BLE Asset Tracker User Guide
T0005946_UG
Version 1.1
TEKTELIC Communications Inc.
Confidential
Page 10 of 21
1.2.1
Bluetooth Low-Energy Scanner
The Tracker is equipped with a BLE module that is embedded in the MCU. It serves as a BLE central
device that periodically searches to discover nearby BLE peripherals. It can be used as a
standalone proximity sensor that can also help at positioning.
The BLE scan can be disabled entirely or enabled at any time. Figure 1-3 shows the BLE scan
scheme when the BLE scan is enabled. As shown in the figure, BLE scans are performed
periodically. Each scan duration is divided into scan intervals. The BLE scan is performed only in
the scan window portion of the scan interval. The ratio of the scan window to the scan interval
shows the scan duty cycle. In the case of the scan window equalling the scan interval, the scan
duty cycle is 100%. This represents a continuous scan over each scan duration. This will increase
the likelihood of finding more beacons, but at the expense of consuming more power. The scan
period, duration, interval, and window are all configurable (see the TRM document for
configuration details [1]).
Figure 1-3: The BLE Scan Schematic Procedure.
At the end of each scan duration,
up to
n
discovered BLE devices with the strongest RSSIs are
reported over LoRaWAN. The value
n
is user configurable (see TRM) [1]. If no devices are found,
an empty list is uplinked. Over each scan duration, a BLE device beacon may be observed
(discovered) more than once, in which case the RSSI associated with the BLE device at the end of
the scan duration is the average value over all observed RSSIs.
The Tracker supports BLE of Bluetooth 5.0. The BLE scan is performed in the passive mode only,
i.e. the Tracker listens to surrounding beacons, but does not transmit to them to request
additional information.
NOTE:
The BLE scan is exclusive to LoRa radio transmission; i.e. they do not overlap. If any
reporting becomes due at the same time of a BLE scan, the reporting will be done after the BLE
scan is complete.
