Off-line, On-line and On-target FD/FDE Test Results for Approach Phases in an Aviation Receiver

J.K. Ray, R.A. Nayak

Abstract:	A GPS-SBAS receiver to be used in an aircraft for navigation purposes requires that the receiver be certified by the Federal Aviation Administration for Technical Standard Order C145. The most critical part of the certification is to ensure that the receiver meets the integrity requirements in terms of detecting satellite failure and if possible to make corrective actions in addition to generate timely alerts. The Failure Detection and Exclusion algorithm, which is often known as FD/FDE is to be implemented in the receiver. The effectiveness of this software has to be tested extensively in off-line condition for availability of satellite failure detection and exclusion. Further, the algorithm has to be tested in on-line conditions as well as on-target. There has to be a match among the off-line, on-line and on-target test results for using the algorithm in the FAA certified receiver. Extensive simulations and analysis is carried out using an FD/FDE algorithm to validate the performance in terms of availability of satellite failure detection and exclusion of the faulty satellite in a FAA certified GPS-SBAS receiver. The simulations are carried out as per the guidelines in RTCA/DO-229D that requires to simulate the GPS orbit, determine satellite visibility at over two thousands grid points on the earth surface and for 12 hours at 5 minutes time intervals. Then the FD/FDE algorithm is validated at each space-time points to determine the availability of failure detection and exclusion. For the non-precision approach the space-time points are arranged in terms of the Horizontal Protection Limit (HPL) and Horizontal Exclusion Limit (HEL), the most difficult to detect/exclude satellite is identified and Monte Carlo simulations are carried out at some of the selected spacetime points to validate the False Alarm and Missed Alarm requirements of DO-229D specifications. Similar tests are carried out for the precision approach, wherein the Vertical Protection Limit (Test threshold) is considered in stead of HPL. Further the test results of the off-line tests are validated through comprehensive on-line and ontarget tests on the selected geometries. The paper identifies the FD/FDE requirements in absence of WAAS as per DO-229D. It then briefly explains the FD/FDE algorithm. Results of exhaustive simulations are summarized and shown to meet the requirements specified in DO-229D. On-line and on-target test results are further explained and compared against the off-line test results to validate the algorithm used in the receiver.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	1971 - 1978
Cite this article:	Ray, J.K., Nayak, R.A., "Off-line, On-line and On-target FD/FDE Test Results for Approach Phases in an Aviation Receiver," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 1971-1978.
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