Proving the Walk Matches the Talk - Verification of GPS Performance Assertions

John W. Lavrakas and Brent A. Renfro

Abstract:	The Global Positioning System, operational since 1995, provides positioning and timing services to civilian users worldwide. Despite this longstanding service to users, the operators of GPS have no capability for continuously monitoring the signal provided to civilian users. The US Government is taking steps to resolve this issue by upgrading its network of monitoring stations and its operational control system to include monitoring of the civil signal. However, while policy documents assert levels of service and interface specification define signals, neither of these types of documents addresses the question of how service and signals will be monitored to verify performance. To address this question, the US Department of Transportation has created a document to define what is meant by monitoring the GPS signals and service, called the GPS Civil Monitoring Performance Specification. This document describes in detail the various elements of the monitoring activity, including monitoring the civil GPS signals (L1C/A, L2C, L5, and L1C) and the civil GPS service (accuracy, availability, reliability). The document also includes helpful use cases describing the concept of operation for each of the major monitoring missions. These include GPS operational command and control, adherence to the GPS service standard, compliance with the GPS Standard Positioning Service and signal interface specifications, situational awareness, past assessment, infrastructure, and assessment of signal power levels. The document includes algorithms and process descriptions that explain how to perform many of the monitoring assessments of the signal and service. The Civil Monitoring Performance Specification is intended to be used as a guide in preparing procurement specifications for the operational control system, and in guiding the missions of organizations supporting the monitoring function, such as the GPS Operations Center at Schriever Air Force Base in Colorado. The main benefit from the improved civil monitoring defined in this document is the reduced probability of failures that adversely affect users. When such failures do occur, the range errors will be small and of short duration. This paper provides a full description of the GPS Civil Monitoring Performance Specification, its purpose, how it is structured, and how it will be used. The paper also describes future plans by the US Government for implementing the requirements set forth in this specification.
Published in:	Proceedings of the 2010 International Technical Meeting of The Institute of Navigation January 25 - 27, 2010 Catamaran Resort Hotel San Diego, CA
Pages:	850 - 858
Cite this article:	Lavrakas, John W., Renfro, Brent A., "Proving the Walk Matches the Talk - Verification of GPS Performance Assertions," Proceedings of the 2010 International Technical Meeting of The Institute of Navigation, San Diego, CA, January 2010, pp. 850-858.
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