Reducing Signalling Overhead and Power Consumption in OWC DCO-OFDM with Adaptive Bit Loading

Light Fidelity (LiFi), using light-emitting diodes (LEDs) to communicate wirelessly via light, predominantly uses orthogonal frequency division multiplexing (OFDM) with adaptive bit loading. In contrast to Radio (RF) communications, on the optical wireless communications (OWC) the gains are substantial while the signalling overhead can be limited. An example is the International Telecommunication Union (ITU) G.9991 standard. This paper shows that the bit loading scheme can be further optimized for LED communication. The LED channel is characterized by a transfer function that is predominantly declining with frequency and does not exhibit severe multipath nulls. In this paper, we describe an algorithm that allows the exchange of a signal-to-noise ratio (SNR) margin on some subcarriers, to improve the SNR on subcarriers that experiences poorer channel responses. It combines a number of subcarriers to get a more equally distributed SNRs. Subcarriers with an excess margin in SNR are used to help subcarriers with insufficient SNR.