Where Satellite Positioning Fails: Fighting Bluetooth RSSI Chaos With Levenberg-Marquardt
Satellite positioning gets you to the building. Inside the building, it abandons you. The signals that triangulate your position to within a few meters outdoors cannot penetrate a roof. Concrete and steel kill the signal. Inside a warehouse, a hospital, a shopping mall, an airport terminal, you are invisible to every satellite constellation humanity has launched.
This is the indoor positioning problem, and it is genuinely hard. Not hard in the "interesting engineering puzzle" sense. Hard in the "the laws of physics are working against you" sense. I built an iOS app called BeaconIL that attempts to solve it using Bluetooth Low Energy beacons and a non-linear optimization algorithm ported from numerical computing. This is the story of what I learned fighting radio physics with math.
A bit of context on why this project exists. By 2020 I had spent twelve years in total across desktop development and embedded work...
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