Fig. 1. The principle of the proposed scheme. The original bit sequence is mapped into the PAM-8 signal. After FFT, two major methods, logistic phase scrambling and conjugate frequency hopping, are implemented. After IFFT and UVLC transmission, the received signal is dehopped and descrambled for DSP and demodulation.

Fig. 2. Logistic maps generated by (a) Eq. (8) and (b) Eq. (9) when the bifurcation parameter μ changes.

Fig. 3. Experimental setup of the proposed scheme for UVLC links. Arbitrary waveform generator, AWG; electric amplifier, EA; positive-intrinsic-negative photoelectric diode; PIN-PD; oscilloscope, OSC.

Fig. 4. BER performance versus the bias current I_b and the peak-to-peak voltage V_pp of the AWG.

Fig. 5. BER versus the transmission speed. Insets are the constellation diagrams.

Fig. 6. BER versus the phase scrambling coding weight w. Insets are the constellation diagrams.

Fig. 7. BER versus the different decryption technology.