Error statistics of 64-QAM signal in AM/64-QAM hybrid optical transmission

This paper describes the performance of an error correction system based on the DAVIC specifications. It also presents an error statistics property and its analytical model for the impulse noise induced by clipping in amplitude modulation (AM)/64 quadrature amplitude modulation (QAM) hybrid optical transmission (hybrid transmission). We found in hybrid transmission that the errors cannot be completely corrected by the error correction of DAVIC after hit error rate (BER) measurement with error correction, and then the error statistics of the 64-QAM channel were evaluated. It was confirmed that errors occasionally occur in long bursts that exceed an interleaver block length of the error correction when the impulse noise degrades the 64-QAM signal´s BER. We believe that the error burst is caused by the slowed fluctuation of the envelope of a frequency division multiplex (FDM) signal in hybrid transmission. Once a portion of the envelope amplitude reaches the clipping level, the duration of maintaining such a condition is much longer than the 64-QAM symbol time. Accordingly, the errors occasionally run for more than 100 symbols. We apply Rice´s fading duration distribution model to explain this error burst occurrence mechanism and its statistical manner and discuss this model´s validity by comparison between the theoretical and measurement data of error statistics property. Consequently, we found that the theoretical value by the proposed model is in excellent agreement with the measurement data and confirmed that the proposed model is valid for analyzing the error manner for the clipping induced error.