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CUE 2004

AEROSPACE ENGINEERING SCIENCES
Advances in GPS Receivers Set Stage for Better Aircraft Landings

Assistant Professor Dennis Akos joined the department in January, adding to the already strong research effort in Global Navigation Satellite Systems.

The Global Positioning System (GPS), or the broader Global Navigation Satellite System (GNSS), has changed the way we navigate by air, land, and sea. Now these systems are taking a quantum leap forward with advances in receiver technology.

Dennis Akos, a new assistant professor in Aerospace Engineering Sciences, is applying software radio design principles to GPS and other navigation systems, turning the "black box" into a software receiver. Exchanging hardware for a programmable processor means that a receiver can take advantage of whatever navigation system works best for a particular application. This flexibility was made possible, in part, by the increasing speed with which we can now process information. For the last 30 years, processing power has doubled about every 18 months, resulting in microprocessors with more than sufficient computational power for the spread spectrum modulation format of the GPS signal.

Using reconfigurable rather than fixed hardware allows the receiver to adapt to a specific environment and extracts optimal performance from the receiver. The ability to obtain precise positioning (at the 5m level or better) and timing (on the nanosecond level) is a technology that is critical to many fields, from aviation to search and rescue.

Next-generation aircraft landing systems will depend upon signals from satellites instead of the current ground-based navigational aids. Akos" research into software-based GPS receivers has been critical in establishing whether or not GPS will provide the necessary accuracy and integrity for such operations. His GPS software receiver is currently being flown on the Boeing 777 to evaluate multipath, or distortion, of the GPS signal resulting from reflections off the aircraft structure.

"Such observability is only available using the unique software radio-based receiver architecture," he says. "Demands for aircraft landing are incredible—imagine the challenge of using signals from orbiting satellites to obtain navigation and position information capable of landing aircraft automatically."

Akos" research covers all aspects of the GNSS receiver from antennas, analog signal conditioning, and digital signal processing to the resulting position solution algorithms. With his software radio ties and RF background, he also has been quite active in radio frequency spectral issues, such as ultra-wide band communications and many aspects of wireless communications.

Akos earned his Ph.D. in electrical engineering from Ohio University, where he focused on GNSS receiver technology applied to aviation. He then served on the faculty at the Luleå University of Technology in Sweden and at Stanford University before coming to CU-Boulder.

aerospace.colorado.edu/

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