Dimming Consideration for OFDM-Based Visible Light Communications

In the field of indoor wireless networks, visible light communications would be contributing a vital role in the future. This paper investigates the performances of data transmissions using visible light based on unipolar orthogonal frequency division multiplexing (OFDM) and discusses possible approach for light dimming. Asymmetrically clipped optical OFDM (ACO-OFDM) is considered as a unipolar modulation scheme for intensity modulation with direct detection (IM/DD) on which visible light communications is based. This modulation can incorporate light dimming while not corrupting the communication link since, compared to the traditional DC biased optical OFDM (DCO-OFDM), ACOOFDM noise clipping component does not fall on data carrying subcarrier. To create more dimming levels pulse width modulation (PWM) is proposed to be used in conjunction with ACO-OFDM.