GNSS SNR testing

[Arthur M]

Hello,

We are currently developing with the nRF9151 and would like to request more information regarding GNSS SNR testing.

We have reviewed the documented GNSS functionality test procedure (GNSS functionality test), which utilizes the AT%XRFTEST (Set command) from the PTI modem. (Set command)

We are wondering how does the "<param0> RX signal power" parameters plays in the calculation of the results returned.
Would it be possible to run the same command (power) with a different signal in input? (more attenuated signal)?
I am not sure why the command output "antenna_power" level changes depending on the "expected power level", shouldn't it be a raw value?
Also I understand that the parameters is the expected power level at the module port, but why is it mentioned as GAIN? Is it because the GAIN applied on the signal is directly linked to the value given?
Would it be possible to have a "raw" level received?

Also, If we are confirming our RF path viability during production, is it recommended to use AFC on or off?

Thanks for you answers,

Arthur M

[Øyvind]

Hello Arthur, apologies for the late reply. 

Here is the answer we got from our R&D team:

We define the GNSS sensitivity like this. Sensivity is the lowest signal level that enables the receiver to output GNSS fix in 2 minutes over 50% of the time. A GNSS simulator is used in the data sheet sensitivity test because it enables setting all the satellite signals to same power level. Yes, this is artificial situation, but that is the industry standard way of doing it because trying to derive any dB value from live signals (with varying power levels) would be nearly impossible.

There is no point in trying to compare results from AT%XRFTEST to our stated GNSS sensitivities due to completely different methodology. But as to why the results differ so wildly, the main reason is probably that the actual GPS signals are spread spectrum signals and for example GPS L1C/A provides processing gain of 30dB. XRFTEST expects a continuous wave input signal.

Let me know how this works for you.

Kind regards,
Øyvind

[Arthur M]

Hello Øyvind,

Thanks for this feedback.

Thank you for clarifying the "OpenSky" test. we where wondering how it could be done, makes more sense that the signal are simulated.

Thanks,
Best Regards,

Arthur M