Qpsk Encoding; Oqpsk Encoding; 8Psk Encoding; C.3.6.2 Qpsk Encoding - Comtech EF Data SDM-300A Installation And Operation Manual

SDM-300A Satellite Modem
C.3.6.2

QPSK Encoding

The demodulator converts transmitted baseband data into a modulated QPSK carrier at
the following parameters:
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.3.6.3

OQPSK Encoding

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 at the convolutional encoder provide the
desired input/output bit rates.
C.3.6.4

8PSK Encoding

The demodulator 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
4.8 kbit/s to 2.5 Mbit/s
7.2 kbit/s to 3.75 Mbit/s
8.4 kbit/s to 4.375 Mbit/s
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
1/2 rate
3/4 rate
7/8 rate
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–15