Functional Description¶
Interactions monitoring¶
The device purpose is to monitor interactions between its user and generate an alert when the distances is getting too close.
The device will maintain awareness of the surrounding and classify their distance using one the three states:
Limit: the device is in range and the Received Signal Strength indicator (RSSI) of its signaled is monitored
Coarse: the device is in range and the distance of the device is roughly estimated
Warning: the device is within 3m range and the a connection will be initiated to confirm the distance and perform Dialog Wireless Ranging measurement
Danger: the distance in monitored in connected mode
Each time a device crosses moves from one state to another, the distance monitoring state machine will log log the interaction in the log area.
Limit State¶
When the signal strength is weak the peer device is considered in the “Limit state”. In order to save energy and maximize battery life time, the signal strength is the only information considered.
Coarse State¶
When the signal strength is increasing the peer device is considered in the “Coarse state”. A connection is established between the devices to try to estimate the distance still based on the signal strength.
Warning State¶
In warning state the device uses WiRa to measure the distance accurately and get ready to inform the user its getting too close to another user.
Alert State¶
As the WiRa measurement indicates close proximity between the devices an alert is issued the device monitors the users distanciate from each other.
Logging¶
The SDT will log interaction on its file system. Each log entry has a unique and incremental timestamp. The timestamp is source from the RTC which itself can be set through bluetooth low energy profile. It is possible to access the logging database of the device wirelessly through a specific GATT service.
The logging mechanism is designed to dump logged generated by interaction in each different state (known, warning, alert) individually. This allows to quickly dump alerts, which are assumed to occur less often, while the device leaves an office area or a factory floor. The extended logs can be dumped while the device is being charged for instance.