New project will develop safer, highly accurate GPS alternative

In a dense forested area, a drone scans the landscape below, helping firefighters spot the best place to fight a raging fire. But in the rural forested territory, the drone struggles to keep track of GPS as it flies through the natural environment, potentially losing its way. 

Ricardo Sanfelice, professor of electrical and computer engineering at UC Santa Cruz, and his team of graduate students and researchers are designing a new Position, Navigation, and Timing (PNT) system that will address this challenge, with novel methods to safely track and direct aerial vehicles in environments where GPS is weak. 

A grant from the Air Force Research Laboratory will provide about $100,000 in funding for the team to develop their resilient system that will improve tracking and navigation of aerial vehicles for search-and-rescue, emergency services, and more. This will provide huge benefits in rural environments and dense urban landscapes, where GPS is often ineffective because signals are blocked by obstacles such as dense trees or tall buildings.

The new system will provide information about where vehicles are by taking advantage of signals of opportunity – signals that come from already established infrastructure such as buildings, cell towers, or ground vehicles, but primarily from low-earth orbiting (LEO) satellites as the project is launched. 

“One of the things we are trying to do is find a way to fuse all sorts of signals of opportunity sources to create a better positioning structure,” Sanfelice said. “Signals of opportunity can be public or private services, AM/FM, Digital TV, 5G, aircrafts, satellites – they can come from a myriad of different assets.” 

The researchers involved, including Research Associates in the UCSC Cyber-Physical Systems Research Center (CPSRC) Marc Weiss and Charles Barry, also intend for their new system to be used even in areas where GPS is present, because GPS can be intercepted and modified – a type of falsification called spoofing. 

In contrast, the new PNT system will be much more resilient to information security attacks, as it would be much harder to intercept the low earth satellites used for signals. In the future, when the signals of opportunity expand to more infrastructure, the evolving security needs will be a point of further development. Sanfelice notes that, in the future, systems such as these will require the establishment of protocols or accreditation to ensure that they are used responsibly. 

Through a meticulous mathematical analysis of timing and delay, the engineers can extract the relative distances between the objects providing the signal of opportunity and the object being navigated or tracked. With four or more signals of opportunity, the researchers are able to triangulate the object being tracked. The researchers aim to make their system accurate down to below a meter – more accurate than most smartphones.  

Using signals of opportunity is a novel concept for PNT systems and is a growing area of interest in the cyber-physical systems research community. Including new sources and LEO satellites into these networks will greatly improve accuracy.  

The research team will be primarily focused on creating mathematical models for the PNT system, simulating the system, and designing and deploying an algorithm on a programmable radio where signals will be received. They will build these systems using off-the-shelf components, rather than building specialized receivers and computers.

The team will test their system on an electric car, which is currently being developed, that will traverse the main UCSC campus. UCSC’s wooded terrain will provide an ideal setting to assess the system, as it will have to navigate through the obstruction from a mix of campus buildings interspersed in thick wooded areas with weak GPS. 

“It’s a very good setup to test the accuracy of our positioning system,” Sanfelice said. “We definitely want to test it here on campus, because it will be a great benchmark – it’s fantastic that this project is well connected to the local geography.”

Weiss has a lifetime of experience in GPS, having worked in the National Institute of Standards and Technology (NIST) Time and Frequency Division for thirty years, supporting the development of GPS and specializing in analysis and predictions of clocks and PNT systems. Barry has exploited signals of opportunity to provide PNT in large cities where GPS can be blocked by tall buildings (and inside these buildings where GPS cannot reach).

Graduate student Aaron Monajjemi is implementing an advanced 3-D positioning algorithm in Python and comparing its reliability and accuracy compared to GPS. Graduate student Shashwat Pandey is using a GPS simulator to validate the positioning algorithm's ability to pinpoint satellites as they orbit the Earth.