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TMBOC / SoftGNSS

Current working ver. of SoftGNSS v3.0 for GN3sV2, GN3sV3, NT1065EVK, and NUT4NT samplers. All known updates included. Navigation module updated.
GNU General Public License v2.0
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I/Q Signal Signal Structure is Different than the General Format #5

Open kucar17 opened 9 months ago

kucar17 commented 9 months ago

In the tracking and postPorcessing functions, it seems like the rawSignal is decompressed into In-phase and Quadrature components in the inverse way of the general format. As far as I know In-Phase component corresponds to the real part and the Quadrature component corresponds to the Imaginary part.

In lines 291, and 292 of the "tracking.m" file the following is written:

qBaseBandSignal = real(carrsig .* rawSignal);
iBaseBandSignal = imag(carrsig .* rawSignal);

What is the reason for that, am I missing something?

unalfaruk commented 9 months ago

Hi @kucar17,

That's a nice question 👍

It made me confused at first, then I remembered the signal plan of L1 C/A.

image

Note that the choice of using a sine carrier (imaginary) or a cosine carrier (real) for "in-phase" extraction is often driven by the specific requirements and constraints of the system being designed.

image

As you can see here in the graph above, y-axis represents C/A signal (quadrature coomponent), therefore, when you multiply this signal by the sine component (imaginary), you are extracting the in-phase (I).

Since I've been away from GNSS-related work for quite some time, I might be mistaken now. But you can have a look at the details here:

https://www.mathworks.com/help/nav/ug/end-to-end-gps-legacy-navigation-receiver-using-ca-code.html (Introduction part, signal definition)

Understanding GPS Principles and Applications, Elliott D. Kaplan (4.3.1, 5.3)

I hope it helps.