How to quickly leverage Bluetooth AoA and AoD for indoor logistics tracking
implemented using Wi-Fi and Bluetooth (Table 1): ■ Wi-Fi fingerprinting uses a database of the location and base station ID (BSSID) of each Wi-Fi access point (AP) in a building. An asset tag scans the Wi-Fi environment and reports the list of Wi-Fi APs and their associated signal strengths. The database from the survey is then used to estimate the tag’s likely position. This technique does not support high-accuracy RTLS ■ Wi-Fi Time of Flight (ToF) is more accurate. It measures the time it takes for Wi-Fi signals to travel between devices. ToF requires a dense deployment of APs to improve the accuracy of RTLS. Both ToF and fingerprinting have high device costs and high energy requirements
■ Bluetooth received signal strength indicator (RSSI) supports RTLS by enabling devices to determine their approximate distance from nearby Bluetooth beacons by comparing the received signal strength with known beacon positions. RSSI uses less energy and is lower cost than Wi-Fi fingerprinting or ToF, but it has limited accuracy. Its accuracy can be further reduced by environmental factors such as humidity levels and robots, or people moving around a facility and interfering with the Bluetooth signal levels ■ Bluetooth AoA is the newest and the most accurate indoor RTLS technology. In addition to providing high accuracy, it uses relatively little power and is low
cost. However, it’s more complex to implement compared with the other alternatives Bluetooth AoA and related AoD, RTLS solutions rely on antenna arrays to estimate the position of an asset (Figure 1). In an AoA solution, the asset sends a specific direction-finding signal from a single antenna. The receiving device has an antenna array and measures the signal phase difference among the various antennas caused by the differing distances of each antenna from the asset. The receiving device obtains IQ information by switching between the active antennas in the array. The IQ data is then used to calculate the location of the asset. In an AoD solution, the locator beacon to which the location is
Wi-Fi fingerprinting
Wi-Fi time-of-flight
Bluetooth AoA
Bluetooth RSSI
Accuracy
10 m
1 m to 2 m
5 m to 10 m 0.5 m to 1.0 m
Power consumption
High
High
Medium
Low
Installation cost
Low
Medium
Low
Medium
Device cost
High
High
Low
Low
Table 1: Indoor RTLS can be implemented using various Wi-Fi and Bluetooth techniques that provide tradeoffs between accuracy, power consumption, and cost. Table source: u-blox
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