Comtech EF Data SDM-300L3 - Manual (Page 28)

SDM-300L3 Satellite Modem Revision 1
Introduction MN/SDM300L3.IOM
1–8
• QPSK (OQPSK): 4 discrete phase angles represent the 4 possible states of a
symbol.
• 8-PSK: 8 discrete phase angles represent the 8 possible states of a symbol.
Note: The code rate determines the number of symbols per bit.
1.6.4 BPSK Encoding
The modulator converts transmitted baseband data into a modulated BPSK carrier at
2.4 kbps to 1.25 Mbps (1/2 rate). Using vector analysis of the constellation pattern, BPSK
represents one symbol with the carrier phase either at 0
° or 180 ° . The 1/2 rate encoding at
the convolutional encoder provides two symbols output for every bit input.
Uncoded (1/1 rate) BPSK operation also is allowed from 4.8 kbps to 2.5 Mbps.
Code Rate Symbols/Bit Bits/Hz
1/2 2 0.5
1/1 1 1
1.6.5 QPSK Encoding
The modulator converts transmitted baseband data into a modulated QPSK carrier at the
following parameters:
• 4.6 kbps to 5.0 Mbps (1/1 rate, uncoded)
• 4.8 kbps to 2.5 Mbps (1/2 rate)
• 7.2 kbps to 3.75 Mbps (3/4 rate)
• 8.4 kbps to 4.375 Mbps (7/8 rate)
Using vector analysis of the constellation pattern, QPSK represents a symbol with the
carrier phase angle at 45
° , 135 ° , 225 ° , or 315 ° . 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 1.33
1.5
7/8 1.143 1.75