Location Accuracy of Decawave Modules

Wireless Connectivity Ultra-Wideband
1

Hello

I have Installed 15 Anchors in a 27m X51m Closed area as shown in the attachment. I have connected one tag to the Raspberry Pi and gathering the data using python Serial. All anchors are placed at a height of 6m. But When I am reading the data , i am not getting more accurate values. Most of the time, the data is either empty (b’\r\n’) or with a confidence rate of 50% or less . Every Anchor is faced vertically upright. Does the orientation of these matter?? I have also mentioned the facing direction of the Anchors in the attached image. Why I am getting results like this. Anyone can help??
[attachment=225]
Thanks & Regards
Shiva

2

Hi Shiva,

How is the line of sight between the tags and the anchors within the network ?

Are there several obstacles ? I may explain why you see poor performance, the tag shoud always be in range with at least 3 anchors. Maybe look at the LES command on the output of the tags. (There are several thread on the forum explaining how to do it, maybe take a look at them)

Thanks
Regards
Yves

3

In my opinion (can be wrong) you are using too many anchors. What i believe is a tag decides its corresponding anchors when it moves from one quadrant to another. I was able to obtain very decent result in 50x50 meter room using 4 anchors only.

4

Hello Bernard

Thanks for your advice. I have increased the height of tag(attached it to a PVC pipe). Now the values are better. The area I have checked was of full metal bins of height around 5m. Maybe because of that I was facing the problems. I can change the Anchors heights a bit to improve the line of sight.

Thanks & Regards
Shiva
[hr]

Yes. We can decrease the number of the Anchors. But the area I was testing was not good for Line of sight. I have tried different topologies. But because of LOS issues, the data was not accurate. As I mentioned in the reply to Bernard, I have increased the height of the Tag and the results are better.

5

Also have a look at the documentation and range for xy or yz plane for antena reception. I believe these modules are optimized for yz orientation.

6

Is location provided by gateway ( mdek1001 + RPI ) just in 2D or 3D ?

I read about pozxy ( they are using decawave’s technology ) and they provide 3D position of tag.

7

Hello gumush,

The location given by gateway is in 3D and in the below format , if you use ‘lep’ command.

b’POS,21.72,65.28,2.76,92\r\n’

Where x=21.72 , y=65.28, z=2.76 with a confidence rate of 92%

8

May be but in my experience Z axis values do not make any sense when deployed.

1 Like
9

The issue with the z axis is that normally your GDOP (Geometric dilution of precision) is terrible in that direction. GDOP (or HDOP/VDOP (horizontal/vertical DOP)) is a term commonly used in GPS, it’s a measure of how the locations of the satellites (or in this case anchors) is impacting your accuracy.

The maths to calculate the numbers involves a few matrix calculations but the basic concept is simple. Lots of anchors evenly spread in all directions gives a good DOP, all of them the same distance in the same direction gives a very poor DOP.

If you put a set of anchors on the ceiling and walk around underneath them then the maths works out that your height accuracy is going to be terrible. Nothing you can do about it.

Varying the heights of the anchors helps but realistically you’re never going to get z anywhere near as good as x and y, it’s easy to get 20 m of horizontal variation but very tricky to get 20 m of height variation.

One other approach I’ve seen to an accurate Z value is to put a barometer on the rover and the anchors. Barometers are terrible for absolute height but good for relative height, if you know the height of the anchors and the air pressures there and you know the air pressure at the rover then you can make a fairly good estimate of height at the rover.

1 Like