Minimizing Separation Distance for Antenna Delay Calibration

Hi, there.

I just recently started working with both DW1000 and DWM1000 for accurate range detection.
All good so far, only i have been thinking of ways to reduce the setup stage required for Antenna Delay Calibration.
We are using a TWR scheme, on Channel 5, with PRF of 16 MHz.
As indicated in the User Manual:8.3.1-Calibration Method, there is a “recomended” Calibration Separation of 7.94m.
After some more reading, I believe the reason for this distance is mostly due to the Range Bias error, as indicated in APS011:3-Ranging Accuracy vs Received Signal Level. Back to the User Manual, now I see why, for the Separation of 7.94m, it is asuming the following:

  • Power at receiver input of -108 dBm/MHz
  • Transmitter set to -41.3dBm/MHz
  • 0dBi antennas

Knowing this, I am thinking of ways to reduce the Calibration Separation and one such way, for example, is to lower the Transmitted Power Level.
The proccess would be
1 - lower the distance down to 1m or even less.
2 - adjust the transmitted Power so that the received power is set around -108dBm/MHz. For this point, I could use the formula described at User Manual:4.7.2-Estimating the receive signal power.
3 - apply the calibration method described both in User Manual:8.3.4-Calibration Method and in APS014.
4 - restore the Transmitted Power to the legally allowed maximum value.

Is there any hole in my reasoning?

You want to avoid having the power at maximum or minimum, it tends to be less linear in those areas, but beyond that there is no reason why you can’t drop the power and use a shorter range.

The reason for wanting to perform this at a fixed range and power level is to avoid the need to have to correct for the receive signal power.
If your signal power level correction is good enough then you can calibrate at any range and power level.

One thing to look out for when using a shorter range, some systems may not handle negative ranges well. You probably want to ensure your distance is greater than your worst case antenna delay error in order to avoid the range being negative.

As for now, I do no intend to apply any correction for the Receive Signal Power.
In my described stage, I am also setting a known received power level of -108dBm/MHz, but in a shorter range.
To my undestanding, the fixed range and power level indicated in the User Manual are both directly related to the transmited power level and antenna gain. Is this incorrect?

You are correct. If you drop the power by 18dB and reduce the range by a factor of 8 the power at the receiving antenna should remain about the same. This should then give you the same characteristics as the configuration in the user manual.

However your first post indicated you wanted accurate range measurement. Without correcting for receive power you won’t get an accurate range measurement at any ranges other than the one you calibrate at.
The best way to calibrate antenna delays is after running the system for half an hour with your intended operating power at your intended typical operating ranges and in your intended operating location at your intended operating temperature. That way any biases caused by power controls not being linear, temperature effect or other environmental effects are all canceled out.

ok, I think I got it.
Thanks for your time!