Time-Difference-of-Arrival (TDoA)

Precise, Reliable and Scalable Positioning Calculations

What is Time Difference of Arrival (TDoA)?


TDoA is a positioning methodology that determines the difference between the time-of-arrival (ToA) of radio signals. TDoA is used in a real-time location system (RTLS) to accurately calculate the location of tracked entities, such as tracking tags affixed to personnel or key assets, in real time.

For example, in Inpixon real-time location systems, TDoA utilizes location data collected by UWB or chirp (CSS) RTLS anchors from transmitting RTLS tags to calculate the real-time positions of the tagged entities. As shown in the accompanying diagram, a RTLS tag (T) will continuously send out RF signals, also known as location blinks at regular intervals. Multiple RTLS anchors within the communication range of the transmitting tag will receive these location blinks and timestamp their exact time-of-arrival (ToA).The anchors then forward this time-stamped location data to our location engine software, Inpixon nanoLES. Inpixon nanoLES will then analyze the difference in arrival times (e.g. ToA1-ToA2) between anchors for the same received location blink to calculate TDoA.

Virtual Anchor Synchronization

To work properly, the fixed anchors need to be accurately synchronized to run on the same clock. Inpixon’s real-time location systems achieve this through our patented virtual anchor synchronization. The calculated TDoAs are represented by hyperbolas and indicate possible tag locations. Three related hyperbolas that intersect at a point describe the position of the tag. A multilateration-based approach then provides the tag’s coordinates. It is recommended that a minimum of four anchors are used for a reliable location estimate.

The resulting positioning coordinates can be used to visualize the location of the tag on a map or leveraged for other use-cases depending on the specific application.

Key Benefits


TDoA ensure high-accuracy location results superior to other traditional methods like RSSI-based positioning.

Low Latency

With TDoA, a RTLS can process thousands of simultaneously received blinks, ensuring low latency and high-performance reliability.

Enterprise Scalability

TDoA-based calculations enable scalable RTLS deployments capable of meeting enterprise needs.

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