High Speed WDM VLC System Based on Multi-Band CAP64 With Weighted Pre-Equalization and Modified CMMA Based Post-Equalization

Multi-user access is one of the key problems in the visible light communication (VLC). In this paper, we propose and experimentally demonstrate an approach for multi-user access based on multi-band CAP modulation over a wavelength division multiplexing (WDM) VLC system using a single RGB LED. In this scenario each wavelength will provide 3 sub-bands. Depending on the combination of the different wavelength and the sub-bands, a dynamic capacity can be achieved for up to 9 users access. At the transmitter a weighted pre-equalization method is proposed to overcome frequency attenuation of the LED, while at the receiver a post-equalizer based on modified cascaded multi-modulus algorithm (CMMA) is utilized. The experimental results show that the bit error rate (BER) for an over-all 1.35 Gb/s CAP64 signal over 30-cm transmission can be under the 7% forward error correction (FEC) limit of 3.8 × 10^-3. The results clearly demonstrate the benefit and feasibility of the multi-band CAP modulation for the short range multi-user VLC systems.