Spectrally enhanced PAM-DMT for IM/DD optical wireless communications

For the same spectral efficiency, pulse-amplitude-modulated discrete multitone modulation (PAM-DMT) has a lower power efficiency in comparison with direct current (DC)-biased optical orthogonal frequency division multiplexing (DCO-OFDM). A power efficient spectrally enhanced PAM-DMT (ePAM-DMT) is proposed in this paper. Superposition modulation of multiple PAM-DMT streams is used to improve the spectral efficiency of PAM-DMT. The ePAM-DMT allows the spectral efficiency gap between DCO-OFDM and other unipolar OFDM schemes to be completely closed. The proposed system is compared with DCO-OFDM in the context of an additive white Gaussian noise (AWGN) channel. A closed-form theoretical bound on the bit error rate (BER) performance of the proposed scheme is derived and verified by Monte Carlo simulations. The proposed scheme is energy efficient in terms of the electrical power consumption. The high optical energy dissipation of the proposed scheme makes it suitable for the illumination-based visible light communications (VLC) applications.