Re: [Discuss-gnuradio] Constellations, EVM and SNR Questions

[Luis Felipe Albarracin Sanchez]

Thank you all,

I will try that.

Kind regards.

On Thu, Jun 7, 2018 at 10:16 PM, Martin K <address@hidden> wrote:

The following call is how I read data into MATLAB from the GNURadio file sink. I think this would almost work in Octave as well but I haven't tried. If not it, it at least illustrates the proper format.

FileID = fopen('Filename','r');

import_channels = 2;

SamplesPerFrame = 1024;

import_format = 'float32';

x = fread(FileID,[import_channels SamplesPerFrame],import_format)';

complex_baseband = complex(x(:,1),x(:,2));

I have this embedded in a MATLAB system class. I extricated the fopen/fread() calls for clarity.

HTH

-- 

Martin K.

On Thu, Jun 7, 2018 at 9:30 AM, Federico 'Larroca' La Rocca <address@hidden> wrote:

Hello again,

To export from GNU Radio to octave, you should first use a "File Sink" block and then one of the scripts in gr-utils/octave. I'm pretty sure they are compatible with matlab too.

About the SNR, that depends on what you want. If you want the power of noise that actually affects your decision system divided by the power of the symbols, then MER is what you are looking for (assuming your sampling and frequency correction works properly). If you want the more classic SNR (i.e. power of the useful signal divided by the total noise power in the band), then that's more involved. You may try the following: since you know the constellation points and the pulse, you may easily calculate the power of the useful signal (assuming your AGC works properly and that the channel is flat fading). The difference between this power and the actual received power is due to noise (assuming independence). 

However, what matters performance-wise is the amount of noise that gets into the decision system, and not the actual SNR. 

Hope it helps!

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Eng. Luis Felipe Albarracin
PMP
CCNA/CCDA/CCNP/CCDP/CCIP
ITIL v3 Foundation
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