Bluetooth® Low Energy for IoT and Asset Tracking - Advantages and Best Practice

Example of Using Bluetooth^® Low Energy: Asset Tracking System

Systems commonly used for asset tracking (i.e., various devices, inventory, or valuable items) can operate by attaching a BLE beacon to each tracked item, which is then detected by strategically placed BLE gateways throughout the premises, and the collected data is transmitted to a cloud service or local server for further processing. This systematic approach allows for effective tracking, management, and security of assets, leading to optimized operational costs and increased efficiency.

Maximum number of BLE beacons and detection speed

For practical use, it is crucial to know how many beacons can be used simultaneously and how quickly they can be detected.

Regarding the maximum number of beacons, a specific limit cannot be predetermined as it significantly depends on the surrounding conditions. Generally, it is recommended to limit the number of active beacons in one area to approximately 100 or fewer to mitigate system overload and mutual interference.

Experiment to determine detection speed and reliability

To illustrate, we created a simulation of an asset tracking system. To determine how quickly and reliably detection can be achieved, we conducted an experiment with the following goals:

1. Determine the scanning time required to detect beacons based on their distance from the gateway.

2. Determine the scanning time required based on the beacons' transmission period.

Test parameters:

10 beacons based on nRF52840 and one gateway based on ESP32.

(Note: During the tests, there were also 20-25 other BLE devices in the area, affecting the measurement results.)

First phase:

BLE beacons were placed 1 meter from the gateway and configured to send an advertising packet every second.

The BLE gateway was configured to scan surrounding devices for 1 second. After completing the scan, the efficiency was evaluated: how many of all present devices were detected.

The scanning intervals were then gradually extended up to 8 seconds, and the efficiency was evaluated each time.

The beacons were then moved to different distances. The same experiment was conducted for distances of 2m, 3m, 5m, and for beacons placed behind a wall in an adjacent room.

Experiment result:

To detect a beacon with a transmission period of 1 second at a distance of 5 meters from the gateway, at least 7 seconds of scanning is required.

Second phase:

In the next phase,the experiment was repeated with the beacons' transmission interval shortened to 100 ms.

Experiment result:

As expected, shortening the interval significantly affected the probability of detection. For close distances (1-2m), a transmission frequency of 100 ms requires only 1second of scanning to successfully detect the beacon. For greater distances (as you can see on the graphs), the difference is even more noticeable.

To detect a beacon with a transmission period of 100ms at a distance of 5 meters from the gateway, only 3 seconds of scanning is required.

Conclusion

While shortening the transmission interval significantly reduces the scanning time required, it also substantially increases power consumption.

By determining the necessary transmission period for the desired scanning time, we can calculate the estimated power consumption.

To estimate power consumption, a manufacturer’s calculator can be used, such as the one from Nordic Semiconductor available on the manufacturer’s website.

According to the calculator, the average consumption with a 100 ms transmission period can reach up to 113 µA. However, with a 1-second period, consumption is only 15 µA.

Using a standard CR2032 battery with a capacity of 230 mAh, the battery life is approximately 80 days with a 100 ms transmission period and nearly 2 years with a 1 second period.

Thus, the transmission frequency of BLE beacons can be configured either according to the desired battery life or the necessary detection speed and reliability.