Global Positioning System Reference
In-Depth Information
(
π
)
cos
2
f
1
t
e
B
(
t
)
L1 OS, data
α
+
−
e
C
(
t
)
L1 OS, pilot
α
+
−
e
A
(
t
)
S
(
t
)
L1 PRS
β
+
+
e
A
e
B
e
C
γ
sin
(
2
π
f
1
t
)
FIGURE 3.1. Galileo modulation scheme. The scheme is based on the modulation principle
coherent adaptive subcarrier modulation (CASM).
Now we have information for defining the binary signal components for chan-
nels B and C. However, information on channel A is not available. Based on this
information and the modulation scheme depicted in Figure 3.1, we will describe
the Galileo signal L1 OS.
The signal component for channel B results from the modulo-2 addition of the
navigation data stream
d
L
1
−
B
, the PRN code sequence
c
L
1
−
B
, and the B subcar-
rier
sc
L
1
−
B
. The final component is called
e
B
. Likewise, the C channel results
from the modulo-2 addition of the C channel PRN code sequence
c
L
1
−
B
with the
C channel subcarrier
sc
L
1
−
C
. The component is
e
C
. The binary signal compo-
nents are as follows:
e
A
(
t
)
=
not available
,
(3.2)
+∞
c
L
1
−
B
,(
i
mod 4 092
)
d
L
1
−
B
,(
i
mod 4
)
rect
T
c
,
L
1
−
B
(
e
B
(
t
)
=
t
−
iT
c
,
L
1
−
B
)
)
sign
sin
i
=−∞
×
(
2
π
R
c
,
L
1
−
B
t
,
(3.3)
+∞
c
L
1
−
C
,(
i
mod 4 092
)
e
C
(
t
)
=
rect
T
c
,
L
1
−
C
(
t
−
iT
c
,
L
1
−
C
)
)
sign
sin
i
=−∞
×
(
2
π
R
c
,
L
1
−
C
t
.
(3.4)
3.2.1 Signal Generation
Signal expressions are given for the power normalized complex envelope (i.e.,
baseband version)
s
. Both are described
in terms of its in-phase
I
and quadrature
Q
components by the following generic
expressions:
(
t
)
of a modulated bandpass signal
S
(
t
)
2
P
L
1
s
L
1
−
I
(
)
S
L
1
(
t
)
=
t
)
cos
(
2
π
f
L
1
t
)
−
s
L
1
−
Q
(
t
)
sin
(
2
π
f
L
1
t
(3.5)
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