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 what the next development points are.

How accurate is the system by default?

Metrology can be a pretty complex and rather impractical science. One asks a simple question: “How precise the system is?” 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?”

Well, we don’t want you and us to engage in that discussion, because it is rather scientific, lengthy and impractical, because doesn’t give usable answers on basic questions.

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

  • Can my robot to 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 sub-cm level with the least or zero additional investments?

First, check the videos on the right to see examples of the current performance of our precise indoor positioning system in comparison with 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 that shows that we nicely fit into the claimed ±2cm accuracy.

Also, remember that the accuracy of position measurements doesn’t really 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 a 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 on the picture.

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 a single physical point for the TX. It is a middle point between the TX transducers

How to measure height of the beacon

The indoor positioning system can automatically measure distances between the beacons, for example, between Super-Beacons or Industrial Super-Beacons – so 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.

Ways to increase accuracy of the tracking system

There are several element that has to be taken into account in order to increase the accuracy of already precise indoor positioning system even further.

Do you really need it?

This can be rather obvious, but do you really need to increase the accuracy? Of course, the higher the better. But everything comes for the expense or for a compromise or a sacrifice. Thus, before engaging, double-check that you really need even more accurate system and ready for additional steps, efforts, trade-offs.

Basics first

  • First of all, it is important to build the map of stationary beacons correctly – not even very precisely, but simply correctly
  • Remember to enter heights of stationary beacons – see a chapter above of how exactly
  • Make sure you are have the right transducers enabled on the right beacons and the right microphones turned on.You may receive or transmit the signal pretty well … but from or to 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” are different from “ultrasound meters” before calibration. Thus, in some cases, there is no point to measure 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 for the 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 very easy

Build submaps with proper geometry

  • The submaps must not be too long or too narrow. Ideally, it shall ration between sizes of 1:3 or less. If it is 1:10, you shall expect about 10-time accuracy degradation on some of the 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 disturbance of the atmosphere will directly affect the accuracy. Thus, additional protections similar to typical protections of microphones can be applied
  • Enable 50 periods of ultrasound signal in order to increase signal/noise ratio
  • However, if the signal is strong enough or the noise is not high, it is recommended to have as short pulse as possible. Sometimes – for very short distance – just 1 period

If anything is unclear, contact us via info@marvelmind.com