Comparison of the Wireless Technologies Most Suitable for Asset Tracking
As we mentioned earlier, asset tracking applications are very similar to indoor navigation applications, so the most suitable wireless technologies are also similar:
- Bluetooth® Low Energy
- Ultra-wideband (UWB)
- LPWAN (LoRa, LTE-M, NB-IoT)
- RFID (active)
One other solution that is not specifically IoT-related but still worth mentioning (and is a popular alternative technology) is the use of Computer Vision for tracking objects and people. Computer vision refers to the implementation of algorithms and techniques that allow computers to recognize people and objects in digital images. With the recent advancements of computer vision techniques, it has become possible to recognize and track assets in real time using camera systems. The main disadvantage of computer vision systems is the extremely large bandwidth required for analysis of the video/images and their content, especially when performed in real time.
Bluetooth Low Energy
Bluetooth® Low Energy is one of the most popular wireless technologies used in asset tracking applications. Some of the most important benefits of using Bluetooth Low Energy in asset tracking applications include:
- Low power consumption
- Low cost
- Support for large-scale deployments
Some of the disadvantages of Bluetooth Low Energy solutions include potential interference from other signals in the same frequency spectrum and medium-level accuracy in systems that rely on RSSI.
Bluetooth beacons are commonly used in asset tracking systems. The implementation involves installing locator devices in specific areas within a facility that receives signals transmitted by tags attached to the different assets (which operate as Bluetooth beacons). The Received Signal Strength Indicator (RSSI) of the packet sent by the beacon to each locator within range is reported to a backend server. The backend server is aware of all locator devices and can utilize the RSSI information to determine an approximate location of the Bluetooth beacon (asset tag) within the facility.
In 2019, a new exciting feature called Bluetooth® Direction Finding was introduced in version 5.1 of the Bluetooth standard specification. This new feature allows Bluetooth Low Energy devices to dramatically increase the accuracy of the location of Bluetooth devices based on either the angle of departure (AoD), the angle of arrival (AoA), or both.
For the case of asset tracking, AoA is the more suitable technique utilized. In this case, multiple locator devices (receivers) are installed in a facility. Each locator has an antenna array that is used to determine the Angle-of-Arrival of the signals received from the Bluetooth beacons (asset tags) which employ a single antenna. The RSSI, along with the AoA information, is then utilized to determine a more precise positioning of the beacons. The locations of the assets are then usually reported to the users of the asset tracking system via a web interface (via a backend server).
Ultra-Wideband is a short-range radio technology that’s popular in indoor navigation and asset tracking systems. UWB operates in the frequency range of 3.1 and 10.6 GHz and has a bandwidth of at least 500 MHz.
Asset tracking systems that are UWB-based differ from Bluetooth® Low Energy beacon solutions in that they utilize Time-of-Flight instead of RSSI or direction finding (AoA, AoD) measurements that are then used in trilateration calculations to determine device location.
The basic principle behind the time-of-flight method is the ability to calculate the distance from one device to another by knowing both (1) the time it took for the signal to propagate from the transmitter to the receiver and (2) the signal velocity. Finally, these values are utilized in a trilateration calculation to figure out the position of the target device.
A couple of the benefits of UWB asset tracking systems:
- Higher accuracy than RSSI-based techniques used in other technologies since they operate in a very broad band of frequencies – measuring the time-of-flight of any radio signal is correlated with its bandwidth
- Reduced interference with other signals due to:
- Operating in a different frequency spectrum
- Low transmit power
- Short transmit duration of a UWB signal
Some of the disadvantages of UWB technology, when utilized for asset tracking implementations, include:
- High cost, sometimes even prohibitive
- The lack of global standardization – regulations differ across different regions of the world
LPWAN Technologies (LoRa, LTE-M, NB-IoT)
LPWAN technologies have recently become more popular in the area of asset tracking applications, especially when long-range tracking is needed. LPWAN-based solutions usually utilize assisted GPS (A-GPS) for determining location. However, this methodology is limited indoors, and so solutions in this case utilize triangulation using RSSI or Time-of-Flight (ToF) instead for determining location.
Due to the high latency of LPWAN technologies, these solutions are usually limited to tracking devices with limited movements instead of more mobile devices. Latency is also directly correlated to accuracy in location calculation, so these solutions usually do not offer accurate enough positioning calculations.
The last potential wireless technology for asset tracking systems we’d like to discuss is Radio Frequency Identification (RFID). RFID-based asset tracking systems usually use RSSI measurements to determine location.
There are two types of RFID tags: Passive and Active. Asset tracking systems usually utilize active RFID tags instead of passive tags since they have a higher range of operation.
Some of the drawbacks of RFID-based asset tracking systems include:
- High cost of active RFID tags
- The need for many tags to provide accurate positioning
- Low accuracy in some cases
Now, let’s compare the most common technologies in terms of the key attributes we listed:
One important aspect to keep in mind is that most asset tracking systems will utilize multiple technologies, each for a different purpose. For example, Wi-Fi can be used for data transfer between the different locators deployed within the facility and the backend server(s), while technologies like Bluetooth® Low Energy and UWB are most commonly used for determining the locations of target devices within an area.
The most important attribute considered in the choice of technologies used in asset tracking is location accuracy. In general, the higher the accuracy, the higher the cost and the more complex the system. This highly affects the choice of technologies being used in an asset tracking system. One important note is that with the addition of direction finding capabilities, Bluetooth technology is able to achieve high accuracy at a lower cost than the other options, especially when considering the total cost of ownership.
Some asset tracking systems may also be utilized for gathering sensor data at the device end. This is accomplished by incorporating sensors in the asset tags that are attached to the devices being tracked. In this case, latency plays a crucial role in the feasibility of the technologies being used.