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 are using a time-of-fligt (ToF) approach. But since the speed of ultrasound is about 1,000,000 times slower than the speed of radio waves, it is virtually 1,000,000 times easier to achieve the same accuracy for ultrasound-based system 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.
No, it doesn’t. UWB needs line of sight as any commercially available positioning system. If you have a non-line of sight, then you shall expect an inaccuracy comparable with the size of an obstacle. At least. Often, it is much more than the obstacle or there will be no tracking at all or tracking in an absolutely wrong location.
One must clearly distinguish what “line of sight” means. Many walls or obstacle are radio transparent. For example, thin wooden walls, regular glass (not metal coated!), etc. They do add inaccuracy in positioning, because the speed of radio wave propagation in them is different than that in the air and the difference cannot be taking into account to currently available UWB positioning systems. 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, that believe in non-line of sight capability of UWB is the biggest and nastiest surprise for the end users with real industrial application. Many real-world objects in industrial world are not radio transparent for UWB, for example, thick brick walls or concrete walls are not transparent. Machines, pallets, 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 not 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 very simple:
Always build real-world UWB positioning system with line of sight requirement in place.