Absolute Value Layered ACO-OFDM for Intensity-Modulated Optical Wireless Channels

Both enhanced unipolar orthogonal frequency division multiplexing (eU-OFDM) and layered asymmetrically clipped optical OFDM (LACO-OFDM) are among the most spectrally efficient modulation techniques for intensity modulated links that layer multiple non-negative signals. In this paper, we propose absolute value layered asymmetrically clipped optical OFDM (ALACO-OFDM) which further improves the spectral efficiency while using a smaller number of layers and no direct current (DC) bias. In ALACO-OFDM, asymmetrically clipped optical OFDM (ACO-OFDM) signals are sent at the first L layers and absolute value optical OFDM (AVO-OFDM) is used for the remaining subcarriers and transmitted simultaneously. Analysis indicates that ALACO-OFDM achieves higher spectral efficiency and smaller peak-to-average power ratio (PAPR) compared to eU-OFDM, LACO-OFDM and asymmetrically clipped absolute value optical OFDM (AAO-OFDM). Monte Carlo simulation results also indicate that ALACO-OFDM achieves significant bit error rate (BER) performance gains compared to its counterparts at the same spectral efficiency.