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nullrecord t1_j9vc0ox wrote

Without that you would never have ADSL or 4G or wifi. Instead of sending 1 bit at the time over the wire, the "bit" can have 64 states, representing 6 bits at a time - a 6-fold increase in bandwidth.

See here for a bit more:

https://en.wikipedia.org/wiki/Quadrature_amplitude_modulation

https://en.wikipedia.org/wiki/Phase-shift_keying#Quadrature_phase-shift_keying_.28QPSK.29

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