Satellite lock after firmware update
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JohnC
Well-Known Member
Even though GPS is global and the NAVSTAR GPS is a complete constellation I wonder if the BaiDou one is complete it only went ‘live’ in 2020 and this may be the issue, I see acquisition in the UK in 90 seconds for a cold start and within 15 seconds for a warm start.
RocketBrew
Well-Known Member
The Mavic 3 uses GPS + Galileo + BeiDou. Here is a high-level primer of GNSS, based on my understanding.
GNSS (Global Navigation Satellite System), colloquially called GPS, is an umbrella term that encompasses a group of artificial satellites that send positioning, navigation, and timing (PNT) data to GNSS receivers down here on earth from their high orbits.
GPS (Global Positioning System) is one component of GNSS owned and operated by the United States military as Navstar. GPS maintains the availability of at least 24 operational GPS satellites and currently operates as a 27-slot constellation. Each satellite circles the earth twice a day. GPS satellites fly in Medium Earth Orbit (MEO) at approximately 20,200 km (12,550 miles) altitude.
GPS and its Russian-owned counterpart GLONASS were the only available GNSS for a long time. GLONASS went through a long period of disrepair during the late 1990s. The fully operational constellation of 24 satellites located in an MEO orbit at 19,100 km (11,900 mi) altitude was restored In October 2011.
BeiDou-3 (BDS-3) is the third iteration of the Beidou Navigation Satellite System owned and operated by the People's Republic of China. In June 2020, the BDS-3 constellation deployment was completed, including three GEO satellites, three IGSO satellites, and twenty-four MEO satellites.
Galileo is the European Union's global GNSS that began offering Early Operational Capability (EOC) in 2016. There are 22 launched satellites in usable condition in the constellation. There will be 24 satellites plus spares in MEO orbit when Galileo is fully operational. The inclination of the orbits was chosen to ensure good coverage of polar latitudes, which has poor service from the US GPS.
A GNSS receiver needs signals from multiple transmitters to get an accurate timing or positional fix, and the most populated systems only include a few dozen satellites. In other words, the loss of a single signal may have a more significant impact in a constellation with fewer members to spare in the first place. Multi-constellation multi-frequency GNSS receivers can access signals from several constellations, resulting in a larger number of satellites in the field of view, which reduces signal acquisition time and improves position and time accuracy.
GNSS (Global Navigation Satellite System), colloquially called GPS, is an umbrella term that encompasses a group of artificial satellites that send positioning, navigation, and timing (PNT) data to GNSS receivers down here on earth from their high orbits.
GPS (Global Positioning System) is one component of GNSS owned and operated by the United States military as Navstar. GPS maintains the availability of at least 24 operational GPS satellites and currently operates as a 27-slot constellation. Each satellite circles the earth twice a day. GPS satellites fly in Medium Earth Orbit (MEO) at approximately 20,200 km (12,550 miles) altitude.
GPS and its Russian-owned counterpart GLONASS were the only available GNSS for a long time. GLONASS went through a long period of disrepair during the late 1990s. The fully operational constellation of 24 satellites located in an MEO orbit at 19,100 km (11,900 mi) altitude was restored In October 2011.
BeiDou-3 (BDS-3) is the third iteration of the Beidou Navigation Satellite System owned and operated by the People's Republic of China. In June 2020, the BDS-3 constellation deployment was completed, including three GEO satellites, three IGSO satellites, and twenty-four MEO satellites.
Galileo is the European Union's global GNSS that began offering Early Operational Capability (EOC) in 2016. There are 22 launched satellites in usable condition in the constellation. There will be 24 satellites plus spares in MEO orbit when Galileo is fully operational. The inclination of the orbits was chosen to ensure good coverage of polar latitudes, which has poor service from the US GPS.
A GNSS receiver needs signals from multiple transmitters to get an accurate timing or positional fix, and the most populated systems only include a few dozen satellites. In other words, the loss of a single signal may have a more significant impact in a constellation with fewer members to spare in the first place. Multi-constellation multi-frequency GNSS receivers can access signals from several constellations, resulting in a larger number of satellites in the field of view, which reduces signal acquisition time and improves position and time accuracy.
JohnC
Well-Known Member
The change DJI has made is it using the BeiDou system instead of GLONASS system I would have thought even with just GPS & Galileo would provide a sufficient spread to get a good acquisition in a reasonable time. GLONASS when combined with GPS gave a very accurate GNSS lock. I noticed that the standard accuracy of the BeiDou system is 3.6mtrs for public use.
Are you referring to “the change DJI has made” as the last firmware update or the Mavic 3 hardware itself? Because it wasn’t a problem until the last firmware update.
ianwood
Well-Known Member
The additional GNSS constellation (BeiDou) helps to modestly improve overall accuracy. It makes a higher overall number of SVs available which can be especially useful in urban areas. This is likely due to the Mavic 3 using a newer uBlox M9 chip which allows for 4 concurrent GNSS constellations.
The time to first fix is entirely dependent on this uBlox chip. These are pretty solid and I doubt there are any significant FW changes being made there. I have noticed the M3 flight controller wants a higher number of available SVs before recording a home point. This is good.
The time to first fix is entirely dependent on this uBlox chip. These are pretty solid and I doubt there are any significant FW changes being made there. I have noticed the M3 flight controller wants a higher number of available SVs before recording a home point. This is good.
You do make a valid point that they might have boosted the requirements for setting home point. And the scale of what is considered weak vs strong. I don’t recall how many Sats it needed for home point before the FW update. But 12 doesn’t seem that high. Nor is it very quick.
bottom line is other drones get a good enough lock deemed by DJI for home point much faster than Mavic 3 now. So if they felt they needed to bump it up. It’s still the same thing. Maybe even worse because they are compensating for a poor implementation.
