Perturbations and Errors Simulation
Satellite Navigation
105
User Manual 1178.6379.02 ─ 01
Satellite clock parameters
Satellite clock offset
Δ
Clock
SV
is described by a second order polynomial given as fol-
lows:
Δ
Clock
SV
= a
f0
+ a
f1
(t – t
0c
) + a
f2
(t – t
0c
)
2
, where:
●
t
0c
is the reference time of clock
●
a
f0
, a
f1
and a
f2
are three coefficients that are broadcasted in the navigation mes-
sage.
Polynomial coefficients
In GPS, Galileo, BeiDou and QZSS, these are:
●
a
f0
: SV clock offset
●
a
f1
: SV clock drift
●
a
f2
: SV clock drift rate
GLONASS considers the first order version of the polynomial (i.e. a
f2
= 0) and transmits
only two clock parameters:
● Τ
n
: SV clock offset, where:
a
f0
= -
Τ
n
● Γ
n
: SV relative frequency offset
a
f1
=
Γ
n
12.1.4 Simulating Errors
Per default, the broadcasted navigation message parameters per SV are set automati-
cally to match the simulated orbit, clock and pseudorange parameters. For example,
the clock parameters in the navigation message of GPS SV ID#1 resembles the simu-
lated clock values for this satellite.
Errors are deviations between the simulated and broadcasted navigation mes-
sage parameters
Changing the default navigation message values leads to deviation between the simu-
lated and the broadcasted navigation information and thus deliberated errors. To simu-
late clock errors, change for example, the parameter a
f0
in the broadcasted navigation
message of SV#1 but maintain the a
f0
value of the simulated clock.
You can also simulate unusual stations, like, for example, the wrongly broadcasted
clock bias between UTC and GPS system clocks. Such situations are simulated by
configuring different time conversion sets for the UTC-GPS conversion parameters in
the broadcasted navigation message and in the simulated UTC time parameters.
About the Errors Sources
