Page 317 - Satellite Communications, Fourth Edition
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Digital Signals 297
Figure 10.11 Some binary digital modulation formats.
Frequency-shift keying (FSK). The binary signal is used to frequency
modulate the carrier, one frequency being used for a binary 1 and
another for a binary 0. These are also referred to as the mark-space
frequencies.
Binary phase-shift keying (BPSK). Polarity changes in the binary
signal are used to produce 180° changes in the carrier phase. This may
be achieved through the use of double-sideband, suppressed-carrier
modulation (DSBSC), with the binary signal as a polar NRZ wave-
form. In effect, the carrier amplitude is multiplied by a 1 pulsed
waveform. When the binary signal is 1, the carrier sinusoid is
unchanged, and when it is 1, the carrier sinusoid is changed in
phase by 180°. BPSK is also known as phase-reversal keying (PRK).
The binary signal may be filtered at baseband before modulation, to
