QPSK
quadrature phase shift keying
QPSK is a digital frequency modulation technique used for sending data over coaxial cable networks. Since it’s both easy to implement and fairly resistant to noise, QPSK is used primarily for sending data from the cable subscriber upstream to the Internet.
64QAM
64-state quadrature amplitude modulation
This digital frequency modulation technique is primarily used for sending data downstream over a coaxial cable network. 64QAM is very efficient, supporting up to 28-mbps peak transfer rates over a single 6-MHz channel. But 64QAM’s susceptibility to interfering signals makes it ill suited to noisy upstream transmissions (from the cable subscriber to the Internet).
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