Custom AGPS: Which data is required for the AGPS?

RE: Custom AGPS: Which data is required for the AGPS?

Didrik Rokhaug — Mon, 20 Jul 2020 14:48:16 GMT

Hi, we are still waiting for answers to Simon's questions internally, but I'll try to add my knowledge here as well.

When it comes to what data is necessary, the answer is the more, the better.

However, the data has different longevity, so not all the data is necessary every time.

E.g. the almanac is valid for weeks (I don't remember the exact number at the moment) but can be used for months with less performance gain. In addition, it is not strictly necessary, so the GPS should be able to get a fix even if it is missing.

Meanwhile, the ephemeris is only valid for a couple of hours, before it must be refreshed.

So, I would say that if you fill out what you can, that should help you a bit. However, this is mostly (somewhat qualified) speculation on my part. It might be that the whole struct must be filled (correctly) for you to get any benefit.

When it comes to the data format, I have seen any specifications, though I would assume it is closely related to the format used by the satellites. The format of the structs is probably specific to the nRF9160, but the data inside should be fairly standard.

I do not believe that any of the structs make any of the other redundant.

If you haven't already, you should take a look at the A-GPS related files in the nrf_cloud library (nrf/subsys/net/lib/nrf_cloud), which shows how that library handles requesting and downloading A-GPS data from nRF Cloud.

Best regards,

Didrik

RE: Custom AGPS: Which data is required for the AGPS?

Jan Erik — Fri, 17 Jul 2020 02:47:54 GMT

Hi, it seems like nrf_sendto() is successful but I'm not noticing a huge TTFF improvement.

In any case it would be great to know which extra pieces of information would increase our GPS performance, and which pieces we can leave out. I have no problem waiting for someone more knowledgeable about AGPS by the way.

Also, are those struct values Nordic specific or based on some external convention?
For example the UTC time one has some weird polynomial values that I can't quite figure out, so even though I have a timestamp I'm not able to feed it to the agps. If it's not Nordic specific I might be able to find some docs about it elsewhere.

And one more thing: I can't find any official google documentation about their SUPL server, does that exist?

RE: Custom AGPS: Which data is required for the AGPS?

Simon — Thu, 16 Jul 2020 15:28:26 GMT

I am not totally sure about this, as I don't know much about AGPS.

Couldn't you just test it out and see if it works? Try using only using type=NRF_GNSS_AGPS_LOCATION and using this struct with all fields set to NULL except for these and run nrf_sendto()?

I've asked internally about this, and hopefully, someone with more knowledge about this can shed some light on your questions.

Best regards,

Simon

RE: Custom AGPS: Which data is required for the AGPS?

Simon — Tue, 14 Jul 2020 19:43:40 GMT

I am currently looking into this and will prioritize it in the next days. The GPS experts in the support team are currently on vacation, so I'll have to do some investigations myself.

Best regards,

Simon

RE: Custom AGPS: Which data is required for the AGPS?

Jan Erik — Tue, 14 Jul 2020 10:31:07 GMT

Hi, any updates here?

RE: Custom AGPS: Which data is required for the AGPS?

Simon — Mon, 06 Jul 2020 23:47:19 GMT

Currently, a huge portion of the support team (including many of the experts on nRF9160) is on summer vacation, and you may experience delayed answers. My apologies for that.

I will try to provide you with an answer within this week.

Best regards,

Simon