i need to know the main difference between QPSK and 4QAM, i have searched over the internet and still i have not found a good explenation.
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2$\begingroup$ I vote to close this questions on the grounds that it is a duplicate of I and Q components and the difference between QPSK and 4QAM. $\endgroup$– Dilip SarwateDec 28, 2016 at 2:40
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1 Answer
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There are different types of QPSK: Offset (staggerd) QPSK, $\pi/4$-QPSK, etc.
In its most known form, QPSK is identical to $4$-QAM or $4$-PSK. That is, the same constellation can be referred to by different names. So there is no difference.
This constellation can be seen in the picture bellow (from Wikipedia)
Similarly, $2$-QAM is actually the same as BPSK, as is also pointed out here.
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$\begingroup$ you mean that there is no difference between them? $\endgroup$ Dec 27, 2016 at 16:00
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$\begingroup$ but when applied both of them for AWGN channel QPSK gives better BER values than 4QAM $\endgroup$ Dec 27, 2016 at 16:03
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$\begingroup$ If one is a subset of the other, the can be an optional difference. $\endgroup$– hotpaw2Dec 27, 2016 at 20:44
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$\begingroup$ @user24907 With equal parameters, their BER is also exactly the same. $\endgroup$– msmDec 27, 2016 at 21:51