Bitcraze Forums

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!

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

hi，
the anchor would send data and the tag would only receive? the way have related paper ?

Yes there is at least one paper from ETH: http://ieeexplore.ieee.org/xpl/articleD ... %3D7353810

hi,

Thank you very much!
I will research and try it.

hi, arnaud:

I have understanded their method, so cool. I think the key point is the piture: About clock skew:
so the anchor 0 transmit timespan, we can set as constant 1ms, so =1ms;
then other anchors or robot record the received time, so we calculate the clock relative skew to anchor 0, .

About TOA and TDOA measures
(1) TOA method 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.

Hi,
Nice analysis, have you made any progress on that?

hi,arnaud:

I have already calculate the time difference with two anchors, test about 1 hour, the data as following: 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.

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?

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!