Hybrid scheme of precoder with μ-law compander for PAPR reduction and nonlinearity improvement in ADO-OFDM system

摘要

The application of orthogonal frequency division multiplexing (OFDM) in a visible light communication (VLC) system increases the peak-to-average power ratio (PAPR) of the system. Owing to high PAPR, the intrinsic nonlinearity of LED is an important issue in an asymmetrically clipped DC-biased optical OFDM (ADO-OFDM) system. In this paper, a hybrid scheme is proposed to reduce the PAPR as well as to mitigate the nonlinearity in an ADO-OFDM system. The proposed method is a combination of two ADO-OFDM formats: precoded ADO-OFDM and mu-ADO-OFDM. The preprocessing of the input using a predetermined matrix (PM) in the precoder relieves the need for a handshake at the receiver. The compression of the peak values and enhancement of low amplitudes of the precoded signal in the time domain yield a low PAPR of 2.4 dB only. Besides PAPR reduction, the union of precoder and compander boosts the bit error rate (BER) performance of the traditional ADO-OFDM system for mu = 128. The combination of precoder with compander decreases the power requirements for high bit rate transmission for a reference BER of 10(-3). In this work, nonlinearity is quantified in terms of error vector magnitude (EVM) in percent. The hybrid scheme shows an EVM of 17.23% for 0 dB input backoff power (IBO) much less than 66.4% EVM for a simple ADO-OFDM system. In addition to low PAPR and mitigation of nonlinearity, the proposed method shows the improvement in power spectral density (PSD) of the system.