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I think you can "spoof" gps satellite timestamp transmissions with single transmitter inside the train. This would require on-train equipment but typically the

I think you can "spoof" gps satellite timestamp transmissions with single transmitter inside the train. This would require on-train equipment but typically the trains know where they are and could translate that into the required gps satellites and timestamp signatures to allow any devices onboard to acquire a "gps" signal and decode the location using timestamp variation. I don't believe any of those are encrypted and transmit ~1000-10000 time per second on 1500-1600mhz spectrum which is fairly simple to reproduce using even a cheap SDR kit. It could also work with 0 input from the train's telemetry - in much the same way as the app - the device would get a reference gps signal (or wifi/BLE when it knows it's in the station), then with a built-in accelerometer (which it has the luxury of direction + stability if it's mounted in the train car) it can determine with greater accuracy where the train is and how far it's moved.

Aurornis 2y ago
> I think you can "spoof" gps satellite timestamp transmissions with single transmitter inside the train. Spoofing GPS as a commercial operation is a quick way to get your company crushed by regulatory agencies.
- bluGill 2y ago
  I think there should be regulations that allow sending real GPS from low power ground based system. Sending incorrect GPS is a major problem, but a lot of location issues would become much easier if the owners of buildings would just install cheap GPS transmitters.
  - acc_297 2y ago
    It seems like this functionality could be tacked on to "MSA" which I just learned is an FCC mandatory technology for most cell phones https://en.wikipedia.org/wiki/Assisted_GNSS https://en.wikipedia.org/wiki/Assisted_GNSS
- cruffle_duffle 2y ago
  I mean obviously you’d set it up through the proper channels. I’m sure there is a regulatory framework for doing exactly this sort of thing already.
acc_297 2y ago
I wonder if you could just create a map of the cellular antennas along the metro/subway tunnels. Maybe I misunderstand how connectivity is delivered in underground systems it may pretend to be a "single cohesive base station" from a phones perspective but if there are thousands of antennas throughout the system and the phone switches from one to the next regularly you can decently estimate the location.

Aurornis 2y ago

> I think you can "spoof" gps satellite timestamp transmissions with single transmitter inside the train. Spoofing GPS as a commercial operation is a quick way to get your company crushed by regulatory agencies.

bluGill 2y ago
I think there should be regulations that allow sending real GPS from low power ground based system. Sending incorrect GPS is a major problem, but a lot of location issues would become much easier if the owners of buildings would just install cheap GPS transmitters.
- acc_297 2y ago
  It seems like this functionality could be tacked on to "MSA" which I just learned is an FCC mandatory technology for most cell phones https://en.wikipedia.org/wiki/Assisted_GNSS https://en.wikipedia.org/wiki/Assisted_GNSS
cruffle_duffle 2y ago
I mean obviously you’d set it up through the proper channels. I’m sure there is a regulatory framework for doing exactly this sort of thing already.

acc_297 2y ago

I wonder if you could just create a map of the cellular antennas along the metro/subway tunnels. Maybe I misunderstand how connectivity is delivered in underground systems it may pretend to be a "single cohesive base station" from a phones perspective but if there are thousands of antennas throughout the system and the phone switches from one to the next regularly you can decently estimate the location.