2/23/2012 Muhammad Ali Jinnah University, Islamabad Digital Communications EE3723 1
EE4723 : Digital Communications II
Week 5:
Line coding schemes
(Details and Characteristics)
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Line Coding Schemes-Digital Communication-Lecture Slides, Slides of Digital Communication Systems
This lecture was delivered by Jai Rathore at Agra University for Digital Communication course. It includes: Line, Coding, Schemes, Decoding, Signal, Data, Element, Synchronization, Clock, Setting, Match, Waveforms, Transmission, Bandwidth
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2011/2012
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EE4723 : Digital Communications II
Week 5:
Line coding schemes
(Details and Characteristics)
Line coding and decoding
Synchronization
Receiver’s clock Setting must match the sender’s one
Effect of lack of synchronization
Considerations for PCM Waveforms
DC components
Transmission bandwidth
Power efficiency
Error detection and correction capability
Favorable power spectral density
Adequate timing content – Self Synchronization
Noise and Interference Immunity
Cost and Complexity
Example
A system is using NRZ-I to transfer 1-Mbps data. What are the average signal rate and minimum bandwidth?
Solution
- The average signaling rate is S = N/2 = 500 k baud. The minimum bandwidth for this average baud rate is Bmin = S = 500 kHz.
RZ scheme
Return to zero
Self clocking
Bipolar schemes: AMI and pseudoternary
In bipolar encoding, we use three levels: positive, zero, and negative.
Pseudoternary:
- 1 represented by absence of line signal
- 0 represented by alternating positive and negative
DS1, E
PSD of various line codes
HDB
The timing information is preserved by embedding it in the line signal even when long sequences of zeros are transmitted, which allows the clock to be recovered properly on reception.
The DC component of a signal that is coded in HDB3 is null.
Bipolar 8-Zero Substitution (B8ZS)
Adds synchronization for long strings of 0s North American system Same working principle as AMI except for eight consecutive 0s
Evaluation
- Adds synchronization without changing the DC balance
- Error detection possible Used in T
Amplitude
Time
1 0 0 0 0 0 0 0 0 0 1
Violation Violation
10000000001 +000+-0-+01 in general 00000000 000V(-V)0(-V)V
Multilevel: 2B1Q scheme
Integrated Services Digital Network ISDN