A Real-time FFT Based Block Processing Method with Near Linear Scaling

M. Turner, A. Richardson

Peer Reviewed

Abstract:	Block processing algorithms have great potential in GNSS receivers. The block processing methods considered here are based on the Fourier correlation method which generates the full correlation function. Historically the large processing power requirements of FFT have prevented these block processing methods being used outside the acquisition phase. This paper presents an algorithm which reduces the processing requirements of FFT-based block processing for GNSS signals by an order of magnitude compared to current techniques. The Multiple Tracking Locked Loop (MTLL) FFT algorithm presented here in the limit of long integration times (circa 20ms or longer) and multiple tracked satellites (circa 10) scales near-linearly with sample rate. The MTLL method can be applied to GPS and Galileo signals and still exhibits its near-linear scaling with either signal constellation. As the MTLL algorithm gives access to the full correlation function further post processing can be done to completely mitigate multipath, where there is line of sight to the satellite and its ability to remove multipath effects is only limited by the initial RF sampling bandwidth. The MTLL method also lends itself to the detection and mitigation of interference as it is based on performing FFTs. The method lends itself to long integration times and can be easily implemented on standard computer hardware. This allows very high sensitive receivers that operate in difficult conditions like indoors, urban environments and under fading due to scintillation. This paper defines the algorithm and the underlying principles, describes how the tracking algorithm works and how it has been implemented in a software receiver using standard commercial computer hardware. Early results of experiments done using GPS and Galileo constellations are also presented.
Published in:	Proceedings of the 2015 International Technical Meeting of The Institute of Navigation January 26 - 28, 2015 Laguna Cliffs Marriott Dana Point, California
Pages:	475 - 483
Cite this article:	Turner, M., Richardson, A., "A Real-time FFT Based Block Processing Method with Near Linear Scaling," Proceedings of the 2015 International Technical Meeting of The Institute of Navigation, Dana Point, California, January 2015, pp. 475-483.
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