Global Positioning System Operational Control System Accuracies

Abstract

In early 1985, an improved ground Operational Control System (OCS) will maintain the navigation service. Primary among the OCS improvements over past GPS navigation systems is a global network of ground antennas (to upload satellite navigation data) and tracking/monitor stations. In addition, a refined Kalman filter will continuously estimate the Global Positioning System (GPS) satellite ephemerides and clock phases and frequencies. Although the user-GPS interface remains unaltered, the accuracy of the GPS navigation service is expected to improve by a factor of three.Using real and simulated GPS pseudo range radiometric tracking data, The Aerospace Corporation has completed a detailed error analysis which shows that the satellite clock noise contributes more than 90 percent of the total satellite-touser pseudo range error. If the number of OCS uploads is increased to three per day (as planned), then the accuracy of the navigation service is also expected to improve by nearly a factor of three because the clock-noise contribution to the range error increases linearly with time. Also, this analysis shows the consequence of satellite ephermeris uncertainties in the GPS navigation application.

A Signal Model for GPS

“…With the model thus verified, two of the filters derived from the SA waveforms were each used to perturb the pseudoranges. The results using the ARMA (2,2) are given in Figure 10 and the results using the AMRA (3,2) in Figure 11. The position errors again appear to be Gaussianly distributed.…”

“…First, 27 ARMA and auto-regressive (AR) filter models of differing order were derived. The simplest acceptable signal generator filter was determined to be an ARMA filter model with three poles and two zeros, ARMA (3,2). To demonstrate this filter's acceptability, the autocorrelation function of the optimum filter output is given (Figure 3).…”

RTK-GPS Correction Generation Technique For Low-Rate Data-Link

“…The length of baseline is about 185 metres and the altitude difference 64 metres. The short-term stability of GPS satellite clock is on the level of 10 x11 y10 x12 second (Bowen, 1985 ;Lutwak, 2001). We used the SNUR-2000 v. 2.2 as a RTK-GPS protocol which is optimized for low-rate data-link.…”

The Global Positioning System Geodesy Odyssey

“…Estimation of this y-bias parameter by the ICS dramatically improved the quality of the broadcast navigation messages. When the ICS was decommissioned in 1985, the broadcast user range error (URE) accuracy was better than 5 m 1 σ [19]. new predicted reference trajectories on a weekly basis.…”

“…A requirement was established for the OCS to provide a 1 URE of less than 6 m 10 h after upload. Initial comparisons of ICS and OCS indicated that this requirement could easily be met [19,21]. The Kalman filter used by the OCS can process up to six satellites in a single partition and uses 15 min pseudorange measurements smoothed using carrier-phase data.…”