How to increase accuracy of precise indoor positioning system

Our precise indoor positioning system – Marvelmind Indoor “GPS” – already has typical ±2cm accuracy, which is enough for 90% of real-world precise indoor positioning and navigation application. But some people ask for more… – “the highest possible”, “sub-cm level”, “mm-level”.

Let us discuss in more detail what can be done to achieve the highest possible level of accuracy from the existing indoor positioning system and the subsequent development points.

How accurate is the system by default?

Metrology can be a pretty complex and rather impractical science. One asks a simple question: “How precise is the system?” and gets a very long answer that refers to the conditions, method of measurement, probability, and confidence … “OK… but what is the accuracy? And how do you measure?”

We don’t want you and us to engage in that discussion. It is somewhat scientific, lengthy, and impractical because it doesn’t give usable answers to basic questions.

Let’s do practical things that give answers to your engineering and commercial questions like:

  • Can my robot drive like that?
  • Will I be able to reach the desired point with the required accuracy, and what is required for that?
  • How to increase accuracy to the sub-cm level with the least or zero additional investments?

First, check the videos on the right to see examples of our precise indoor positioning system’s current performance compared to UWB.

Another video – hints, and advice on the settings to achieve the sub-cm level of accuracy for the expense of latency – by employing the embedded into the Dashboard or the beacons themselves Realtime Player.

The last video is about the testing method, a lot of statistics, and results show that we fit nicely into the claimed ±2cm accuracy.

Also, remember that the accuracy of position measurements doesn’t depend on the location update rate. At the same time, if your system can tolerate more latency in the position measurements, it is possible to achieve higher accuracy of measurements.

See more: Does accuracy depend on the location update rate?

 

Where is origin of Super-Beacon

Center of the beacon for transmission (TX):

  • About 1cm inside the beacon if looking from the top to RX4/TX4
  • The origin TX point is a point of virtual superposition of 5 transmitters. Each of them is slightly offset inside the beacon, i.e., there is no single physical point for the TX. It is a middle point between the TX transducers

Center of the beacon for reception (RX):

  • Center of the microphone – a small 1mm hole covered by a membrane
  • Very precisely known

See more detail and graphics in the picture.

A similar approach is used with other beacons. See more about their geometry:

  • The origin TX point is a point of virtual superposition of 5 transmitters. Each of them is slightly offset inside the beacon, i.e., there is no single physical point for the TX. It is a middle point between the TX transducers
Origin of Super-Beacon for indoor positioning system

How to measure the height of the beacon

The indoor positioning system can automatically measure distances between the beacons, for example, between Super-Beacons or Industrial Super-Beacons – called dual-use beacons. They can transmit and receive ultrasound. By measuring distances to several beacons, building a table of distances, and employing trilateration

However, even they cannot know their height because it is a relative term.

See more detail and graphics on the picture.

How to measure height of the beacon for indoor positioning system

Ways to increase the accuracy of the tracking system

Several factors have to be taken into account to increase the accuracy of the already precise indoor positioning system even further.

Do you need it?

Do you need to increase the accuracy? Of course, the higher, the better. But everything comes at the expense of a compromise or a sacrifice. Thus, before engaging, double-check that you need an even more accurate system and are ready for additional steps, efforts, and trade-offs.

Basics first

  • First of all, it is essential to build the map of stationary beacons correctly – not even very precisely, but simply correctly. See more about building maps in the Operating Manual, Placement Manual, How to build submaps part I and part II
  • Remember to enter the heights of stationary beacons – see a chapter above on how exactly
  • Make sure you have the correct transducers enabled on the beacons, and the right microphones turned on. You may receive or transmit the signal pretty well … but from or to the wrong direction and pick up reflection, but not a direct line of sight signal
  • Measure the distances correctly: from the right point to the right point, from the right plane to the right plane
  • Measure to the millimeter level
  • Remember that “physical meters” differ from “ultrasound meters” before calibration. Thus, in some cases, there is no point in measuring ultra-precisely (mm-level) in “physical meters”, because the difference with “ultrasound meters” will level any further potentially expected improvements in accuracy
  • In many cases, it is better to let the system measure all distances except height. Mixing “physical meters” and “ultrasound meters” before calibration may lead to accuracy degradation

Enable Realtime Player

  • Realtime Player is the easiest way to improve accuracy 2-10 times. Enable it. How to do so – see in the Operating Manual
  • There is no free cheese. Realtime Player does increase the accuracy for the expense of the latency. Instead of typical 8Hz and 125ms latency, you will have 8Hz, but 1-3 second latency – depending on your chosen settings of the Realtime Player. But it is very efficient and straightforward

Build submaps with proper geometry

  • The submaps must not be too long or too narrow. Ideally, it shall be a ratio between sizes of 1:3 or less. If it is 1:10, you shall expect 10-time accuracy degradation on some dimensions. Other dimensions will have the same accuracy as usually – ±2cm.
  • See more explanations in the video.

Noise or wind

  • Since our system is acoustic, any atmosphere disturbance will directly affect the accuracy. Thus, additional protections similar to typical protections of microphones can be applied
  • Enable 50 periods of ultrasound signal to increase the signal/noise ratio
  • However, if the signal is strong enough or the noise is not high, it is recommended to have an as short pulse as possible. Sometimes – for very short distances – just one period
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