Global Positioning System Reference
In-Depth Information
6.2 Matlab-based simulation
Simulation has been carried out in closely spaced multipath environments for CBOC(-)
modulated Galileo E1C (i.e., pilot channel) signal for a 24.552 MHz front-end bandwidth.
The simulation profile is summarized in Table 1. Rayleigh fading channel model is used in
the simulation, where the number of channel paths follows a uniform distribution between
two and five.
The successive path separation is random between 0.02 and 0.35 chips.
The
(
τ
l
− τ
1
)
=
channel paths are assumed to obey a decaying PDP according to Eqn. 6, where
0
>
μ
=
for
l
0.1. The received signal is sampled such that there are
48 samples per chip. The received signal duration is 800 milliseconds (ms) or 0.8 seconds for
each particular C/N
0
level. The tracking errors are computed after each
N
c
1, and the PDP coefficient
∗
N
nc
ms (in this
case,
N
c
20 ms) interval. In the final statistics, the first 600 ms are ignored in order
to remove the initial error bias that may come from the delay difference between the received
signal and the locally generated reference code. Therefore, for the above configuration (i.e.,
code loop filter parameters and the first path delay of 0.2 chips), the left-over tracking errors
after 600 ms are mostly due to the effect of multipath. The simulation has been carried out for
100 random realizations, which give a total of 10*100=1000 statistical points, for each C/N
0
level. The RMSE of the delay estimates are plotted in meters, by using the relationship:
∗
N
nc
=
RMSE
m
=
RMSE
chips
cT
c
(9)
where
c
is the speed of light,
T
c
is the chip duration, and RMSE
chips
is the RMSE in chips.
Parameter
Value
Channel model
Rayleigh fading channel
Number of paths
between 2 to 5
Path Power
Decaying PDP with
μ
=
0.1
Path Spacing
Random between 0.02 and 0.35 chips
Path Phase
Random between 0 and 2
π
Samples per Chip,
N
s
48
E-L Spacing,
Δ
EL
0.0833 chips
193
1
Number of Correlators,
M
Double-sided Bandwidth, BW
24.552 MHz
Filter Type
Finite Impulse Response (FIR)
Filter Order
6
Coherent Integration,
N
c
20 ms
Non-coherent Integration,
N
nc
1 block
Initial Delay Error
0.1 chips
First Path Delay 0.2 chips
Code Tracking Loop Bandwidth 2 Hz
Code Tracking Loop Order
±
1
st
order
Table 1. Simulation profile description
RMSE vs. C/N
0
plot for the given multipath channel profile is shown in Fig. 10. It can be
seen from Fig.
10 that the proposed RSSML clearly achieves the best multipath mitigation
1
Not all the correlators are used in all the tracking algorithms.
For example, nEML only requires 3
correlators.
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