Global Positioning System Reference
In-Depth Information
where
P
Ea
r
x
5
is the E5a total received power,
τ
E
5
a
is the delay between transmission and
reception for L1,
θ
E
5
a
is the received phase.
In the same way, the E5b signal can be received and processed in isolation from
the E5b signal, as if it was transmitted alone as a signal with in-phase and quadra-
ture components according to the following:
∆
f
E
5
a
is the carrier frequency offset, and
(
)
(
)
(
)
(
)
t
s
t
−
τ
×
cos
2
π
f
−
∆
f
t
−
τ
+
θ
−
x
()
r
r
Ebd
5
-
Eb
5
Eb
5
Eb
5
E
5
b
E b
5
s
t
=
2
P
⋅
x
x
(
)
(
(
)(
)
)
Eb
5
Eb
5
t
s
t
−
τ
×
sin
2
π
f
−
∆
f
t
−
τ
+
θ
x
Eb
5
Eb
5
Eb
5
Eb
5
Eb
5
Ebp
5
-
where
P
Eb
r
x
5
is the E5b total received power,
τ
E
5
a
is the delay between transmission and
reception for L1,
θ
E
5
a
is the received phase.
Finally, and as said previously, the E5 signal can be processed as a single large
bandwidth signal into a receiver with an adequate processing that would generate a
local replica with an AltBOC modulation. The receiver then would perform a com-
plex correlation between the received signal and the local replica, using all four
codes of the E5a and E5b signals.
A simplified implementation technique for the generation of the local replica is
possible in the receiver, considering that the E5 AltBOC baseband signal
St
E
∆
f
E
5
a
is the carrier frequency offset, and
t
x
5
()can
be also described as an 8-PSK signal with values [4]:
π
()
{
}
t
x
St
=
exp
j
⋅
⋅
k
with
k
∈
12345678
,,,,,,,
E
5
4
The relation of the 8-phase states to the 16 different possible states for the qua-
druples
s
t
x
t
x
t
x
t
x
5-
()depends also on time. Therefore, time is
partitioned first in subcarrier intervals
T
sc
E
5
and further subdivided in eight equal
subperiods. The index
i
Ts
of the actual subperiod is given by:
5-
(),
s
t
5-
(),
s
t
5-
(),
s
t
t
Ead
Eap
Ebd
Ebp
8
(
)
{
}
i
=
integer
−
part
⋅
t
modulo
T
with
i
∈
1
, ,,,,,
234567
Ts
sc
Ts
T
E
5
sc
E
5
and determines which relation between input quadruple and phase states has to be
used.
The dependency of phase-states from input-quadruples and time is given in
Table 10.7.
This representation allows the implemention and generation of the E5 signal
using a look-up table according to the diagram shown in Figure 10.4.
GALILEO Spreading Codes
The PRN code sequences used for the GALILEO navigation signals determine
important properties of the system. Therefore, a careful selection of GALILEO code
design parameters was necessary. These parameters include the code length and its
relation to the data rate, as well as the auto- and cross-correlation properties of the
code sequences. The performance of the GALILEO codes is also given by the target
acquisition time.
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