Department of Transportation Releases Civil Monitoring Performance Document

May 1, 2009

On April 30, the U.S. Department of Transportation released a Civil Monitoring Performance Specification document for GPS.

The Global Positioning System Civil Monitoring Performance Specification (CMPS) is published and maintained at the direction of the program manager for civil applications, GPS Wing. The document outlines current requirements for monitoring of the civil service and signals for use by the U.S. government in planning GPS development efforts. As a result, many of the requirements contained in this CMPS may be incorporated into the next-generation operational control system (OCX), while other requirements may be allocated to other government entities for implementation.

The CMPS addresses the current L1 C/A signal and the GPS Standard Positioning Service (SPS) provided via that signal. It also includes the planned L1C, L2C, and L5 signals along with semi-codeless use of the GPS signals.

"The purpose of this document is to provide a comprehensive compilation of requirements for monitoring the GPS civil service and signals based on top-level requirements to monitor all signals all the time," reads the Executive Summary. "Upon approval this CMPS will be used by the GPS community to determine the adequacy of civil monitoring and provide focus for any needed monitoring improvements."

The CMPS defines a set of metrics for assessing GPS performance against standards and commitments defined in official U.S. Government documents such as the Standard Positioning Service Performance Standard, the Navstar GPS Space Segment/Navigation User Interfaces (IS-GPS-200), Navstar GPS Space Segment/User Segment L5 Interfaces (IS-GPS-705), and Navstar GPS Space Segment/User Segment L1C Interfaces (IS-GPS-800). The CMPS will be revised to track changes in these key reference documents.

"The implementation of a system that satisfies these requirements will allow operations as well as users to verify that civil GPS performance standards and commitments are achieved," the document reads. The document also defines the scope and range of monitoring needs not directly traceable to the key reference documents but expected by civil users, such as the ability to detect defects in signal and data, the rapid report of anomalous service behavior to satellite operations for resolution, and notification to users of the causes and effects of such anomalies for their various service types (e.g., positioning, timing, and navigation).

The document also addresses the need for archives of key data and events to support future improvements in GPS service and to respond to external queries about actual GPS service levels.

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