A Phase-Reconstruction Technique for Low-Power Centimeter-Accurate Mobile Positioning
Recent technological advances in embedded systems have enabled designers of Global Navigation Satellite System (GNSS) receivers to produce ever smaller, cheaper, and more energy-efficient devices. However, despite these advancements, the underlying positioning accuracy of consumer-grade GNSS receivers (such as those in smartphones and tablets) has somewhat stagnated. The most notable advances in positioning accuracy have been occurring in non-consumer, industrial-grade receivers, for example, in receivers designed for agriculture and surveying purposes. So-called carrier-phase positioning techniques provide these receivers with centimeter-level positioning accuracy. However, carrier-phase positioning techniques currently have costs unfavorable to consumer-device implementations: they consume much more energy than traditional code-phase techniques and they require the resolution of so-called carrier-phase ambiguities, which extends the time for an initial positioning fix.
Considering these challenges, WNCG graduate student Ken Pesyna and WNCG Professors Todd Humphreys and Robert W. Heath, Jr. developed a carrier phase reconstruction technique to reduce the power consumption of carrier-phase positioning techniques in mobile devices. Reliable carrier phase reconstruction permits the duty cycling of a GNSS receiver whose outputs are used for precise carrier-phase differential GNSS (CDGNSS) positioning. Existing CDGNSS techniques are power intensive because they require continuous tracking of each GNSS signal's carrier phase. By contrast, the less precise code-ranging technique commonly used in mobile devices for 3-to-10-meter-accurate positioning allows for aggressive measurement duty-cycling, which enables low-power implementations. The technique developed reduces the CDGNSS continuous phase tracking requirement by solving a mixed real and integer estimation problem to reconstruct a continuous carrier phase time history from intermittent phase measurement intervals. Theoretical bounds on the probability of successful phase reconstruction, corroborated by Monte-Carlo-type simulation, were used to investigate the sensitivity of the proposed technique to various system parameters, including the time period between successive phase measurement intervals, the duration of each interval, the carrier-to-noise ratio, and the line-of-sight acceleration uncertainty. A demonstration on real data indicates that coupling a GNSS receiver with a consumer-grade inertial measurement unit enables reliable phase reconstruction with phase measurement duty cycles as low as 5%.
This research supported by the National Science Foundation and the U.S. Department of Defense.