Study of dimming and LED nonlinearity for ACO-OFDM based VLC systems

In this paper, the performance of an asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) indoor wireless system is investigated. In particular, the illuminance distribution inside a room (5m×5 m×3m) under different brightness conditions, i.e. dimming levels, and the electrical signal-to-noise ratio (SNR) at the receiver are considered. The system performance is also assessed in terms of bit-error-ratio (BER) as a function of average transmitted optical power. Brightness control is achieved using the continuous current reduction (CCR) technique to assure higher luminous efficacy compared to the pulse-width modulation (PWM) dimming technique. In addition, the impact of the induced distortions due to the nonlinear behavior of the light-emitting diode (LED) as a light source is included in the simulation model. For a circular area of about 1m radius located directly below one of the four LED illumination modules utilized in the room, having illuminance values above 300 lx (10% brightness), a 9 dB average electrical SNR is achieved at the receiver located on a desktop.