perrysou / gnss_sdr Goto Github PK

Hi there, I have been trying to process a signal that I have created using GPS-SDR-SIM.

the signal has 0 Hz IF because it is a baseband signal in the .bin file. Similarly, the sampling frequency is 2.5e6 and the total duration of the signal is 300 seconds.

Apart from that, I have another signal that I caught with RTL-SDR and it has a sampling frequency of 2.048 MHz. However, when I was trying to process these signals, I noticed that no satellites were being acquired during the acquisition phase. So I reduce the Det. Acquisition from 2.5 to 1.5 and after that Selected the sampling frequency to 2.048 and IF to 0.

When I run the code again I can acquire all the PRNs available in the channels. However, when it comes to tracking it says invalid preamble. Can you help me what could be the reason behind this error?

Here are the screenshots of the settings and results

Greetings,

So I have 2 questions, regarding the acquisition.m

1. At line 155. If I understand correctly there has to be a second high peak not closer to 1 chip to the first peak. There is also a check that considers the matrix's boundaries. But why check against the number 2. (if excludeRangeIndex1 < 2) This condition seems wrong to me, and it would make more sense if it would be checking against 1 (if excludeRangeIndex1 < 1).
   An example: What if samplesPerChip = 12 and first peak is at index 13. Then excludeRangeIndex1 = 13 - 12 = 1 < 2 which follows to (... samplesPerCode + excludeRangeIndex1) where samplesPerCode + 1 will exceed the boundaries in results.

2. I struggle to understand the part at 203 [fftMax, fftMaxIndex] = max(fftxc(5 : uniqFftPts-5));
   Why is the range 5 : uniqFftPts-5, what is that 5 number?

Thanks

Hello,

I have a doubt in the step where you are mixing the incoming signal to baseband. As in you are using cosine carrier to Q channel and sine carrier to I channel as given below:
% First mix to baseband
qBasebandSignal = carrCos .* rawSignal;
iBasebandSignal = carrSin .* rawSignal;

and later in PLL discriminator you are using Q/I which will in this case become Cosine/Sine.

Then how is it possible to take atan of this value here to get the desired result?

Also everywhere in books as well its written as the Phi=tan(Q/I) which is only possible if it is sin(theta)/cos(theta).

Kindly explain me the logic behind this and I'll be very grateful to you.

Thanks,
Priyanka

Hello,

My doubt is related to the code file (initsettings.m).

In code line no: 43, How the processing time selected is 37000 ms?

I am mentioning the code line below:

settings.msToProcess = 37000; %[ms]

Waiting for the positive reply

Thank you
Raza Javed