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These
are the different types of modulation
used for spacecraft communications. Digital techniques
are gaining popularity for their small semiconductor
components, signal stability, adaptability to information
systems and compatibility to error correction and
security coding.
Modulation
AM
(Amplitude Modulation) is analog modulation that
varies the carrier signal amplitude to convey the
baseband signal.
FM
(Frequency Modulation) is analog modulation that
varies the carrier signal frequency to convey the
baseband signal.
SSB
(Single Sideband) is AM using only one of two sidebands
to conserve bandwidth.
BPSK
(Binary Phase Shift Keying) is digital modulation
that varies the carrier signal phase with with a
binary signal to convey baseband information. This
requires a coherent carrier signal reference at
the receiver for demodulation, which is cumbersome
from a systems standpoint.
DBPSK
(Differential Binary Phase Shift Keying) is digital
modulation that varies the carrier signal phase
with with a binary signal in such a way using baseband
bit comparisons that a coherent carrier signal reference
is not required at the receiver for demodulation.
QPSK
(Quadriphase Phase Shift Keying) is similar to BPSK
but only requires half the bandwidth.
MFSK
(Multiple Frequency Shift Keying) is digital modulation
that varies the carrier signal frequency with the
digital value of the baseband signal.
QAM
(Quadrature Amplitude Modulation) is digital modulation
capable of high information rates over a small transmission
bandwidth. This technique conserves limited bandwidth
resources.
