Spotlight on Multipath Fingerprinting Technology

GPS World
July 22nd, 2009

In past columns, I covered Skyhook, TruePosition, WirelessWERX, and Andrew Corporation's efforts to produce indoor location positions for E9-1-1 or commercial location-based services (LBS). The spotlight today is on Wireless Location Signature (WLS), a multipath fingerprinting location technology offered by Polaris Wireless.

WLS is a software-only solution, so it does not require radio hardware at the base station or handset. Nor does it require special software or Wi-Fi on the handset or GPS/A-GPS chip support on the handset. That makes it unique among its competition. Despite its lack of infrastructure and handset requirements, Polaris hasn't broken into the large U.S. Tier 1 carriers, but has captured small carriers. They report use by 20 networks covering 11,000 cell towers.

Polaris can identify a handset location by pattern-matching locations using a series of unique measurements, including server and neighbor cell signal strengths, time delays, and other network parameters. The layers of its WLS solution include local GIS data, a carrier's cell network data, and unique multipath data. These measurements are aggregated into a "signature" at the Polaris location server, where they are matched against a prediction database to determine the handset's location.

Did someone say road trip? Collecting multipath data requires drive testing. In an urban environment every road stretch is driven upon deployment, and usually annually. Suburban and rural roads, which are less "noisy" and more static, don't require the same intensity of driving, but the demands are still significant. Sometimes the carrier will add the Polaris requirements into drive testing that they already perform, but it doesn't always work out that way.

The WLS system works best in high cell density, cluttered environments, such as urban and indoor areas. In these environments, measurements from many base stations can be made, and shadowing effects make the radio signatures unique. WLS capitalizes on the complex obstructions in shadowing environments to improve location performance.

In less populated areas where base-station densities are low, WLS is challenged. Martin Feuerstein of Polaris Wireless says in those situations a hybrid solution of WLS and GPS performs well.

Polaris Wireless self reports location accuracy performance in urban areas, "as better than 50 meters for 67% of cases. In indoor urban settings, WLS performance is typically 60-70 meters at 67th percentile. For suburban environments, WLS is better than 100 meters for 67% of cases. For rural and sparse rural settings, results vary considerably depending upon the cell spacings and topologies." For a hybrid of WLS and A-GPS, the company reports accuracy "typically within 50 meters for 67% of cases across the range of urban, suburban, rural, indoor and outdoor settings."

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