Global Positioning System Reference
In-Depth Information
With a 2 MHz front-end bandwidth receiver
, the current standard for GPS receivers, things are a
little bit different
25
. The performances are in this case reduced (the efficiency is not as good
for mitigation), and a typical result is an equivalence between the SMICL (at 2 MHz) and the
NC (at 8 MHz). Thus, the SMICL allows one to obtain performances of the NC with the
current available bandwidth. This is a nice result but it is not sufficient since we showed that
10 to 12 metres of accuracy is not enough indoors. Thus, a 2 MHz bandwidth is not
sufficient.
With an 8 MHz front-end bandwidth receiver
, which is an intermediate plausible value for
future GNSS receivers (including Galileo), the ACF is very close to that obtained with the
theoretical unlimited bandwidth. The performance of the SMICL is then acceptable, as
shown in figure 21 which compares NC and SMICL. Note that the vertical axis is now given
in “chip” (0.01 is equivalent to approximately 3 metres). Based on this figure, multipath
errors are reduced with the SMICL to three meters in the worst case (very short out-of-phase
multipath) and to 0.7 m when the relative delay is between 0.1 and 0.5 chip.
Please keep in mind the fact that these results are obtained with only one reflected path.
Some other simulations were carried out in the case of a typical environment involving
several multipath rays and showed that the code measurement error due to multipath is
also significantly reduced when the SMICL is considered.
0,05
0,03
0,01
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0,5
-0,01
Out-of-Phase, SMICL
In-phase, SMICL
In-Phase, NC
Out-of-Phase, NC
-0,03
-0,05
Multipath relative delay (chips)
Fig. 21. Comparison of SMICL and NC for an 8 MHz bandwidth
4.6 Discussion
If one combines all the advantages of both pseudolites and repeaters, only the need for a
local infrastructure and the multipath effects are not dealt with. The repeater based
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Once again, there is a direct link between multipath mitigation efficiency and bandwidth.
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