Fwd: Galileo Frequency Shifting and Filtering

[David Dima]

---------- Forwarded message ---------
De: David Dima <daviddimavd@gmail.com>
Date: mar, 28 feb 2023 a las 17:55
Subject: Re: Galileo Frequency Shifting and Filtering
To: Marcus Müller <mmueller@gnuradio.org>

Hi Marcus,

According to Galileo's signal plan (https://gssc.esa.int/navipedia/index.php/Galileo_Signal_Plan), E5b bandwidth is  25MHz, but to save memory and resources, I sample at 20MHz because I demonstrated by testing that is enough to process the signal without losing information.

Regarding the Xlating filters: if I tune the USRP in the middle of the signals (1164MHz + (1215-1164)/2)MHz = 1189.5MHz) , then I have to shift the spectrum +- 15.345 (According to Daniel: "The band plan you posted is slightly wrong. The distance between the
AltBOC sidebands and the centre frequency is 15 * 1.023 MHz.") to be able to record at 25MHz each band (E5a and E5b). I am trying to do the following:

Kind regards,

David

El mar, 28 feb 2023 a las 17:25, Marcus Müller (<mmueller@gnuradio.org>) escribió:

Hi David,

On 28.02.23 17:17, David Dima wrote:

Dear Marcus, all

Thank you for your response. You are right, I will try to better explain the problem:

Well, when I record the signals separately (for example E5b) as shown in the below picture, and after that I try to process the file containing the IQ samples by means of GNSS-SDR free-tool, I can parse the messages to generate ephemeris, almanac or Rinex files. Even if E5b bandwidth is 25MHz, it works sampling at 20 MHz.

You're losing 1/5 of the relevant spectrum. That doesn't mean it *can't* work, it's just unnecessarily bad – honestly, **why** are you using a sampling rate that's not fit to represent the *full* signal? Can you please state *reasons*?

The issue comes when I try to record both signals at the same time. Taking into account the suggestions Jim, Daniel and you have given me in the forum, I have made a couple of changes in the program resulting in:

Now, at least I think I am closer to getting what I need but I am not sure if there are more mistakes in the flowgraph. So, I have tried to record the signals according to the above flowgraph but after that I still cannot read any signal from the satellites whereas if I record them separately I can.

This makes no sense at all. Where do your "Center Frequencies" in the Freq.-Xlating filters come from?

Best regards,
Marcus