Global Positioning System Reference
In-Depth Information
cos(
t+ )
ωθ
1
18.625
18.875
−
X9
BPF*
Frequency
synthesis
18.625
18.875
−
cos(
t+ )
ωθ
2
BPF*
X7
511 KHz
90
C(t)
C/A code
D
(t)C(t)
ca
50 bps
B(t)=D
(t)C(t)sin(
t+ )
1
ωθ
D
(t)
S1(t)=A(
t)+B(t)
ca
ca
C/A message
Σ
5.11 MHz
P code
P(t)
A(t)=D (t)P(t)cos(
t+ )
1
ωθ
p
D (t)P(t)
p
50 bps
S2(t)=D (t)P(t)cos(
2
ωθ
t+ )
P message
D (t)
p
p
5 MHz
*BPF = Passband determined by satellite frequency assignment number.
Frequency synthesis is fork=0to24;this will change for new satellites.
Figure 11.4
GLONASS signal generator.
K
⋅
(
)
f
=
1780
.
+
Z
MHz
16
where:
K
=
an integer value between
−
7 and
+
12
Z
=
9 for L1, 7 for L2.
The spacing between adjacent frequencies on L1 is 0.5625 MHz and L2 is
0.4375 MHz. Originally,
K
was a unique integer for each satellite and varied from 0
to 24. But, due primarily to interference with radio astronomy measurements, the
Russians have proposed the following modifications to their frequency assignments
[24]:
•
Through 1998:
K
=
0 to 12;
From 1998-2005:
K
=−
7 to 12;
•
After 2005:
K
−
7 to 4.
•
The end result is to move the frequencies away from the radio astronomy band.
Additionally, the final configuration will only use 12 values of
K
(
K
=
7to4)for
the 24 satellites. The plan is to have satellites on opposite sides of the Earth (antipo-
dal) share the same
K
number (i.e., broadcast on the same frequency). This center
−
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