Pre-clipping method to reduce clipping-induced degradation in hybrid analog/digital subcarrier-multiplexed optical transmission systems

Using a precoding technique to reduce the BER penalty of an M-QAM channel in hybrid AM-VSB/M-QAM subcarrier multiplexed lightwave systems

“…an L-pulse amplitude modulation (L-PAM) signal, where L is a positive integer. The precoded symbol b is then given by b=(a,1+bD)modL (1) where D is the number of delayed symbols. Similarly, after the comb filter and the modulo operator, the recovered…”

“…The first is the preclipping method [1][21, which used a limiter before the laser diode so that the laser diode will not clip, and a low pass filter or a band stop filter after the limiter to remove the clipping-induced NLD's. The drawback of this technique is that the BER performance of the M-QAM channel depends critically on the filter design which may not be practically feasible.…”

Using precoding technique to reduce the BER penalty of an M-QAM channel in hybrid AM-VSB/M-QAM subcarrier multiplexed lightwave systems

“…To show that the overall coding system works, assume that the input data symbol i.e., an -pulse amplitude modulation -PAM) signal, where is a positive integer. The precoded symbol is then given by (1) where is the number of delayed symbols. Similarly, after the comb filter and the modulo operator, the recovered symbol is…”

“…In the past few years, several techniques have been proposed to overcome this problem. The first is the preclipping method [1], [2], which used a limiter before the laser diode so that the laser diode will not clip, and a low pass filter or a band stop filter after the limiter to remove the clipping-induced nonlinear distortions (NLD's). The drawback of this technique is that the BER performance of the -QAM channel depends critically on the filter design which may not be practically feasible.…”