Treviasty wrote:
> Hello !
> 
> I'm starting experiments with compressed pulse radar and I have to choose
> the best signal to transmit - low autocorrelation sidelobes, good ambiguity
> function etc. .

STUDIOT, hehe.
Haven't you learned yet that there is no such thing as "best" signal, 
and while improving one property you are compromising something else? 
If you use the word "best", you must clarify "best" with respect to what.

> But there is one thing I can't understand - why there are
> so many publications and researches about sequences with good periodic
> autocorrelation?

Those are used for data transmission.
Those are simpler for analysis.

> After matched filtering of incoming single pulse I have
> on the output the aperiodic autocorrelation, which has completely different
> sidelobes than periodic one.

Of course.

> If the pulse train had been used with matched
> filter looking for single pulse, then periodic autocorrelation would be
> visible on output, but it should result in train of periodic
> autocorrelation pulses as well - I have never met this situation.

So, what's the problem with that?

> I would appreciate any hint.

Google, wikipedia?

> Dominik

VLV

On 14 Jun, 13:36, "Treviasty" <dominik.rzepka@n_o_s_p_a_m.gmail.com>
wrote:
> Hello !
>
> I'm starting experiments with compressed pulse radar and I have to choose
> the best signal to transmit - low autocorrelation sidelobes, good ambiguity
> function etc. . But there is one thing I can't understand - why there are
> so many publications and researches about sequences with good periodic
> autocorrelation ? After matched filtering of incoming single pulse I have
> on the output the aperiodic autocorrelation, which has completely different
> sidelobes than periodic one. If the pulse train had been used with matched
> filter looking for single pulse, then periodic autocorrelation would be
> visible on output, but it should result in train of periodic
> autocorrelation pulses as well - I have never met this situation.

There are a number of possible reasons:

- There are computational savings in the periodic computations
  compared to the aperiodic computations.
- The academics who publish papers don't understand (or appreciate)
  the difference between idealized computations and real-world work
- There are several radar pulses in the air at any one time
- The radar signal is not pulsed but CW cyclic

and so on.

Rune

On Jun 14, 7:36=A0am, "Treviasty" <dominik.rzepka@n_o_s_p_a_m.gmail.com>
wrote:
> Hello !
>
> I'm starting experiments with compressed pulse radar and I have to choose
> the best signal to transmit - low autocorrelation sidelobes, good ambigui=
ty
> function etc. . But there is one thing I can't understand - why there are
> so many publications and researches about sequences with good periodic
> autocorrelation ? After matched filtering of incoming single pulse I have
> on the output the aperiodic autocorrelation, which has completely differe=
nt
> sidelobes than periodic one. If the pulse train had been used with matche=
d
> filter looking for single pulse, then periodic autocorrelation would be
> visible on output, but it should result in train of periodic
> autocorrelation pulses as well - I have never met this situation.
>
> I would appreciate any hint.
> Dominik

Sequences with low periodic autocorrelation are useful for direct-
sequence spread spectrum (DSSS) systems. In such an application, the
sequence in question is transmitted repeatedly with some additional
information-based modulation applied. Thus, there is some periodicity
to the transmitted waveform, and the periodic autocorrelation behavior
of the sequence is important. You would like a sequence that has large
spikes at maximum correlation, separated by periods of flat
correlation that is as small as possible. An example of a family of
sequences with this type of behavior is the Gold codes; they are used
in the GPS system.

This differs somewhat from the characteristics that you want for a
radar pulse. In that case, you're looking for the presence of a pulse
buried in the RF background only. In order to accurately detect the
time of arrival of the pulse, you want a sequence whose aperiodic
autocorrelation contains a single spike at maximum correlation and
"nothing" at all nonzero lags. Apparently this is a much more
stringent requirement than the periodic case, as optimal aperiodic
correlation sequences, like Barker codes, are not particularly long.

Jason

Hello !

I'm starting experiments with compressed pulse radar and I have to choose
the best signal to transmit - low autocorrelation sidelobes, good ambiguity
function etc. . But there is one thing I can't understand - why there are
so many publications and researches about sequences with good periodic
autocorrelation ? After matched filtering of incoming single pulse I have
on the output the aperiodic autocorrelation, which has completely different
sidelobes than periodic one. If the pulse train had been used with matched
filter looking for single pulse, then periodic autocorrelation would be
visible on output, but it should result in train of periodic
autocorrelation pulses as well - I have never met this situation.

I would appreciate any hint.
Dominik