Error Rate Monitoring in a Partial Response System

Pseudoerror monitoring techniques, besides providing a precursive, measure of system degradation, can also be used in extrapolation schemes to estimate the actual bit error rate of a digital link. This study examines pseudoerror techniques as applied to a precoded, modified duobinary system. Two known methods of pseudoerror generation, namely, threshold modification and sampling offset, are compared with two new monitors using controlled amounts of amplitude and phase distortion. The threshold modification monitor is most robust to channel degradations, while amplitude or phase distortion monitors seem to be more accurate in estimating the actual error rate but less robust. The sampling offset monitor seems to be less robust than the other monitors due to its unavoidable sensitivity to degradations affecting the system phase. Methods of improving the estimation accuracy by the choice of degradation parameters are also examined.