This document discusses different types of line codes used for digital communication systems. It begins by introducing line codes as electrical representations of encoded binary data streams produced by transmitters. It then describes several common line coding techniques like unipolar NRZ, polar NRZ, unipolar RZ, bipolar RZ, and Manchester coding. For each technique, it discusses properties like bandwidth requirements, error detection capabilities, and power spectral density. It also provides examples of polar NRZ signals and Manchester encoding. The document aims to analyze and characterize various line coding techniques in both the time and frequency domains.

1. DIGITAL COMMUNICATION
SYSTEMS (ECE4001)
Dr. Arvind Kumar | School of Electronics Engineering, VIT Vellore |
https://sites.google.com/view/arvindk

2. LINE CODES
| School of Electronics Engineering, VIT Vellore |

3. Module 3: Line Codes
|Dr.Arvind Kumar| ...... https://sites.google.com/view/arvindk
Representation of Line
Codes
Properties and
Applications of Line
Codes
Power Spectral Density
of NRZ Unipolar, NRZ
polar, NRZ Bipolar and
Manchester
Objectives: To analyze various line coding techniques in time and frequency domains.
Outcomes: Characterize various line coding techniques in time and frequency domains

4. Line Codes: Introduction
|Dr.Arvind Kumar| https://sites.google.com/view/arvindk
Three basic waveform-coding schemes: PCM, DPCM, and DM.
Naturally, they differ from each other in several ways:
Transmission–
bandwidth,
requirement
Transmitter–
receiver structural
composition and
complexity
Quantization noise
All three of them have a common need: line codes for electrical representation of
the encoded binary streams produced by their individual transmitters

5. Line Codes
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6. Line codes
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(a) Unipolar nonreturn-to-zero (NRZ) signaling;
(b) Polar NRZ signaling;
(c) Unipolar return-to-zero (RZ) signaling;
(d) Bipolar RZ signaling;
(e) Split-phase or Manchester code.
Assuming:
 Symbols 0 and 1 are equiprobable,
 Average power is normalized to unity, and
 Frequency f is normalized with respect to the bit rate 1/Tb
.

7. Preliminary: Bit Rate vs. Symbol Rate (Baud Rate
• The speed of data is commonly expressed in bits/second or bytes/second. The data rate Rb is
related to the bit period Tb (duration of a bit).
• The bit rate is commonly referred to as the channel capacity.
• Communication systems use symbols to convey information.
• A symbol may be one bit per symbol (called binary), or a group of bits, or a collection of
defined voltage levels (multiple level symbols), etc.
• The symbol rate RS is related to the symbol’s period (or duration) TS by:
• The symbol rate is also called Baud rate. Bit rate Rb can be written as:
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8. Properties of Line Codes
• As the coding is done to make more bits transmit on a single signal
• Bandwidth.
• 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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9. Categories of Line Coding – Overview
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Line codes
Bipolar Multi-level
Multi-level
Transition
Uni-Polar Polar
A line code is a specific code (with precisely defined parameters) used for transmitting
a digital signal over a channel. Line coding is used in digital data transport – the
pattern of voltage, current or photons used to represent digital data on a transmission
link is called line encoding.

10. Unipolar – RZ and NRZ (“On-Off Keying”)
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ADVANTAGES DISADVANTAGES
1. Simplicity
2. Doesn’t require a lot of bandwidth
1. Presence of DC level
2. Contains low-frequency
components (leads to drooping)
3. No clocking component to
synchronize to at receiver
4. Long string of zeros causes loss of
synchronization

11. Unipolar NRZ Signal Droop Problem
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12. Polar – RZ and NRZ
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13. Power Spectral Density Example: Polar NRZ
Signal
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14. Bipolar NRZ
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15. Bipolar RZ
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16. Manchester (Bi-Phase or Split-Phase) Encoding
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17. Manchester (Bi-Phase or Split-Phase) Encoding
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18. Differential Manchester (Bi-Phase) Encoding
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19. |Dr.Arvind Kumar| https://sites.google.com/view/arvindk
Flat top sampling of low pass
signals
a)gives rise to aperture effect
b)implies oversampling
c)leads to aliasing
d)introducing delay distortion

20. THANKYOU!