RTLS/TDOA for 3D locating


#1

I’ve been trying to download the “DWUSB Kit Instructions” however the link is broken. I’m wondering for doing 3D locating and specifically also getting the z height do I need to mount the 4 anchors at different heights in the environment?


#2

Thank you for bringing this to our attention. We will fix this shortly.

In order to get a good Z-height, you do not have to mount the 4 anchors at different heights in the environment, but it does help. The only caveat to this is that if the anchors are all mounted at approximately the same height as the anchor, the system will have troubles calculating Z-height. Thus, if you do put all the anchors at the same height, make sure it’s either significantly higher or significantly lower than the expected height of the tag.


#3

One more question with respect to the following statements- “If you want to track more than one tag, you will need an additional DWUSB unit for each tag. The demo software supports up to 48 tags, each tag being tracked at 20 Hz for a total of 960 locates per second. The primary limitation on locates per second is using the UWB radio for anchor data backhaul to the master node to feed the location engine.” Is the one locate approx every 50 milliseconds/tag a restriction when you are running all 48 tags at once or all of the time? If I have one TAG will I get the locate once each millisecond + a little overhead for transport of the anchor data ? If that is a firmware imposed restriction for 48 tags is it an easy tweak for us to change it? We have done a lot of work with DW1000 two way ranging.
thanks, Jon


#4

The 50 milliseconds / tag limitation was true regardless of the number of tags you were using in the Zeno release. Unfortunately, this was a server software limitation, not a firmware limitation.

However, as of the Archimedes release, we added support for configurable tag rates (see https://static1.squarespace.com/static/58936611e4fcb5ade61e6837/t/595507a5d1758efae8ea57fb/1498744751546/CuwbServer-Instructions.pdf page 10 section 5.6.1 for more details).

Hopefully Archimedes has the functionality that you were looking for.


#5

Yes, looks like Archimedes does have that functionality. My application is sports so the turnover time is critical along with some base level of accuracy. So if I assume one tag and six anchors as my base case what will my locate turnover time and accuracy be with no smoothing ie a smoothing factor of zero? Does that level of accuracy utilize inputs from the IMU also and how does that impact the accuracy? I assume smoothing is just a rolling average so I can figure out how increases in smoothing will impact my accuracy and timing- is that correct ? Thanks, this is very helpful.


#6

In Archimedes, you can compute the approximate worst-case turnaround time for your tags with the following equation:
(1,000 / Location_Rate) + Network_Latency = Turnaround_Time.

The Location_Rate is the configured Location Rate (Hz) that is selected on the config tab on the CUWB Server. The Network_Latency is whatever the latency is of your particular network connection in milliseconds. After computing the above, this will provide you with the approximate Turnaround_Time in milliseconds.

Also, please see the following post for details on system accuracy: What accuracy can be achieved?.

Currently, we do not utilize the IMU data in our position calculation, but as of the Archimedes release, we do allow you to configure a number of different IMU settings to be provided through our system, so that information is still available to you.

Yes, as of right now, the smoothing is just a simple rolling average.


#7

Ok, thank you. To follow up what then is the fastest setting that I can use for the Location_Rate? Because it’s a sports application I have a requirement for a fast turnaround.
Also, the accuracy link gives me this, “Oops! That page doesn’t exist or is private.”


#8

Whenever you configure the location rate, it will tell you how many tags it can run on the network at that rate given your current settings. There are a lot of settings that go into determining what rates are possible, such as the number of anchors, number of tags, amount of IMU data being sent, etc. For a 6 anchor 1 tag network with no IMU data, the fastest configurable location rate is 164 Hz.

Sorry about that. I have now corrected the link in the previous post. I’ll also link it again here so you don’t have to go looking for it: What accuracy can be achieved?.