64 - QAM, signal to noise ratio (SNR) for a 6 bit QAM modulation?

Thread Starter

Filipe001

Joined Mar 18, 2022
4
Hey,
Can someone tell me what’s the minimum signal to noise ratio (SNR) for a 6 bit QAM modulation?
 
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drjohsmith

Joined Dec 13, 2021
421
Hey,
Can someone tell me what’s the minimum signal to noise ratio (SNR) for a 6 bit QAM modulation?
Look at a QAM 64 constellation
1647630444317.png

Thats fine,
but with noise , each "point" is going to have a fuss

1647630481635.png

If the fuzz of one point overlaps the fuzz of another point,
how do you know which of the two points its meant to be

So if max signal range is "1"
whats the fraction of 1 that a signal has to be less than so as not to interfere

https://www.electronics-notes.com/a...ypes-8qam-16qam-32qam-64qam-128qam-256qam.php
 

Thread Starter

Filipe001

Joined Mar 18, 2022
4
Thank you so much both, i really aprecciate your help!
I knew what consists the 64QAM modulation, i just couldn't relate it with the SNR, but know i understand!
Have a great week!
 

drjohsmith

Joined Dec 13, 2021
421
How does one get a 64 QAM with 6 bits?
2 to power 6 is 64,
QAM has 64 points, each point is assigned one of the 64 codes,

each point is called a symbol
each symbol is 6 bits,
hence the data rate is symbols per second,
the encoding between the raw data and the symbols
is application specific
look on line..
 

Thread Starter

Filipe001

Joined Mar 18, 2022
4
Sorry to bother you again but in this case, for example, what is the solution?
1647788359438.png
I dont know if the answer is in dB or not... does anyone know? Its for a TPC nothing to important!
 

Thread Starter

Filipe001

Joined Mar 18, 2022
4
Yes, i Know he wouldn't make sense but as i dont know how to get any of that numbers i honestly dont know what's really wrong or not!
But What is the answer there? If i use the 20-23db i can get the 1st number but im not sure.
 

michael8

Joined Jan 11, 2015
295
Just a guess, I pick (c) 31. And it's likely a wrong answer to a "wrong question".

You're sending 64 different symbols and depending on the S/N level it becomes hard to determine which is which.
It says "ratio" which I guess is just a ratio not dB.

Say the S/N ratio was X. So the signal is X times the noise. But you need to determine which of the
64 symbols is being received. Each symbol lives in 1/64 of the signal space and has full noise.
So I'm looking for a S/N ratio (answer) close to 64, of the choices 31 is closest.

Oh, QAM so the 64 points are 2 dimensional so the spread/error of symbols is different, possibly 8 x 8.
So an answer of 64 might be high...

Wrong question: For many types of links, the S/N is not going to be high enough for perfect reception. Thus error
correcting codes. These can correct and/or help the receiver decide which symbol is most likely and thus
error free symbol decoding isn't necessary and the link can "work" with a worse S/N than you'd expect.
 

bertus

Joined Apr 5, 2008
21,939
Hello,

On the give page this is given:
RS SNR is useful for channel detection and PDSCH SNR of Data decoding,PUSCH SNR and PUCCH SNR is applicable for Uplink data and Control channel detection.
Each channel have its minimum level SNR requirements for detection.
This SNR requirement depend on the modulation means to decode 64 QAM the SNR should be high close to 25 dB or more and likewise to decode an QPSK it is low may be about 2dB or less.
Each channel in LTE uses particular modulation so SNR requirement is also accordingly.

What is 25 dB in ratio?

Bertus
 
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