Comtech EF Data SNM-1001L - Manual (Page 32)

SNM-1001L Satellite Modem Revision 1
Introduction MN/SNM1001L.IOM
1–8
1.6.3.3 Offset QPSK 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 at the convolutional encoder
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
1.6.3.4 8-PSK Encoding
The modulator converts transmitted baseband data into modulated 8-PSK carrier at the
following parameters:
• 64 kbps to 5.000 Mbps (2/3 rate)
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 2/3
rate encoding provides the desired input/output bit rates.
Code Rate Symbol/Bit Bit/s Hz
2/3 1.5 2