Modulation Types; Bpsk; Qpsk; Offset Qpsk - Comtech EF Data SLM-7650 Installation And Operation Manual

SLM-7650 Satellite Modem
Theory of Operation
4.3.4

Modulation Types

4.3.4.1

BPSK

Binary Phase Shift Keying uses vector analysis of the
constellation pattern to represent one symbol per carrier phase
at either 0 or 180 degrees. The rate 1/2 provides 2 symbol
outputs for every input bit. The symbol rate is two times the
data rate for BPSK 1/2. Decoder lock is achieved very
quickly
4.3.4.2

QPSK

Quaternary Phase Shift Keying differs from BPSK by
representing two symbols in one of four phase angle
positions; 45, 135, 225, or 315 degrees. Uncoded 1/1, 1/2,
3/4, and 7/8 FEC rates are used for QPSK. The symbol rate
for QPSK with an FEC of 1/2 is the same as the data rate.
The symbol rate is 2/3 of the data rate for 3/4.
4.3.4.3

Offset QPSK

Offset Quaternary Phase Shift Keying is a variation of QPSK.
The offset prevents any succession of symbols going through
the zero point of the quadrature. The RF envelope will not
collapse when the modulation format is set to OQPSK. It is
possible to operate high power amplifiers with less then
recommended back off when using this type of modulation.
4.3.4.4

8-PSK

8-Phase Shift Keying Pragmatic trellis coded modulation
encoding is used to transmit baseband data for 8 phase shift
keying. Eight discrete phase angles represent the 8 possible
symbol combinations of three bits. The symbol rate for 2/3
rate 8PSK is 1/2 of the data rate. The symbol rate for 5/6
FEC 8PSK is 3/5 of the data rate.
Reed Solomon is recommended to achieve acceptable performance.
4–10
Revision 4
MN/SLM7650.IOM