SIM548C Hardware Design
4 GPS application interface
A GPS receiver with high performance has been integrated to offer GPS full function, it
continuously tracks all satellites in view and provides accurate satellite position data. Otherwise,
the GPS part can run separately even while the GSM part of SIM548C has been deregistered form
the GSM network.
4.1 Theory of operation
The theory of operation is shown in the following figure:
Figure 33: Theory of operation
The Module’s GPS part is designed to use L1 Frequency (C/A Code) GPS receiver and performs
the entire GPS signal processing, from antenna input to serial position data output.
The processing steps involved are:
RF section
In the RF section the GPS signal detected by the antenna is amplified, filtered and converted to an
intermediate frequency (IF). An A/D converter converts the analogue intermediate frequency into
a digital IF signal.
GPS channels
The received digital IF signal bit stream is passed to the baseband section, where it is fed into the
correlators. The function of the correlators are to acquire and track the satellite signals. There are
12 channels used in parallel, with each correlator looking for a characteristic PRN code sequence
in the bit stream. Once the correlator has found a valid signal, pseudo range, carrier phase and
orbit information can be extracted from the GPS signal.
SIM548C_HD_V1.01
09.05.2008
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