Efficient transmission under low dimming control levels in indoor visible light communications

In indoor visible light communication (VLC) systems based on orthogonal frequency division multiplexing (OFDM), employing multi-pulse position modulation (MPPM) for dimming control will affect the receiver (Rx) sensitivity requirement particularly at low dimming levels (DLs), thus affecting the system bit error rate (BER) performance. In this paper, we propose a hybrid visible light (VL) and infrared (IR) link, where the IR is used for downlink when the DL for VLC is very low. The “off” periods of MPPM is utilized for data transmission without affecting the illumination level. This arrangement will ensure data transmission under all illumination and dark conditions. Numerical results show that by adopting the IR link, low level M-ary quadrature amplitude modulation can be always used. At low DLs, both the Rx sensitivity requirement of the VL signal and the required transmit power can be significantly alleviated while keeping a constant data rate at a BER <; 10-3.