Fig. 1. Schematic diagram: (a) CAP-64 system; (b) OFDM 64QAM system; (c) DFT-S OFDM 64QAM system.

Fig. 2. Structure of the RLS-Volterra post-equalizer.

Fig. 3. CCDF versus PAPR of CAP-64, OFDM 64QAM, and DFT-S OFDM 64QAM.

Fig. 4. Experimental setup of (a), (b) the underwater VLC system and (c) the free-space VLC system.

Fig. 5. Block diagram of post-equalization in the CAP, DFT-S OFDM, and OFDM systems.

Fig. 6. Spectrum maps for the UVLC system at the transmitter, at the receiver, and after the first post-equalization: (a) CAP at the transmitter; (b) DFT-S OFDM at the transmitter; (c) OFDM at the transmitter; (d) CAP at the receiver; (e) DFT-S OFDM at the receiver; (f) OFDM at the receiver; (g) CAP after the first post-equalization; (h) DFT-S OFDM after the first post-equalization; and (i) OFDM after the first post-equalization.

Fig. 7. Amplitude to amplitude (AM/AM) response of CAP modulation in (a) the UVLC system and (b) the VLC system.

Fig. 8. BER versus LED current in (a) the traditional VLC system and (b) the UVLC system.

Fig. 9. BER versus order of Volterra in the UVLC and VLC systems with (a) CAP, (b) DFT-S, and (c) OFDM.

Fig. 10. BER versus number of taps in the UVLC and VLC systems with (a) CAP, (b) DFT-S, and (c) OFDM.

Fig. 11. BER performance of the 2nd post-equalization for OFDM and DFT-S OFDM in the UVLC system: (a) with different number of pilot, (b) channel curve when the number of pilot is 2, and (c) channel curve when the number of pilot is 256.

Fig. 12. BER versus LED optical power of CAP, DFT-S, and OFDM systems.

Fig. 13. BER versus peak-to-peak voltages (V_pp) of the LED in CAP, DFT-S OFDM, and OFDM systems.

Fig. 14. BER performance versus bandwidth of three advanced modulation formats in the UVLC system.

Table 1. Summary of Research Results of VLC Systems

Table 2. Summary of Research Results of LED UVLC Systems