Optimum Signal Shaping in Double-Sided Clipping DCO-OFDM

Because of the nonnegative requirement for intensity modulation (IM) and the limited dynamic range of light-emitting diodes (LEDs), double-sided clipping is inevitable in direct-current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) systems. Therefore, we should design proper signal shaping by finding a suitable bias and time-domain signal power to reduce the impact of clipping distortion. In this paper, we propose an optimal signal shaping scheme for double-sided clipping DCO-OFDM visible light communication (VLC) systems. We first model the double-sided clipping process, and formulate the signal shaping as an optimization problem in terms of the bias and time-domain signal power. We then analytically characterize the optimization problem and find the optimal signal shaping scheme. Based on the obtained optimal solution, we reveal several useful insights for practical DCO-OFDM design. The superiority and optimality of our proposed signal shaping scheme are verified by simulations.