Microsoft proposes LED light positioning system
A system to do this, called Epsilon, has been developed by researchers from Microsoft Research in Beijing, China, the University of Massachusetts at Amherst and Ohio State University. Epsilon, is explained in a presentation that could be found here.
The system has the advantage that with LED fixtures being installed for the primary purpose of providing light there is little additional cost to provide the beaconing system, unlike the case with radio-frequency beacons or the use of Wi-Fi.
A description on the Microsoft Research website states that Epsilon addresses several practical challenges to using visible LED lights for tri-angulate the position of devices with a light sensor coming up with localization accuracies of less than a meter in typical office environments. Guiding consumers to shops and even products are also use cases for the system. In essence the LED lights are the infrastructure and smartphone.
The authors propose the use of binary frequency shift keying (BFSK) and channel hopping to enable reliable location beaconing from multiple, uncoordinated light sources. The authors have implemented and evaluated Epsilon in a small-scale physical test-bed as well as moderate-scale simulation.
The researchers added a control board implementing BFSK beaconing to an off-the-shelf LED bulb and a light sensor board to a mobile phone that communicated with the phone via the audio jack. Modulation of the optical spectrum was done at 10kHz to 19kHz to produce 30 channels of 300Hz bandwidth.
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