What technology is more accurate than UWB?

Ultrasound-based systems are about 10 times more accurate than UWB and about 100 times more accurate than BLE:

Both systems – ultrasound-based and UWB-based – are great because they use a time-of-flight (ToF) approach. However, since the speed of ultrasound is approximately 1,000,000 times slower than that of radio waves, it is virtually 1,000,000 times easier to achieve the same accuracy for ultrasound-based systems than for UWB-based systems. Of course, it is a great over-simplification, but the main point is clear: 

If you need the highest accuracy, select ultrasound-based systems – they give about ±2cm localization accuracy; then goes UWB with ±10-30cm; and only then – BLE with about 2-5m.

Does UWB work with non-line of sight?

No, it doesn’t. UWB needs a line of sight, as does any commercially available positioning system. If you have a non-line of sight, then you shall expect an inaccuracy comparable to the size of an obstacle. At least. Often, it is much more than just an obstacle, or there will be no tracking at all, or tracking in an absolutely incorrect location.

One must clearly distinguish what “line of sight” means. Many walls or obstacles are radio-transparent. For example, thin wooden walls, regular glass (not metal-coated!), etc. They introduce inaccuracy in positioning because the speed of radio wave propagation in them differs from that in air, and currently available UWB positioning systems cannot account for this difference. Thus, you have a less accurate than ±10-30cm, but UWB positioning will work through such thin objects. There will be a line of sight for UWB. Thus, you may not see through them, because they are non-line of sight for visual light, but they are line of sight for UWB.

However, the belief in the non-line-of-sight capability of UWB is the biggest and most significant surprise for end users with real industrial applications. Many real-world objects in the industrial world are not radio-transparent for UWB, for example, thick brick walls or concrete walls are not transparent. Machines, pallets, and forklifts are not radio transparent. And, of course, metal walls – absolutely not radio-transparent. There will be no line of sight, and there will be no UWB positioning.

Some cases are on the border. For example, our own body is semi-transparent. It is probably even worse than non-transparent. Because some signal is coming through, it is too weak to use in some cases, but disturbs in other cases.

Therefore, the recommendation is straightforward:

Always build a real-world UWB positioning system with a line of sight requirement in place.

Key elements of UWB positioning system

  • Stationary UWB beacons (UWB anchors)
  • Mobile UWB beacons (UWB tags)
  • Modem (Gateway)
  • Backbone
  • Software platform

Stationary beacons

  • Very good when they are radio-connected with the modem, which only requires basic power. Wiring Ethernet or similar cables can be more expensive than the cost of beacons in many cases

Mobile beacons

  • Can be in various forms and sizes: for people, forklifts, pallets, etc.
  • May require a very long battery life for static or semi-static objects, such as pallets. It is relatively easily achievable by decreasing the update rate to the minimum, once every 1-60 seconds, or even disabling it altogether. The mobile tracking will be triggered by an IMU (inertial measurement unit), which will detect the start of movement. Only then will it begin the localization
  • May require high-speed update rate for the expense of the battery for drones or VR/AR, for example

Modem

  • Modem controls stationary and mobile beacons, orchestrates the time, collects telemetry and often calculates the position of mobile beacon – depending on the architecture
  • Usually linked via backbone with a software platform or cloud or even beacons
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