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SDM-300A Satellite Modem
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.
C.2.19.3
OQPSK Encoding
The modulator PCB converts the transmitted baseband data into a modulated OQPSK
carrier within the same parameters as QPSK.
The OQPSK modulation is mainly different from QPSK by offsetting the I and Q channel
modulation signals. This offset prevents the RF envelope from going through zero. Under
certain conditions, this may allow less back-off in the High Power Amplifier (HPA)
system. The 1/1, 1/2, 3/4, and 7/8 rates encoded at the convolutional encoder provide the
desired input/output bit rates.
C.2.19.4
8PSK Encoding
The modulator converts transmitted data into modulated 8PSK carrier at the following
parameters:
•
Using vector analysis of the constellation pattern, 8PSK represents a symbol with carrier
phase angles at 22.5°, 67.5°, 112.5°, 157.5°, 202.5°, 247.5°, 292.5°, or 337.5°. The 2/3,
rate encoding provides the desired input/output bit rates.
Rev. 4
Code Rate
1/2
3/4
7/8
Code Rate
1/1
1/2
3/4
7/8
64 kbit/s to 5.000 Mbit/s (2/3 rate)
Code Rate
2/3
Symbols/Bit
Bits/Hz
2
1
1.5
1.33
1.143
1.75
Symbols/Bit
Bits/Hz
1
2
2
1
1.333
1.5
1.143
1.75
Symbols/Bit
Bits/Hz
1.5
2
Specifications
C–11
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