GPS World, April 2014

INNOVATION System Design Test Ground Based Augmentation Combining Galileo with GPS and GLONASS Mirko Stanisak Mark Bitter and Thomas Feuerle GPS SAFER FLIGHT While reviewing material for an article celebrating the 25th anniversary of the launch in February 1989 of the first Block II or operational GPS satellite I was yet again annoyed by many articles on the Web stating that GPS only became available for civil use after the launch of this satellite Some sources get closer to the truth when they say that GPS was opened for civil use in 1983 following the shoot down of the Korean Airlines Flight 007 In fact GPS was designed to serve the needs of both the military and civil communities from the outset A government memo from April 1973 clearly states Civil user needs should be considered in the design of the spaceborne equipment One of the first demonstrations of the use of GPS for aircraft navigation occurred in July 1983 when a Sabreliner business jet was flown in stages from Cedar Rapids Iowa to the Paris Air Show flying only when a sufficient number of the experimental or Block I satellites were in view The first standalone GPS receivers certified for aviation use with Receiver Autonomous Integrity Monitoring or RAIM became available by the mid 1990s But already the Federal Aviation Administration had been looking into the development of a system to provide INNOVATION INSIGHTS with Richard Langley GBAS protocols can accommodate multiple constellations higher accuracies and better integrity than that afforded by standalone receivers In 1994 the FAA announced the development of the Wide Area Augmentation System its brand of a system generically known as satellite based augmentation Geostationary satellites transmit corrections and integrity information to GPS receivers permitting GPS use for en route navigation all the way down to traditional Category I approach and landing CAT I approaches can be flown down to a decision height of 61 meters 200 feet WAAS was declared operational on July 10 2003 but enhancements to the system continue Japan Europe and India also have operational SBAS based on GPS Ground based GPS augmentation was first developed for maritime applications with the U S Coast Guards low frequency system coming on line in the mid 1990s Also in the mid 1990s the FAA began the development of the Local Area Augmentation System generically known as a ground based augmentation system GBAS to provide aircraft with approach and landing capabilities from CAT I down through CAT II 30 meter or 100 foot decision height and CAT III no decision height but certain visual range minima using a VHF datalink Initial CAT I systems are being operated at Bremen Germany and at Newark Liberty International Airport and Houston George Bush Intercontinental Airport While a GPS based GBAS will definitely offer improved navigation services for aircraft might these services be even better if the systems were to use satellites from other constellations besides GPS In this months column we look at a straw man concept for modifying the GBAS protocols to accommodate multiple constellations and the results of preliminary tests using GPS GLONASS and Galileo simultaneously Innovation is a regular feature that discusses advances in GPS technology and its applications as well as the fundamentals of GPS positioning The column is coordinated by Richard Langley of the Department of Geodesy and Geomatics Engineering University of New Brunswick He welcomes comments and topic ideas To contact him see the Contributing Editors section on page 4 E ver since the declaration of Full Operational Capability FOC of the U S Global Positioning System in April 1995 GPS has dominated satellite navigation especially in aviation applications By contrast the Russian GLONASS system cannot be used in western aviation because no approval guidelines exist for GLONASS equipment Thus GPS has been the de facto standard in aviation for years However within the last few years PDMRU FKDQJHV KDYH HYROYHG LQ WKH HOG of GNSS providing a wide variety of useable satellite navigation systems The European Union launched its Galileo project which will provide global multifrequency services in the near future China is upgrading its BeiDou system formerly called Compass to provide global coverage with more medium Earth orbit MEO satellites The operators of GPS and GLONASS have started modernization programs that will enable multi frequency operations in the future too Therefore a large number of usable satellites and signals from multiple systems will soon be available In aviation almost all phases of flight can be assisted by satellite navigation systems nowadays The most challenging phase of flight with respect to accuracy continuity availability and integrity is the approach and landing phase The Ground Based Augmentation System see FIGURE 1 courtesy of the European Organization for Civil Aviation Equipment allows precision approaches to be performed using satellite navigation It uses a VHF data link to broadcast differential GNSS corrections integrity information and approach definitions to approaching aircraft These aircraft combine the differential corrections with their own GNSS measurements calculate a GBAS corrected position solution and GPS World April 2014 www gpsworld com 44