- 2070 Asar · 3+8 marks
Line coding: properties; encode 01001100011
Short answer
Unipolar NRZ-L: 1=+V, 0=0V; NRZ-I: toggle at 1, start low; RZ: 1=+V half-bit, 0=0V. Polar NRZ-L: 1=+V, 0=-V; NRZ-I: toggle at 1; RZ: 1=+V half-bit, 0=-V half-bit. Manchester: 1=low-to-high, 0=high-to-low mid-transition. AMI: 0=0V, 1s alternate ±V: 0+00-+000-+.
What is line coding? What are the desired properties of a line code? Encode the bit stream 01001100011 using the following encoding schemes: Unipolar NRZ-L, Unipolar NRZ-I, Unipolar RZ, Polar NRZ-L, polar NRZ-I, polar RZ, Manchester, and Alternate Mark Inversion (AMI).
Line coding
Line coding is the conversion of digital data (bits) into a digital signal (voltage levels) for transmission.
Desired properties of a line code
- No DC component (or small), so it passes through transformers and AC-coupled links.
- Self-synchronisation: enough transitions so the receiver can recover the clock, even for long runs of 0s or 1s.
- Narrow bandwidth (low baud rate for the data rate).
- Error detection capability (for example AMI violations).
- Noise immunity and low error rate.
- Low cost and simplicity, with no ambiguity in decoding.
- Polarity insensitivity (as in NRZ-I and differential Manchester).
Encoding of 0 1 0 0 1 1 0 0 0 1 1
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
0 1 0 0 1 1 0 0 0 1 1
+V |---| |-------| |-------
0 ----| |-------| |-----------|
Unipolar NRZ-I
0 1 0 0 1 1 0 0 0 1 1
+V |-----------| |---------------| |---
0 ----| |---| |---|
Unipolar RZ
0 1 0 0 1 1 0 0 0 1 1
+V |-| |-| |-| |-| |-|
0 ----| |---------| |-| |-------------| |-| |-
Polar NRZ-L
0 1 0 0 1 1 0 0 0 1 1
+V |---| |-------| |-------
0 | | | | |
-V ----| |-------| |-----------|
Polar NRZ-I
0 1 0 0 1 1 0 0 0 1 1
+V |-----------| |---------------| |---
0 | | | | |
-V ----| |---| |---|
Polar RZ
0 1 0 0 1 1 0 0 0 1 1
+V |-| |-| |-| |-| |-|
0 |-| |-| |-| |-| |-| |-| |-| |-| |-| |-| |-
-V --| |-| |-| |-| |-| |-|
Manchester
0 1 0 0 1 1 0 0 0 1 1
+V --| |---| |-| |-| |---| |-| |-| |-| |-
0 | | | | | | | | | | | | | | | |
-V |---| |-| |---| |-| |-| |-| |---| |-|
Bipolar AMI
0 1 0 0 1 1 0 0 0 1 1
+V |---| |---| |---
0 ----| |-------| | |-----------| |
-V |---| |---|
AMI pulses: 0 + 0 0 - + 0 0 0 - +.
✓ Answer checked by Claude Sonnet 5.5
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