I know on Phones they rely on GPS assist tables that they get over the internet and they also use towers to speed up cold starts by a lot. I don’t know what DJI does on these newer systems.
So was the Mavic 3 less accurate in the same amount of time as prior drones and now has to wait longer to get more Sats to be as accurate?
There has never been a simple. single number of sats required to register the home point.
What's important is that the flight controller is satisfied that it has good GPS location data.
The number of sats is not the important factor, it's that there are sufficient sats in a good geometric spread to provide good location data.
12 sats when there are three different systems doesn't guarantee a good geometric spread.
With three sat systems, it's likely that you would have more sats before the flight controller records a homepoint.
I can't see the relevance of that.
What do you think DJI "needed to bump up"?
Once the flight controller determines that the GPS location data is good, the accuracy is as good as it's going to get.
You either have GPS accuracy, or you don't have GPS.
Except the minor issue that 30 seconds after you get home point suddenly GPS accuracy is poor again.
It appears 12 Sats (regardless of quality) seems a crude measure it’s using now. It will get home point as soon as it hits 12. If it drops below 12 it immediately says weak GPS. Every time.
I don’t understand why folks keep defending the way it’s behaving. Because it’s absolutely crap now. I don’t feel very safe with it, because after quality is good for home point it constantly teeter totters back down to 10 Sats or so (and it puts up a warning that it’s poor) and back to 12 a bunch of times. It will get up to 16 or so eventually after 5 minutes or so and then it stays Strong GPS even if it bounces around a few. And that’s the only time I will fly it now.
That’s what’s really bad. It is NOT stable after home point is established. And not safe to fly.
If it stays that way through Jan, it’s all going back. All $4000 worth. Thank goodness I bought it all on Amazon prime. It will give DJI plenty of time to address it. Currently it’s a bad experience IMHO And it wasn’t that way before the firmware update.
And if I do return it, I will comfortably label it as defective.
I'm not sure what you are talking about here, but if you can post recorded flight data, it would help.
You either have GPS or you don't. GPS accuracy doesn't get poor.
It's hard to discuss this productively if you don't have a basic understanding of how GPS works.
That's not true.
There has never been a simple, single number at all.
I'm not defending anything.
I'm trying to get an understanding of if there is an issue and what the issue might be.
Cutting through the misunderstanding is part of that.
Is this happening out in the open with an unobstructed skyview?
Post some flight data so I can see what you are talking about and get an idea of whether there is a problem.
I think we can all agree there is an issue, it's why there are multiple threads on this now.
Even if DJI made a change this is poor user experience feedback. I really do hope this was made in error.... having to wait longer for my drone to get home point and only to lose it for a min after that unless I fly up with the flyapp telling me it's has crappy signal isn't a user experience I like for their top teir new drone. It's already half baked, one more coffin nail for them as well as a end user.
Even if DJI made a change this is poor user experience feedback. I really do hope this was made in error.... having to wait longer for my drone to get home point and only to lose it for a min after that unless I fly up with the flyapp telling me it's has crappy signal isn't a user experience I like for their top teir new drone. It's already half baked, one more coffin nail for them as well as a end user.
JohnC
Well-Known Member
No, the cha
The M3 has always used GPS + Galileo + BieDou.
Personally I have not experienced any issues prior to, or after, the update. I am nearly pointing out the published differences in the hardware.
No, I am not referring to the firmware, the GPS module appears to be the first from DJI that uses the BieDou GPS system instead of GLONASS All recent DJI consumer drones prior to the M3 used GPS + Galileo + GLONASS.
The M3 has always used GPS + Galileo + BieDou.
Personally I have not experienced any issues prior to, or after, the update. I am nearly pointing out the published differences in the hardware.
No, that’s F’n problem.
No, it’s not you have GPS and done. It bounces between Strong and weak before it’s stable. And may get a home point in the middle. Maybe it’s behaving different in UK.
Yes, it’s open sky. Where else do you fly a freaken Drone? Same place I’ve flown it since I got it. My back yard.
Yes, it is true. That’s how it’s acting. Dumber than a year 20 year old GPS device.
Post some data, because your description isn't helpful to tell whether you have a real problem, or what it might be.
Same problem everyone else is posting.
I never took off on a bunch of flights because I didn’t like what I was seeing for GPS so I’m not sure it recorded anything on those.
Just switched to RC Pro with one flight. Have not checked it.
There is no such thing as "weak GPS", that's DJI's odd way of saying no GPS.
Your flight data would show a lot more information to help understand what's going on, if it's a real problem or DJI falsely reporting an issue (which has happened before).
Lots of flyers launch from spots without a good skyview and that has a big impact on the number of sats available to the GPS receiver.
If you don't explain, it has to be asked to eliminate a common issue.
Here is a Video showing how bad it is.
At 1:00 it connects to Mavic 3
At 3:58 it got 12 Sats and immediately set Home Point
At 9:40 I pointed the Camera to show the Clear Sky.
At 12:20 it shows it drops to "Weak GPS" (8 minutes after Home point).
It dropped to 11 and Weak again quite a bit later too but only for a short bit.
At 1:00 it connects to Mavic 3
At 3:58 it got 12 Sats and immediately set Home Point
At 9:40 I pointed the Camera to show the Clear Sky.
At 12:20 it shows it drops to "Weak GPS" (8 minutes after Home point).
It dropped to 11 and Weak again quite a bit later too but only for a short bit.
Last edited:
ianwood
Well-Known Member
I have not experienced any issues.
I stand corrected. Thanks for this. uBlox m9 supports 4 concurrent constellations. Silly to drop GLONASS. (I am assuming it is an M9.)
As for cold starts, the easiest solution would be to enable GPS assist via the phone or wifi connection. You'll have a dozen SVs in 30 seconds or less.
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