A Novel Index Modulation for Dimming in LiFi Systems

This paper introduces a novel dimming method for Light Fidelity (LiFi) based on index modulation (IM). A time-domain sample-index modulation (TIM) is proposed for indexed dimming (iDim). The aim is to maintain a high communication performance measured in signal to noise ratio (SNR) and a high transmission rate for a wide light emitting diode (LED) brightness range. Direct current optical orthogonal frequency division multiplexing (DCO-OFDM) is used. The system performance is experimentally validated by an implementation on a National Instruments (NI) PXIe-1085 and NI-7966R Field Programmable Gate Array (FPGA). The proposed iDim offers a wider dimming range and an improved SNR/symbol when compared to amplitude-modulation dimming (AM dimming). In particular, the iDim system provides a SNR/symbol of 22.5 dB for all brightness levels. The lowest optical power is measured at 20 μW which is 10 times lower than the measured limit of AM dimming. This reduces the cost of the optical power per bit. Therefore, iDim is a promising dimming method for applications targeting extremely low illumination levels.