# The Principle of UWB Positioning Technology TWR|TOA|TDOA|PDOA

## 1.TWR positioning technology based on UWB

TWR (Phase-Difference-of-Arrival) is a two-way ranging, that is, the ranging module sends an ultra-wideband pulse signal back and forth, and the flight time can be obtained by subtracting the delay of the module from the received time difference.

Each module of TWR will generate an independent timestamp from the start. The transmitter of module A transmits a request-type pulse signal at Tsp on its timestamp. Module B transmits a response-type signal at TSR time, which is received by module A at its own time stamp TRR time, and then sends a signal to be sent by module B received at TRF. These two data can calculate the flight time T of the pulse signal between the two modules, so as to determine the flight distance S.

## 2.TOA Positioning Technology Based on UWB

The TOA positioning method is mainly based on measuring the arrival time of the received signal between the base station and the mobile station, and then converting it into a distance for positioning. This method requires at least three base stations to calculate the position of the target, and the schematic diagram of its positioning is shown in the figure.

## 3.TDOA positioning technology based on UWB

Based on the TDoA (Time Difference of Arrival) positioning algorithm, the distance difference is calculated by measuring the message transmission time difference between the measured label (B) and the known location base stations (P1, P2, P3); the position of the measured label is calculated. . Clock synchronization between base stations with known locations is required.

The distance from B to P1 - the distance from B to P2 = (the flight time from B to P1 - the flight time from B to P2) * the speed of light

The distance from B to P2 - the distance from B to P3 = (the flight time from B to P1 - the flight time from B to P2) * the speed of light

The distance from B to P1 - the distance from B to P3 = (the flight time from B to P1 - the flight time from B to P2) * the speed of light

The coordinates of point B can be calculated by solving the system of hyperbolic equations.

## 4.UWB-based PDOA positioning technology

The ranging scheme based on the PDOA algorithm of the DW1000 scheme is as follows. In order to realize the angle estimation of the tag, two identical and spaced d<λ/2 antennas are placed on the UWB base station. The phase difference between a signal on the tag and the two antennas is -180° to 180° range.

Use the measured phase difference (△φ) to convert the distance difference (P=λ*△φ/(2π)), and use the flight time to obtain the distance r. The geometric relationship series equations are as follows:
r^2=x^2+y^2; (x-d)^2+y^2=(r-p)^2

Finally, the positioning coordinate data (x, y) of the tag tag is obtained, and the architecture is shown in the following figure.

Note: If the known distance difference P is used, the hyperbolic equation of the position of the column label is used, and the asymptote is used to obtain an approximate value, the slope of the asymptote is the angle where the label is located, and the AOA positioning of the angle of arrival is realized.

You may be interested in UWB positioning solutions: UWB Indoor Solutions

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