications. The scheme combines an asymmetrically clipped optical OFDM (ACO-OFDM) sequence with an information-carrying brightness control sequence (BCS). We show that the new scheme can create a wide range of brightness levels whilst transmitting extra information using the BCS to enhance the spectral efficiency. The detector which can recover information from both sequences is derived based on maximum likelihood (ML) detection and estimation. It is shown that the information carried by the BCS using variable on-off keying (VOOK) can be detected with extremely low bit error rate (BER) and that the resulting overall BER of FRPO-OFDM is constant over a wide dimming range.