Line coding
- 1. LINE CODING BY- VAIBHAV SINHA
- 2. OBJECTIVES •WHY LINE CODING? •INTRODUCTION TO LINE CODING •PROPERTIES OF LINE CODING •TYPES OF LINE CODING •EXAMPLE OF LINE CODING
- 3. WHY LINE CODING? • Spectrum Shaping and Relocation without modulation or filtering. • Bit clock recovery can be simplified. • Error detection capabilities. • Bandwidth usage; the possibility of transmitting at a higher rate than other schemes over the same bandwidth.
- 4. INTRODUCTION TO LINE CODING Binary data can be transmitted using a number of different types of pulses. The choice of a particular pair of pulses to represent the symbols 1 and 0 is called Line Coding and the choice is generally made on the grounds of one or more of the following considerations: – Presence or absence of a DC level. – Power Spectral Density- particularly its value at 0 Hz. – Bandwidth. – BER performance (this particular aspect is not covered in this lecture). –Transparency (i.e. the property that any arbitrary symbol, or bit, pattern can be transmitted and received). – Ease of clock signal recovery for symbol synchronisation. – Presence or absence of inherent error detection properties. After line coding pulses may be filtered or otherwise shaped to further improve their properties: for example, their spectral efficiency and/ or immunity to intersymbol interference.
- 5. PROPERTIES OF LINE CODING •Transmission Bandwidth: as small as possible • Power Efficiency: As small as possible for given BWand probability of error • Error Detection and Correction capability: Ex: Bipolar • Favorable power spectral density: dc=0 • Adequate timing content: Extract timing from pulses • Transparency: Prevent long strings of 0s or 1s
- 6. TYPES OF LINE CODING Unipolar Non-Return to Zero (NRZ):Duration of the MARK pulse (Ƭ ) is equal to the duration (To)of the symbol slot. Advantages: •Simplicity in implementation • Dosen’t require a lot of bandwidth fortransmission.
- 7. DISADVANTAGES: •Presence of DC level (indicated by spectral line at 0 Hz). •Contains low frequency components. Causes “Signal Droop” •Does not have any error correction capability. •Does not posses any clocking component for ease of synchronisation. Unipolar Return to Zero (RZ): •MARK pulse (Ƭ ) is less than the duration (To) of the symbolslot. •Fills only the first half of the time slot, returning to zero for the second half.
- 8. ADVANYAGES: •Simplicity in implementation. •Presence of a spectral line at symbol rate which can be used as symbol timing clock signal. DISADVANYAGES: •Presence of DC level (indicated by spectral line at 0 Hz). •Continuous part is non-zero at 0 Hz. Causes “Signal Droop”. •Does not have any error correction capability. •Occupies twice as much bandwidth as Unipolar NRZ. •Is not Transparent
- 9. Polar NRZ: •A binary 1 is represented by a pulseg1(t) •A binary 0 by the opposite (or antipodal) pulse g0(t) =-g1(t). ADVANTAGES: •Simplicity in implementation. •No DC component.
- 10. DISADVANTAGES: •Continuous part is non-zero at 0 Hz. Causes “Signal Droop”. •Does not have any error correction capability. •Does no posses any clocking component for ease of synchronisation. •Is not transparent. Polar RZ: •A binary 1: Apulse g1(t) •A binary 0: The opposite (or antipodal) pulse g0(t) =-g1(t). •Fills only the first half of the time slot, returning to zero for the second half.
- 11. ADVANYAGES: •Simplicity in implementation. •No DC component. DISADVANTAGES: •Continuous part is non-zero at 0 Hz. Causes “Signal Droop”. •Does not have any error correction capability. •Occupies twice as much bandwidth as Polar NRZ. Bipolar NRZ:
- 12. Bipolar RZ: ADVANTAGES: •No DC component. •Occupies less bandwidth than unipolar and polar NRZ schemes. •Does not suffer from signal droop (suitable for transmission over AC coupled lines). •Possesses single error detection capability.
- 13. DISADVANTAGES: •Does not posses any clocking component for ease of synchronisation. •Is not Transparent Manchester Signaling:
- 14. ADVANTAGES: •No DC component. •Does not suffer from signal droop (suitable for transmission over AC coupled lines). •Easy to synchronise. •Is Transparent. DISADVANTAGES: •Because of the greater number of transitions it occupies a significantly large bandwidth. •Does not have error detection capability.
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