Logistic-function-based nonlinear companding transform for asymmetrical hybrid optical orthogonal frequency division multiplexing visible light communications systems

In this paper, a logistic-function-based nonlinear companding transform (LNCT) is proposed to reduce the peak-to-average power ratio of asymmetrical hybrid optical orthogonal frequency division multiplexing (AHO-OFDM) signals in visible light communications (VLC). First, the positive and negative amplitudes of the bipolar AHO-OFDM signal are divided into two groups as the positive and nonnegative groups. Then, a peak detection is employed frame-by-frame to locate the group where the maximum peak occurs. Finally, the piecewise companding transform consisting of the nonlinear logistic function and a linear function is performed on the amplitude groups with and without the maximum peak, respectively. The simulation results show that the proposed LNCT scheme outperforms the classical linear nonsymmetrical transform method in terms of the complementary cumulative distribution function with a competing bit error rate performance, thus demonstrating its application potential in AHO-OFDM-based VLC systems.