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The US Department of Transportation recently tested various Positioning, Navigation, and Timing technology solutions as potential GPS backups, and detailed their findings in a report published on January 14, 2021. Skyhook was selected to compete in the testing and demonstrated a high technology readiness level, low cost deployment, and strong accuracy results. 
 

Department of Transportation study of GPS alternatives

Skyhook was selected as one of 11 companies to demonstrate to the Department of Transportation technologies that can complement a Global Positioning System (GPS). Skyhook submitted its Precision Location System technology for demonstration. Skyhook participated in several scenarios including dynamic outdoor positioning, static outdoor positioning, static indoor positioning and airborne 3D positioning. 
 
The intent of this demonstration was for the federal government to explore commercially available technology in order to understand the current solutions that can serve as a back up to GPS technology, as Federal departments and agencies have been depending on GPS since 2001. 
 

Vulnerabilities of GPS 

GPS is vulnerable to disruptions as it relies on signals from satellites, and does not return an accurate location when it does not have a clear signal to the sky. GPS is at risk to threats such as jamming and spoofing, in which GPS signals are interrupted as a way of interfering with operations. Federal departments and agencies rely on GPS, as do businesses and consumers.  It was determined that a common denominator in reducing economic and safety risk exposures due to dependence on GPS, is to explore complementary PNT services.  
 

Skyhook’s Precision Location 

One of Skyhook’s many strengths is positioning with WiFi access points (APs).  In this test Skyhook demonstrated both power-based and timing-based WiFi location techniques. The power approach for WiFi ranging uses the Received Signal Strength Indicator (RSSI) of a passive transmission or a probe response from a WiFi AP, which is obtained at the device to be located. The timing approach for WiFi ranging uses the Round Trip Time (RTT) calculation, which is retrieved from an AP. RTT measurements are standardized in IEEE 802.11mc and require support from both UE and AP chipset. New UEs and APs are expected to support this feature widely in the future. In addition to 2D-positioning, Skyhook can provide vertical positioning by integrating a barometric pressure sensor in the UE. Combining raw pressure sensor measurements with RTT ranging measurements allows high precision 3D positioning.
 

Skyhook Testing Performance

The test was conducted in a NASA facility in Langley, Virginia.  The test included stationary and moving devices, indoor and outdoor scenarios, and drone flights. 
 
In order simulate a typical WiFi environment, Skyhook installed 17 sites (15 in the field and 2 indoor).  Each of the sites included a commercial off the shelf WiFi AP in a weatherproof box with a battery. 
 
Skyhook participated in testing on a drone aircraft system, pictured below, to collect 3D flight data. Data was collected throughout the demonstration area at up to 400 feet. 
 
Skyhook performed well in these tests, as shown in the following figures. To rate the performance of participants, subject matter experts used a measure of rubrics to asses the strengths and performance of technologies in various scenarios. The graphic representations below are the measure of effectiveness ‘scorecards created in the overall report. To highlight Skyhook’s performance, we’ve highlighted some relevant performance information below. 
 

Technology Readiness Level 

Only two vendors who competed had a technical readiness level (TRL) of nine, which is the highest rank available, in all positioning cases. This includes dynamic indoor, dynamic outdoor, indoor and airborne. The technology readiness refers to if a system can be demonstrated in the field, and if the service could be rapidly implemented. Technical readiness and accuracy of location data are essential when analyzing performance in these tests. 
 
 
 

Outdoor Positioning Accuracy

Four positioning scenarios were conducted during the demonstration: dynamic outdoor positioning with holds, static outdoor positioning, static indoor positioning, and airborne positioning, Skyhook performed the best in both outdoor positioning accuracy scenarios, with highly accurate performance specifically in static outdoor positioning. The static outdoor positioning scenario involved gathering data at three surveyed static points.

The figure below demonstrates Skyhook achieved location error accuracy below 1.8m for 95% of the time in the stationary outdoor testing across all scenarios. That level of accuracy indicates WiFi positioning can be as accurate as GPS in outdoor environment and not just indoor.
 
The figure below shows Skyhook Wi-Fi RTT accuracy in the dynamic outdoor test:
 

Service Deployment Effort and Cost Effectiveness

The demonstration considered the cost of implementation of a PNT service based on the technologies and the time and effort needed to execute the technology’s function. The subject matter experts from the government team observed the Federal acquisition process, demonstration site installation, the dry run of the demonstration, and the actual demonstration. Rating for the service deployment effort was assigned a low, medium, or high rank based on how much effort would be required for implementation. Skyhook’s solution had the lowest effort of deployment, even better than GPS, flexible integration offerings, and Skyhook’s availability as a global solution makes Skyhook a strong option. 
 

Conclusion

The DoT concluded that commercial technologies exist that could be used a backups to GPS. Their findings indicate that the best strategy for achieving resilient PNT service is to pursue multiple technologies to promote diversity in the PNT functions that support transportation and other critical infrastructure sectors.  Given Skyhook’s ease of deployment, accuracy, and international coverage, Skyhook is well positioned to be an integral part of a resilient PNT service.
 

Topics: Precision Wifi Location

   

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