0 <==> high level
1 <==> low level
Require time coordination "synchronization": As all pulses have equal duration and there is no seperation between them.
Contain non zero DC component that is difficult to transmit, carries no information.
Invert on ones, a transition (low-to-high or high-to-low) at the beginning of bit time denotes a binary 1
for that bit time. No transition indicates binary 0.
Reliable to detect in presence of noise.
Not polarity sensitive.
Needs less power to transmitt.
Long string of 0s. (disadvantage)
Bipolar-AMI
Binary 0 is represented by no line signal and a binary 1 is presented by a positive or nagative pulse.
Pseudoternary
In that case the binary 1 is represented by no line signal and a binary 0 is presented by a positive or nagative pulse.
No DC component.
Easy to synchronize.
Easy to detect one lost pulse.
Long strings of 0s (Bipolar-AMI) or long strings of 1s (pseudoternary).
Needs more power to transmitt.
Manchester code
0s reprsent a transition from high to low in middle of pulse interval and 1s represents a transition
from low to high in pulse of intervals.
Differential Manchester
0s represents transition at the beginning of pulse interval while 1s represents absence of transition at the beginning of pulse interval.
Reciever can synchronize on transitions.
No DC component.
Bandwidth is wider than the bandwidth for multilevel binary code.
Widly used in long-distance applications.
B8ZS- Bipolar with 8-zeros substitution
If last pulse before 8 0s is positive, then encode as 000+-0-+
If last pulse before 8 0s is negative, then encode as 000-+0+-
HDB3 high-density bipolar-3 zeros
Replacing any string of four zeros by three zeros followed by violation that is the same polarity as previous transition.
No. of 1 since last sub. | No. of 1 since last sub | |
Polarity of Preceding Pulse |
Odd |
Even |
- |
000- |
+00+ |
+ |
000+ |
-00- |
References
Telesystem Winter 97, Period 3
Telesystem coursehttp://www.it.kth.se/htbin/finger?waseem@it.kth.se
Lastest update 970128