Presentation on theme: "International Civil Aviation Organization Spectrum Seminar Nairobi, Kenya February 17-19, 2004 Global Navigation Satellite System (GNSS) Overview and Spectrum."— Presentation transcript:
International Civil Aviation Organization Spectrum Seminar Nairobi, Kenya February 17-19, 2004 Global Navigation Satellite System (GNSS) Overview and Spectrum Implementation
Basic GNSS System Space Segment –Orbiting Satellites GPS GLONASS Future … Galileo? –Geostationary Satellites SBAS Ground Segment –Satellite Control Stations –Augmentation Systems GBAS Future … GRAS?
a b c Satellite Navigation … Basically Multilateration Multilateration: By knowing your distance from at least 3 points of known-position, you can determine your own position. For Satellite Navigation: a, b & c are satellites, and a fourth is needed to solve for clock variations.
Earths Ionosphere Actual Path Assumed Path Approach: t arrival – t transmitted ~ distance from satellite Assumes straight path of radio frequency signals Earths ionosphere actually disrupts/bends that path Augmentations correct for that bend using dual-frequency measurements Currently not possible in aircraft; L2 signals not protected. GNSS Ranging and Timing
FAA Satellite Based Augmentation System (WAAS used as example) L1, L2
Ground Based Augmentation System (GBAS) Architecture GBAS Reference Station (Integrity Accuracy Availability) Processor GNSS Receiver VHF Transmitter Monitor Status Pseudolite
Planned GNSS Modernization Addition of satellite constellations –Galileo, additional GLONASS satellites –Improves user availability Addition of civil signals – MHz band –Facilitates user ionospheric corrections –Possible broadcast of integrity signal May limit need for external augmentations Increased power, improved coding –Better resistance to interference
GNSS Frequency Bands Frequency (MHz)Function GBAS broadcast link GPS L5, Galileo E5, future SBAS, GLONASS L GPS L2 (site-by-site ground use only) SBAS, GPS L1, GLONASS, Galileo E1
Spectrum Issues GNSS signals are very weak –~ 50,000 times weaker than the minimum specified edge-of-coverage DME signal Aviation spectrum managers must be constantly watching to ensure spectrum incursion from in- band/adjacent band systems does not cause interference. One example: ITU Footnotes and –Allow fixed service in GNSS bands in some countries –Countries encouraged to remove their names from the footnotes.