How does the SafeDistance Proximity Detection work?

Modified on Fri, 9 Oct, 2020 at 4:33 PM

A SafeDistance Badge will beep and vibrate when other badges are within the proximity range. This is a configurable parameter and is set to approximately 2meter, or 6 feet, by default.

Default parameters of the SafeDistance Badge are as follows:

  • Bluetooth receiving window opens for 1second, every 3seconds.
  • Bluetooth transmit power is set to 0dBm.
  • Bluetooth receiving threshold is set to -70dBm. (This reflects a SafeDistance Badge that is picked up from 2meter, or 6feet, away)
  • LoRa transmit interval is set to every 10seconds when other badges are detected and within proximity range, default value is 2meter (6feet).
  • LoRa Transmit interval is set to every 5minutes for Heartbeat messages. This includes the SafeDistance Badge's battery state, etc.

The detection works as follows:

  • The SafeDistance Badge broadcasts as a Bluetooth beacon, every 100ms.
  • All SafeDistance Badges use as default BLE UUID F2A52D43E0AB489CB64C4A83001467FD to broadcast.
  • The SafeDistance Badge turns on Bluetooth receiving at a random time within 3 seconds, for 1 second.
  • The receiving SafeDistance Badge can receive the same transmitting SafeDistance Badge multiple times within the 1 seconds receive window. 
  • The SafeDistance Badge calculates the averages RSSI levels received during this period.
  • If the RSSI is larger than the receiving threshold (-70dBm by default), the SafeDistance Badge will beep and vibrate simultaneously, and send all the SafeDistance Badges within proximity range their BLE Major, Minor and RSSI parameters to the LoRa Gateway.
  • The LoRa Gateway will forward these messages to the SafeDistance LoRaWAN Network Server.
  • The SafeDistance Application Server will then receive the payload information from each SafeDistance Badge for visualization to the user.

The detection area:

The distance can be 2~3m when two people are within 150° in front of each other. When one person is on the side of another person, from 0° to ~ 15°, the distance of detection is only half the regular distance!

The figure below illustrates this as a reference of the detection and the distances. The actua angle and distance could change with different environments!

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