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Types of line coding
- 1. TYPES OF LINECODING R.Ramalakshmi Assistant Professor Ramco Institute of Technology Rajapalayam
- 3. Unipolar Signaling • Unipolarsignaling 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. • There are two variations in Unipolar signaling • Non Return to Zero (NRZ) • Return to Zero (RZ)
- 4. Unipolar Non-Return toZero (NRZ) • In this type of unipolar signaling, a High in data is represented by a positive pulse called as Mark, which has a duration T0 equal to the symbol bit duration. • A Low in data input has no pulse.
- 5. Unipolar Non-Return toZero (NRZ)
- 6. Advantages of UnipolarNRZ The advantages of Unipolar NRZ are • It is simple. • A lesser bandwidth is required.
- 7. Disadvantages of UnipolarNRZ The disadvantages of Unipolar NRZ are • No error correction done. • Presence of low frequency components may cause the signal droop. • Loss of synchronization is likely to occur (especially for long strings of 1s and 0s).
- 8. Unipolar Return toZero (RZ) • In this type of unipolar signaling, a High in data, though represented by a Mark pulse, its duration T0 is less than the symbol bit duration. • Half of the bit duration remains high but it immediately returns to zero and shows the absence of pulse during the remaining half of the bit duration.
- 9. Unipolar Return toZero (RZ)
- 10. Advantages of UnipolarRZ The advantages of Unipolar RZ are • It is simple. • The spectral line present at the symbol rate can be used as a clock.
- 11. Disdvantages of UnipolarRZ The disadvantages of Unipolar RZ are • No error correction. • Occupies twice the bandwidth as unipolar NRZ. • The signal droop is caused at the places where signal is non-zero at 0 Hz.
- 12. Polar Signaling There aretwo methods of Polar Signaling. They are • Polar NRZ • Polar RZ
- 13. Polar NRZ • Inthis type of Polar signaling, a High in data is represented by a positive pulse, while a Low in data is represented by a negative pulse.
- 14. Advantages of PolarSignaling The advantages of Polar NRZ are • It is simple. • No low-frequency components are present.
- 15. Disadvantages of PolarSignaling The disadvantages of Polar NRZ are • No error correction. • The signal droop is caused at the places where the signal is non-zero at 0 Hz.
- 16. Polar RZ • Inthis type of Polar signaling, a High in data, though represented by a Mark pulse, its duration T0 is less than the symbol bit duration. Half of the bit duration remains high but it immediately returns to zero and shows the absence of pulse during the remaining half of the bit duration. • However, for a Low input, a negative pulse represents the data, and the zero level remains same for the other half of the bit duration.
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- 18. Advantages of PolarRZ • The advantages of Polar RZ are • It is simple. • No low-frequency components are present.
- 19. Disadvantages of PolarRZ The disadvantages of Polar RZ are • No error correction. • Occupies twice the bandwidth of Polar NRZ. • The signal droop is caused at places where the signal is non-zero at 0 Hz.
- 20. Bipolar Signaling orPseudoternary Signaling • 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. Even in this method, we have two types. • Bipolar NRZ • Bipolar RZ
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- 22. • The abovefigure has both the Bipolar NRZ and RZ waveforms. • The pulse duration and symbol bit duration are equal in NRZ type, while the pulse duration is half of the symbol bit duration in RZ type.
- 23. Advantages of BipolarSignaling • It is simple. • No low-frequency components are present. • Occupies low bandwidth than unipolar and polar NRZ schemes. • This technique is suitable for transmission over AC coupled lines, as signal drooping doesn’t occur here. • A single error detection capability is present in this.
- 24. Disadvantages of BipolarSignaling • No clock is present. • Long strings of data causes loss of synchronization.
- 25. Manchester Signalling • Theduration of the bit is divided into two halves • A ‘One’ is +ve in 1st half and -ve in 2nd half. • A ‘Zero’ is -ve in 1st half and +ve in 2nd half.
- 26. Manchester Signaling orBiphase Baseband Signaling
- 27. Advantages of ManchesterSignaling • No DC component. • Does not suffer from signal droop (suitable for transmission over AC coupled lines). • Easy to synchronise. • Is Transparent.
- 28. Disadvantages of Manchester Signaling •Because of the greater number of transitions it occupies a significantly large bandwidth. • Does not have error detection capability.
- 29. Comparison of LineCodes
- 30. Power Spectral Densityof Line Codes • The function which gives distribution of power of a signal at various frequencies in frequency domain. • PSD is the Fourier Transform of autocorrelation
- 31. REFERENCES • S.Haykin, “DigitalCommunications”, John Wiley, 2005 • B.Sklar, “Digital Communication Fundamentals and Applications”, 2nd Edition, Pearson Education, 2009 • B.P.Lathi, “Modern Digital and Analog Communication Systems” 3rd Edition, Oxford University Press 2007
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