Study of statistical model and power measurement results for distortions due to clipping in SCM optical transmission system

In the SCM optical transmissions used in optical CATV, it has been pointed out that the distortion generated by clipping behaves in the same way as impulse noise. In this paper, it is assumed that the distortion due to clipping is generated following the Poisson distribution, with the same characteristics as the band‐limited noise, and it is demonstrated theoretically that the amplitude distribution follows Middleton's class A model. On the other hand, there have been many discussions of the theoretical value of the distortion power due to clipping. This study notes that the measurement of the noise power by the spectrum analyzer essentially contains a measurement error. Using the statistical model for the distortion amplitude derived in this paper, the measurement error is calculated for the case in which the amplitude distribution of the distortion due to clipping follows that of the impulse noise. The calculation result is compared to the measurement results and the amount of correction is theoretically derived for the very large error present in the distortion value indicated by the spectrum analyzer. In the SCM optical transmission used in optical CATV, the measured distortion is smaller than the actual value at the ordinary employed optical modulation index. The difference may sometimes reach 20 dB. When the measured value is corrected for the error by the method presented in this paper, the theoretical value of the distortion by clipping, as obtained from Saleh's expression, is almost entirely adequate. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(8): 13–22, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ecja.1114