Global Positioning System Reference
In-Depth Information
Hint: Use the fastest computer available because the computations are heavy.
Start MATLAB with matlab - nojvm - nosplash to increase performance. Load
the data with
load data.mat;
x = double(data');
Load the C/A sequences with
load gold1.mat;
code = double(code);
15. Run the same scenario with the parallel code phase search algorithm found
in the M -file acquisitionConvolution.m . Compare the results and performance of
the two algorithms.
16. Tracking only the C/A-code in the signal . Load the M -file data_long.mat .
This M -file contains the same data sequence as data.mat , except it is just about
30 s long. Use the block diagram in Figure 7.12 to track the code in the incoming
signal data_long.mat .
Keep the frequency of the “Local Oscillator” constant at the frequency at which
you have acquired the signal. This means that the phase of the local carrier is not
locked, which implies that if the frequency is not 100% correct, the signal power
will be switching between the In-phase and Quadrature arm.
The “PRN Code Generator” from Problem 12 should be used to produce three
local code replicas. There should be 1 chip between the early and prompt replica.
One chip corresponds to about 38 samples at 38
.
192 MHz.
- Make an acquisition on the first 1 ms of data_long.mat .
- Track the first 1 ms by using the scheme above, and use the “frequency”
and “code phase” from the acquisition.
- After the first ms, construct the Code Lock Loop discriminator from the six
outputs as
D
=
I P (
I E
I L ) +
Q P (
Q E
Q L ).
- Use the output of the discriminator to adjust the “code phase” in the PRN
Code Generator and continue to track the signal in 1-ms blocks.
Hints: When the code tracking is working, the sum of the squared prompt out-
puts is higher than the sum of the early and late outputs. This means that the local
prompt code replica has a larger correlation value than the other two replicas.
17. Load the M -file navigation.mat . It contains synchronized navigation data
bits represented by
[−
11
]
. Find the first beginning of a subframe in the navi-
gation data sequence.
Hint: Use correlation with the preamble
[
1
1
1
11
111
]
.No-
tice that the sequence can be inverted!
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