Comtech EF Data SNM-1010L - Manual (Page 173)

SNM-1010L Data/Control Modem Revision 0
Theory of Operation MN/SNM1010L.OM
6.3.2 Theory of Modulation Types
The modulation types for the modem include BPSK, QPSK, OQPSK, or 8PSK.
The PSK data transmission encoding method uses the phase modulation technique. This
method varies the phase angle of the carrier wave to represent a different bit value for the
receiver. The higher levels of modulation are required for an operating range that has a
limited bandwidth.
The order of modulation is represented by mPSK, where “m” relates to the number of
discrete phase angles. Refer to the following list for a brief description of the modulation
types.
• • BPSK: 2 discrete phase angles represent the 2 possible states of a
symbol.
• • QPSK, OQPSK: 4 discrete phase angles represent the 4 possible
states of a symbol.
• 8PSK: 8 discrete phase angles represent the 8 possible states of a symbol.
•
Note: The code rate determines the number of symbols per bit.
6.3.2.1 BPSK Encoding
The modulator converts transmitted baseband data into a modulated BPSK carrier at
2.4 kbit/s to 1.25 Mbit/s (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.
Code Rate Symbols/Bit Bits/Hz
1/1 1 2
1/2 2
0.5
6–11