An Analysis of the Duobinary Technique

The spectral shaping characteristics of Lender's duobinary transformation are examined and illustrated by several examples. It is found that the duobinary transformation does not compress bandwidth in a sense that would be directly applicable to the Sampling Theorem, but rather shapes the spectrum such that it becomes possible for samples sent at Nyquist rate through a nonflat filter to convey one bit of information each, even though they are statistically dependent and restricted to three levels. Thus the duobinary technique might be quite efficient for certain nonflat, band-limited channels which have a poor signal-to-noise ratio.