Global Positioning System Control/User Segments. Volume II. System Error Performance.

The Global Positioning System GPS Phase 1 is a space-based radio navigation system which will provide GPS-equipped users the capability to precisely determine three-dimensional position, velocity and system time information within designated test areas. An analysis has been performed to compute the errors to be expected in a users position and time fix, for various user types, environmental conditions, and test locations. The purpose of this report is to present the results of this analysis and the assumptions and methodology which led to them. The error analysis described herein addresses Phase I of the GPS program, during which four satellites are employed. Subsequent phases of the GPS program, in which a greater number of satellites will be employed are not treated. The analysis is also based on a single typical system configuration e.g., a single arrangement of monitoring station locations and a single set of satellite orbits, and on steady-state conditions i.e., the system has been operating for a sufficiently long period that the residual errors in satellite orbit estimation have reached steady-state cyclic values. The primary consideration is estimating single-fix accuracies, with minimal analysis of the problem of improving position and system time accuracies by smoothing or averaging fixes over a period of time. The performance degradation due to user dynamics is not considered.