4 ms·

Hah yes we did. Wires. Of course everyone wants wireless though and while it would've improved the overall experience I'm not sure it would've saved the compa

Hah yes we did. Wires. Of course everyone wants wireless though and while it would've improved the overall experience I'm not sure it would've saved the company. Other market factors were making more of a problem than just delivering good tech :/ In further thinking about the idea, once the wifi devices are time synced like this, you can also begin to use that signal for localization in addition to the traditional optical or electromagnetic tracking. Fun!

kbaker 10y ago
You need better sync than ~1 microsecond to do time-of-arrival localization for Wi-Fi style signals, though... since RF waves travel at around 1 ft per nanosecond. Ultra-Wideband devices can get this synchronization though, and can be used for localization.
- sargun 10y ago
  How can you use UWB for this? Doppler?
  - webmaven 10y ago
    The Doppler effect would only help with a moving source or target, so probably not. I would guess that what was meant was using two (or more) frequencies at the same time would produce harmonics that reinforce and cancel the combined signal at set distances from the source that can be used to get distance info, and if you can get distance to three different points, you get a 3D location[0]. The technique dates back to WWII. Further, I think it works best if the frequencies are each a different prime (otherwise you get many beats). There are probably additional tricks you can do by varying the precise frequency combination to extract very fine-grained location data. [0] Technically, you get two solutions, one on each side of the plane connecting the three points, but they can be disambiguated as long as direction can at least crudely be determined within 180°.
  - jburgess777 10y ago
    DecaWave sell UWB modules that perform real-time location to ~10cm in a controlled environment: http://www.decawave.com/ http://www.decawave.com/ I imagine that they use a system which is not too different to the way GPS combines the signals from multiple satellites to calculate the receiver location. When you receive have a receive lock against multiple receivers, the spreading code allows you to determine time of flight to the nearest carrier cycle, and the carrier phase can provide even more precise timing. See also: https://en.wikipedia.org/wiki/Multilateration https://en.wikipedia.org/wiki/Multilateration

kbaker 10y ago

You need better sync than ~1 microsecond to do time-of-arrival localization for Wi-Fi style signals, though... since RF waves travel at around 1 ft per nanosecond. Ultra-Wideband devices can get this synchronization though, and can be used for localization.

sargun 10y ago
How can you use UWB for this? Doppler?
- webmaven 10y ago
  The Doppler effect would only help with a moving source or target, so probably not. I would guess that what was meant was using two (or more) frequencies at the same time would produce harmonics that reinforce and cancel the combined signal at set distances from the source that can be used to get distance info, and if you can get distance to three different points, you get a 3D location[0]. The technique dates back to WWII. Further, I think it works best if the frequencies are each a different prime (otherwise you get many beats). There are probably additional tricks you can do by varying the precise frequency combination to extract very fine-grained location data. [0] Technically, you get two solutions, one on each side of the plane connecting the three points, but they can be disambiguated as long as direction can at least crudely be determined within 180°.
- jburgess777 10y ago
  DecaWave sell UWB modules that perform real-time location to ~10cm in a controlled environment: http://www.decawave.com/ http://www.decawave.com/ I imagine that they use a system which is not too different to the way GPS combines the signals from multiple satellites to calculate the receiver location. When you receive have a receive lock against multiple receivers, the spreading code allows you to determine time of flight to the nearest carrier cycle, and the carrier phase can provide even more precise timing. See also: https://en.wikipedia.org/wiki/Multilateration https://en.wikipedia.org/wiki/Multilateration