Analysis of a Real-Time Genetic NIORAIM Implementation on a WAAS Beta 3 Receiver

Angelo J. Joseph and Gerard Lachapelle

Abstract:	Airborne WAAS Beta 3 sensors have to perform receiver autonomous integrity monitoring (RAIM) and fault detection and exclusion (FDE) operations that determine horizontal and vertical protection levels (HPL/VPL) and also detect and exclude biased measurements from failed satellites. The RAIM and FDE algorithms employed have to meet the availability and performance requirements specified in DO-229D in order to be used during Non- Precision Approach (NPA) and Precision Approach (PA) modes of the flight. NIORAIM (Novel Integrity- Optimized RAIM) is a method presented by Hwang and Brown (2005) to improve availability of RAIM by weighting the pseudo range measurements in a non-linear fashion. The non-linearly weighted range measurements are then used to compute a position fix. The NIORAIM weights are chosen to improve availability of integrity with a slight cost to accuracy. The NIORAIM algorithm helps to lower the minimum detectable bias (MDB) for the given geometry and noise model. NIORAIM methods that have been published are difficult to implement on real-time airborne GPS receivers that have strict memory and processing constraints. This paper presents a method of implementing NIORAIM on a real-time WAAS Beta 3 sensor. The paper also presents a genetic algorithm approach to determine the NIORAIM weights. A comparative availability analysis is presented here that compares RAIM and NIORAIM when used over the continental United States. The challenges involved in calculating the protection levels and the software optimizations required is discussed. The paper also outlines a number of efficient numerical methods that were implemented on the embedded receiver software. The paper will present the comparative availability test results for both single and double satellite faults during both NPA and PA modes of flight. It is seen that NIORAIM consistently out-performs RAIM in all situations. The improvement in availability performance offered by NIORAIM is far more pronounced when considering a GPS only constellation as opposed to a GPS+Galileo constellation. To the author’s knowledge this work is the first published real-time implementation of NIORAIM.
Published in:	Proceedings of the 2009 International Technical Meeting of The Institute of Navigation January 26 - 28, 2009 Disney's Paradise Pier Hotel Anaheim, CA
Pages:	221 - 235
Cite this article:	Joseph, Angelo J., Lachapelle, Gerard, "Analysis of a Real-Time Genetic NIORAIM Implementation on a WAAS Beta 3 Receiver," Proceedings of the 2009 International Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2009, pp. 221-235.
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