Re: LF: ebnaut results depend on sample rate

[Paul Nicholson <vlf0403@abelian.org>]

Jacek wrote:
> the results i get from ebnaut are different depending on
> signal bandwidth.

This is possible and quite common.

> 10Hz:
> found rank 6348 ber 4.2147e-01 Eb/N0 -2.0
> carrier Eb/N0: -0.3 dB

> 240Hz:
> found rank 16679 ber 4.3029e-01 Eb/N0 -3.1
> carrier Eb/N0: -1.6 dB

For the carrier Eb/N0, the value of N0 is measured using the full
bandwidth of the input signal.   When the band is wider it may
present a higher N0 because of things like mains sidebands and
harmonics, and other interference.  That's probably the case
here.

For the decode there should not be much difference, and indeed we
see a similar BER. 42.1% and 43.0%.

The Eb/N0 in the 'found' log message is estimated from the BER and
the slope is quite steep, accuracy is poor for weak signals.
The carrier Eb/N0 is usually more realistic, unless you have
interference in the input band.

I usually resample down to about 10 or 20 times the symbol rate,
but at least 10Hz so as to get a reasonable N0 estimate.  If I
expect to have to sweep for the time stamp I might use a higher
sample rate to get more resolution with the -T argument.

--
Paul Nicholson
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