Enabling Technologies for High-Speed Visible Light Communication Employing CAP Modulation

High-speed light emitting diode (LED) based visible light communication (VLC) system is restricted by the limited LED bandwidth, low detector sensitivity, and linear and nonlinear distortions. Thus, single- and two-cascaded constant-resistance symmetrical bridged-T amplitude hardware pre-equalizers, carrierless amplitude and phase (CAP) modulation, and a three-stage hybrid postequalizer are investigated to increase transmission data rate for a high-speed LED-based VLC system. The schemes utilized by the hybrid postequalizer are modified cascaded multimodulus algorithm, Volterra series based nonlinear compensation algorithm and decision-directed least mean square algorithm. With these technologies, we successfully implement high-speed CAP32, CAP64, and CAP128 VLC experimental system over 1-m free space transmission with bit error rate under the hard decision-forward error correction threshold of 3.8 × 10 -3 . System performance improvement employing these key technologies is also validated through experimental demonstration. With the superposition of each stage of the hybrid postequalizer, system performance will be improved. And utilizing two-cascaded hardware pre-equalizer will provide more accurate channel compensation than a single pre-equalizer.