SPS Performance 2001

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Unformatted text preview: elements: • SIS PPS URE includes satellite clock and ephemeris prediction error, OCS state estimate process noise, and residual curve fit error, as well as negligible residual noise from the measurements themselves (to include small residual errors from the troposphere and ionosphere propagation effects correction process) does not include instantaneous single-frequency ionosphere model errors, troposphere model errors, receiver noise or multipath effects • C/A to P(Y) Code Phase Bias – includes satellite unique offsets as measured by the Jet Propulsion Laboratory (JPL) Figure A-2-4 illustrates the PPS SIS URE trend over the past several years. The OCS uses the Estimated Range Deviation (ERD) quantity as its metric for monitoring PPS SIS UREs. Performance as of April 2001 across the constellation was 1.4 meters Root Mean Square (RMS), following the general trend witnessed over the past three years. Performance has gradually Page A-10 October 2001 GPS SPS Performance Standard improved as older Block II satellites leave the constellation and newer Block IIR satellites with clocks exhibiting better short-term stability (to date) enter service. Current constellation URE performance is driven by the OCS upload policy. Currently the OCS schedules one upload per day for each satellite, with a contingency upload executed if the instantaneous PPS SIS URE value exceeds three meters. This policy is adjusted depending on factors such as changing satellite clock stability characteristics and OCS resource status. GPS SIS User Range Error Trend: 1 January 1997 - 30 April 2001 10 9 8 7 1997 1998 1999 2000 2001 Maximum Daily SV RMS ERD Daily Constellation RMS ERD Minimum Daily SV RMS ERD 6 5 4 3 2 1 0 Year-Day of Year Figure A-2-4. PPS SIS URE Historical Trend When defining SPS UREs, it is necessary to include the effects of C/A to P(Y) code phase biases for each satellite and a residual noise value of one nanosecond (1σ) to represent uncertainties in Jet Propulsion Laboratory (JPL) measurements of TGD (the estimated group delay differential as defined in ICD-GPS-200C). The C/A to P(Y) code phase bias information used in the analysis was obtained from JPL via the Aerospace Corporation and is presented in Table A-2-4. JPL provides updates to the values in Table A-2-4 on a quarterly basis and whenever a new satellite is launched or an on-orbit satellite redundancy configuration is changed. Figure A-2-5 contrasts PPS and SPS SIS URE statistic values over the one-week interval of 1017 June 2000. The most significant contributor to URE as experienced by the end user is generally the error in the ionosphere single-frequency model (as defined in ICD-GPS-200C). Model coefficient values are selected based on the current solar flux density, and placed in each navigation upload. Errors in the single-frequency model due to the coefficients or limitations in the model itself are not within the control of the U.S. Government, and are not included in the SPS SIS URE performance s...
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This document was uploaded on 09/26/2013.

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