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).
http://www.cnet.com/Resources/Info/Glossary/Terms/64qam.html
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