An Optimum DC-Biasing for DCO-OFDM System

Selecting an appropriate direct current (dc) bias is crucial to obtain positive and low-peak-to-average-power-ratio electrical signals in the dc optical orthogonal frequency-division multiplexing (DCO-OFDM) system. In this letter, our goal is to propose an optimization strategy of dc bias under given lower and upper clipping bounds. We characterize the mean square error between the original signals and the clipped ones as the metric of clipping distortion. Finding the optimum dc bias can be formulated as a nonconvex optimization problem. However, the optimum dc bias can be obtained from a numerical method. The simulation results show that the bit error ratio performance can be improved when employing the optimum dc bias obtained by the proposed numerical method.