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DO-253D Change 1
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Note: This evaluation method is based on the assumption that a least-squares position
algorithm (per Section 2.3 .9) is implemented. If a different form of positioning is
used, this evaluation method may not be appropriate.
Simulator and Interference Conditions
The simulation and interference conditions shall [LAAS-220] conform to the following
a) For all test scenarios, the broadband GNSS test noise and Nsky,antenna shall [LAAS-
313] be simulated. There are three sets of interference test scenarios: broadband
external interference noise, Continuous Wave Interference, and pulsed
1) The broadband external interference noise (IExt,Test) has a spectral density equal
to -170.5 dBm/Hz at the antenna port.
2) The CW power and frequencies are listed in Table 2-46.
3) For the pulsed interference tests, a pulse-modulated carrier at 1575.42 MHz
with a signal bandwidth of 1 MHz, with peak carrier level of +10 dBm, pulse width
of 125 μs, and duty cycle of 1% shall [LAAS-222] be used. This corresponds to
an I/S ratio of +144 dB for GPS and SBAS satellites.
b) The GNSS test noise depends on the number, power, and type of satellites
simulated during the test. The power spectral density of the total GNSS Noise
(IGNSS) is -171.9 dBm/Hz (See Appendix D.2.3). This GNSS Noise was derived
for GPS tracking but is used in the test for both GPS and SBAS tracking to allow
simultaneous testing of GPS and SBAS thereby reducing test time. However it is
acceptable to run the SBAS testing separately using a total GNSS Noise (IGNSS) of
-172.8 dBm/Hz for accuracy verification and/or collection of the SBAS message
loss rate data. The effective noise power spectral density (ITest) of the satellites
present in the simulator scenario may be removed from the total GNSS Noise; to
do so, the satellite equivalent power spectral density specified in Table 2-47 (IGH,
IGL, ISH, and ISL) is removed for each satellite present. The number of maximum
power GPS satellites is NGH, the number of minimum power GPS satellites is NGL,
the number of maximum power SBAS satellites is NSH, and the number of
minimum power SBAS satellites is NSL. The GNSS test noise is determined by
removing ITest from IGNSS as follows:
IGNSS,Test = 10log10[10-171.9/10
ITest = 10log10[(NGL)10IGL/10 + (NGH)10IGH/10 + (NSL)10ISL/10 + (NSH)10ISH/10]
Note: The indicated power levels (both signal and noise) are for the steady-state
portion of the tests; power levels are set to the required values once steady
state navigation has been achieved. Refer to Appendix H for an explanation
of how ITest is derived and examples of the computation of IGNSS,Test and how it
may be applied.
c) Simulated GPS and SBAS RF shall [LAAS-223] be at the minimum power level
for the equipment (as described in Section 184.108.40.206), except for the broadband
external interference noise case that shall [LAAS-224] be tested at the maximum
power level (as described in Section 220.127.116.11) as well as the minimum power level.
For test cases that require the minimum power level, one GPS satellite shall
[LAAS-314] be set to the maximum power level (including maximum transmit
power and maximum combined satellite and aircraft antenna gain). For these cases
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