Global Navigation Satellite System GNSS Overview and Spectrum

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

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)

Satellite Navigation … Basically Multilateration: a c b 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.

GNSS Ranging and Timing Actual Path Earth’s Ionosphere Assumed Path • Approach: tarrival – ttransmitted ~ 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.

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

Satellite Based Augmentation System (WAAS used as example) L 1, L 2 FAA 288 -021

Ground Based Augmentation System (GBAS) Architecture Pseudolite Processor Pseudolite GNSS Receiver VHF Transmitter Monitor Status GBAS Reference Station (Integrity Accuracy Availability)

Planned GNSS Modernization • Addition of satellite constellations – Galileo, additional GLONASS satellites – Improves user availability • Addition of civil signals – 1164 -1215 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 108 -117. 975 GBAS/GRAS broadcast link 1164 -1215 GPS L 5, Galileo E 5, future SBAS, GLONASS L 3 GPS L 2 (site-by-site ground use only) SBAS, GPS L 1, GLONASS, Galileo E 1 1215 -1240 1559 -1610

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 inband/adjacent band systems does not cause interference. • One example: ITU Footnotes 5. 355 and 5. 359 – Allow fixed service in GNSS bands in some countries – Countries encouraged to remove their names from the footnotes.