Simulating Locator Beacons

Recently I’ve been thinking a lot about how a locator system that satisfies my own requirements could be put together. My current approach is a system of beacons in fixed positions that communicate with each other and broadcast to receivers via radio. This is basically the same system described in Rainbow’s End

Both receivers and beacons use transmit time to compute distance. Beacons use those distances (and the knowledge that they are all actually in fixed positions) to build an accurate mesh of their relative positions to each other. Those relative positions are fixed to absolute positions by including beacons with very precise known positions in the network.

I wanted to see if I could figure out how to actually find beacon positions relatively and then absolutely based on those few known beacons, so I built a simulator. The beacons use a mass and spring system to push and pull each other around into usually the right positions. This has the advantage of working without any central authority computing beacon positions. If its neighbors are trustworthy, each beacon can “move” itself around until it finds a stable location.┬áThis simulation is in 2D, but there’s nothing preventing it from working just as well in 3D.

The simulator is in Javascript, so I’ve just embedded it below. You can find some instructions on how to use it if you scroll down. Comments appreciated!

Select a beacon type from the UI and click anywhere in the frame to add a beacon at that location. Or click Random to add a new beacon.

Units are in pixels, except for the mass and spring weight values which are in Foozles and Smurfs respectively.

You can also use these key equivalents:
k: select Known
u: select Unknown
g: select GPS
r: place a beacon of the selected type at a random location


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  1. Pingback from Figuring out a common time base « Programmer Joe on :

    [...] the locator beacon network from the simulator for an indoor navigation system that follows my own requirements means that a receiver must be able [...]

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