I've read that ADSL uses frequency-divided multiplexing and only analog signals use FDM. Then why there's the term 'digital' in ADSL(Asymmetric digital subscriber line) if it uses analog signals?
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1The "D" in any xDSL variant stands for "Digital." ADSL is Asymmetric _Digital_ Subscriber Line. – Ron Maupin Sep 06 '21 at 16:28
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A simple way to imagine it, digital signal is broken into different frequencies like a piano keys.
Then each tone is sent down the copper wire like a sound, this is then picked up at the far end and then Demodulated back into a digital string of 1s a nd 0s.
A modems name is created from the job it does as a Modulator / Demodulator.

Jay Best
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The signal is digital, the line encoding that implements this signal is described in the real macro world with analog.

Andrew
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Yes, in layman's terms. it's a combo of phase, frequency, and amplitude modulation/"shift-keying", aka "QAM". – Andrew Sep 10 '21 at 23:50