F9P and RTK @ 20hz update, possible by 'removing some constellations'?

Q&A forumF9P and RTK @ 20hz update, possible by 'removing some constellations'?
Benjamin Himberg asked 3 months ago
Hi Ardusimple,
I saw in a forum post mention of 20hz RTK updates when some constellations are removed. Do you have any more details on this? I’m trying to increase my update rate for an F9P u-blox module, however I can’t seem to get past 5hz…
 
Thanks!
clive1
replied 3 months ago

What kind of dynamics are you dealing with that needs 20 Hz ? And less than 4G..

8 Hz should be possible without significant alteration.
Have you tried doing GPS only? See Series 9 Advanced configuration GNSS pane.
That and only sending 1074/1077 MSM frames would limit the computational/tracking load to less than 16 satellites (32 measurements).

Can’t say I’ve spent a lot of time on the problem, I’m not working with rockets/missiles currently, and most of the issues here can be better solved with a systemic understanding of time, and physics of time and motion,not just jamming up the solution rate.

The F9R can do 20 – 30 Hz, but the solution here is somewhat synthetic, in that its less RTK solutions, but those are melded with sensors and model of time/motion.

clive1
replied 3 months ago

Considerations with High Rate Systems.
You need high enough baud rates to export the data with low latency, and provide sufficient bandwidth to accommodate the data generated.
You need to cull the messages significantly to those you actually need/use.
Your system needs to be able to sink and process data efficiently, quickly and properly.
A “$GxTXT txbuf alloc” warning means you have a mismatch in data flow, and messages going to interfaces that you aren’t using or lack sufficient bandwidth.

You need a systemic understanding of time, you need a connection to the TIMEPULSE, and perhaps also TIMEMARK, to establish time on your MCU/SBC. The GNSS reports historical information, and the latency may be large and variable, and further degraded by the ability of your system to ingest and act on it. If you’re moving remotely rapidly you need to account for this.