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Grace Xingxin Gao: Amazing Grace

A Hot Start for a Young Engineer from China’s Ice City


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Gao’s coordinates:
37.428178, -122.172173

SIDEBAR: Grace Gao’s Compass Points

Imagine that your only light source is a 50-watt bulb. Visualize it shining at you from 20,000 kilometers (about 12,000 miles) away.

That’s about how weak the signals are from the new Galileo and Compass satellites, and that’s why Grace Xingxin Gao’s accomplishments in being the first to derive the code generators for both systems are so amazing.

Now that GPS is no longer the only game in space, it’s crucial to manage the mushrooming number of signals that will beam down on us from new GNSS systems. Gao’s work already has driven development of new receivers capable of acquiring and tracking these signals.

In the future, each satellite will generate multiple signals, creating possibilities for new applications and products we’ve yet to imagine.

A research associate at the Stanford GPS Laboratory, Gao received her doctorate from Stanford University last September, just four years after arriving in the United States from China.

The 28-year-old electrical engineer was a stranger to GNSS when she came to Palo Alto in 2004. However, her breakthroughs since being introduced to the field by GPS icon Per Enge, professor of astronautics and aeronautics and director of Stanford’s GPS Research Laboratory, already have had such impact that she received the Institute of Navigation’s Early Achievement Award for 2008.

Just one year earlier, as an ION GNSS sponsored student, her paper received both the Best Presentation Award and the Student Paper Award.

Enge said Gao is among the most impressive people ever to survive Stanford’s tough rite of passage known as the Ph.D. Qualifying Exam in electrical engineering, an ordeal involving 10 one-on-one interviews with faculty members in a single day.

“I was stunned by her cool and comprehensive answer to my question,” Enge recalled. “I later learned she had been in the U.S. for only four months. She finished in the top few percent of students. Fortunately, she subsequently asked to join the GPS Laboratory, and her colleagues here and in the larger navigation community are the richer for it.”

The More Signals, the Merrier
Gao remembers being struck by the warmth of Enge’s personality. She said that, when he invited her to visit the lab, what she saw captured her curiosity, and GNSS became her calling. The next thing she knew, she was immersed in efforts to understand the signals of the new GNSS systems, which may contribute to a total of about 120 satellites in the future.

“When there are more satellites it can be the more the merrier,” Gao said. “On the other hand, the satellites share or partially share the same frequency bands, so it’s also more crowded.”

Greater numbers of satellites increase redundancy, which is a good thing because if one fails, you still have the others. However, much as AM radio stations with closely neighboring frequencies interfere with each other in the wrong conditions, the new satellite signals will drown each other out unless they are managed.

“The satellite-transmitted power is less than 50 watts and the satellites are about 20,000 kilometers above the Earth,” Gao explained. “We already use a high-gain antenna but the signal is still buried in noise. The signal structure is so complicated. For example, the satellites are moving so there’s the Doppler effect, and both the satellite and the receiver clocks may drift.”

Separating the code from all that noise required every bit of the competitive intensity that helped Gao excel academically in China and the United States. However, she says the collaborative culture of the GNSS research community has become far more important to her than the drive to be first.

“To do anything, even just pure research, I need a lot more skills than just getting a good score or being smart,” she said. “I need help. I need people I can discuss the problem with.”

Three Code Breakthroughs in Three Years
Gao uncorked the code for Europe’s first prototype satellite for Galileo, named GIOVE-A, within weeks after its signals became active in January 2006. She derived the underlying algorithms that generate the codes so that she could decode its signals on all three frequency bands.

“I was very excited,” she recalled. “I stayed up every night. I even dreamed about the code, and I would try something else when I woke up. I’m very grateful that I had wonderful mentors and colleagues to help me.”

The following year, in April 2007, China launched the first medium earth orbiting satellite belonging to their Compass system.

Using her new techniques, Gao blitzed through demodulation of the Compass-M1’s civil codes in all three frequency bands, proved that all Compass-M1 codes are Gold codes, and derived their code generators as linear shift feedback registers. Then she applied the codes in a software receiver for the Compass-M1.

