Introduction - Fundamentals of Global Positioning System Receivers: A Software Approach - page 5

signals from programs processing real signals or vice versa with some simple
modifications. A program can be used to process signals digitized with various
sampling frequencies. Therefore, a software approach can almost be considered
as hardware independent.
New algorithms can easily be developed without changing the design of the
hardware. This is especially useful for studying some new problems. For example,
in order to study the antijamming problem one can collect a set of digitized signals
with jamming signals present and use different algorithms to analyze it.
1.7 ORGANIZATION OF THE TOPIC
This topic contains twelve chapters. Chapter 2 introduces the user position require-
ments, which lead to the GPS parameters. Also included in Chapter 2 is the basic
concept of how to find the user position if the satellite positions are known.
Chapter 3 discusses the satellite constellation and its impact on the GPS signals,
which in turn affects the design of the GPS receiver. Chapter 4 discusses the earth-
centered, earth-fixed system. Using this coordinate system, the user position can
be calculated to match the position on every-day maps. The GPS signal structure is
discussed in detail in Chapter 5. Chapter 6 discusses the hardware to collect data,
which is equivalent to the front end of a conventional GPS receiver. Changing the
format of data is also presented. Chapter 7 presents several acquisition methods.
Some of them can be used in hardware design and others are suitable for software
applications. Chapter 8 discusses two tracking methods. One uses the conventional
phase-locked loop approach and the other one is more suitable for the software radio
approach. Chapter 9 is a summary of the previous chapters. It takes all the informa-
tion in the first eight chapters and presents in it an order following the signal flow
in a GPS receiver. Chapters 10 and 11 are devoted to weak GPS signal processing.
Not only the processing but the limitation of an autonomous GPS receiver is also
defined. Chapter 12 includes various subjects related to GPS receivers.
Computer programs written in Matlab are listed at the end of several chapters.
Some of the programs are used only to illustrate ideas. Others can be used in
the receiver design. In the final chapter all of the programs related to designing
a receiver will listed. These programs are by no means optimized and they are
used only for demonstration purposes.
REFERENCES
1. Parkinson, B. W., Spilker, J. J. Jr., Global Positioning System: Theory and Applica-
tions , vols. 1 and 2, American Institute of Aeronautics and Astronautics, 370 L'Enfant
Promenade, SW, Washington, DC, 1996.
2. “System specification for the navstar global positioning system,” SS-GPS-300B code
ident 07868, March 3, 1980.
3. Spilker, J. J., “GPS signal structure and performance characteristics,” Navigation ,
Institute of Navigation, vol. 25, no. 2, pp. 121 - 146, Summer 1978.