Modulus-Based OFDM Signaling for Visible Light Communications Based on Kramers-Kronig Relation

The Kramers-Kronig (KK) relation, which has been explored in low-complexity receivers for coherent optical communications, is extended to visible light communication (VLC) systems with intensity modulation and direct detection (IM/DD). To generate a real-valued, non-negative signal suitable for IM/DD channels, a KK optical orthogonal frequency division multiplexing (KKO-OFDM) system is proposed with modulus operation on the quadrature signal with minimum phase condition. The modulus operation alleviates the constraints of Hermitian symmetry, and results in a double side-band (DSB) signal with a DC bias, enabling the re-utilization of the DC power already prescribed for illumination. Moreover, the modulus-based KKO-OFDM (MKKO-OFDM) exhibits about 1dB lower peak-to-average power ratio (PAPR) compared with DC-biased OFDM (DCO-OFDM). Experimental results demonstrate that the proposed system achieves approximately 10% higher data rates than DCO-OFDM, attributed to its lower PAPR which enhances immunity to channel nonlinearity. This approach provides a low-complexity and energy-efficient solution for VLC systems, leveraging the DC component to satisfy the minimum phase condition in signaling for data transmission.