Digital to Digital Conversion Conversion Techniques Line Coding Relationship Between Data Rate and Signal Rate Line Coding Schemes Unipolar Polar Bipolar Block Coding Scrambling

1. Topic: Digital Data to Digital Signal Conversion
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2. Contents
• Digital to Digital Conversion
• Conversion Techniques
• Line Coding
• Relationship Between Data Rate and Signal Rate
• Line Coding Schemes
• Unipolar
• Polar
• Bipolar
• Block Coding
• Scrambling
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3. Digital to Digital Conversion
In Digital to Digital Conversion, we see how we can represent digital
data by using digital signals. This type of conversion is required to send
data from one destination to another.
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4. Conversion Techniques
• Line Coding
• Block Coding
• Scrambling
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5. Line Coding
• Line coding is the process of converting digital data to digital signals.
• Data may be in the form of text, numbers, graphical images, audio, or
video, are stored in computer memory as sequences of bits.
• Line coding converts a sequence of bits to a digital signal. At the
sender, digital data are encoded into a digital signal; at the receiver, the
digital data are recreated by decoding from the digital signal.
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6. Relationship between data rate and signal rate
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‘r’ is the ratio of data elements carried by a signal element.
r=
𝐷𝑎𝑡𝑎 𝐸𝑙𝑒𝑚𝑒𝑛𝑡
𝑆𝑖𝑔𝑛𝑎𝑙 𝐸𝑙𝑒𝑚𝑒𝑛𝑡

7. Line Coding Schemes
• Unipolar(Non Return to Zero)
• Polar(NRZ,RZ)
• Bipolar(AMI and Pseudoternary)
• Multilevel
• Multitransition
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8. Unipolar
• Signal levels are on one side of the time axis - either above or below
• NRZ - Non Return to Zero scheme is an example of this code. The
signal level does not return to zero during a bit transmission.
• It has no synchronization or any error detection. It is simple but costly
in power consumption.
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9. Polar
• The voltages are on both sides of the time axis.
• Polar NRZ scheme can be implemented with two voltages. 1 for +V
and 0 for -V
• It has two versions:
• NZR-Level - positive voltage for one symbol and negative for the other
• NRZ-Inversion - the change or lack of change in polarity determines the value
of a symbol. “1” inverts the polarity a “0” does not.
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10. Polar(Continue)
Polar(Return to Zero)
• The Return to Zero (RZ) scheme uses three voltage values. +, 0, -.
• Each symbol has a transition in the middle. Either from high to zero or
from low to zero.
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11. Bipolar
• Code uses 3 voltage levels: +, 0, -, to represent the data.
• Voltage level for one symbol is at “0” and the other alternates between + & -.
• Bipolar Alternate Mark Inversion (AMI): the ‘0’ symbol is represented by
zero voltage and the “1” symbol alternates between +V and -V.
• Pseudoternary is the reverse of AMI.
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12. Block Coding
• Block coding is a technique of sending data in a set of sequence.
• Block coding is done in three steps:
• Division
• Substitution
• Combination
• Need to add redundancy. such as, adding extra bits with the data bits.
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13. Block Coding(Continue)
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14. Scrambling
Block coding with NRZ is not suitable for long-distance encoding
because of the DC component. If we can find a way to avoid a long
sequence of 0’s in the original stream, we can use bipolar AMI for long
distances. Scrambling is the solution of avoiding long sequence of 0’s.
Common scrambling technique is B8ZS. Which sequence is 000+-0-+(if
previous pulse is +) or 000-+0+-(if previous pulse is -).
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