Fig. 1. Block diagram detailing an ACom-based VLC system using OFDM, depicting the transmitter, receiver, and the optical channel in between.

Fig. 2. Example of the time-domain representation of an ACom signal, with an IFFT length of 16. The construction is showing the parameters η and α and their effect on the generated signal s for a specific b.

Fig. 3. Simulation results depicting the relative spectral efficiency gain of ACom versus various system parameters. (a) Modulation order M at η=N=64, (b) IFFT length N at η=N and M=4, and (c) η for various M.

Fig. 4. BER versus SNR performance with the solid red line denoting the analytical performance and the remaining curves showing ACom at different γ for both the legitimate user (User) and the eavesdropper (Eve) at η=N=64.

Fig. 5. Effective SNR reduction versus γ showing that at γ=0.2 the effective SNR is reduced to only be 0.3 dB.

Fig. 6. Experimental setup of ACom using a USRP-N210 with two integrated daughterboards showing the optical frontends and the NUC used for ACom signal processing.

Fig. 7. Experimental BER performance at 4-QAM with an IFFT length of 64 for the legitimate user at η=N, where γ=0 is equivalent to conventional DCO-OFDM transmission.

Fig. 8. Experimental BER performance of the eavesdropper as a function of η and γ at an SNR level of 20 dB at 4-QAM with an IFFT length of 64.