Where to place the anchors
Technology

Where to place the anchors

This article is part of the Pozyx Academy and is the last in a series of five articles that explain how the Pozyx Technology works and what to account for when installing the Pozyx System.

Rules of thumb

The following rules apply to the anchors from both the Creator and Enterprise series.

  1. Place the anchors high and in line-of-sight of the user
  2. Spread the anchors around the user, never place them in a straight line
  3. Place the anchors vertically with the antenna at the top or bottom
  4. Keep the anchors away from metal
  5. For 3D positioning: place the anchors at different heights

Rule 1: Place the anchors high and in line-of-sight of the user

The first rule is straightforward: placing the anchor high (on the ceiling or walls) increases the chance of receiving a good signal because there are fewer obstructions. As stated in the previous article on obstacles, obstructions harm the accuracy of the range measurements which has a direct effect on the positioning accuracy.

Rule 2: Spread the anchors around the user, never place them in a straight line

For range-based systems, single range measurements will only give information in a single direction. This direction is exactly the direction from the tag to the anchor. Because of this, it is best to spread the anchors such that they cover all directions. Placing all the anchors in a straight line will produce a positioning error. A small change in radius will result in a very large change in the position of the intersection(s). In other words, the error on the range measurements is amplified. This is the same principle as in GPS, where it is called the geometric dilution of precision (GDOP).

Rule 3: Place the anchors vertically with the antenna at the top

The Pozyx system uses wireless ultra-wideband signals for positioning which requires an antenna. The monopole antenna (the white chip) on the Pozyx devices radiates omnidirectionally in the xz-plane, but doesn't radiate as well along the y-axis (see figure). In order to have the best possible reception, it is recommended to place the anchor vertically. Note that the same is true for the Pozyx tags.

Rule 4: Keep the anchors away from metal

When you place an anchor directly on a metal plate, the metal will affect the antenna behavior. It is advised to keep a distance of 20cm clear from the antenna with metal. The antenna itself is a metal conductor that is carefully designed to radiate on the UWB frequencies. Any metal nearby will reduce the antenna's efficiency or will make the antenna less omnidirectional and less predictable.

Rule 5: For 3D positioning: place the anchors at different heights

If the user and the anchors are all in the same horizontal plane, it is not possible to have good accuracy for height (it is the same principle of GDOP as in rule 2). So it is recommended to place the anchors at different heights if three-dimensional positioning is desirable.