Global Positioning System Reference
In-Depth Information
TABLE 3.2. Galileo ephemeris parameters
Parameter No. of Bits
Scale Factor
Unit
2
−
31
µ
0
32
semicircle
2
−
43
n
16
semicircle/s
2
−
33
e
32
dimensionless
√
a
2
−
19
m
1
/
2
32
2
−
31
0
32
semicircle
2
−
31
i
0
32
semicircle
2
−
31
ω
32
semicircle
˙
2
−
43
24
semicircle/s
i
2
−
43
14
semicircle/s
2
−
29
C
uc
16
radian
2
−
29
C
us
16
radian
2
−
6
C
rs
16
m
2
−
6
C
rc
16
m
2
−
29
C
ic
16
radian
2
−
29
C
is
16
radian
t
oe
14
60
s
IOD
nav
9
—
—
-
Interleaved data output for transmission
x
16
x
12
x
8
x
4
x
15
x
11
x
7
x
3
x
14
x
10
x
6
x
2
x
13
x
9
x
5
x
1
This block interleaving has interleaving depth 4. In this simple example three
consecutive errors in the transmitted data, let us say
x
1
,
x
5
,
x
9
, are translated into
three isolated, single errors in the de-interleaved data.
3.4
Message Contents
The freely accessible navigation message on L1 OS contains all parameters nec-
essary to compute the position of a Galileo satellite, clock correction parameters,
parameters for conversion of Galileo System Time (GST) to UTC and GPS Time
(GPST), and service parameters including an almanac.
A Galileo ephemeris contains 17 parameters as defined in Table 3.2. The unit
semicircle is converted to radian by multiplication with
.
A Galileo ephemeris is valid for four hours. Every three hours a new ephemeris
is uploaded. Hence an overlap of one hour occurs. And four ephemerides cover a
12-hour orbit prediction.
π
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