Last year in April, when the Europeans launched GIOVE-B, a pre-production prototype satellite for Galileo, Gao again was the first to discover the underlying code generators.

Growing Up in “Ice City”
Gao grew up in Harbin, an ancient Chinese city of about ten million located within 300 kilometers of Russia and nearly as close to Korea and Japan as well. Known as “Ice City” and likened both to Moscow and Paris, Harbin ranks among the world’s foremost centers of snow and ice culture.

With China’s best ski resort and a host of sparkling new venues built to Olympic specifications, Harbin has designs on the 2018 Winter Olympics.

This year’s 25th annual Harbin Ice and Snow Sculpture Festival featured a life-size frozen replica of Disneyland plus a 525-foot-wide sculpture of Santa Claus’s head. By comparison, the faces of U.S. presidents carved into Mt. Rushmore are only 60 feet high.

As a child, Gao was inspired by some unusual feats of engineering during winters with temperatures as frigid as minus 35 degrees Celsius (-31˚F).

She remembers making her own ice creations while the adults cut enormous ice blocks from the river in the center of Harbin. They created fanciful structures four and five stories high, wired for electricity, and unbelievably colorful at night.

A Father’s Dream
Gao’s father had dreamed of becoming an engineer from boyhood, a dream crushed by the social and political upheavals of China’s Cultural Revolution in the mid-1960s and 1970s. He was in middle school when all schools were closed and students were sent to work on farms.

Although her father didn’t pressure her to pursue the career that he had missed out on, Gao says he encouraged her interest in engineering at every turn. And it is normal for Chinese girls to excel in math and science. “In China, when I grew up, smart kids preferred engineering,” she said.

When she began her undergraduate studies at Beijing’s Tsinghua University — China’s MIT — Gao decided to choose an English name because her American friends had difficulty saying her Chinese name, Xingxin (pronounced “shing-sheen”). “I chose Grace because of its meaning,” she explained.

“In Chinese culture, people care mainly about what names stand for,” Gao adds. The Chinese characters for her name are “高醒心.” The first character, 高, is the family name Gao, which means “tall” or “high.” The last two characters are her given name. 醒 (Xing) means “awake” or “sober” and 心 (Xin) means “heart.”

After earning her bachelor’s and master’s degrees—and numerous awards, including recognition as the Exceptional Graduate of Tsinghua and Exceptional Graduate of Beijing—Gao joined IBM’s China Research Laboratory as a research engineer.

California Dreaming
“I realized I really like doing research,” she said. “I came to the United States because I wanted to see the world and to know different cultures.” She had many offers, but chose Stanford because of its reputation, a terrific scholarship, and California’s balmy climate and cultural diversity.

Three years ago she met her husband, David Varodayan, a fellow Ph.D. candidate in electrical engineering, while accompanying mutual friends on a road trip to Oregon.

As they took in the sights from California’s Mt. Lassen to Oregon’s Crater Lake, she learned they had taken some of the same classes. They’d even been assigned to the same small study group, but hadn’t met in person because somehow both never showed up in person at the same time.

“We complement each other,” Gao says of the relationship, “At the same time, we share many common interests. The kitchen is our favorite place to discuss research.”

While Varodayan completes his doctorate, Gao is keeping her options open and looking forward to starting a family.

Meanwhile, she continues to collaborate with colleagues around the world working on the GPS Evolutionary Architecture Study. Her projects involve analyzing the overall performance and the potential for interference among multiple GNSS constellations. She also is helping build a system to monitor GNSS in real time to detect issues such as power failure and changes in signal transmission.

“There are always new problems and challenges,” she said.

Editor’s note: Three articles reflecting Grace Gao’s work in decoding GNSS signals have appeared in Inside GNSS with her as a coauthor: “GNSS Album: Images and Spectral Signatures of the New GNSS Signals,” May/June 2006, “GNSS over China: The Compass MEO Satellite Codes,” July/August 2007 and “GIOVE-B on the Air: Understanding Galileo’s New Signals,” May/June 2008.

Human Engineering is a regular feature that highlights some of the personalities behind the technologies, products, and programs of the GNSS community. We welcome readers’ recommendations for future profiles. Contact Glen Gibbons

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