Gao's GPS research points to more reliable, secure systems

The Global Positioning System (GPS) does more than get you from point A to point B. It also serves as the backbone of many critical systems, ranging from the power grid to the stock market, that are essential to daily living and economic prosperity.

CSL’s newest researcher, Grace Xingxin Gao, is helping to develop a secure and reliable framework for such capabilities. An assistant professor of aerospace engineering, Gao’s work focuses on building collaborative multi-agent Global Navigation Satellite Systems (GNSS), such as the United States’ GPS, that enable new breakthroughs while creating more robust, reliable, secure and accurate systems.

Such systems consist of satellites (the United States has at least 24 in operation at any given time, according to gps.gov) and receivers, which may number in the thousands. Gao’s challenge is to better coordinate the receivers – and the data they receive and generate – to maximize the system’s cooperative positioning, navigation and sensing capabilities.

“Most people think of GPS as just a positioning device, but GPS is actually capable of timing and sensing as well,” Gao said. “It is essential in critical systems where timing is imperative.”

For example, GPS synchronizes phasors for the power grid, cell calls between towers, and transactions for high-frequency trading on the stock market. Because it’s available to anyone with a receiver – most cell phones sold in the U.S. have some sort of GPS receiving capability – it’s a nearly ubiquitous technology with widespread applications.

But it comes with several limitations. The GPS civil signals are vulnerable to jamming and spoofing, the act of tricking a GPS receiver by broadcasting a more powerful signal than generated by GPS satellites. In addition, the signals are not particularly robust, originating from satellites orbiting 20,000 kilometers above the earth’s surface and projecting a power output of about 50 watts, akin to a home light bulb shining from outer space.

Gao’s research is addressing these challenges in several ways. She is working to improve the security of GPS for power grid systems with the Illinois-based Trustworthy Cyber Infrastructure for the Power Grid. Phasor Measurement Units (PMUs) employ satellite signals to measure the phasors of electricity waves and sync input for the power grid system. Gao aims to reduce the ability to spoof PMUs, which could cause the power grid to become unstable.

She’s also working to improve the availability of GPS signals in unfriendly environments such as urban canyons. This requires establishing strong coordination between receivers and determining what type of data to share. On a high level, receivers can exchange location information. On a low physical level, receivers can share raw data.

“The challenge is how to select the receivers you want, what type of data you want from them and how frequent the communication exchange should be,” Gao said. “If some receivers are malfunctioning, it becomes especially tricky because bad information isn’t helpful.”

Cooperation between receivers is also critical in turning GPS into a sensing tool. Gao has used the technology to profile the wind velocity and distribution within a wind farm, helping wind “farmers” understand when it’s most cost-effective to produce wind power. Similarly, GPS could be used to sense arctic ice. The error sources of GPS are challenging from a positioning perspective, but helpful from a sensing perspective as they can be used in reflectometry, which monitors the earth’s characteristics.

Gao has a rich history in the technology. She came to the University from the renowned GPS Research Laboratory at Stanford University, where she was a PhD student and then a research associate.

Having earned a bachelor’s degree in mechanical engineering in 2001 and a master’s in electrical engineering in 2003, both from Tsinghua University in China, Gao was introduced to GNSS through her doctoral work in electrical engineering at Stanford, where she earned her PhD in 2008. Her breakthroughs in the field had such impact that she received the Institute of Navigation’s (ION) Early Achievement Award for 2008. A year later, she was awarded the William E. Jackson Award by RTCA, the U.S. aviation standards organization. She was also named as one of the 50 GNSS Leaders to Watch by GPS World Magazine. She has won a number of ION GNSS Conference’s Best Presentation and Best Student Paper awards. Most recently, she was elected to be an ION council member. She serves a two-year-term as an air representative for ION.