Global Positioning System Reference
In-Depth Information
is set equal to the averaged value, which represents one false alarm of every
100 acquisitions performed. If the noncoherent integration number is 10, then 10
outputs obtained from coherent integration will be summed together. In order to
generate 1,000 runs, the acquisition must be performed 10,000 times because each
time 10 acquisitions will be performed. Thus, to generate the threshold is time-
consuming, and this is why only one data point (19 summations) was obtained
above 10 summations. The result is shown in Figure 10.16. An extrapolated
line is drawn through all the points. The threshold values are obtained from the
extrapolated line at each summation value from summation equal to 1 to 20. The
values are also listed in Table 10.2 as well as in Figure 10.16.
These results are obtained from a noise with standard deviation of 1 and
0 mean. In actual collected data the noise usually still has a mean close to
zero, but the standard deviation can be any value. In order to use the values
in Figure 10.16, the threshold must be a function of the standard deviation of
the noise. The relationship between the threshold values and the standard devi-
ation of the noise can be found through the following method. The standard
deviation of the noise is varied and the 10 ms acquisitions without summation
are used to determine the threshold. This operation is performed 1000 times to
obtain the desired threshold. The results are shown in Figure 10.17. Similar tests
are performed with summations. Figures 10.18a and 10.18b show the results of
summing 2 and 5 times.
TABLE 10.2 Measured and Extrapolated Thresholds for 1 to 20 Noncoherent
Integrations for 1 False Alarm in Every 100 Acquisitions
Number of Summations
Measured Threshold
Extrapolated Threshold
1
1814
1998
2
2754
2712
3
3518
3412
4
4214
4097
5
5486
4768
6
6600
5424
7
7826
6066
8
6693
9
7306
10
7904
11
8488
12
9057
13
9612
14
10153
15
10678
16
11190
17
11686
18
12168
19
12,660
12636
20
13090
Search WWH ::




Custom Search