by Andy Slote - Mar 01 2020
For many Internet of Things use cases, the geographic locations (latitude, longitude) of the “Things” are essential. Many implementations use wireless networks, which means deriving a location from multiple reference points using various algorithms.
What is a point of reference? For a Wi-Fi network, it is generally a router or Wi-Fi access point. All of the satellites in a satellite network in view are potentially usable. A cellular network base station is another example. Location is derivable using many other technologies, including laser, infrared, and ultrasound, so emitting devices of these types qualify, as well.
The first step in determining a wireless device’s location is to measure the distance to at least three of these points of reference. Distance calculations come from derived values like Received Signal Strength Indicator (RSSI) or Time of Flight (ToF), with ToF producing a more accurate measurement. For some technologies (Wi-Fi, for example), RSSI or ToF are potentially usable. GPS distance calculations make use of ToF only. For these to work, the device has to be “seen,” which may mean something different depending on the technology.
Laser, infrared, and ultrasound use ToF, as well. These technologies have an additional requirement for line-of-sight and are generally useful for short distances only. Distances calculated with any of these are usually highly accurate.
Once distance calculations are obtained, the next step is to use an algorithm to determine the location. The most commonly used are triangulation and trilateration.
When looking at the entire expanse of solutions, there are variations providing improvements to accuracy. GPS is more precise when incorporating a Real-time kinematic (RTK) positioning technique, using a network of land-based reference stations. A combination of GPS and a technology called a Wi-Fi Positioning System (also vendor-supplied) improves results for mobile assets, with the WPS providing a location in places where GPS can’t (indoors or in areas with an obstructed view to the sky, for example).
Technology is advancing to provide improvements and new alternatives. New satellites launching over the next few years will make GPS more accurate due to advancements in technology and a larger number of satellites available. The Bluetooth 5.1 specification enhances location services with a direction-finding feature using a concept called “Angle of Arrival,” which purports to achieve sub-meter location accuracy with both direction and elevation measurements. The newest Ultra-Wideband offerings have demonstrated extremely accurate positioning in short-range, typically indoor environments.
Location determination isn’t the only consideration when selecting a wireless IoT technology, but if it is an aspect of what you need, make sure you have a clear understanding of the requirements. Suppose you have your wireless technology selection already made based on environmental and distance criteria, for example. In that case, the location accuracy needed may mean adding a component or service to your plan (like the RTK positioning enhancement for GPS referenced earlier).
There are quite a few other potential factors to weigh, including the need for asset tracking both outdoors and indoors, how often location needs to be updated, device battery life, etc. The key is being aware of all your options with their associated benefits, costs, and constraints.|