Hi,
I was running the NoneRT mode with only one type signal: GPS L1 C/A, I found that the range value is greater than the PSR value. Can someone explain why? PSR should involve all kinds of delays, thus I expect to see PSR being greater than geometrical range.
Thanks,
Hongzhao Zheng
The positions of satellites at signal transmission time (I believe it is “PSR satellite time”) seem to be not provided, the positions of satellite at signal reception time(I believe it is “elapsed time”) is provided. Could anyone confirm or clarify this?
Hi @hongzhaozheng,
Yes indeed, the value of the PSR is greater than the value of the range.
But in Skydel, we automatically add error values on the clock.
Setting → GPS → Signal control
But you can also set this value to zero and in this case you will have a PSR value which is greater than the geometrical range.
Grace
Hi @hongzhaozheng,
the positions of satellites at signal transmission time in the Skydel Logging are recorded in the files of the various satellites and the positions of the satellite at signal reception time is recorded in the file “receiver antenna” in the Skydel raw logging folder.
Grace
Thank you Grace. I get it.
Hi @Grace,
I believe someone asked the same question but I didn’t fully get your point. I noticed that the Range provided in the .csv file does not exactly equal to the difference between the sat position in ECEF frame and the receiver position in ECEF frame. There is a small difference of around 10m, could you clarify this?
Many thanks,
Hongzhao Zheng
Hi @hongzhaozheng,
To calculate the correct value of the Range measurements, you have to consider the Sagnac effect caused by the rotation of the ECEF reference frame during the signal propagation.
To have the PSR (pseudorange) equals to Range in Skydel, you have to do the following:
We have prepared and attached a configuration file for your Demo to this reply. I will send it to you by email.
Best regards,
Grace Oulai
App Eng
Hi @Grace ,
Thank you for your answer, but I think you misunderstood my question. My question was that why does the Range provided in the .csv file do not exactly equal to the difference between the provided sat position in ECEF frame and the provided receiver position in ECEF frame. “Provided” means those data provided in the generated .csv file.
Many thanks,
Hongzhao Zheng
Hey @hongzhaozheng 
,
As I mentioned in my previous reply, Skydel considers the Sagnac effect on calculating the Range in the raw logs. This is the reason why the “Range provided in the .csv file do not exactly equal to the difference between the provided sat position in ECEF frame and the provided receiver position in ECEF frame”.
You must consider the Sagnac effect in your calculations by using a transformation matrix to calculate the sat. position in the ECEF frame during the signal propagation, then calculate the difference between the transformed sat. positions and the receiver posistion in the ECEF. This is well described in the literature and the ICD.
Please, feel free to continue the discussion if there are points where you want more details.
Best regards,
Grace
What is the transformation matrix for the Sagnac effect? Could you provide me with a link to it? I saw GNSS-SDR.org talks about sagnac effect when doing PVT calculation, but I don’t see they correct satellite position when considering it. Here is the link: PVT - GNSS-SDR
Thank you,
Hongzhao Zheng
Several references in the literature discuss the Sagnac effect correction, and it’s rotation matrix. I suggest checking section #2.2 of the following paper. It will give you the necessary background and the details of the rotation matrix.
Sagnac Effect and SET Error Based Pseudorange Modeling for GPS Applications (cyberleninka.org)
Thank you very much M.Tamazin, the problem is finally solved.
