Software based GPS Receiver

Global Positioning System or GPS is a space-based global navigation satellite system (GNSS) that provides location and time information in all weather, anywhere on the earth provided there is an unobstructed line of sight (los) to four or more GPS satellites. From military applications to tracking and navigation, it has myriad applications in several domains. Basically, the GPS system provides a set of coordinates which represents the location of the GPS unit with respect to its latitude, longitude and elevation on planet earth. The devices used to receive and track GPS signals from the satellites are called GPS receivers. The GPS Receiver can be either software based or hardware based not in totality though. The unit which performs signal processing on the received GPS signals decides be it hardware based or software based. The world is now evolving to software based GPS receiver system where high level programming languages like C, C++ and Matlab are used for signal processing. Software-defined receivers are used to implement and test various algorithms before hardware implementation. In this project, a real time software-defined GPS receiver has been implemented on a dual core 3.0GHz x86 platform running Windows XP.

The major reason to switch to software based receiver system is that Software allows for switching between algorithms depending upon the received signal strength. The GPS civilian signal of 1575.42 MHz is received by the antenna followed by a Bandpass filter and a low noise amplifier. The SiGe GNS3 sampler then takes this signal downconverts it to 4MHz and samples it at a rate of 16MHz to a USB port on a pc. The computer then performs various algorithms on the sampled signal to generate the GPS coordinates.

The software for this project can be bifurcated into various levels as;

· Start-up

· Acquisition

· Tracking loop and

· Position Calculation

Go for a rich, enriching hands-on experience in making this project.