International Civil Aviation Organization Spectrum Seminar Cairo, Egypt June 4-6, 2006 Global Navigation Satellite System (GNSS) Overview and Spectrum Implementation

Basic GNSS System Core Constellations –GPS –GLONASS –Galileo (under development) Augmentation Systems –Aircraft-Based Augmentation System (ABAS) –Space-Based Augmentation System (SBAS) Uses geostationary satellites India, Japan, Europe, US –Ground-Based Augmentation System (GBAS) –Ground-Based Regional System (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.

Earth’s Ionosphere Actual Path Assumed Path Approach: t arrival – t transmitted ~ distance from satellite Assumes straight path of radio frequency signals Earth’s ionosphere actually disrupts/bends that path Augmentations correct for that bend using dual-frequency measurements Currently not possible directly in aircraft; some signals not protected. GNSS Ranging and Timing

Satellite Navigation’s Mission SBAS/GBAS Implementation GBAS SBAS/ GRAS

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/GRAS 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.