SLM-3650 Satellite Modem
Revision 3
Theory of Operation
MN/SLM3650.IOM
4–14
4.3 Demodulator
A block diagram of the demodulator is shown in Figure 4-3.
The demodulator converts PSK modulated carriers within the 50 to 180 MHz range to a
demodulated baseband data stream. The converted modulation types are BPSK, QPSK,
and 8PSK (refer to Section 4.2.3 for a description of modulation types). The demodulator
then performs FEC on the data stream using Viterbi or Sequential decoding algorithms.
DI
G
I
T
A
L
SI
G
N
A
L
PROC
E
S
S
I
N
G
DI
G
I
T
A
L
C
L
O
C
K
REC
O
V
E
R
Y
-
L
O
O
P
S
W
I
T
C
H
R
E
F
V
C
X
O
R
E
F
P
L
L
O
C
X
O
O
P
T
H
I
G
H
S
T
A
B
I
L
I
T
Y
A
G
C
LPF
BPF
LO #2
L
O
O
P
B
A
C
K
R
F
I
N
P
U
T
R
F
I
N
P
U
T
5
0
T
O
1
8
0
M
H
z
B
P
F
A
T
O
D
CON
V
E
R
T
E
R
LO #1
REFERENCE
VITERBI
DECODER
SEQUENTIAL
DECODER
OPTIONAL
REED-SOLOMON
CODEC
DOPPLE
R
/
PLESIOCHRO
N
O
U
S
BUFFE
R
MUX
I
N
T
ERFACE
OPTIONAL
OVERHEAD DEFRAMING
IBS/IDR, ASYNC/AUPC
DROP & INSERT
E
X
T
R
E
F
E
R
E
N
C
E
Optional
Turbo
Codec
Figure 4-3. Demodulator Block Diagram
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