At the worst case location from a position solution

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Unformatted text preview: ance standards include only those factors under the control of the U.S Government. Accuracy standards were established with the worst two satellites removed, and with a six-meter constellation RMS SIS URE. For comparison purposes, Table A-5-6 contrasts the SIS position accuracy standard established in Section 3.3 against a conservative estimate of end-user performance for a user equipped with a representative receiver. The environmental and receiver error contributions included in the singlefrequency end user performance estimates in Table A-5-6 are as follows: • Single-frequency ionosphere propagation model error: 7 meters (1σ) • Troposphere propagation model error: 25 centimeters (1σ) • Receiver thermal noise: 80 centimeters (1σ) Table A-5-6. Comparison of SIS Performance Standards and End-User Performance SPS Position Accuracy SIS Position Accuracy Single-Frequency User Parameter Standard (Section 3.3, Performance Given Accuracy Table 3-6) Standard Conditions Global 95% Horizontal Error 13 meters 33 meters Global 95% Vertical Error 22 meters 73 meters A-5.6 Range Rate and Range Acceleration Error Behavior After SA Previous documents established standards for range rate error and range acceleration error as follows: • Range Rate Error: 2 meters/second Not-to-Exceed (NTE) • Range Acceleration Error: 8 millimeters/second2 95% 19 millimeters/second2 NTE These standards were established specifically as a bound on SA contributions to civil differential systems. With the removal of SA, the behavior of range rate and range acceleration error has changed considerably. Representative examples of current performance for these metrics are presented in Figure A-5-20 and Figure A-5-21. PRN1 Range Rate Error Sitka, Alaska National Satellite Test Bed Reference Station 0.04 22 May 2001 0.03 0.02 0.01 0 -0.01 -0.02 -0.03 -0.04 3 4 5 Time of Day (Hours UTC) 6 7 Figure A-5-20. Representative Example of Current Measured Range Rate Error Page A-37 October 2001 GPS SPS Performance Standard PRN1 Range Acceleration Error Sitka, Alaska National Satellite Test Bed Reference Station 0.008 22 May 2001 0.006 0.004 0.002 0 -0.002 -0.004 -0.006 -0.008 4 4.5 5 5.5 6 6.5 7 Time of Day (Hours UTC) Figure A-5-21. Representative Example of Current Measured Range Acceleration Error High frequency noise characteristics seen in the above figures are indicative of noise inherent in the measurement process, These noise characteristics are due almost entirely to receiver thermal noise in the tracking loops, although a small amount is contributed by the short-term stability of the L1 frequency source on-board the satellite. For the receiver used to track the above measurements, range rate error was typically below one centimeter/second Root Mean Square (RMS), while range acceleration error was typically below two millimeters/second2 RMS. Low frequency noise characteristics are not readily visible in a plot, since they are driven by slowly changing errors in measured navigation sig...
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