- 2079 Baisakh · 2+2+2+2 marks
Line coding waveforms for 1101110111
Short answer
Line coding provides clock recovery, DC balance, bandwidth reduction, and error detection. For 1101110111: Unipolar NRZ uses +V for 1, 0V for 0; Polar RZ uses +V then 0 for 1, -V then 0 for 0; Manchester uses low-to-high mid-bit for 1, high-to-low for 0; AMI alternates +V,-V for 1, 0V for 0, yielding +-0+-+0-+-.
What are the needs of line coding in data communication? Given the binary data sequence 1101110111 represent it in unipolar NRZ, polar RZ, Manchester and AMI waveform.
Needs of line coding
Line coding converts digital data into a digital signal that suits the channel. It is needed to:
- Give the receiver enough transitions to recover the clock (synchronisation).
- Remove the DC component, which cannot pass through transformers or AC-coupled links.
- Reduce the bandwidth needed.
- Give error detection (for example, AMI violations) and noise immunity.
- Keep the cost and complexity of the circuits low.
Waveforms for 1101110111
Conventions used (state these in the exam, as books differ): level before the first bit is low (-V); NRZ-L/RZ: 1 = +V, 0 = -V (unipolar: 0 = 0 V); NRZ-I: a 1 toggles the level at the start of the bit, a 0 keeps it; RZ: the pulse returns to zero in the middle of the bit; Manchester: 1 = low-to-high and 0 = high-to-low transition at mid-bit; differential Manchester: always a mid-bit transition, an extra transition at the start of the bit for a 0 and none for a 1; AMI: 0 = 0 V, 1s alternate +V and -V starting with +V.
Unipolar NRZ
1 1 0 1 1 1 0 1 1 1
+V --------| |-----------| |-----------
0 |---| |---|
Polar RZ
1 1 0 1 1 1 0 1 1 1
+V --| |-| |-| |-| |-| |-| |-| |-|
0 |-| |-| |-| |-| |-| |-| |-| |-| |-| |-
-V |-| |-|
Manchester
1 1 0 1 1 1 0 1 1 1
+V |-| |---| |-| |-| |---| |-| |-| |-
0 | | | | | | | | | | | | | | |
-V --| |-| |---| |-| |-| |---| |-| |-|
Bipolar AMI
1 1 0 1 1 1 0 1 1 1
+V ----| |---| |---| |---|
0 | |---| | | |---| | |
-V |---| |---| |---| |---
AMI pulse sequence: + - 0 + - + 0 - + - (the 1s alternate +, -, +, -, ...).
✓ Answer checked by Claude Sonnet 5.5
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