4 ms·

Haven't read through the code yet, but the only thing I need to know is if these guys know what Rayleigh scattering is. If not, this probably isn't going to wor

Haven't read through the code yet, but the only thing I need to know is if these guys know what Rayleigh scattering is. If not, this probably isn't going to work so great. I worked on an indoor tracking system several years ago that used custom hardware. Since then, I've seen a lot of crappy solutions that use BLE RSSI measurements. This is simply not an easy problem to solve with crude methods.

mlevental 9y ago
they're fingerprinting locations based on rssi from devices in the signal environment. meaning your phone tries to connect, gets a set of rssis back and that then finger prints where you're standing with the phone (by the collection of rssis). the "space" it's locating in isn't physical space but "rssi tuple" space.
- konschubert 9y ago
  So, how does it get mapped to physical space then? As long as I am in "rssi tuple" space, I maybe know if I am in a place where I have been before, and I can learn the topology of the place in terms of "which places are adjacent". But I can't put my location on a map. How do they do the mapping?
  - mlevental 9y ago
    >So, how does it get mapped to physical space then? don't quote me but i don't think it does. you basically go around and set up hotspots in rssi space that the server knows about. when other people enter that hotspot things happen. this isn't as silly as it sounds because for a lot of applications you don't need to know where you are in physical space but just what you're near (i.e. i put my tv somewhere, hotspot it, then when my phone gets near that hotspot it's near the tv).
    - coupdejarnac 9y ago
      Yeah, that makes sense. But that's not going to be very accurate. That will be accurate at the tuple space, but not down to the nearest centimeter in X Y coordinates or anything like that. Plus, if there is any mass between the marker and the tracked device, that will throw off readings. RSSI measurements are really only good for open air measurements or if you have characterized all the materials the rf passes through.
      - mlevental 9y ago
        >lus, if there is any mass between the marker and the tracked device there are no markers so there is no attenuation happening in that way.
      - nonis 9y ago
        Yeah, BLE beacons aren't particularly accurate for an IPS. I worked on this problem a few years ago at FB, for the purposes of helping employees find themselves + meeting rooms on a mobile app. We really only needed 2-3 meter accuracy, so people could figure out approximately where they are. BLE signals are crazy noisy, so you need to tack on a lot of filtering (kalman filter, etc) and it really helps if you have multiple data sources (wifi signals, gyroscope, RF, etc). We could also kinda cheat by adding a track to the center of each hallway on the map, then magnet users towards the track.
        qrv3w 9y ago
        That sounds very similar to this! Did FB ever open-source it?
        nonis 9y ago
        Unfortunately no. Last I worked on it it was pretty heavily integrated with their mobile maps application (https://code.facebook.com/posts/504406169737284/instrumenting-meetings-at-facebook/ https://code.facebook.com/posts/504406169737284/instrumentin...) and there wasn't any plan on open sourcing.
        ghaff 9y ago
  - MrQuincle 9y ago
    This is kind of the resolution you can get with fingerprinting: https://youtu.be/ZtnYH53A4zE https://youtu.be/ZtnYH53A4zE But it all depends on the density of nodes. If you are also allowed to use odometry on the phone you can suddenly go up in resolution quite a bit. In that case you'll have a conventional SLAM problem from robotics, which can be considered more or less solved.
agotterer 9y ago
WIFI RSSI on its own is incredibly inaccurate. In our research (previous company) we found it performed decently well in an environment with little to no other devices and simple materials. Once you add into the mix industrial material, other devices, and signals the accuracy fluctuates tremendously. We started looking into triangulation, but didn’t have a chance to compete the project.

mlevental 9y ago

they're fingerprinting locations based on rssi from devices in the signal environment. meaning your phone tries to connect, gets a set of rssis back and that then finger prints where you're standing with the phone (by the collection of rssis). the "space" it's locating in isn't physical space but "rssi tuple" space.

konschubert 9y ago
So, how does it get mapped to physical space then? As long as I am in "rssi tuple" space, I maybe know if I am in a place where I have been before, and I can learn the topology of the place in terms of "which places are adjacent". But I can't put my location on a map. How do they do the mapping?
- mlevental 9y ago
  >So, how does it get mapped to physical space then? don't quote me but i don't think it does. you basically go around and set up hotspots in rssi space that the server knows about. when other people enter that hotspot things happen. this isn't as silly as it sounds because for a lot of applications you don't need to know where you are in physical space but just what you're near (i.e. i put my tv somewhere, hotspot it, then when my phone gets near that hotspot it's near the tv).
  - coupdejarnac 9y ago
    Yeah, that makes sense. But that's not going to be very accurate. That will be accurate at the tuple space, but not down to the nearest centimeter in X Y coordinates or anything like that. Plus, if there is any mass between the marker and the tracked device, that will throw off readings. RSSI measurements are really only good for open air measurements or if you have characterized all the materials the rf passes through.
    - mlevental 9y ago
      >lus, if there is any mass between the marker and the tracked device there are no markers so there is no attenuation happening in that way.
    - nonis 9y ago
      Yeah, BLE beacons aren't particularly accurate for an IPS. I worked on this problem a few years ago at FB, for the purposes of helping employees find themselves + meeting rooms on a mobile app. We really only needed 2-3 meter accuracy, so people could figure out approximately where they are. BLE signals are crazy noisy, so you need to tack on a lot of filtering (kalman filter, etc) and it really helps if you have multiple data sources (wifi signals, gyroscope, RF, etc). We could also kinda cheat by adding a track to the center of each hallway on the map, then magnet users towards the track.
      - qrv3w 9y ago
        That sounds very similar to this! Did FB ever open-source it?
        nonis 9y ago
        Unfortunately no. Last I worked on it it was pretty heavily integrated with their mobile maps application (https://code.facebook.com/posts/504406169737284/instrumenting-meetings-at-facebook/ https://code.facebook.com/posts/504406169737284/instrumentin...) and there wasn't any plan on open sourcing.
      - ghaff 9y ago
- MrQuincle 9y ago
  This is kind of the resolution you can get with fingerprinting: https://youtu.be/ZtnYH53A4zE https://youtu.be/ZtnYH53A4zE But it all depends on the density of nodes. If you are also allowed to use odometry on the phone you can suddenly go up in resolution quite a bit. In that case you'll have a conventional SLAM problem from robotics, which can be considered more or less solved.

agotterer 9y ago

WIFI RSSI on its own is incredibly inaccurate. In our research (previous company) we found it performed decently well in an environment with little to no other devices and simple materials. Once you add into the mix industrial material, other devices, and signals the accuracy fluctuates tremendously. We started looking into triangulation, but didn’t have a chance to compete the project.