Research on partial linear companding transform for reducing the clipping distortion of visible light OFDM system

To handle the significant clipping distortion of light emitting diode (LED) in visible light orthogonal frequency division multiplexing (OFDM) system, a partial linear companding transform method is proposed. Under the higher or lower optical power constraints, the positive or negative signal of bipolar direct current optical orthogonal frequency division multiplexing (DCO-OFDM) signal is linearly compressed at the transmitter. In the receiver, the companded signal is linearly expanded. So it can effectively reduce the clipping noise. With a certain input signal power, the best system performance is achieved by optimizing the coefficient of partial linear companding transform and the DC bias based on the principle of maximum effective signal to noise ratio (SNR). Simulations show that the system performance becomes worse with the increase of optical power constraint. Also the optimal value of the compressing coefficient becomes smaller. With the increase of QAM modulation order, the system performance gain obtained by partial linear companding transform becomes smaller.