Quadrature Signaling for Intensity Modulated and Direct Detection Visible Light Communications Based on Kramers-Kronig Relation

It is long believed that the phase information in a complex signal is lost in visible light communications (VLC) with intensity modulated and direct detection (IMDD). While Kramers-Kronig (KK) relation is recently explored in coherent optical communications to reduce the receiver complexity, and a KK receiver performs phase retrieval from the amplitude received by the square-law photodiode (PD). In principal, once a modulated waveform is generated with minimum phase condition, the phase information can be reconstructed only from its amplitude. This manuscript extends KK relation into an IMDD system, and a quadrature signaling is generated with only amplitude. The single amplitude stream is used to drive the light-emitting diode (LED), where the optical intensity instead of the electrical field is modulated. A KK receiver is used to retrieve the phase and thus demodulate the quadrature signal. Simulation results show that the proposed systems for single- and multi-carrier quadrature signaling can achieve high spectrum and power efficiency with low complexity. In particular, it is attractive for VLC where the DC prescribed for illumination can be utilized for constructing a minimum phase condition. Moreover, the data rate with KK relation in VLC is doubled compared to other modulations that only encode information in amplitude.