FirstNet Evaluating Key Indoor Location Technologies to Help Solve 'Z-Axis’ Challenges for Public Safety

June 29, 2015
FirstNet is moving forward on researching and analyzing different indoor location technologies at its technical headquarters in Boulder, Colorado.
FirstNet is moving forward on researching and analyzing different indoor location technologies at its technical headquarters in Boulder, Colorado.

Jeff Bratcher, Acting Chief Technology Officer

If you’ve ever tried to use a mobile device’s location-based functions in a densely built high-rise building, you know that it can often be inaccurate. The necessity for vertical location identification (height above or below ground level) is even more critical for first responders. When public safety personnel are responding to incidents in dense urban environments, the ability of incident commanders to track firefighters as they ascend in a tall building or law enforcement in below-ground subway systems would be extremely helpful to response operations.

Commonly referred to by location-services industry experts as the "z-vector" or “z-axis” or “3-D Geolocation,” its solution is a complicated issue for both the public and private sectors. With that challenge in mind, FirstNet is exploring ways to provide these types of location services for public safety personnel.

As FirstNet Vice Chair Jeff Johnson explains, FirstNet views in-building coverage as a critical part of public safety’s needs in the field. “To that end, I think FirstNet is going to have a big obligation in terms of laying out the technical expectations of what the network expects and that will bring people to design around that ecosystem,” he says.

FirstNet is moving forward on researching and analyzing different indoor location technologies at its technical headquarters in Boulder, Colorado. Below are some of the areas of focus:

  • Barometric or atmospheric air-pressure sensors: These sensors are now being placed within mobile devices and can assist in estimating z-axis location or altitude. This is similar to how an air-pressure altitude meter (or altimeter) determines a plane’s altitude. However, these sensors can be affected by local conditions and environment, and thus require periodic calibration.
  • Terrestrial location service beacons: High power terrestrial beacons are able to penetrate buildings and structures that normally block conventional Global Navigation Satellite System (GNSS) signals such as GPS. The key purpose of these beacon systems is to maintain a baseline calibration for the mobile barometric pressure sensors. Such terrestrial beacon systems are deployed for development and test scenarios in many areas already.
  • Uplink Time Difference of Arrival: This is a network based location measurement technique that utilizes specialized receivers deployed at cell sites to measure uplink transmissions from devices and determine their location. This technique is in use today to determine the X, Y axis geo-location or the location of a device in many commercial cellular networks.
  • RF pattern matching: The network can also determine the mobile device’s location based upon measuring the downlink signal level received from multiple cell sites and matching this information to a database of RF patterns within the network. This approach is also currently used to find the X, Y axis geo-location in many commercial cellular networks.
  • Smart building technology: Wi-Fi and Low Energy Bluetooth devices are deployed within structures that broadcast location information which can be accessed by mobile devices. The information would normally include the address within the structure where the Wi-Fi/BT device is deployed.
  • OTDOA (Observed Time Difference Of Arrival): A positioning feature introduced in 3GPP LTE Release 9 in which the mobile device measures the time difference between downlink positioning reference signals broadcast from multiple cell sites. The downlink measurements are provided to a location server within the network where the device location is calculated.

A new generation of location technology could collect altitude data from smartphones, tablets, dongles and other devices to not only enhance emergency response efforts, but spur innovation as industry looks to develop solutions for such a critical need. FirstNet Acting Executive Director TJ Kennedy believes z-axis location accuracy is the “holy-grail” for firefighters and other public safety personnel. “FirstNet takes that very seriously, that’s why we’re actively analyzing potential solutions,” he says. “Solving it will improve operations and the safety of our nation’s first responders.”


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