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

Abstract

AbstractIn 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.