One of the most important applications for wireless technology is location and tracking. The best-known innovation here is radar (which actually stands for radio detection and ranging) and the principles behind it go back well over 100 years. Modern life would clearly be impossible without radar in its many forms, from airplanes to cars.
Ditto for GPS (the global positioning system), that is—just like radar—absolutely vital in a huge range of applications.
And there’s another range of wireless positioning technologies that are at work in enhanced 911 (E-911) services on cellular networks – again, absolutely vital.
But there’s a key limitation in every case above: all of these systems and services are designed for use outside, and are not appropriate for indoor applications.
A different set of wireless technologies, and strategies, are required for in-building location and tracking. And, properly deployed, these can provide exceptional accuracy, rapid time to solution, excellent spatial resolution, and remarkably low cost, often based upon existing Wi-Fi infrastructure with unmodified client devices and no additional client software.
And why is indoor positioning so important? Let’s take a look at a couple of scenarios:
Suppose you’re at a conference and want to find a particular meeting room, or vendor in an exhibit hall, or the nearest taxi stand, or you simply just want to navigate the conference venue with minimal time and effort.
Suppose someone in a shopping mall has a medical or other emergency – a “panic button” app could be just what the doctor ordered. And, speaking of medical applications, how about immediately knowing the location of the nearest defibrillator or medical professional in a hospital?
Let’s not stop there. Assisted-living facilities. Location-based services. Even location-based advertising. In-building location and tracking is more than just convenient, then – it’s a vital, vibrant, exciting complement to in-building wireless communications.
There are two key technologies at work here, and the first as we noted above is Wi-Fi.
Almost everyone carries a Wi-Fi-enabled device, and, whether connected to the local wireless LAN or not, the signals emitted can be used to localize and track any device with Wi-Fi enabled.
The most common technique here is the use of signal strength, which fades exponentially as radio waves travel from transmitter to receiver. Radio waves can also fade due to interference and other factors. But, if enough samples of a given signal are taken we can end up with an inference as to where a device is, how fast it is moving, and in what direction.
Key to this calculation is triangulation, which starts with a signal from a client device received by multiple access points. Add in some mathematics, and we can obtain location and tracking information with very good accuracy—down to one square meter in many cases.
It’s also possible with Wi-Fi to use more sophisticated technologies that ignore the vagaries of signal strength, including time distance of arrival (TDOA) and angle of arrival (AOA).
Both of these involve a radio signal sent from the device being tracked and received by multiple access points. TDOA uses the constant speed of light and a little math to triangulate in this case. AOA actually senses the direction of radio waves. The processing involved here is more complex, and neither is in wide use in Wi-Fi solutions today.
But both of these technologies have been applied to E-911, and a variant using round-trip timing, is now under consideration in a new 802.11 standard, 802.11az. Yes, a new standard. That’s how important in-building location and tracking have become.
The second key technology, which is rapidly gaining popularity, is the use of Bluetooth Low Energy (BLE) beacons.
Beacons operate in the 2.4 GHz. band also available to Wi-Fi. Beacons also use signal strength to determine range, and this is about as simple as it gets: each Beacon transmits a unique identifier, which is received by an app running on a mobile device.
Since Beacons are designed as infrastructure and do not move, the app can use Wi-Fi (or even another wireless network) to access a database to determine the physical location of each Beacon, and thus the location of the client device.
The app can report the estimated distance between the Beacon and the device. The use of multiple Beacons enables a form of triangulation, and thus the potential for good accuracy. And while a significant number of Beacons may be required in a given venue, they are individually inexpensive.
Since Beacons are based on BLE, their battery life is excellent - some vendors quote up to three years. And with and increasing number of mobile devices equipped with BLE and Wi-Fi, the use of Beacons is rapidly gaining popularity.
Which of these two alternatives is better? It can be argued that the Wi-Fi solution is superior because Wi-Fi service is well on its way to ubiquity indoors, and the cost of the additional infrastructure required is negligible when compared to the total cost of the Wi-Fi solution.
Assuming the installation of a large number of Beacons, though, one could obtain performance very similar to that of Wi-Fi in terms of both spatial and temporal resolution.
But we’ll still argue that Wi-Fi will remain the preferred solution over time, given the increasing density of APs deployed in response to the demand for more communications capacity, and the cost (equipment and labor) involved in deploying what might be a very large number of Beacons indeed. Hybrid Wi-Fi/Beacon location and tracking solutions will also see service.
Regardless of the specific technology selected, in-building wireless location and tracking will become common over the next few years.
Who could live without GPS today? With little more end-user experience, exactly the same will be said for in-building location services.