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Ileen Roychoudhury
2 months ago
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What is correlative coding. Explain with an example.

What is correlative coding. Explain with an example.

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teacher3

Anusree sanyal 1 month ago

ISI is an unwelcome phenomenon and the signal is degraded. But if the same ISI is used in a managed manner, a bit rate of 2W bits per second in a W Hertz bandwidth channel can be achieved. Correlative coding or partial response signalling systems is one such scheme.   

It is simple to build the receiver according to the requirement, since the amount of ISI is known, to avoid the impact of ISI on the signal. Considering an example of Duo-binary Signaling, the basic principle of correlative coding is accomplished.

Duo-binary Signaling

The name duo-binary implies doubling the transmitting power of the binary system. Let us consider a binary input sequence {ak} consisting of uncorrelated binary digits, each with a Ta-second duration, to understand this. The signal 1 is represented by +1 volt, and the symbol 0 is represented by -1 volt.

Therefore, as shown in the following equation, the duo-binary coder output ck is given as the sum of the present binary digit ak and the previous value ak-1,

c_k=a_k+a_(k-1)

In the above equation, the input sequence of the uncorrelated binary sequence {ak} is changed into a sequence of three-level pulses {ck} that are correlated. This connection between the pulses can be interpreted as the artificial injection of ISI into the transmitted signal.

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