What are the positioning accuracies that can be achieved by UWB TWR and TDoA2/TDoA3, respectively ?

[bitdeckai]

Hi,

What are the positioning accuracies that can be achieved by UWB TWR and TDoA2/TDoA3, respectively ?
The second question is: what are the respective aircraft capacities and positioning update rates for TWR, TDoA 2, and TDoA 3?

[stefanthorstenson]

Hi @bitdeckai !

1. The position accuracy is roughly 10-30 cm with the Loco positioning system. same for TWR and TDOA2/3.
2. The Kalman filter updates on every measurement.

• TWR: 500 Hz (spread across anchors).
• TDoA2: Per-anchor rate is 62.5 Hz, so multiply with the number of anchors.
• TDoA3: Per-anchor rate is about 45 Hz, multiply with the number of anchors.

Does this also answer your question about aircraft capacities? I'm not exactly sure what you mean.

Best regards,
Stefan

[stefanthorstenson]

Hi!

As @ArisMorgens mentions, TWR potentially has better precision than TDoA. TDoA is better for swarms as the drones are passive listeners. See his answer for more details.

What are your requirements for your system?

[bitdeckai]

I want to implement swarm control for robots, that is, 40 to 80 drone, robotic dogs or robots. I hope to use UWB for positioning, but the required accuracy is within 10 cm, so I am deciding whether to use TWR or TDOA.

[stefanthorstenson]

Ok, I understand! For 40 to 80 UWB tags operating in the same space, I would say you need to use TDoA. TWR requires active TX from the robot, and the risk of packet collision grows with every robot you add, since there is no sync between tags and the tags depend on the response from the RX from their own request.

So, for UWB, I recommend TDoA in your case. You have to use the assumption of 30 cm accuracy. If you want to do tight trajectories, add some margin on that (so no trajectories within a sphere with maybe 50 cm radius).

If you want to reach 10 cm, I'd recommend the Lighthouse positioning system, which typically has an accuracy of 1-2 cm. It requires line of sight, but thanks to sensor fusion it works anyways for swarms. We have flown over 50 drones in a limited space without issues.

Let us know if you need more help!

[bitdeckai]

Lighthouse positioning systems do indeed offer very high accuracy, but they become ineffective when the line of sight is blocked.
If TDoA positioning is fused with an IMU, can the accuracy be improved from 30 cm to within 10 cm?

[stefanthorstenson]

IMU is already fused into the position estimate. However, the IMU doesn't help with absolute accuracy, so the 30 cm is still what you need to expect. IMU does help short term when losing UWB or Lighthouse data, so that is why Lighthouse is still effective even though the measurements require line of sight.

When you say that your requirement on positioning is 10 cm, does that mean that the mean error should be less than 10 cm, or is the position never allowed to be more than 10 cm? I have been interpreting it as the latter, but if the mean error should be around 10 cm, you might be fine with UWB and TDoA.