Global Positioning System Reference
In-Depth Information
•
The L1F pilot channel (L1F-p):
The modulation on this channel results from
the modulo-two addition of the L1F-p channel PRN code sequence
c
L
1
F
-
p
(
t
)
with the L1F-p subcarrier
sc
L
1
F
-
p
(
t
). The BOC subcarrier has sine phasing. The
signal corresponds to BOC
s
(1,1) modulation by the p-channel code sequence.
The L1P channel:
The modulation on this channel results from the modulo-2
addition of three components—the L1P navigation data stream
d
L
1
P
(
t
), the L1P
channel PRN code sequence
c
L
1
P
(
t
), and the L1P subcarrier
sc
L
1
P
(
t
). The BOC
subcarrier has cosine phasing. The signal corresponds to BOC
c
(15,2.5) cosine
modulation by the code sequence and data signal.
•
The L1 signal components are multiplexed into the L1 carrier using the modified
hexaphase modulation [6]. The L1F signal is modulated onto the carrier in-phase
component while the L1P signal is modulated onto the quadrature component. The
composite signal may be expressed as:
[
]
()
()
(
)
t
t
t
2
⋅
P
α
⋅
s
t
−
α
⋅
s
t
×
cos
2
π
f
t
−
x
x
x
()
L
1
L
1
LFd
1
-
L
1
LFp
1
-
L
1
tx
St
=
[
]
L
1
()
()
(
)
2
⋅
P
t
β
⋅
s
t
t
+
γ
⋅
s
t
t
×
cos
2
π
f
t
x
x
x
L
1
L
1
LP
1
L
1
L
1
,int
L
1
where:
t
LFd:s
1-
()
t
=
d
()
t c
⋅
()
t sc
⋅
()
t
x
LFd
1
-
LF
1
LIFd
-
LFd
1
-
t
LFp:s
1
-
()
t
=
c
()
t sc
⋅
()
t
x
LFp
1
-
LFp
1
-
LFp
1
-
t
LP:s
1
()
t
=
d
()
t c
⋅
()
t sc
⋅
()
t
x
LP
1
LP
1
LIP
LP
1
t
t
t
s
the intermodulation product in the
modified hexaphase modulation, which ensures the constant envelope
property of the transmitted carrier signal
int
()
t
=
s
()
t
⋅
s
()
t
⋅
s
()
t
=
x
x
x
L,
1
LFd
1
-
LFp
1
-
LP
1
γ
L
1
, adjust the relative power of the four compo-
nents. The values determine the distribution of the total useful power among signal
channels. The power distribution, shown in Table 10.3, aims at an equal sharing
between L1P and L1F transmit power.
At reception, the L1 modulation scheme allows independent processing of the
L1F and L1P signals in a GALILEO receiver.
The L1F received signal can be written as:
The coefficients,
α
L
1
,
β
L
1
, and
[
]
()
(
)
(
)
r
r
t
t
St
=
α
2
Ps
t
−
τ
−
s
t
−
τ
x
x
x
x
LF
1
L
1
L
1
LF d
1
-
L
1
LFp
1
-
L
1
(
)
(
)(
)
×
cos
2
π
f
−
∆
f
t
−
τ
+
θ
L
1
L
1
L
1
L
1
where
P
L
r
1
is the L1 total received power,
τ
L
1
is the transmission delay at L1,
∆
f
L
1
is the
carrier frequency offset (including Doppler offset), and
θ
L
1
is the received phase.
Equivalently, the L1P received signal can be written as:
(
)
(
)
(
)(
)
r
r
t
s
=
β
2
P
⋅
s
t
−
τ
⋅
sin
2
π
f
−
∆
f
t
−
τ
+
θ
x
x
x
LP
1
L
1
L
1
LP
1
L
1
L
1
L
1
L
1
L
1
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