Gao Brings GPS Expertise to AE
Currently a Research Associate in the Global Navigation and Satellite Systems Laboratory at Stanford University, Gao has gained a reputation in sorting out and identifying the myriad of signals beaming down on Earth from GNSS systems. These include not only the established GPS system of the United States and GLONASS of Russia, but also newer systems: COMPASS of China and GALILEO of the European Union.
Some of the signals transmitted by these satellite systems are only as powerful as a 50-watt bulb shining from 12,000 miles away. And, just like AM radio stations, their reception becomes more jumbled the more crowded the frequencies get. On the other hand, more satellites and signals from the new systems can bring better accuracy and more redundancy to the GPS system. That’s where engineers like Gao come in.
“I work on how the systems can work together,” she said. “By making the systems more redundant, we can make GPS more robust against errors.”
The various countries realize the value of coordinating their work. Gao attended and helped produce a report of a meeting in Shanghai in May 2011, in which scientists from the U.S. and Chinese National Academies of Engineering sought coordination between GPS and COMPASS. Gao feels fortunate to have been included in such important work.
“I think I’m quite lucky in this way,” she said. “It is the right time as China is at the developing stage.”
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.
Gao emphasizes that satellite navigation is not just for getting us from one place to another. It plays pivotal roles in many aspects of our normal, everyday lives:
- Navigation systems are key for synchronization in cell phone use.
- Navigation systems provide precise timing in transactions such as buying and selling stock.
- Phasor measurement units (pmu) employ GPS to synchronize power grid operations.
- Farmers use GPS for precise placement of fertilizers and seeds. Gao said that, without GPS, fertilizer applications tend to overlap by 10 percent, while precision is within centimeters using GPS. Also, farmers can now work at night or in fog, thus substantially reducing the number of tractors required.
- Continued research into GNSS applications could reduce air traffic delays and fuel consumption. The next generation of ATC is expected to fully depend on GNSS.
Gao used her own experience in traveling to the Urbana campus this summer as an example of how a further-developed navigation system might have improved her trip. “My plane was delayed because of fog in San Francisco,” she said. “I got to Chicago at 2 a.m., and Champaign at 5 a.m.” With improved GPS technology, Gao maintains, “GPS would enable better capacity of runways and would reduce delays.”
Planes now fly in a stair-step pattern when they go up and come down. Gao said satellite navigation can help smooth an aircraft’s ascent and descent, reducing the amount of fuel needed. “Air traffic controllers can know exactly where to route airplanes in real time,” she said.
An issue that currently impedes airports’ reliance on GPS is the use of unlawful personal privacy devices, which are inexpensive appliances that jam GPS signals. In her research, Gao is investigating the impact of such devices by using live data collected at Wide Area Augmentation System (WAAS) reference stations. She also is using multiple networked GPS receivers to collaboratively localize the jammers.
Gao said some people mistakenly believe they can be tracked by GPS. “GPS is passive; it does not broadcast where you are,” she said. Cell phones that can trace users have added applications to provide that capability.
Mother Nature can also interfere with GPS signals, particularly when they pass through free electrons in the ionosphere. But navigation system scientists can turn this phenomenon to their advantage in their research. "If you can quantify this interference on the GPS signal, you can then characterize the ionospheric effect," Gao said.
Multi-technique remote sensing of the Earth’s ionosphere is an objective of Jonathan J. Makela, associate professor of Electrical and Computer Engineering at Illinois, who will be collaborating with Gao. This spring, Makela and Gao will co-teach a GPS class with applications for remote sensing.
Gao also plans to work with AE assistant professors Soon-Jo Chung and Timothy Bretl in applying GPS navigation to the development of unmanned, autonomous aircraft and formation flying.
Widely sought for a faculty position at a number of universities, Gao said it was Illinois’ collaborative atmosphere that won her over. “I interviewed at many places. I feel that here, the faculty are very supportive of interdisciplinary research,” she said. Gao believes this environment will help her achieve her ultimate goals.
“Long term, I hope to develop applications to produce a smarter transportation system,” she said. “I would like to reduce human error and make transportation more fuel efficient.”