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 GPS signal it and is such low strength of signal okay for GPS acquisition or not?
Thanks, Priyanka On Wed, Apr 18, 2018 at 9:41 AM, Jean-Michel FRIEDT < jean-michel.fri...@femto-st.fr> wrote: > 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 > http://jmfriedt.free.fr/sdr_gps_eng.pdf > > JM > > I want to acquire first the GPS L1 signal to get a basic idea of how >> acquisition works and then move to Galileo E1 signal, but I am facing some >> problems. >> >> 1. I am using RTL-SDR Dongle, with Rafael R820T Tuner, and I want to >> acquire GPS L1 signal with that. >> >> 2. I am using GNURadio to receive the data. In GNURadio, in the RTL-SDR >> Block, I am giving my sample rate of 2.048 Msps. >> >> 3. Incoming L1 signal has frequency of 1575.42 MHz and I am using GPS >> active antenna with 40 db gain. >> >> 4. In RTL-SDR dongle, it will be down-converted to IF (that is unknown to >> me), through local oscillator. and after the down-conversion, it will be >> passed to ADC. >> >> 5. In some articles, I have studied that RTL-SDR dongle that I am using >> has >> IF= (3.57 MHz or 4.57 MHz). (*http://superkuh.com/rtlsdr.html >> <http://superkuh.com/rtlsdr.html>)* >> >> 6. Now my question is that if it is true, then the signal going into the >> ADC has frequency of (3.57 MHz or 4.57 MHz) , and my sample rate is 2.048 >> Msps, that is below the frequency of the incoming signal, then it is not >> following the Nyquist Criterion. Also, according to this, the incoming >> signal must be at (3.57 MHz-2.048 MHz= 1.652 MHz). Is it Right? >> (screenshot >> attached for reference) >> >> 7.The samples coming out of RTL-SDR are complex (I & Q). In one articles I >> have studied that the I-part are the C/A codes and the Q-part are P-Codes >> and these samples are at Baseband(zero-frequency). If I just want to >> acquire C/A code, then shall I need to just take I-part of the output >> samples coming out of the RTL-SDR? Or what should be my data on which I >> need to do the further DSP? >> >> These are my problems till now. I have studied dozens of web-pages and >> articles, but couldn't find the fruitful answer. I shall be very thankful >> for any help. >> >> Thanks a lot for your time. >> >> Regards, >> Priyanka >> >> > > > -- > JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 26 rue de l'Epitaphe, 25000 > Besancon, France > > ---------------------------------------------------------------- > This message was sent using IMP, the Internet Messaging Program. > >
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