Difference between QPSK and 4 QAM

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Hana Elenany
Hana Elenany 2016-6-21
回答： Darel 2021-6-9
I need to know the difference between QPSK and 4 QAM, are they same?

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Darel
Darel 2021-6-9
Yes, QPSK and 4-QAM are effectively the same. Higher order PSK and QAM would be different, but they reduce to the same thing if you only have 4 constellation points. For more information about digital modulation, see Digital Modulation.

更多回答（2 个）

Rahul Narendra Shanbhag
PSK and QAM are two different modulation schemes. QAM can be thought of as a combination of amplitude-shift keying and phase-shift keying, since QAM converts two digital bit streams, by changing the amplitudes of two carrier waves, using the ASK, while the carrier waves are out of phase with each other by 90 degrees.
M-PSK for M<=4 is always the same as M-QAM(assuming there is no offset in PSK), since the constellation diagrams turn out to be same because the modulators used to achieve this are very similar.
Hope this helps.
Saurabh Kumar
Saurabh Kumar 2020-6-18
编辑：Saurabh Kumar 2020-6-18
Hi Hana,
Though, theoritically both QPSK and 4-QAM are different as in QPSK all symbols lie on the unit circle and in QAM the symbols lie on straight line that form a square, But, both QPSK and 4-QAM use same symbol sets so both QAM and QPSK performs same function.

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