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Pathmetric
M
a1
Branchmetric
a
a
Branchmetric
a
b
Fig. 5-52 Basic Flow of ACS Operation
This concludes a brief explanation of the principles of Vitterbi decoding.
When this trellis coding/Vitterbi decoding scheme is used for voice band-
width lines, generally, the branchmetric or pathmetric to the receive data
string is calculated as a Euclidean distance. Though the
is generally expressed as a Euclidean distance, the Euclidean distance is
expressed as an analog amount. Conversion of the analog amount of this
Euclidean distance to a digital amount is called "soft-judgment Vitterbi
decoding."
G3 FACSIMILE COMMUNICATIONS
Pathmetric
M
c1
Branchmetric
c
a
Comparison
Selection
Storage
Path update/storage
Pathmetric
Path memory
M
ai+1
Branchmetric
c
b
Comparison
Selection
Storage
Path update/storage
Pathmetric
M
bi+1
1
2
3
A
ai+1
4
5
6
Path memory
A
bi+1
ït
çi
Hamming distance
5–61
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