Wolfgang,
I have checked several sources, and they match up with the IEEE 1139 in
this regard.
I have also evaluated the equation for Allan variance for the random
walk noise, and it matches up with the references and what I put here:
https://en.wikipedia.org/wiki/Allan_variance#Power-law_noise
So, the A formula you have matches up.
You will need to find another source of the mismatch.
Cheers,
Magnus
On 03/06/2015 11:04 AM, Wolfgang Wallner wrote:
On 03/05/2015 07:23 PM, Attila Kinali wrote:
Servus!
Servus :)
On Thu, 05 Mar 2015 14:35:51 +0100
Wolfgang Wallner <wolfgang-wall...@gmx.at> wrote:
For the random walk noise the expected line is off by a factor of
exactly 2 from the calculated plot, and I don't know how to explain this
behavior.
I'm probably the wrong one to answer, as I have never done any noise
simulation or even read up the relevant papers, but...
A factor of 2 sounds like the difference you would get between one sided
and two sided noise PSD's.
I calculate the one-sided PSD of the FFD data as described in [1] (first
paragraph), so the code looks like this:
xdft = fft(x);
xdft = xdft(1:N/2+1);
psdx = (1/(Fs*N)) * abs(xdft).^2;
psdx(2:end-1) = 2*psdx(2:end-1);
Remark: Before calculating the PSD, I split the data into parts of equal
size, calculate the PSD for each one, and average over the set of PSDs.
This improves the graphical visualization a lot.
As the result matches my expectation exactly for 4 different kinds of
noise, I would have assumed that this PSD calculation approach is quite
reasonable.
As I see the unexpected behavior only with random walk noise, and the
main difference in the calculation is the term A, I would suspect that
it has something to do with it.
However, I'm a novice in this field, so any hint is very appreciated.
regards, Wolfgang
[1] http://de.mathworks.com/help/signal/ug/psd-estimate-using-fft.html
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