A Spectrum Enhanced ACO-OFDM Scheme for Optical Wireless Communications

In the context of optical wireless communications (OWC), the conventional asymmetrically clipped O-OFDM (ACO-OFDM) is easy to be implemented, but suffers from spectral inefficiency. Although more advanced schemes, such as layered ACO-OFDM, can improve spectral efficiency by superimposing multiple streams of O-OFDM signals for simultaneous transmission, the receiver complexity is increased with the number of the superimposed O-OFDM signals. Therefore, in this letter, considering the balance between spectral efficiency and receiver complexity, a spectrum enhanced ACO-OFDM (SEACO-OFDM) scheme is proposed with a novel symbol mapping strategy, in which an efficient positivity-forcing signal is elaborately conceived for maintaining the non-negative of the transmitted signal. By doing so, the proposed SEACO-OFDM is capable of achieving the same spectral efficiency as LACO-OFDM, while having much lower receiver complexity. Our simulation results show that the proposed SEACO-OFDM outperforms the conventional O-OFDM schemes in terms of peak-to-average power ratio (PAPR) and bit-error rate (BER).