Time-efficient adaptive modulation scheme for LACO-OFDM in VLC systems

In this paper, an adaptively layered asymmetrically clipped optical orthogonal frequency division multiplexing (LACO-OFDM) scheme is proposed and experimentally demonstrated in the visible light communication (VLC) system. Aided by the measured signal-to-noise ratio (SNR) as channel state information (CSI), adaptive modulation at the transmitter side can balance the bit-error ratio (BER) of subcarriers, and the inter-layer interference (ISI) of LACO-OFDM is accordingly mitigated. However, the sequential demodulation of LACO-OFDM determines that the SNR calculation of subsequent layers is in high latency compared to that of the first layer. Therefore, we reuse the loading information of the first layer to relax the feedback on subsequent layers. Compared to the traditional 16-quadrature amplitude modulation (QAM) with same spectral efficiency, a 0.68dB signal-to-noise ratio (SNR) improvement can be achieved by the proposed adaptive modulation scheme at BER of 3.8x10−3 for LACO-OFDM in VLC systems.