GPS World - January 2008 - (Page 62)

INNOVATION | Avionics & Transportation Good, Better, Best Expanding the Wide Area Augmentation System Timothy R. Schempp AIR TRAVEL PROMISES to become safer and cheaper thanks to the Wide Area Augmentation System (WAAS). It assists or augments GPS by providing the increased accuracy, availability, continuity, and integrity necessary for aircraft navigation. Unaugmented, or standalone, GPS isn’t accurate enough for some types of runway approach procedures. Using geostationary Earth orbit (GEO) communications satellites, WAAS provides corrections to the GPS satellite orbit and clock information in a satellite’s navigation message as well as ionospheric delay information. These corrections permit a user’s receiver to compute a more accurate position, often to better than 1 meter horizontally and 2 meters vertically, with a 95% confidence. WAAS also increases the availability and continuity of GPS for aircraft navigation by requiring fewer redundant observations for determining a valid position. Availability is also increased through the provision of the additional GEO ranging signals. But perhaps most importantly, WAAS provides the increased integrity needed for a safety-of-life navigation system. Within 6 seconds of a fault detection, an alarm message INNOVATION INSIGHTS corrects the error or allows a safe transition with Richard Langley to an alternative navigation procedure. The WAAS also benefits GPS advantages of WAAS for aviation include greater runway capability, reduced separation standards which allow increased capacity in users on the ground. a given airspace without increased risk, more direct enroute flight paths, new precision approach services, reduced and simplified equipment onboard aircraft, and significant government cost savings due to the elimination of maintenance costs associated with older, more expensive ground-based navigation aids. But WAAS not only benefits GPS users in the sky. Many GPS users on terra firma are making use of the increased accuracy and availability afforded by WAAS. For example, according to the FAA, OnStar has added WAAS capability to the GPS receivers in General Motors 2008 product year vehicles. And even surveyors are making use of the WAAS ranging signals for improving real-time kinematic survey operation. While WAAS was already a much-valued addition to standalone GPS, significant improvements were made to WAAS over the past three years, including expansion of the reference station network and the commissioning of two new GEOs. 2008 will see even more enhancements. In this month’s column, we take a look at WAAS’s recent upgrades and take a peek into its future. “Innovation” is a regular column that features discussions about recent 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 at the University of New Brunswick, who welcomes your comments and topic ideas. To contact him, see the “Contributing Editors” section on page 10. 62 GPS World | January 2008 T he Wide Area Augmentation System (WAAS) enhances the GPS Standard Positioning Service, providing sufﬁcient integrity, accuracy, availability, and continuity for use in commercial aviation. Fielded by the U.S. Federal Aviation Administration (FAA), the system provides enroute through non-precision approach, lateral navigation / vertical navigation (LNAV/ VNAV), and localizer performance with vertical guidance (LPV) runway approach capabilities (see the “Navigating Aircraft with GPS and WAAS” sidebar for deﬁnitions of these terms). But WAAS is more than a navigation system for pilots. Most any GPS receiver you buy today is WAAS-enabled, allowing everyone from hikers and bikers to surveyors, farmers, and rescue workers to enjoy the benefits of improved accuracy and integrity in their day-to-day activities. Since WAAS is compliant with the same international standards used to build Japan’s MTSAT Satellite-based Augmentation System (MSAS) and Europe’s European Geostationary Navigation Overlay Service (EGNOS) along with several other systems under development, a WAAS-enabled GPS receiver will improve the accuracy, integrity, availability, and continuity of GPS for users around the world. Over the last three years, WAAS has undergone a major expansion, adding reference stations in Alaska, Mexico, and Canada; upgrading processing software; and replacing the legacy geostationary Earth orbit (GEO) satellites with new satellites that are well positioned to give dualsignal coverage to users in North America. Many of these enhancements were fielded in September 2007, resulting in a significant performance improvement for every WAAS user in North America. www.gpsworld.com http://www.gpsworld.com

Table of Contents Feed for the Digital Edition of GPS World - January 2008

GPS - January 2008 Contents Out in Front Expert Advice The Money-Go-Round u-Nav Latest Acquisition Apples to Apples Global SBAS 2008 GPS Receiver Survey Advertisers Index & Company Directory The Manufacturer's Road Year of the Who Working Indoor Up and Down Good, Better, Best Marketplace Classifieds Seen + Heard

GPS World - January 2008

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