Where to place the anchors?
For 2D positioning
- Place the anchors high and in line-of-sight of the user:
Placing the anchor high (on the ceiling or on the walls) increases the chance of receiving a good signal because there are less obstructions. Obstructions generally have a negative influence on the accuracy of the range measurements which has a direct effect on the positioning accuracy.
- Spread the anchors around the user. Don't place them on a straight line:
For range-based systems, a single range measurements will only give information in a single direction. This direction is exactly the direction from the user to the anchor. Because of this, it is best to spread the anchors such that they cover all directions. If the anchors are all on a straight line, the positioning error will be very large: A small change in radius (for example due to noise), 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).
- Make sure each anchor sees at least two, but preferably more neighbouring anchors at a distance of not more than 20 to 30 meters, or even less in environments with many obstacles
- Place anchors vertically, with the connectors at the top. This keeps the antenna at the bottom
- Materials like metal, water and wires should stay away from the anchors, especially the antenna:
Within a few centimeters from the antenna, there should be no metal at all, not even small screws (this holds for the tag antenna too).
- It is recommended to have a separation of 20 cm between the anchor and walls. Extra mounting equipment can be used to achieve this
For 3D positioning
- Keep to the guidelines from above but place anchors at different heights:
The accuracy of the z coordinate will highly depend on the spread in heights of your anchors. Ideally, it is advised to place your anchors in the shape of a cube around your positioning zone as shown below. Try to maximize the distance between the lower and higher anchors.
- Twist the base surface of your cube 45 degrees as compared to the top surface:
Twisting the base surface will reduce the 3D convex hull of the anchors (e.g. the bottom corners of the cube are outside of the convex hull), but it will generally give you a higher chance of line-of-sight between a tag and the anchors. E.g. when your body is blocking 1 corner of the room it will just block line-of-sight with 1 anchor instead of 2.
Furthermore its better for the tag to be surrounded by anchors from as much directions as possible.
- Keep the same max distance between the anchors as for 2D positioning (10 to 20 m depending on the environment)
- With only 6 anchors, it is possible that the resulting positions will be noisier. Here we recommend placing 3 anchors in the top surface and 3 in the bottom surface
Connecting the anchors
The anchors each have two ethernet (RJ45) ports. These can be used to link up anchors in sequence which reduces the total amount of wiring required. We call this daisy chaining of anchors. Power only needs to be provided to the first anchor in such a chain. This can be done in two ways, either using the DC power jack, or by Power over Ethernet. For Power over Ethernet PoE+ (802.3at) is required.
Below are the two setup types shown:
Setup type A using DC jacks to power the first anchor in each chain:
Setup type B using a PoE+ switch to power each chain:
Ports on the Enterprise anchor v1:
Ports on the Enterprise anchor v2:
PoE IN and OUT-going cables are installed in a crossed way:
The maximum number of anchors in one chain depends on how they are powered, and the quality of the cables. Using cables and switches which comply with our specs below you'll be able to have a maximum of 4 anchors on a chain, with a maximum of 50 m between each anchor (which means that 1 chain of anchors will have a maximum length of 200m). More anchors on a single chain will cause issues. Make sure you use shielded cables to eliminate cross talk.
Which cables to use
The quality of the cables is determined by the material they're made of, the shielding of the cable, the category of the cable and the wire diameter of the cable (expressed by the AWG number).
Your cables should be:
- Pure Copper (CU) and not Copper Clad Aluminium (CCA)1
- Shielded Foil Twisted Pair (S/FTP)2
- CAT6 (or better)3
- AWG24 (or better)4. Both AWG 24/1 and AWG 24/7 will work.
It is of great importance that the connectors on the cables are properly fixed and tested with a cable tester.
Which switches to use
An anchor uses ± 5 W (watt), therefor your switches should:
- Have PoE+ (802.3at)
- Deliver at least (5 W x max number of anchors connected on 1 port) per port.
E.g. If you want to go up to 4 anchors on a chain you'll need a switch that delivers at least 5 W x 4 = 20 W per port.
- Deliver at least (5 W x total number of anchors connected to the switch) in total.
E.g. If you want to have 16 anchors connected to the switch you'll need a switch that delivers at least 5 W x 16 = 80 W in total.
For smaller setups we can recommend the Ubiquiti UniFi Switch 8-150W (https://www.ui.com/unifi-switching/unifi-switch-8-150w/) as an affordable and good price-quality switch.
Validating the anchors
Each anchor has a LED light on it which will give you feedback about the current state of the anchor. This LED light can be very useful during installation to detect problems on the spot, and will allow you to take immediate action on common issues like cabling issues. But the LED will only give you useful feedback when the anchor gets connected to the gateway, which means it's best to already have the gateway and switches in place before the installation of the anchors.
When you plug in the Ethernet cable in the anchor, and it gets power, the anchor will start up in bootloader mode in which the LED will be blue. After approximately 7 seconds the anchor will then go to the firmware and follow this flow:
|No LED||The anchor is powered off|
|LED blinking red||The anchor has a general malfunction|
|LED solid blue||The anchor is in support / maintenance mode|
|LED solid red||The anchor has no link (= it is powered but not linked to the network)|
|LED blinking orange||The anchor is linked but did not receive an IP address|
|LED solid orange||The anchor has received an IP address|
|LED blinking green||The anchor received a heartbeat / is starting up tasks|
|LED solid green||The anchor is in normal operation mode|