FAA researching advanced RAIM for GPS approaches
An official evaluation of Advanced RAIM (ARAIM), a GPS technique used in aviation receivers for safer landings and take-offs, is being conducted by the William J. Hughes Technical Center (WJHTC) of the U.S. Federal Aviation Administration (FAA).
The WAAS Test Team at the technical center has begun to monitor the Integrity Support Data (ISD) parameters of ARAIM using evaluation tools and methods developed by both the center and Stanford University. Results of this monitoring will be published in a quarterly report on the WAAS Test Team website.
ARAIM addresses various weaknesses of Receiver Autonomous Integrity Monitoring (RAIM).
To assure the integrity of GPS, aviation receivers implement RAIM, which detects any GPS satellite fault, and can then isolate and remove it from the navigation solution.
However, RAIM provides integrity only for horizontal operations, such as enroute and non-precision approach. Additional integrity is needed to allow advanced capabilities, such as vertically guided approaches. Other integrity systems, including the Wide Area Augmentation System (WAAS), provide the integrity needed to permit these additional operations.
Since RAIM’s debut, GPS and other GNSS have evolved to improve their performance and upgraded to add an additional civilian signal, making possible ARAIM architecture.
ARAIM increases the geometric diversity and integrity availability by using two core GNSS constellations (such as GPS and Galileo). ARAIM takes advantage of the second civilian signal by specifying dual-frequency processing so that the ionospheric error from GNSS signals is directly measured by the user equipment.