This document discusses duobinary signaling and modified duobinary signaling. Duobinary signaling is a form of partial response signaling where the pulse response spans two signaling intervals. Modified duobinary signaling corrects the deficiency of duobinary signaling having a nonzero frequency response at the origin by using a class IV partial response. It achieves a spectral shape with a gradual cutoff but requires a larger SNR to achieve the same error probability compared to binary signaling.

1. Pulse Generation
 Generalized form of
correlative-level
coding
(partial response signaling)
Figure 7.18
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2. Duobinary signaling
 Duobinary signaling (class I partial response)
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3. Example
 Duobinary Pulse
– p(nTb)=1, n=0,1
– p(nTb)=1, otherwise
 Interpretation of received signal
– 2: 11
– -2: 00
– 0: 01 or 10 depends on the previous transmission
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4. Duobinary signal and Nyguist Criteria
 Nyguist second criteria: but twice the bandwidth
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5. Differential Coding
 The response of a pulse is spread over more than one signaling
interval.
 The response is partial in any signaling interval.
 Detection :
– Major drawback : error propagation.
 To avoid error propagation, need deferential coding (precoding).
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6. Modified duobinary signaling
 Modified duobinary signaling
– In duobinary signaling, H(f) is nonzero at the origin.
– We can correct this deficiency by using the class IV partial
response.
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7. Modified duobinary signaling
 Spectrum
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8. Modified duobinary signaling
 Time Sequency: interpretation of receiving 2, 0, and -2?
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9. Tradeoffs
 Binary data transmission over a physical baseband channel can
be accomplished at a rate close to the Nyquist rate, using
realizable filters with gradual cutoff characteristics.
 Different spectral shapes can be produced, appropriate for the
application at hand.
 However, these desirable characteristics are achieved at a price :
– A large SNR is required to yield the same average probability of
symbol error in the presence of noise.
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