UWB DWM1000: Time-Delay Problems, Solutions & Trilateration

• Ultra-Wideband (UWB) is famous for giving precise ranging down to a few centimeters, but only when the system is calibrated correctly.
• The Deca wave/Qorvo DW1000 / DWM1000 is sensitive to a variety of time-delay and environment-dependent effects. If these aren’t handled, you may see systematic range offsets, inconsistent measurements, or unstable trilateration positions.

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1. What “time delay error” really means in UWB (DW1000/DWM1000)

• The DW1000 measures distance using Time of Flight (ToF) of RF pulses.
• Your measured distance becomes wrong when the ToF is wrong.

Sources of ToF bias in DW1000-based modules

1. Antenna delay (biggest cause)

• Every module has internal TX/RX delay (RF front-end + antenna path).
• Adds a constant offset to all distance measurements.

2. Clock offset & drift

• Each node has its own oscillator.
• Single-Sided TWR is very sensitive to this.

3. Power-dependent bias

• Received signal strength changes timestamp extraction → distance shifts.

4. Multipath & NLOS

• Reflections cause the chip to timestamp the wrong path.
• Usually creates longer distances.

2. Antenna Delay - Fix for DW1000 Range Errors

• Antenna delay is a constant nanosecond-scale offset caused by:

  • RF transceiver output path
  • PCB traces
  • Antenna feed If this is uncalibrated, your error will be large and constant (10–50 cm not unusual).

• What proper antenna delay calibration achieves

  • Removes 90% of the systematic bias
  • Makes ranges consistent across different distances
  • Stabilizes trilateration position
  • Reduces anchor-to-anchor variation

• How antenna delay affects raw ranging

  • If true distance = 1.00m and antenna delay adds +0.45 m then your system will always show ~1.45 m (constant offset)

This explains why many users see stable but wrong distances.

3. Ranging protocol choice: DS-TWR is mandatory for accuracy

• SS-TWR (Single-Sided Two-Way Ranging)
  • Fast, simple, but highly inaccurate when clocks drift.
• DS-TWR (Double-Sided Two-Way Ranging)
  • Cancels clock offset effects
  • Less sensitive to timestamp error
  • Recommended for all accurate positioning
• SDS-TWR / Symmetric TWR
  • Variants exist for even better cancellation
  • Useful when nodes cannot guarantee regular message spacing

4. Multipath, NLOS & Environment Effects

UWB is resistant to multipath, but not immune.

• Problems caused by NLOS:

  • Long positive bias (since first path is blocked)
  • Unstable range (large variance)
  • Trilateration “pull” toward one anchor

• Mitigation

  • Median filtering
  • Reject packets with high CIR noise
  • Detect absence of a clean first-path peak
  • If multiple anchors → down-weight the suspicious anchor in calculations

5. Temperature & Clock Drift Effects

The DW1000’s internal oscillator drifts with temperature:

• Anchor inside hot enclosure vs tag in open air → measurable bias
• Long-term TSF drift adds long-term offset

Solutions:

• Periodic recalibration
• Temperature compensation models
• DS-TWR (removes most clock effects)
• Anchors placed in thermally stable locations

6. Trilateration - How Position Is Computed from Distances

Trilateration uses circles (2D) or spheres (3D).
Each measured distance defines a circle around
anchor_i: (x − xi)² + (y − yi)² = ri²

In reality, circles don’t meet perfectly

Because ranges include noise, the circles often:

• Don’t intersect
• Intersect in a small region
• Intersect in multiple points (bad anchor geometry)

Thus practical trilateration uses:

Least-squares solution

• Minimize error between predicted and actual ranges.
• Weighted LSQ is best when some anchors are less reliable.

Outlier rejection

• If one anchor is too far off, remove or reduce its weight.

Good anchor geometry

• Avoid placing anchors in a line - the intersection becomes ambiguous.
• Use a triangle (2D) or tetrahedral shape (3D).

Diagram

Conclusion

• The DW1000/DWM1000 can deliver accurate UWB ranging only when calibrated properly.
• Antenna delay is the main cause of constant distance error and must be corrected.
• DS-TWR provides stable measurements, while SS-TWR suffers from clock drift.
• Environment, NLOS, and temperature variations strongly affect range quality.
• With proper calibration and robust trilateration, true centimeter-level accuracy is achievable.