If you just want to see constellation points with the QT GUI Constellation Sink block, you can try the DVB-S2X Modulator in the Digital Television component. It has a bunch of built-in constellations. Or you can use the "Chunks to Symbols" block and define your own constellation.
That's just a starting point. Actual EVM measurements is a complex topic.
Ron
On 06/07/2018 03:24 AM, Luis Felipe
Albarracin Sanchez wrote:
Hello Everyone,
I am trying to run a model with different modulations, and to see different measurement values ( Constellation Diagram, EVM, and SNR). i have done the following but it does not seem to work:
1- I try plotting a DQPSK modulation with "QT GUI Constallation Sink" (directly form the modulating block and it shows a graph like this:
As you can see i have dots that are not where they are supposed to be (in every corner), to try to solve this i placed a "sink file" block from the out of the "modulating block", and i tried to plotted in matlab to see if i had a better image. Unfortunately it went worse. In matlab i read the bin file it showed a row with many numbers (none of them bigger than 255) so i assumed it came formatted every 8 bits .
Fist thing i separated what i have read is the real and the complex part, and i tried to plotted, and it did not work....show many points none of them in the corners where they are supposed to be. After that i thought maybe the Most Significant Bit is the "sign", so i adjusted the program in matlab and ran the plot, but it also did not work.
Below the plot i get:
I wanted this so i can design a program on Matlab to calculate EVM for future measurements, nevertheless i wanted to measure EVM on GNURadio, and also i am looking for a way to measure SNR with different modulations.
Given this, i would appreciate your help with the following:
1- How can i have a graph of the constellation for different modulations in GNURadio, that is accurate.
2- How can i export data file form GNURadio (the output of a modulator block) and plot the costellation in matlab properly?
3- Is there any git repository where i can find blocks for EVM and SNR for different modulations, if not is there a way or known resources, or flowgraphs to do SNR measurements and EVM measurements?
Once again thanks for all the help.
Kind regards.
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