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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
7 1997 1998 1999 2000 2001 Maximum Daily SV
Minimum Daily SV
RMS ERD 6
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
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This document was uploaded on 09/26/2013.
- Fall '09