Bluetooth 5.1 introduced special direction finding signals, where a constant tone extension (CTE) is appended at the end of a certain packet. The CTE itself consists of only digital ones, so the whole CTE is transmitted on the same frequency and same wavelength, which of course boosts the accuracy of the localization.
I have 2 questions about this process and I cannot find answers in literature or Bluetooth specifications:
- Having two connected devices A and B, is it possible to do two-way direction finding in a time-division duplex manner.
Example: let's say we configure the CTE exchange to happen over multiple packets, can we do the following:
1 - A sends CTE to B (B estimates the location of A)
2 - B sends CTE to A (A estimates the location of B)
3 - A sends CTE to B (B estimates the location of A)
4 - B sends CTE to A (A estimates the location of B)
and so on?
- Does the devices perform frequency hopping during the CTE exchange?
Example: Instead of sending a single CTE on a single frequency (in step 1 and 3 from the previous question), is it possible that A sends multiple CTEs over multiple frequency (Same for device B in steps 2 and 4)?
Any suggestions/information is welcome.
well technically df could be bidirectional. BUT it requires multiple antennas at all receivers.
the CTE enables phase shift detection at the receiver. it 'knows' what the waveform 'should' look like (constant signal value at a known frequency) so it can sample multiple antennas to detect the differences
but no general purpose devices (phones, computers, laptops) have antenna arrays. that is why AoA is the 'easiest' to implement. add a few specialized receivers, and voila!...
currently the antenna array I have for testing is just under 4 inches square.
I don't know the signal processing limits on miniaturizing such arrays while still having them be effective