TruePosition released testing results of its indoor location technology in April (press release). These tests put the company squarely into the Federal Communication Commission explorations of indoor locating for emergency response. Rob Andersen, chief technology officer of TruePosition, descibes the company’s technology and plans for the future.
Rob Andersen (RA): U-TDOA is a network-based location technology. It calculates location by analyzing the cellular signal sent by the handset. Although it only connects to one cell tower, a cellular signal touches many towers. By comparing the length of time the signal takes to reach multiple cell towers, an accurate location can be determined. Because the calculation is done by equipment installed on the network, no additional chip or software needs to be installed in the handset, and any handset can be located. Simply stated, if your phone is connected to the network, it can be accurately located. Therefore, unlike A-GPS, U-TDOA works well in all environments, including inside buildings, in densely forested areas and in urban canyons.A-GPS uses an antenna and chip within the mobile phone to receive signals from orbiting satellites. Assistance data is provided by the cellular network to improve the time to first fix. A-GPS does not work well indoors or in cities with tall buildings – due to line of sight issues. Most, but not all, cell phones are GPS-enabled (legacy phones, etc.).A hybrid location is produced by initiating both a U-TDOA location and an A-GPS location at the same time. When both the U-TDOA and A-GPS locations are computed, an uncertainty value is computed for each technology. The uncertainty value provides an estimate of the accuracy of the location. The hybrid solution is generated from a weighted average of the individual latitudes and longitudes returned by the A-GPS and U-TDOA solutions.
RA: Yes. TechnoCom Corporation, the same company that conducted indoor location accuracy testing for CSRIC in San Francisco, worked with AT&T and True Position to test the capabilities and performance for indoor location accuracy of U-TDOA technology in Wilmington, Delaware. The characteristics of Wilmington replicated to a large degree the characteristics of San Francisco. U-TDOA technology is fully deployed and updated in Wilmington, allowing for complete and accurate testing of the technology in that location.Although the San Francisco network was fully-compliant with outdoor location accuracy requirements, the commercially deployed U-TDOA network in San Francisco was not suitable for indoor testing for reasons including:1. It supported 2G only2. It was deployed and configured to support current outdoor requirements3. It is a legacy system with decreasing investment and lower LMU (Location Measurement Unit) density than would be deployed for 3G and 4G
RA: Although NextNav reported a vertical location, NextNav’s beacon-based location technology does not itself purport to provide vertical (z-axis) location data. In its CSRIC test, NextNav collected vertical location information by installing a stand-alone, “off the shelf” barometer in its test equipment, and calculating the altitude based on changes in barometric pressure. This is not a proprietary solution and can be installed by handset manufacturers regardless of the underlying horizontal location technology in use.
RA: That technology, which is now referred to as TrueFix, is alive, well and under further development. It is similar in general approach to the NextNav solution, but relies on existing DTV transmissions (so no spectrum interference issues). Some additional transmitters may be required to increase accuracy in certain areas, but the bulk of transmission resources are already in place. We hope to release accuracy data in the near future.
RA: As it relates to the U.S. E-911 system, U-TDOA is currently deployed on AT&T’s and T-Mobile’s 2G (GSM) networks, and is already protecting the millions of AT&T and T-Mobile customers who dial 911 from their wireless phones, making it easier and faster for first responders to find them indoors. Moreover, as indicated, U-TDOA can easily be paired with existing A-GPS capabilities in a “hybrid” solution – a solution that will provide accurate locations with nearly 100% yield in all environments.However, as carriers make large investments to upgrade their networks, they are making long-term decisions right now about the future of their E-911 location capabilities. As the wireless carriers replace 2G hardware and move to 3G and 4G, they have no commercial incentive to continue current or improve indoor E-911 location accuracy. This is why the FCC is gathering data to determine the best way to proceed to address the problem.