Functional Description
Interactions monitoring
The purpose of this device is to monitor interactions between its users and generate an alert when the devices are within close proximity.
The device will maintain awareness of the surroundings and classify their distance using one the four states:
Limit: the device is in range and its Received Signal Strength indicator (RSSI) 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 is monitored in connected mode
Each time a device crosses or moves from one state to another, the distance monitoring state machine will log the interaction.
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 estimate the distance still based on the signal strength.
Warning State
In warning state the device uses WiRa to measure the distance accurately and prepares to inform the user that its getting too close to another user. This triggers a low alert which is one LED flash.
Alert State
As the WiRa measurement indicates close proximity between the devices and an alert is issued. The device continues to monitor the users until they increase the distance between each other.
Logging
The SDT will log interaction on its file system. Each log entry has a unique and incremental timestamp. The timestamp is sourced from the RTC which itself can be set through bluetooth low energy current time service 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 logs generated by interaction in each different state (coarse, warning, alert) individually. This allows to quickly dump alerts, which are assumed to occur less often, when the device leaves an office area or a factory floor. The extended logs can be dumped while the device is being charged for instance.