Ranging & Positioning

DS-TWR

Updated 2026-04 · 4 min read

DS-TWR: Double Sided Two-Way Ranging

SS-TWR is simple, but the clock reference difference between transmitter and receiver introduces ToF error. Chipsbank has done extensive development work to address this shortcoming of SS-TWR by compensating for the clock error: clock frequency error is generally at the ppm level and can be compensated down to ppb. When signal strength is poor, ranging error exceeds 2 m without compensation; with compensation we can reduce the error to less than 2 cm.

If Chipsbank's clock compensation scheme is not used, Double Sided Two-Way Ranging (DS-TWR) can solve this problem, as shown below.

Each device can compute its own ToF, and then improve measurement accuracy by compensating for the clock differences between the two devices.

This method consumes more power because it involves the transmission of three frames.

DS-TWR three-frame exchange: poll / response / final between Initiator A and Responder B
DS-TWR uses three frames (poll, response, final) so that A and B each compute the loop and reply times, cancelling out clock error.
DS-TWR ToF calculation formula
DS-TWR combines the δloop and δreply values from both A and B to obtain a more accurate one-way ToF.

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