Comtech EF Data SNM-1001L - Manual (Page 250)

SNM-1001L Satellite Modem Revision 1
Specifications MN/SNM1001L.IOM
A–12
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 provide
the desired input/output bit rates.
Code Rate Symbols/Bit Bits/Hz
1/1 1 2
1/2 2 1
3/4 1.5
1.33
7/8 1.143 1.75
A.6.2 OQPSK Encoding
The modulator PCB converts the transmitted baseband data into a modulated Offset QPSK
carrier within the same parameters as QPSK.
The Offset QPSK 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 provide the desired input/output bit
rates.
Code Rate Symbols/Bit Bits/Hz
1/1 1 2
1/2 2 1
3/4 1.333
1.5
7/8 1.143 1.75
A.6.3 8-PSK Encoding
The modulator converts transmitted baseband data into modulated 8-PSK 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°, and 337.5°. The rate
encoding provides the desired input/output bit rates.
Code Rate Symbol/Bit Bit/s Hz
2/3 1.5 2
3/4 1.333 2.25