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From: electrical_storm on 19 Apr 2010 07:58
Hello,

I am looking for ideas to synchronize an incoming signal with a template
signal.

I also want to detect if the incoming signal is valid or not. For this, I
cross-correlate a small length of the input signal with the template. This
seems to work fine.

How can I then find out a synchronization point between the noisy input and
the template? I have been doing this in MATLAB. My initial idea was to find
the point of maximum correlation and use this as the sync point. But this
does not seem to work for noisy signals.

If it is important, my template size is around 6000 sample points.

I appreciate any comments and suggestions you may have about this.

Thanks much.


From: Rune Allnor on 20 Apr 2010 05:52
On 20 apr, 10:28, "electrical_storm"
<gauripatil24(a)n_o_s_p_a_m.gmail.com> wrote:
> Thanks for your comments.
>
> My problem is slightly more complicated because the input signal has a
> different sampling rate than the what the template was recorded at.

Then get a new template signal. Either record a new template
at the same sample rate as it will be used, or resample the
template you have to the sampling rate it will be used.

Mind you - if your template is sampled at a lower rate than
the signal itself, you might find that significant details
in the pre-sampling analog template waveform are missing from
the sampled version.

Rune
From: electrical_storm on 20 Apr 2010 06:03
The sampling rate of the input signal varies. So to have the same sampling
rate for the template and the input is not an option.

On second thoughts, maybe I could vary the sampling rate of the template
according to some algorithm and then correlate it with the input. But the
sampling rate of the input is always unknown and a variable.

>On 20 apr, 10:28, "electrical_storm"
><gauripatil24(a)n_o_s_p_a_m.gmail.com> wrote:
>> Thanks for your comments.
>>
>> My problem is slightly more complicated because the input signal has a
>> different sampling rate than the what the template was recorded at.
>
>Then get a new template signal. Either record a new template
>at the same sample rate as it will be used, or resample the
>template you have to the sampling rate it will be used.
>
>Mind you - if your template is sampled at a lower rate than
>the signal itself, you might find that significant details
>in the pre-sampling analog template waveform are missing from
>the sampled version.
>
>Rune
>
From: Rune Allnor on 20 Apr 2010 06:43
On 20 apr, 12:03, "electrical_storm"
<gauripatil24(a)n_o_s_p_a_m.gmail.com> wrote:
> But the
> sampling rate of the input is always unknown and a variable.

In that case you are screwed. You have to know *something* about
the data to get anything useful out of them. That additional
knowledge is the difference between 'data' and 'a sequence of
numbers'.

Rune
From: Rune Allnor on 19 Apr 2010 08:54
On 19 apr, 13:58, "electrical_storm"
<gauripatil24(a)n_o_s_p_a_m.gmail.com> wrote:
> Hello,
>
> I am looking for ideas to synchronize an incoming signal with a template
> signal.
>
> I also want to detect if the incoming signal is valid or not. For this, I
> cross-correlate a small length of the input signal with the template. This
> seems to work fine.
>
> How can I then find out a synchronization point between the noisy input and
> the template? I have been doing this in MATLAB. My initial idea was to find
> the point of maximum correlation and use this as the sync point. But this
> does not seem to work for noisy signals.

That's the way to do it. But the reliability of the peak depends
on signal design. If you have a well-designed sync sequence you
will get a nice, narrow peak even in low SNRs. Correlate the whole
sync template with your signal, and see if the match is better.
You need the *whole* template, and the max peak only occurs if the
signal contains the the *whole* sync sequence.

Rune
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