Global Positioning System Reference
In-Depth Information
Incoherent integration gain
25
20
P d =
0.9
P fa =
15
10 7
10
5
0
10 0
10 1
Number of incoherent integration
10 2
10 3
FIGURE 10.4 Noncoherent integration gain.
noncoherent integrations. In order to sum the results from data without navigation
data phase transition, a maximum of 38 data blocks of 10 ms will be processed
coherently. The coherent results from blocks 1, 3, 5, etc., will be summed and the
results from blocks 2, 4, 6, etc., will be summed. One of these two summations
should provide the desired results.
However, in actual acquisition all the results obtained from coherent integra-
tions will be summed together without separation into odd and even groups. In
actual processing, the peak obtained in the time domain will be shifted because of
Doppler frequency. This shift must be considered when performing noncoherent
integration.
An article by Psiaki ( 11 ) states that by processing 4 seconds of data through
the 10 ms coherent integration, a C / N 0 of 18 dB can be achieved. Four seconds
of data mean that n
200 because the odd and the even 10 ms of data are
added separately. From Figure 10.4 the noncoherent integration gain is slightly
over 16 dB. Thus the overall gain is about 26 dB: 10 dB from the coherent
integration and 16 dB from noncoherent gain. The sensitivity can be improved
by 26 dB from C / N 0 = 18 dB to the desired value of 44 dB (18 + 26). This can
be considered as another example to illustrate the noncoherent integration gain.
=
10.8 ACQUISITION CONSIDERATIONS OF WEAK SIGNALS ( 12 )
The actual acquisition method will be discussed in the following sections. The
method discussed is without a priori information, such as knowing the range of
 
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