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From: Eric Jacobsen on 20 Jul 2010 12:39
On Tue, 20 Jul 2010 08:10:24 -0700 (PDT), John <sampson164(a)gmail.com>
wrote:

>On Jul 20, 7:15=A0am, "mtr" <baranov.mv(a)n_o_s_p_a_m.gmail.com> wrote:
>> Hello. We are making some sdr thing. So there is a need to catch carrier
>> frequency for down shifting. We know nothing about baseband signal, excep=
>t
>> may be that it was digital or analogue modulated. Could anyone suggest an=
>y
>> method?
>> We're computing everything with modern pc, so there is no problem with
>> arg(), log10(), sin()/cos(), =A0square or square root and so on.
>>
>> Thank you in advance
>
>The most universal method is to provide a tuning knob and a
>constellation display.

What if it's OFDM?


Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.abineau.com
From: Eric Jacobsen on 20 Jul 2010 12:44
On Tue, 20 Jul 2010 06:15:33 -0500, "mtr"
<baranov.mv(a)n_o_s_p_a_m.gmail.com> wrote:

>Hello. We are making some sdr thing. So there is a need to catch carrier
>frequency for down shifting. We know nothing about baseband signal, except
>may be that it was digital or analogue modulated. Could anyone suggest any
>method?
>We're computing everything with modern pc, so there is no problem with
>arg(), log10(), sin()/cos(), square or square root and so on.
>
>Thank you in advance

I'm still trying to wrap my head around "omnivorous" carrier recovery.
I'm not sure whether the methods I've used previously are carnivorous
or vegetarian or what.

As mentioned by others, there is no universal method. IF, and it's a
significant IF, you can assume that there are no signals in adjacent
spectrum you can just take the power difference in both halves of the
extended baseband channel. If one side has more power than the
other, and the spectrum is symmetric, then there's an offset.

That'll work with most modulation methods, but it's generally not
accurate enough for fine tuning. It won't work if there's an
adjacent channel within the ambiguity range. It won't work if the
spectrum isn't symmetric.


Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.abineau.com
From: Vladimir Vassilevsky on 20 Jul 2010 13:13


Eric Jacobsen wrote:

> I'm still trying to wrap my head around "omnivorous" carrier recovery.
> I'm not sure whether the methods I've used previously are carnivorous
> or vegetarian or what.
> As mentioned by others, there is no universal method. IF, and it's a
> significant IF, you can assume that there are no signals in adjacent
> spectrum you can just take the power difference in both halves of the
> extended baseband channel. If one side has more power than the
> other, and the spectrum is symmetric, then there's an offset.

This is essentially a discriminator; the output is going to be something
like a centroid of the signal + noise in the bandwidth.

> That'll work with most modulation methods, but it's generally not
> accurate enough for fine tuning. It won't work if there's an
> adjacent channel within the ambiguity range. It won't work if the
> spectrum isn't symmetric.

1. Perform the FFT in the sliding window of one symbol.
2. Interpolate the FFT to get fractional bins.
3. Perform N-th power operation for each fractional bin.
4. Perform a long FFT on the result.

Pretty heavy, but it works for any single- or multi-carrier signal.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com


From: Jerry Avins on 20 Jul 2010 14:20
On 7/20/2010 10:40 AM, mtr wrote:
> 1 -- 100 Mhz. Do not worry about sampling jitter, it would be small enough.

The sampling period is 10 nanoseconds. 1% jitter -- a large amount -- is
100 picoseconds. What operating system will you use?

Jerry
--
Engineering is the art of making what you want from things you can get.
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From: John on 20 Jul 2010 15:24
On Jul 20, 12:39 pm, eric.jacob...(a)ieee.org (Eric Jacobsen) wrote:
> On Tue, 20 Jul 2010 08:10:24 -0700 (PDT), John <sampson...(a)gmail.com>
> wrote:
>
> >On Jul 20, 7:15=A0am, "mtr" <baranov.mv(a)n_o_s_p_a_m.gmail.com> wrote:
> >> Hello. We are making some sdr thing. So there is a need to catch carrier
> >> frequency for down shifting. We know nothing about baseband signal, excep=
> >t
> >> may be that it was digital or analogue modulated. Could anyone suggest an=
> >y
> >> method?
> >> We're computing everything with modern pc, so there is no problem with
> >> arg(), log10(), sin()/cos(), =A0square or square root and so on.
>
> >> Thank you in advance
>
> >The most universal method is to provide a tuning knob and a
> >constellation display.
>
> What if it's OFDM?
>
> Eric Jacobsen
> Minister of Algorithms
> Abineau Communicationshttp://www.abineau.com

Turn knob until all constellations look good.

John
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