High spectrum compression scheme based on DNN post equalization for multiband quadrature dual-quaternary coded FTN CAP 49QAM signals in visible light communication system

摘要

In this article, we utilize the Faster-Than-Nyquist (FTN) mechanism combined with the deep neural network (DNN) nonlinear post-equalization scheme to achieve spectrum compression of the multiband carrierless amplitude phase (CAP) signal in the case of a fixed channel spacing for visible light communication (VLC) system. We found that the number of input layer nodes plays a decisive role in the DNN equalization effect. And a 1.26 Gbps FTN CAP 49QAM VLC system over 1 m free space transmission is successfully demonstrated. We reduced the normalized bandwidth of the CAP 16QAM signal for each sub-band from 1.05 to 0.9 after quadrature dual-quaternary (QDQ) coding combined with DNN post-equalizer, and the total bandwidth of three bands is compressed from 315 MHz to 270 MHz. The spectrum compression ratio is 14.29% while ensuring BER below 7% FEC threshold (3.8e-3), and the spectral efficiency (SE) is 4.67 b/s/Hz. To the best of our knowledge, this is the first time achieving such high compression ratio in Gb/s level DNN based multiband FTN CAP signals in VLC system.