Bench Talk

Realizing the full potential of location-based services requires much better indoor accuracy than is available today. As Global Positioning System (GPS) doesn’t work indoors, the only alternative is Wi-Fi, but Wi-Fi’s accuracy is too low to provide the precision that many services require. Fortunately, there appears to be an indoor location solution that Wi-Fi will soon deliver: IEEE 802.11mc (better known as Wi-Fi round-trip time, or RTT), which can increase accuracy to 1m while providing vertical (Z-axis) location information that has been long awaiting a solution. It is making its debut later this year in the Android P operating system and probably in an update to iOS 11 as well.

Wi-Fi RTT operates according to the Fine Timing Measurement (FTM) protocol within the IEEE 802.11-2016 standard that uses a variety of techniques to pinpoint the location of someone’s smartphone or tablet. Although 802.11mc has been in the works for years, it was formally announced early in 2017 by the Wi-Fi Alliance^®, who calls the capability a “Wi-Fi Certified Location,” (the logo for which manufacturers can paste on their products after meeting compliance requirements). It’s a major enhancement to Wi-Fi Location, which currently relies on measuring signal strength or a technique called fingerprinting, both of which have disadvantages. For example, signal strength varies dramatically especially when the target device is moving, and fingerprinting accuracy depends on a stored database of signal strength for known areas.

However, Wi-Fi Location is not a simple add-on but a major update that requires reconfiguring existing access points, Wi-Fi systems on chips (SoCs) (and the access points and routers that use them), and apps to exploit the new feature. To achieve all its goals, Wi-Fi Location will require every access point to include its exact location, including precise latitude, longitude, and altitude coordinates.

It should be worth the wait, which could be lengthy, for all this to occur. For example, Wi-Fi Location allows indoor, turn-by-turn wayfinding with accuracy at about 1m and potentially less. So, it’s realistic to assume that Google Maps™ and later Apple Maps will incorporate it. For anyone (myself included) who has gotten lost in a hospital or some other huge, convoluted structure, the app can provide step-by-step directions until we reach our destination. I (for one) can’t wait.

Its high accuracy also makes asset management possible, such as locating forklift trucks in warehouses, “missing” wheelchairs in airports, and roving portable diagnostic equipment in hospitals. Another application is geofencing in which Wi-Fi Location creates a virtual perimeter that when breached triggers an alert. It also has the potential to compete with applications like Google Nearby and other Bluetooth^®-beacon-centric approaches for use in public parking, street lighting, security cameras, and other places as well as for targeted location-based marketing.

However, its greatest strength may be in its promotion of public safety. Right now, the ability of first responders to respond to 911 calls from smartphones is a huge problem for several reasons. First, none of the currently available solutions provide three-dimensional location capability (Figure 1)—that is, left, right, horizontal, and vertical (Z-axis). Using various techniques such as identifying the base station from which a 911 call comes in, it’s only possible today to achieve a two-axis location and, even then, with accuracy within about 100m. This information is available only outdoors, as indoor cellular infrastructure currently has limitations in these places.

Figure 1: Precise positioning requires pinpointing a location using three axes, which is extremely difficult to achieve indoors in the vertical direction, a problem Wi-Fi Location hopes to solve. (Source: Wikipedia)

First responders didn’t have this problem before mobile wireless devices proliferated because calls invariably came from wired telephone connections of which the locations were easy to pinpoint almost instantaneously. However, about 70 percent of 911 calls today come from smartphones that can be anywhere rather than tethered to a wall jack. Public safety answering points (PSAPs) must rely on what base station handles the call and possibly Wi-Fi. Accuracy is too imprecise to allow first responders to reach their target location in time to make a difference in the outcome, and if the caller is in a multistory apartment building, there’s no way to determine what apartment or even what floor the call came from without vertical position information. Obviously, something needs to change.

The likelihood of solving this problem is increasing as AT&T^® deploys the country’s first Nationwide Public Safety Broadband Network in the next few years. Among its many goals is to deliver superior location-finding capabilities indoors and outdoors, and AT&T is exploring various techniques. Although the new Wi-Fi Location capability does not focus on public safety, it’s almost certain that it will be part of the solution, as it relies on the ubiquity of Wi-Fi and the ability to deliver location information in all three axes—indoors.

Google unveiled Android P during the Google I/O 2018 conference on May 8–10. However, the ability to take advantage of Wi-Fi Location depends on several things, including how long it takes owners of Wi-Fi access points to upgrade configurations, whether your smartphone or tablet has any of the Wi-Fi Certified Location chipsets, and how quickly apps take advantage of the technology. Of the three, only the chipset question is not in doubt—along with the routers that use the chipsets—as there are devices available from Intel^®, Marvell^® (whose first was introduced in 2015), Qualcomm^®, MediaTek, and Realtek, with more suppliers surely to come.