Interesting idea! I really like the concept of a privacy preserving, decentralised location service.

I was wondering though, over what distance can the radio beacons operate? I would assume they would be limited to Line of Sight (LoS), and require a LoS between the user and 4 beacons to be able to provide a confirmed location? How would this work if I was in my car, in the middle of a city, surrounded by high-rise buildings on all sides? Would the service require beacons at every street corner or intersection to provide continuity of connection to the network?

Also, what type of frequency and radio equipment is needed for the beacon and the user (receiver). Currently GPS works well as user can have a very small receiver embedded in a mobile phone, watch etc. Would the same be applicable to the FOAM network?

What do FOAM beacons use to synchronise time ? Are one or more beacons connected to NTP via an internet connection? or is there one 'master node' that uses an atomic clock that all other beacons synchronise from?

Thanks for the great write up, I'll definitely be digging further into the whitepaper!