SLM-3650 Satellite Modem
Revision 3
Theory of Operation
MN/SLM3650.IOM
4–13
4.2.3.1 BPSK
Encoding
The modulator converts transmitted baseband data into a modulated BPSK carrier at
2.4 kbps to 1.25 Mbps (1/2 rate). Using vector analysis of the constellation pattern, BPSK
represents one symbol with the carrier phase either at 0
°
or 180
°
. The 1/2 rate encoding at
the convolutional encoder provides two symbols output for every bit input.
Code Rate
Symbols/Bit
Bits/Hz
1/2 2
0.5
4.2.3.2 QPSK
Encoding
The modulator converts transmitted baseband data into a modulated QPSK carrier at the
following parameters:
•
4.8 kbps to 2.5 Mbps (1/2 rate)
•
7.2 kbps to 3.75 Mbps (3/4 rate)
•
8.4 kbps to 4.375 Mbps (7/8 rate)
Using vector analysis of the constellation pattern, QPSK represents a symbol with the
carrier phase angle at 45
°
, 135
°
, 225
°
, or 315
°
. The 1/2, 3/4, and 7/8 rates encoded at the
convolutional encoder provide the desired input/output bit rates.
Code Rate
Symbols/Bit
Bits/Hz
1/2 2 1
3/4 1.5
1.33
7/8 1.143
1.75
4.2.3.3 8-PSK
Encoding
The modulator converts transmitted baseband data into modulated 8-PSK carrier at the
following parameters:
•
64 kbps to 5.0 Mbps (2/3 rate)
Using vector analysis of the constellation pattern, 8-PSK represents a symbol with carrier
phase angles at 22.5
°
, 67.5
°
, 112.5
°
, 157.5
°
, 202.5
°
, 247.5
°
, 292.5
°
, and 337.5
°
. The 2/3
rate encoding provides the desired input/output bit rates.
Code Rate
Symbol/Bit
Bit/s Hz
2/3 1.5 2
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