In short, the answer is yes. Wi-Fi Access Points can be used for RTLS Asset Tracking. However, like most technologies, some pros and cons need to be considered. Before we get into the weeds it might be helpful to understand what Wi-Fi positioning is.
- What is Wi-Fi positioning?
- How does Wi-Fi positioning work?
- What are some Wi-Fi positioning techniques?
- Should I use Wi-Fi positioning for RTLS asset tracking?
What is Wi-Fi Positioning?
We live in an environment where Wi-Fi is ubiquitous. It is used by many common wireless devices, including smartphones, computers, IoT devices, routers, and more. Like other communication protocols, including Bluetooth Low Energy and UWB, Wi-Fi transmits data between devices using radio waves. However, it can also be used to detect and track the location of people, devices, and assets. Wi-Fi can be an effective option for indoor positioning, although it is typically less accurate than competing positioning technologies like BLE and UWB. Wi-Fis continued significance as a technology for location-based applications is due to an established Wi-Fi infrastructure throughout indoor spaces; its vast presence and accessibility make it a convenient standard for indoor positioning applications. The existing Wi-Fi infrastructure makes it easier than ever to find these use cases.
How does Wi-Fi Positioning Work?
Wi-Fi indoor positioning solutions use existing Wi-Fi access points or sensors to detect and locate transmitting Wi-Fi devices, such as smartphones and tracking tags throughout indoor spaces. Location data collected by sensors or access points, or sent from APs to client devices, is ingested by various location applications and translated into insights that power multiple location-aware use cases. Wi-Fi-based positioning systems can use different methods to determine the location of devices.
Wi-Fi Positioning using Access Points
Wi-Fi positioning with access points relies on the existing Wi-Fi infrastructures installed throughout indoor spaces. This infrastructure allows organizations to save costs on additional hardware. Building APs can detect transmissions from surrounding Wi-Fi devices, both on and off the network. This location data is then sent to a server or central IPS to calculate the location.
Wi-Fi Positioning Using Sensors
With this method, Wi-Fi-enabled sensors are deployed in fixed positions throughout an indoor space. These sensors passively detect and locate transmissions from smartphones, asset tracking tags, beacons, personnel badges, wearables, and other Wi-Fi devices. The location data is collected and sent to a server. The location engine analyzes the data to determine the location of the transmitting device.
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Wi-Fi Positioning Techniques
There are four techniques to determine location with Wi-Fi positioning.
RSSI Multilateration
Wi-Fi access points and sensors can measure received signal strength from connected devices. In multilateration systems, a location engine uses these measurements to estimate the location of transmitting devices. Similarly, devices can use the signal strength of nearby APs to determine their location. Using an RSSI-based method with multilateration is an easily implemented and low-cost option for Wi-Fi positioning. However, it does not deliver a high degree of positional accuracy because it is subject to signal attenuation, absorption, reflection, and interference.
RSSI Fingerprinting
Wi-Fi positioning via fingerprinting involves using a database that records the location and signal strengths of surrounding APs paired with the receiver’s position (determined either via GPS or direct measurement). This time-consuming survey process may need to berepeated several times for accuracy. When tracking a device, the RSSI values are compared to these fingerprints in the database to estimate the device’s location. This low-cost method for Wi-Fi positioning requires continuous updating of the trained RF patterns in the database. Fingerprinting approaches are also affected by signal attenuation (most influence), absorption, reflection, and interference.
Time of Flight (ToF)
ToF is a highly accurate indoor positioning method used by precision technologies like UWB. This technique measures the distance between Wi-Fi devices by calculating the time it takes for signals to travel between devices. ToF requires a dense deployment of APs or sensors to detect a Wi-Fi device. Time based positioning requires highly precise time synchronization–on the order of picoseconds–which can be difficult or impossible to achieve. Further, the relatively limited bandwidth of WiFi signals limits their ranging resolution to several meters at best.
Angle of Arrival (AoA)
AoA is an advanced method that delivers Wi-Fi positioning with enhanced accuracy. This technique is possible due to Multiple Input Multiple Output (MIMO) Wi-Fi interfaces. This method works when a mobile asset, such as a tag, transmits to a Wi-Fi sensor with a multi-antenna array. The phase shift of the signal received at each of the antenna elements is measured and calculated to determine the angle of the transmitting mobile device. If the mobile device is seen by sufficient APs, its location can be estimated via triangulation. While indoor positioning via AoA can be more accurate than signal strength approaches, solutions that leverage this technique are only just entering the market and the custom antenna arrays required mean they can be costly.
Should I use Wi-Fi positioning for RTLS Asset Tracking?
Wi-Fi based positioning is an attractive solution given that most indoor spaces already have some Wi-Fi infrastructure installed, and–as discussed in this blog–there are many approaches to implementing it. However, there are some significant drawbacks as well, such as the high cost of tags and infrastructure, especially in quantities required to achieve accurate positioning.
Ultimately, the primary driver in choosing a wi-fi based positioning scheme would be if you needed to track existing wifi devices (e.g. phones, computers, etc.) For general-purpose RTLS, a Bluetooth Low Energy system (such as AirFinder) will provide better performance at far lower cost and with longer battery life. If you want to learn more about AirFinder, book a demo today.
