Layered Generalized Adaptively Biased Optical OFDM for IM/DD OWC Systems

Due to the high spectral efficiency and robustness against inter-symbol interference (ISI), orthogonal frequency division multiplexing (OFDM) is attracting increasing attention in sixth-generation (6G) optical wireless communication (OWC) systems. In this paper, based on generalized adaptively biased optical OFDM (GABO-OFDM), we propose a novel power and spectrally efficient scheme of layered GABO-OFDM (LGABO-OFDM). The subcarriers in LGABO-OFDM are divided into several layers and conveyed simultaneously. Each layer employs GABO-OFDM which adds an adaptive bias to generate nonnegative signals. The added bias is orthogonal to the occupied subcarriers in each layer, therefore the transmitted information can be recovered iteratively at the receiver side. Theoretical derivation demonstrates that LGABO-OFDM is more spectrally efficient than traditional asymmetrically clipped optical OFDM (ACO-OFDM) and hybrid ACO-OFDM (HACO-OFDM). In order to optimize the power efficiency and reduce bit error rate (BER), we novelly propose an optical power allocation method and the principle of subcarrier allocation of LGABO-OFDM after analyzing the statistical properties of the adaptive bias. Numerical results further suggest that the proposed LGABO-OFDM has lower BER and peak-to-average power ratio (PAPR) than its conventional counterparts, which demonstrates its high power efficiency and capability of resisting the nonlinear distortion.