Duration of Clipping-induced Distortion and its Effect on BER Performance of QAM Signals in Optical Cable TV Systems

Abstract

In a hybrid analog (AM VSB) /digital (QAM) sub carrier multiplexed (SCM) optical cable TV system, clipping induced impulsive distortion occurs when the SCM signal's amplitude drops below the laser diode (LD) threshold This distortion may induce bursts of bit errors in digital channels We have investigated the duration of clipping induced distortion and its effect on the BER performance of QAM signals As a result, we found that the frequency accuracy of the analog sub carriers is one of the main factors that characterize the clipping induced impulsive distortion which affects the performance of the digital channel The more accurately the frequencies of the analog sub carriers are set, the longer the duration of the clipping induced distortions becomes If the duration exceeds the ability of the forward error correction (FEC) system, the FEC system will not work well because of the error bursts This factor has not been considered in previous approaches