dwm1000 add more tag?

Firmware/software/electronics/mechanics
justinleeyang
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dwm1000 add more tag?

Post by justinleeyang »

Hi,everyone:

Now a tag with muti-anchor, but I want to add more tag mount on aircraft with multi-anchors, what method to achieve it?
Thanks!
arnaud
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Re: dwm1000 add more tag?

Post by arnaud »

Hi,

This is not implemented yet. The crazyflie is currently ranging in round-robin to all anchor as fast as possible. There is multiple way to achieve multiple tag, one is to synchronize the tags so that they range one after each other, another would be to range slower and at random interval so that many tag can coexist.

Ultimately I want a system where the anchor would send data and the tag would only receive. This way there will not be any tag limit. This is what ETH has done in the Ted talk demo for example.

We have not had time to work on that yet so please update us if you make any progress!

Best,
/Arnaud
justinleeyang
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Re: dwm1000 add more tag?

Post by justinleeyang »

hi,
the anchor would send data and the tag would only receive? the way have related paper ?
arnaud
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Re: dwm1000 add more tag?

Post by arnaud »

Yes there is at least one paper from ETH: http://ieeexplore.ieee.org/xpl/articleD ... %3D7353810
justinleeyang
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Re: dwm1000 add more tag?

Post by justinleeyang »

hi,

Thank you very much!
I will research and try it.
justinleeyang
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Re: dwm1000 add more tag?

Post by justinleeyang »

hi, arnaud:

I have understanded their method, so cool. I think the key point is the piture:
1.png
About clock skew:
so the anchor 0 transmit timespan, we can set as constant 1ms, so
2.png
2.png (1.57 KiB) Viewed 4784 times
=1ms;
then other anchors or robot record the received time, so we calculate the clock relative skew to anchor 0,
3.png
3.png (1.32 KiB) Viewed 4784 times
.

About TOA and TDOA measures
(1) TOA method
4.png
4.png (2.33 KiB) Viewed 4784 times
But the anchor 0 tx time, from the code, when transmit complete, handle interrupt, then record the tx time, so we cann't send the tx time to robot.
how to calculate the distance? next measure transmit the previous tx time?

(2) TDOA method
I have understanded the method, we don't need concern the tx time, only need the timespan = 1ms OK.
5.png
5.png (4.64 KiB) Viewed 4784 times
arnaud
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Re: dwm1000 add more tag?

Post by arnaud »

Hi,
Nice analysis, have you made any progress on that?
justinleeyang
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Re: dwm1000 add more tag?

Post by justinleeyang »

hi,arnaud:

I have already calculate the time difference with two anchors, test about 1 hour, the data as following:
tdoa.png
these values are dw1000 timestamp, so we need covert to time:
X/(499.2*128*1000) = x ns
so these values range from -2200 to -3500, so the time difference is about -34ns to -54ns.
the result right ? hope your reply.
arnaud
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Re: dwm1000 add more tag?

Post by arnaud »

If I am not calculating completely wrong 34ns corresponds to about 10m difference, this looks a little bit big, did you have 10m difference between the tag and the two anchors?
justinleeyang
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Re: dwm1000 add more tag?

Post by justinleeyang »

Hi, arnaud:

the range of two anchor only ~20cm, and I will do more test.

another issue, reference your code, when sync anchor(TX anchor) send sync message to another anchos, when send completed,
we can get the send timestamp, so another anchors how to get the TX anchor's send timestamp?
Hope your reply!
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