Line coding methods in Digital Communication for Data transmission

1. Digital Communication
Line Coding
Presented By:
Smt. S. B. Sunagar
Lect, ECE
B.L.D.E.A’s SSM Polytechnic,
Vijayapur
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2. Contents
1. Definition
2. Need of line codes
3. Types
4. Disadvantages
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3. Definition
Digital Line Coding is a special coding
system chosen to allow transmission to take
place in a communications system. The chosen
code or pattern of voltage used to represent
binary digits on a transmission medium is
called line encoding.
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4. • Converting Digital Data into binary signals. i.e
1’s or 0’s.
• For example a high voltage level (+V) could
represent a “1” and a low voltage level (0 or -
V) could represent a “0”.
• Binary 1’s and 0’s, such as in PCM signaling,
may be represented in various serial–bit
signaling formats called line codes.
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5. Need of Line Coding:
• As the coding is done to make more bits transmit on a
single signal, the bandwidth used is much reduced.
• For a given bandwidth, the power is efficiently used.
• The probability of error is much reduced.
• Error detection is done and the bipolar too has a
correction capability.
• Power density is much favorable.
• The timing content is adequate.
• Long strings of 1s and 0s is avoided to maintain
transparency.
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6. Types of Line Coding:
There are 3 types of Line Coding
• Unipolar
1. Unipolar Return to Zero (Unipolar RZ).
2. Unipolar Non Return to Zero (Unipolar NRZ)
• Polar
1. Polar Return to Zero (Polar RZ).
2. Polar Non Return to Zero (Polar NRZ)
• Bi-polar
1. Bipolar NRZ
2. Bipolar RZ
• Manchester.
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Unipolar:
Unipolar signaling is also called as On-Off Keying or simply
OOK. The presence of pulse represents a 1 and the absence of
pulse represents a 0.

8. • Polar:
In Polar signaling, a High in data is represented by a positive
pulse, while a Low in data is represented by a negative pulse.
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9. • Bipolar:
• This is an encoding technique which has three voltage levels namely +, - and 0.
Such a signal is called as duo-binary signal.
• An example of this type is Alternate Mark Inversion (AMI). For a 1, the voltage
level gets a transition from + to – or from – to +, having alternate 1s to be of
equal polarity. A 0 will have a zero voltage level.
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10. • Manchester :
• Each binary 1 is represented by a positive half–bit period pulse
followed by a negative half–bit period pulse. Similarly, a binary
0 is represented by a negative half–bit period pulse followed
by a positive half–bit period pulse. This type of signaling is also
called split–phase encoding.
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11. Disadvantages:
• No error correction.
• No clock is present.
• RZ uses twice the bandwidth of NRZ.
• Long strings of data causes loss of synchronization.
• Do not possess of clock for ease of
synchronization.
• Contains low voltage signal causes “ Signal Drop”.
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12. Thank You.
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