Triangulate example for iBeacons

Question

I am looking into the possibility to use multiple iBeacons to do a \'rough\' indoor position location. The application is a kind of \'museum\' setting, and it would be easie

Answer 1

Accurate indoor positioning with iBeacon will be challenging for the following reasons:

1. As pointed in earlier comments, iBeacon signal tend to fluctuate a lot. The reason include multipath effect, the dynamic object obstructions between the phone and iBeacon when the person is moving, other 2.4GHz interferences, and more. So ideally you don't want to trust 1 single packet's data and instead do some averaging for several packets from the same beacon. That would require the phone/beacon distance doesn't change too much between those several packets. For general BLE packets (like beacons from StickNFind) can easily be set to 10Hz beaconing rate. However for iBeacon, that'll be hard, because
2. iBeacon's beaconing frequency probably cannot be higher than 1Hz. I will be glad if anyone can point to source that says otherwise, but all information I've seen so far confirms this assertion. That actually make sense since most iBeacons will be battery powered and high frequency significantly impact the battery life. Considering people's average walking speed is 5.3km (~1.5m/s), so even if you just use a modest 3 beacon packets to do the averaging, you will be hard to get ~5m accuracy.

On the other hand, if you could increase iBeacon frequency to larger than 10Hz (which I doubt is possible), then it's possible to have 5m or higher accuracy using suitable processing method. Firstly trivial solutions based on the Inverse-Square Law, like trilateration, is often not performing well because in practice the distance/RSSI relationship for different beacons are often way off from the Inverse-Sqare Law for the reason 1 above. But as long as the RSSI is relatively stable for a certain beacon in any certain location (which usually is the case), you can use an approach called fingerprinting to achieve higher accuracy. A common method used for fingerprinting is kNN (k-Nearest Neighbor).

Update 2014-04-24

Some iBeacons can broadcast more than 1Hz, like Estimote use 5Hz as default. However, according to this link: "This is Apple restriction. IOS returns beacons update every second, no matter how frequently device is advertising.". There is another comment there (likely from the Estimote vendor) saying "Our beacons can broadcast much faster and it may improve results and measurement". So whether higher iBeacon frequency is beneficial is not clear.