Priyanka,
I believe the easiest way to find GPS satellites* is to perform an FFT on
the baseband as well as FFT of each of the 32 PRN sequences (in reality you
don't need to look at all 32 of them)
Perform a cross correlation with something like (pseudocode follows):
for binshift = -n:n
{
a=
at least your fc in the Matlab script is incorrect: removing the
carrier frequency has been taken care of by the RF frontend (R820T2).
You are only left with the offset between the GPS carrier and the frontend
carrier + Doppler shift. Doppler is in the +/5 kHz range, but offset can
be up to
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
Thank you JM and Sakthi,
To Jean- I tried taking the absolute square of the collected complex signal
and got the peaks in range of e-3(1/1000). Also to add to your notice the
signal that I am collecting from the RTL-SDR dongle has amplitude in range
of 0.04(peak to peak). Can we be sure of having
If you want to make sure that your collected data include GPS signals, get
rid of the BPSK modulation by squaring the complex signal, see
http://jmfriedt.free.fr/trans_num_l3_1_eng.pdf
slides 37-38.
I tried to do my best to describe the demodulation process in
