Ultra-wideband (UWB) solutions are based on Time of Flight (ToF) method for measuring the distance between two radio transceivers by multiplying the ToF of the signal by the speed of light. From this basic principle, UWB technology can be implemented in different ways according to the targeted applications needs: 1- Two-way ranging (TWR) or double-sided two-way ranging (DSTWR) and phase difference of arrival (PDoA) or angle of arrival (AoA) or 2- Time difference of arrival (TDoA).
The TWR method relies on two-way communication between two devices. As they communicate, the devices also measure the ToF of the UWB radio frequency (RF) signal between them. By multiplying the round trip time of the signal by the speed of light, and then dividing by 2, you can derive the actual distance between the two devices. If you apply the TWR scheme between two devices, you will get the distance between the two devices. Based on the TWR scheme, you can also implement 2D or even 3D location by measuring the distance between your mobile tags and fixed beacons.
and phase difference of arrival (PDoA / AoA)
The PDoA method consists in combining the TWR scheme that delivers the distance between two devices with the measure of the bearing between the two devices. The combination of distance and bearing allows the calculation of the relative position of two devices without any other infrastructure. To do so, one of the devices carries two antennas and is able to measure the PDoA of the RF signal.
- System synchronization is not required
- Easy deployment
- TWR enables downlink data and control
- Higher power consumption
- Limited number of mobile devices (in the hundreds)
The TDoA method is very similar to GPS. Multiple reference points, called anchors, are deployed in a venue and are time synchronized. The mobile devices will blink, and when an anchor receives this blink it will timestamp it. The timestamps from multiple anchors are then sent back to a central location engine which will run multilateration algorithms based on TDoA of the beacons signals to compute the X, Y, Z of the mobile devices.
- Better battery life for the tag
- Very high density of devices (in the thousands)
- More complex deployment
- Anchors need to be time synchronized