The spectral efficiency augmented HACO-OFDM based visible light communications

Abstract The conventional hybrid asymmetrically clipped optical orthogonal frequency division multiplexing (HACO-OFDM) has an obvious spectral efficiency loss due to the fact that the real part of the even subcarriers are not utilized. This paper proposes a scheme to augment the spectral efficiency of HACO-OFDM. In this scheme, more spectrum resources are exploited because the real part of selected even subcarrier group is utilized for data modulation at different depths. When the same modulation orders are used, the proposed scheme is able to achieve higher spectral efficiency than HACO-OFDM at the cost of acceptable increased computational complexity. When this scheme takes 5 depths, the joint modulation scheme uses 16QAM-4PAM and 64QAM-4PAM, the spectral efficiency of the proposed scheme can be increased by 31.33% and 23.48%, respectively. Moreover, compared with HACO-OFDM, the proposed scheme has advantages of lower PAPR and higher immunity to LED nonlinearity.