Please note that the very first fix after device start-up is a rather different measurement than any of the following consecutive fixes.

[Roman Veselskyi]

Hello,

We’re testing the nRF9160 GNSS performance on our custom PCB and have noticed that, even with A-GPS, the first fix after powering on the device takes significantly longer than subsequent fixes. This is a bit confusing because we’re using the GNSS sample for testing, and it should clear the GPS data during TTFF testing. While reading an article, we came across the following statement:

"Please note that the very first fix after device start-up is a rather different measurement than any of the following consecutive fixes."

Could someone please explain why this first fix behaves differently and is also related to AGPS? 

[Edvin]

Hello,

I believe this would be as expected. Even though you have A-GPS, you still need to download the Almanac from the network. So you need to connect to the cellular network, download the Almanac, and then use this to get a fix (which would be quicker than doing a cold start of the GPS). But when you have your first fix, the GPS data is already present on the nRF91, and it is more accurate than the Almanac data that you would download (I think). So 1: You don't need to download the data, and 2: it is more accurate. Therefore the consecutive fixes will be quicker.

Please note that we are short staffed due to public Holiday in Norway. Please expect some delay in our answers for the next week. We will be almost full staffed from Tuesday next week.

Best regards,

Edvin