The U.S. Global Positioning System (GPS) Standard Positioning Service (SPS) consists of space-based positioning, navigation, and timing (PNT) signals delivered free of direct user fees for peaceful civil, commercial, and scientific uses worldwide. This SPS Performance Standard (SPS PS) specifies the levels of SPS performance in terms of broadcast signal parameters and GPS constellation design. The U.S. Government is committed to meeting and exceeding the minimum levels of service specified in this SPS PS and this commitment is codified in U.S. Law (10 U.S.C. 2281(b)).

Since GPS initial operational capability (IOC) in 1993, actual GPS performance has continuously met and exceeded minimum performance levels specified in the SPS PS and users can generally expect improved performance over the minimum levels described here. For example, with current (2007) Signal-in-Space (SIS) accuracy, well designed GPS receivers have been achieving horizontal accuracy of 3 meters or better and vertical accuracy of 5 meters or better 95% of the time. A number of U.S. agencies continually monitor actual GPS SPS performance, including the Federal Aviation Administration (FAA) which publishes quarterly Performance Analysis Reports at its National Satellite Test Bed (NSTB) web site (http://www.nstb.tc.faa.gov/). Interested readers are encouraged to refer to this and other sources for updated GPS performance. As an additional example of improved U.S. commitments to the worldwide GPS user community, the U.S. President announced in 2007 that Selective Availability will not be built into modernized GPS III satellites.

Although GPS will provide three new modernized civil signals in the future: L2C, L5, and L1C, the performance specifications in this version of the SPS PS apply only to users of the L1 (1575.42 MHz) Coarse/Acquisition (C/A) signal, since this is the only civil GPS signal that has reached full operational capability at this time. Furthermore, an “Expandable 24-Slot” GPS constellation with more than 24 satellites is introduced in this document and the “Baseline 24-Slot” GPS constellation definition remains unchanged from the previous version of the SPS PS.

The SPS PS will be updated periodically as GPS modernizes its civilian services. This version of the SPS PS revises and supersedes the previous version, published 4 October 2001, and meets or surpasses all the performance commitments of the previous version. Significant changes to this update include a 33% improvement in the minimum level of SIS range accuracy, from 6 meters root mean square (rms) accuracy to 4 meters rms (7.8 meters 95%), as well as the addition of minimum levels of SIS range velocity accuracy and range acceleration accuracy, which were unspecified in the previous version of the SPS PS.

In addition to specifying GPS minimum performance commitments, the SPS PS serves as a technical document designed to complement the GPS SIS Interface Specification (IS-GPS-200). Readers interested in GPS tutorial information are encouraged to refer to the wide range of reference material available on the subject.

Finally, in line with the U.S. Space-Based PNT Policy (http://pnt.gov/policy/), the SPS PS underscores the U.S. commitment to cooperate with Global Navigation Satellite System (GNSS) and Satellite-Based Augmentation System (SBAS) providers to ensure compatibility and interoperability of GPS with emerging systems for peaceful, civilian worldwide use.