Digital Signal Processing Reference
In-Depth Information
Faltungskodierer
Zustandsdiagramm
State diagram
Convolutional Encoder
1/10
+
+
1
11
d
e
Eingangs-
daten
Input data
Ausgangs-
daten
0 0
Output data
0/10
b
+
01
10
2
c
1/00
a
f
00
B eispiel für E ingangsbitfolge
Assumed information of source
1
0
1
1
0
0
0
K odierte B itfolge für die Ü bertragung
Encoded bit sequence for transmission
g
0/00
11
10
00
01
01
11
00
N etzdiagramm (Trellisdiagramm)
Net diagram (Trellis diagram )
0/00
00
01
10
11
Time axis
Zei ttak t
t0 t1 t2 t3 t4 t5 t6 t7
Illustration 253:
Trellis diagram for a specific input bit sequence
The state diagram applies for all kinds of input bit pattern sequences and not just for a specific one. On the
other hand the trellis diagram can describe the course of the state sequence and the output signals for a
specific input bit sequence.
The above example leads to a specific coded bit sequence at the output. The trellis diagram shows the path
for this signal. In order that you can follow the course, changes of state and the output signals the path in
the state diagram is marked with the letters a,b,c….
In decoding the following problem awaits us: how can this path be reconstructed if the bit sequence of the
output signal was distorted at one or several points on the transmission path or by the storage medium?
VITERBI decoding provides the answer (see Illustration 254)
