Re: [Discuss-gnuradio] GPS Signals recorded IQ samples file

On Fri, 21 Aug 2015, Francisco Albani wrote:

> Wang: Sounds good! Thanks! Did you try it?

Yeah. It works like a charm, in both HackRF and BladeRF.

>
> Jean: many many thanks for sharing all the scripts! Your paper has caught
> my attention. I will print it and read it.
>
> Marcus: I was not expecting to "see" the signal because I already knew it
> was under noise floor. My conclusion of "signal absence" was after my GPS
> receiver was not able to decode it when I replayed it with an USRP.
> However, due to my little knowledge of GPS, it did not occur to me any
> other way of searching, so I thank you for your suggestion. I nearly killed
> my pc with a naive approach. :P I need a wiser one.
>
> Sylvain: interesting. I will try that too. Thanks!
>
>
> 2015-08-21 9:07 GMT-03:00 Sylvain Munaut <246tnt@gmail.com>:
>
>> Hi,
>>
>>> are you sure you did not see GPS? The problem is that GPS is often below
>> the
>>> thermal noise floor and only detectable by the virtue of processing gain.
>>> I'd try and take a whole lot of samples (like: 2s worth of samples), and
>>> calculate the autocorrelation[1]. You should see peaks at multiples of 1
>> ms,
>>> because that's the spreading code's period.
>>
>> You can also square the signal, then decimate it a bit and FFT it and
>> you'll see peaks at whatever doppler the sat currently has. (so you'll
>> see different peaks for different sats).
>>
>>
>> Cheers,
>>
>> Sylvain
>>
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>

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