Adaptive bias layered optical OFDM based on precoding for IM/DD systems

Abstract

An adaptive bias layered optical orthogonal frequency division multiplexing (ABLO-OFDM) scheme based on real-valued precoding is proposed in the intensity modulation and direct detection (IM/DD) system. In ABLO-OFDM scheme, multilayer subcarriers are used to transmit data, which can achieve high spectral efficiency (SE) and reduce the peak average power ratio (PAPR). Compared with layered asymmetrically clipped O-OFDM (LACO-OFDM) scheme, only one inverse Fast Fourier transform (IFFT) block is needed in ABLO-OFDM. At the same time, the signal can be demodulated directly using the standard OFDM receiver. In addition, to resist the selective fading effect of the system, low-complexity real-valued precoding, namely discrete cosine transform (DCT) and discrete Hartley transform (DHT), are used to effectively balance the signal-to-noise ratio (SNR) between subcarriers and further reduce the PAPR. The result shows that the PAPR of the ABLO-OFDM system is reduced by 2.7 dB after adaptive bias layering, and the PAPR is further reduced by 2.4 dB at most after precoding. For the layered ABLO-OFDM system with DCT precoding, as the number of subcarrier layers decreases from L = 8 to L = 1, the required receiver optical power (ROP) is reduced by 6 dB. It proves that the ABLO-OFDM system with DCT precoding can achieve higher SE and effectively improve receiver sensitivity.