Receiver Autonomous Integrity Monitoring, Using the NMEA 0183 Message: $GPGRS

Frank Van Digglelen

Abstract:	The National Marine Electronics Association (NMEA) sets standards for interfacing marine electronic devices. The NMEA 0183 standard has been adopted by most GPS receiver manufacturers. To allow GPS users to monitor the integrity of a GPS receiver solution, a new NMEA message will shortly be adopted into the standard. The new message, SGPGRS, contains the pseudo-range residuals for each satellite in the navigation solution. These pseudo-range residuals contain information to facilitate real-time integrity monitoring of the accuracy and precision of the navigation solution. NAVSAFE” is a software package developed by NAVSYS Corporation to provide real-time integrity monitoring using the NMEA message SGPGRS. NAVSAFE uses the pseudo-range residuals alone to compute the variance of the pseudo-range errors, detect biases when they occur, and compute the distribution of the navigation solution, thus guaranteeing a predetermined level of navigation accuracy. The user specifies the required navigation accuracy by setting the maxi- mum Radial Position Error, the maximum Probability of Missed Detection, and the maximum Probability of False Alarm. The Receiver Autonomous Integrity Monitoring (RAIM) algorithm within NAVSAFEreduces integrity monitoring to a simple alarm structure. There are three alarm states, red, yellow, and green, analogous to a traffic light. A green alarm state guarantees that the required navigation accuracy has been met. A yellow alarm indicates a possible navigation outage but also shows a high probability of false alarm. A red alarm confirms that the required navigation accuracy has not been met. This paper describes the operation of the RAIM algorithm and presents results obtained with GPS receivers which already include the SGPGRS message.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	531 - 538
Cite this article:	Van Digglelen, Frank, "Receiver Autonomous Integrity Monitoring, Using the NMEA 0183 Message: $GPGRS," Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993), Salt Lake City, UT, September 1993, pp. 531-538.
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