Comtech EF Data SDM-300L3 - Manual (Page 336)

SDM-300L3 Satellite Modem Revision 0
Specifications MN/SDM300L3.IOM
14–30
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 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
14.11.3 OQPSK Decoding (Optional)
The demodulator 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 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
14.11.4 8-PSK Decoding
The demodulator converts transmitted baseband data into modulated 8-PSK carrier at the
following parameters:
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 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