Galileo OS SIS ICD.indd - GSA - Europa

leap seconds. Since the next leap second was inserted at 01.01.2006, this implies that
as of 01.01.2006 GST is ahead of UTC by fourteen (14) leap seconds.
The epoch denoted in the navigation messages by TOW and WN will be measured
relative to the leading edge of the fi rst chip of the fi rst code sequence of the fi rst page
symbol. The transmission timing of the navigation message provided through the TOW
is synchronised to each satellite’s version of Galileo System Time (GST).
5.1.3. Clock Correction Parameters
The clock correction parameters are transmitted according to the values stated in Table
64.
Parameter Defi nition Bits Scale
factor
Unit
t0c Clock correction data reference Time of Week 14 60 s
a f0 SV clock bias correction coeffi cient 31* 2 -34 s
a f1 SV clock drift correction coeffi cient 21* 2 -46 s/s
a f2 SV clock drift rate correction coeffi cient 6* 2 -59 s/s 2
Total Clock Correction Size 72
Table 64. Galileo Clock Correction Parameters
* Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB.
Each Galileo satellite broadcasts its own clock correction data for all signals through
the relevant signal, according to Table 65.
Message
Type
Clock Model
X=(f1,f2)
Satellite Time
Correction Model
Parameters
F/Nav (E1,E5a) af0 (E1,E5a)
af1 (E1,E5a)
af2 (E1,E5a)
t0C (E1,E5a)
I/NAV (E1,E5b) af0 (E1,E5b)
af1 (E1,E5b)
af2 (E1,E5b)
t0C (E1,E5b)
5.1.4. Satellite Time Correction Algorithm
Table 65. Galileo Clock Correction Data
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Document subject to terms of use and disclaimers p. ii-iii
OD SIS ICD, Issue 1, February 2010
Services
Dual-Frequency (E1,E5a)
Single-frequency E5a
Dual-Frequency (E1,E5b)
Single-frequency E5b
Single-frequency E1
Each satellite transmits time correction data. The predicted offset of the physical
satellite signal TOT relative to the satellite signal TOT in GST can be computed for the
dual frequency signal combination using the following formula:
where
TOT c(X) = TOT m(X) - Δt SV(X) Eq. 12
● (X)=(f 1,f 2) is the dual frequency combination f 1 and f 2 used for the clock model
● TOT C(X) is the corrected satellite TOT in GST for the signal combination X
47