Real-Time Dual Frequency Software GPS Receiver

Aleksandar Jovancevic, Andrew Brown, Suman Ganguly, Michael Kirchner and Slavisa Zigic

Abstract:	Past several years have seen a tremendous increase of microprocessor computational power. As a result of that process the boundary between analog and digital processing has been moving steadily towards higher frequencies. The consequence of that trend is proliferation of software radio techniques in which signals, after downconversion to a suitable intermediate frequency, are digitized and processed entirely in the digital domain. GPS field has also seen several software implementations of the receiver functionality. While C/A-code bandwidth is sufficiently low so that the processing can be performed in real-time, the other GPS codes such as P and emerging new military code will still have to wait for more powerful signal processors to achieve entirely software real-time processing. Still, one can utilize reprogrammable hardware devices to perform the most computationally intensive operation – the correlation of GPS signals. Even though devices such as FPGAs are not software in the strict sense, they sill retain most of the benefits of software approach, namely its flexibility and reconfigurability. This paper describes the structure, operation and performance of a real-time dual frequency software GPS receiver. The receiver consists of the hardware front-end which downconverts and digitizes the signals from L1 and L2 frequencies, followed by the FPGA which performs signal correlation. The correlator output is fed to the PC which then continues signal processing entirely using software. The dual frequency processing is performed using semicodeless technique which provides independent carrier and code tracking of the L2 signal. Software processing of the signals has been extended to include advanced signal processing techniques such as beamforming, interference rejection, multipath mitigation etc. Addition of any novel type of processing using software approach is greatly simplified. This reduces development time and effort by an order of magnitude.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	2471 - 2482
Cite this article:	Jovancevic, Aleksandar, Brown, Andrew, Ganguly, Suman, Kirchner, Michael, Zigic, Slavisa, "Real-Time Dual Frequency Software GPS Receiver," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 2471-2482.
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