Digital Signal Processing Reference
In-Depth Information
Accumulated
error metric
Path history
000
State: 00
0
0
111
State: 01
State: 10
3
1
State: 11
Received Input = 000
(
a
)
Accumulated
error metric
Path history
000
000
State: 00
0+2=2
0 0
111
111
State: 01
3+3=6
1 0
001
State: 10
0+1=1
0 1
110
State: 11
1 1
3+0=3
Received I
nput = 110
(
b
)
Accumulated
error metric
Path history
000
000
000
State: 00
2+1, 6+1: 3
0 0 0
111
111
111
011
State: 01
1+2, 3+0: 3
0 1 0
100
00 1
001
State: 10
6+2, 2+2: 4
0 0 1
11 0
010
110
State: 11
0 1 1
3+3, 1+1: 2
101
Received Input = 010
(
c
)
FIGURE 10.50.
Trellis diagrams to illustrate Viterbi decoding:(
a
)
t
=
1; (
b
)
t
=
2; (
c
)
t
=
3.
16 channel symbol triads are read, the path history becomes full. The path history
in this source code is an array named
path
_
history
. Each variable of this array main-
tains the path history for a particular state, with each bit in the variable storing a
selected path with the rightmost bit storing the most recent path. Therefore, before
processing the 17th channel symbol triad, the minimum branch metric state is found,
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