Comtech EF Data SDM-300L3 - Manual (Page 29)

SDM-300L3 Satellite Modem Revision 1
Introduction MN/SDM300L3.IOM
1–9
1.6.6 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.
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
1.6.7 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, 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