GPS Software Receivers - Fundamentals of Global Positioning System Receivers: A Software Approach - page 209

FIGURE 9.9 Doppler frequency versus slopes of the accumulative lines.
program. Therefore, the two parameters, carrier frequency and the beginning of
the C/A code, can be used for a real-time receiver.
9.16 SUMMARY
This chapter describes a GPS receiver by following the signal flow. Digitized data
are used as input to perform acquisition and find the signals of all the satellites.
Once the signals are found they will be tracked. The results of the tracking
program can be converted into navigation data. In general, 30 seconds of data
should contain the information of subframes 1, 2, and 3. The preamble words
and the subframe numbers can be used to find the subframes. Parity checking
must be performed to ensure that the data are without errors. Ephemeris data
can be found from subframes 1, 2, and 3. The GPS time at time of transmission
can be found from the beginning of subframe 1 and the time of the week. The
pseudoranges for different satellites can be found from the relative beginning
points of subframe 1. The use of subframe 1 as a reference is arbitrary. From
the data obtained, the positions of the satellites and the user position can be
obtained. Finally, it is illustrated that the transition from acquisition to tracking
in a software receiver can be achieved for real-time applications.