Theory and Applications of Signal Compression in GNSS Receivers

Lawrence R. Weill

Abstract:	The last two decades have seen the evolution of increasingly sophisticated GNSS signal processing technology. Examples are new methods for acquiring and tracking a wide variety of new signal structures, advanced multipath mitigation techniques, the development of high-sensitivity receivers for reliable operation indoors and in urban canyons, high-speed processing to reduce time to first fix, and algorithms for improved ranging accuracy and attitude estimation. Common to many of the new signal processing methods is the need to process the millions of chips in a GNSS signal in unconventional ways, which can dramatically increase the amount of computation the receiver must perform. For example, in typical GNSS receivers the computation of correlation functions is not difficult because the correlator reference waveform can be an ideal chipping sequence with only the values ±1, and multiplications become trivial. However, the high performance of the Multipath Mitigation Technology (MMT) algorithm developed by the author and a colleague requires correlator reference waveforms which include the effects of filtering in the receiver and the satellite [1-6]. Thus, in MMT many millions of multibit multiplications would be needed to compute the correlation function for just one delay value, notwithstanding that many high-resolution delay values are actually needed. The computational demands in the above example and in many other advanced processing techniques can be dramatically reduced by first implementing a process called signal compression, for which a patent is pending [7]. In signal compression a large number of raw digitized baseband signal samples (typically on the order of 107-108) is reduced to a small vector having only a few tens of samples (the exact number depends on the type of GNSS signal being processed). The compressed signal has the appearance of a single chip of the received signal (or two separate chips in some of the newer chipmultiplexed signals considered for GPS L1C and Galileo). Compression requires only simple additions to generate, and preserves all signal range and phase information. Subsequent processing of any type is dramatically simplified because of the extremely small size of the compressed signal. Therefore, huge advantages accrue in a wide variety of endeavors, such as range and phase extraction, phase ambiguity resolution, multipath mitigation, integrity monitoring, and many others.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	708 - 719
Cite this article:	Weill, Lawrence R., "Theory and Applications of Signal Compression in GNSS Receivers," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 708-719.
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