Measuring short distances

Question

What's the best way to wirelessly measure the distance between two objects (computer, smartphones or a specialised device) that are a few meters apart down to a ~10cm accuracy? Is this possible by piggybegging on WLan, bluetooth or GPS?

Answer 1

Ekahau specialise on doing this kind of thing with WiFi. You're better off using light to get precision measuring as RF (Radio Frequencies) can be distorted by the environment. There are numerous patents in this area for many of the 'good' solutions.

Answer 2

GPS won't give you 10cm accuracy. You might get something like on the order of metres.

It sounds like Bluetooth can be used for indoor localization, but I am not sure as to the availability of API's and the like to make the job easier.

Answer 3

Not Bluetooth, not Wi-Fi, not GPS and not even ultra wide band (UWB) can reliably achieve this type of accuracy. I'd like to provide you with a solution but it would require very, very sophisticated HW + SW.

Wi-Fi is the most common location technology for indoor enterprise, but even that can go just down to about one meter. To assist Wi-Fi, for example we at Ekahau have "location beacons" that are separate battery-powered transmitters to enhance accuracy further in critical areas. But even they don't really help if you want to measure the distance between two mobile devices within 10cm radius.

UWB boasts "3 feet or better" accuracy, but I wouldn't trust that it goes down to 10cm granularity (plus it's highly expensive and not present in the devices you're tracking).

GPS doesn't really work indoors, and outdoors, like is said before, the accuracy is several meters, not cm.

Bluetooth works over the same frequency as Wi-Fi, and thus has the same accuracy limitations.

Answer 4

Getting a precision RF positioning system would be nice, but costly. Inertial measurements can provide 10cm accuracy. However, there two issues that make inertial measurement units (IMU) less practical.

1. Error accumulates over time and accuracy degrades.
2. IMU needs to be initialized at a known location. For example, devices may be physically brought together.

$0.02