Thanks for the useful info but I am stuck after trying all the
possibilities which I could possibly understand from the internet. Here is
what I am doing:
I am taking signal of 1ms from RTL-SDR using GNURadio Companion at
Samp_rate 2.048M, and the flow graph is attached. after receiving the data
(I and Q complex samples) the shape of the signal is shown in the figure
attached.
Since it is the complex IQ data, so for demodulation I used complex
exponential function (exp(j*2*pi*fc*ts)). And after that I am doing the
acquisition using 'Parallel Code Phase Search Acquisition' algorithm. But I
am not getting the required result, instead I am getting some random peaks
of correlation (very low amplitude) for every satellite PRN's. I am also
attaching the MATLAB code for acquisition and example plot for one PRN.
Even after reading so many articles online, I couldn't find the solution
for that. I am not getting that what mistake am I doing in this whole
process of acquisition?
One problem that according to my understanding is that, may be the signal I
am getting is very weak, or it's just Noise. because I have tried all the
possible solutions, but couldn't find the good correlation peak for any
satellite.
And I am also getting two type of complex data from RTL-SDR, when I just
plug-in my dongle, I am getting a complex signal of random amplitude, but
when I take the data after some time then I am getting the data of constant
amplitude. I don't know which of them is correct, so I tried processing
both of them but results are same.
Any help would be highly appreciated.
Thank you
Priyanka
On Thu, Apr 19, 2018 at 8:14 AM, Jean-Michel FRIEDT <
address@hidden> wrote:
I am collecting from the RTL-SDR dongle has amplitude in range
of 0.04(peak to peak). Can we be sure of having GPS signal it and is such
low strength of signal okay for GPS acquisition or not?
that's the beauty of spectrum spreading and pulse compression: despite
the signal being below thermal noise level, pulse compression by 1024-fold
(1.024 Mb/s and 1 ms code repetition rate) will increase signal to noise
ratio by 10 bits. So even a single-bit A/D converter (comparator) is enough
to collect GPS data. You cannot see GPS unless you compress the pulse
(either
by squaring the signal to get rid of BPSK, or correlating with the local
copy of the Doppler shifted PRN).
JM
--
JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 26 rue de l'Ep
<https://maps.google.com/?q=SeOR,+26+rue+de+l'Ep&entry=gmail&source=g>itaphe,
25000 Besancon, France
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