Spectrum-Efficient Hybrid Modulation Based on VOOK and Layered OFDM for Visible Light Communications

In order to satisfy the requirements of illumination and high-speed transmission in Visible Light Communications (VLC), a novel spectrum- efficient hybrid modulation based on Variable On-Off Keying (VOOK) and layered Orthogonal Frequency Division Multiplexing (OFDM) is proposed in this paper. First, the VOOK signal is designed to avoid the interference with the layered OFDM transmission. In order to ensure that the hybrid signal operates in the linear dynamic range of Light-Emitting Diode (LED), a novel Reconstructed Layered Optical OFDM (RLO-OFDM) is further conceived. Then, the RLO-OFDM and VOOK signals are combined for simultaneous transmission to realize the dual functionalities of dimming control and spectrum-efficient data transmission. At the receiver side, the VOOK and RLO-OFDM signals are detected in parallel. Moreover, a standard OFDM receiver can be directly employed to detect the RLO-OFDM signal without requiring successive interference cancellation, which reduces notably the receiver complexity and processing latency. Simulation results show that the proposed scheme is capable of supporting the linear dimming control, and achieving high spectrum efficiency.