Acquisition of GPS C/A Code Signals - Fundamentals of Global Positioning System Receivers: A Software Approach - page 155

beginning point of the C/A code and the frequency are the correct values. The
beginning of the C/A code and the fine frequency can be found by adding more
calculations incoherently. The correct results are different from the maximum
shown in Figures 7.14 and 7.15.
7.16 SUMMARY
The concept of signal acquisition is discussed in this section. The circular correla-
tion method can provide fast acquisition without sacrificing detection sensitivity.
Although there are methods that can operate at a faster speed than the circular
correlation method, they usually have lower detection sensitivity. It appears that
the circular correction method using 1 ms of data is able to acquire signals from
most satellites. The delay and multiplication method must use more than 1 ms of
data to acquire a signal because of the high noise level created. The acquisition
provides the beginning of the C/A code and a coarse frequency. The fine fre-
quency can be found through phase comparison to within a few tens of Hertz. To
speed up the operation of the acquisition process is always desirable in software
GPS receivers.
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