A Frequency Domain Quasi-Open Loop Tracking Loop for GNSS Receivers

E. Anyaegbu

Abstract:	Frequency domain processing will drive the proliferation of navigation services to wireless devices including mobile phone as it increases the flexibility and reduces the hardware required for processing Global Navigation Satellite System (GNSS) signals while maintaining a performance comparable to the conventional time-based algorithms. The emergence of new navigation applications will accentuate the need for the software radio. Studies have shown considerable reduction in the acquisition time, an improvement in the ability of the receiver to maintain lock in environments with a low received signal to noise ratio (SNR) and an improvement in the ability of the receiver to detect and suppress interfering signals when frequency-based techniques are employed. Hence, the increased flexibility and reduced hardware offered by frequency domain processing techniques will facilitate the development of software radios. A quasi-open tracking loop is based on the idea that the acquisition process is repeated on each segment of the received signal and can be implemented using frequency domain techniques. However, in the tracking phase, the entire correlation map is no longer required as the receiver now has an initial estimate of the code phase and carrier frequency values. Hence, a pruning technique such as the zoom FFT, which only computes the correlation totals of the area around the peak, can be employed. The zoom FFT reduces the size of the correlation energy map required and offers a resolution better than that of a transform with the same reduced size. It involves taking smaller transforms on selected data points from different segments of the data set. The paper investigates the effectiveness of frequency domain transforms in tracking GNSS signals and describes how the quasi-open tracking loop operates. It presents an analysis of the zoom FFT technique that is employed to reduce the computational complexity of the standard FFT computation. A performance evaluation of this technique is then carried out by evaluating the size of the zoom window, the processing requirements and the update rate of the loop. Previous work on frequency domain tracking of GNSS signals focused on the design of the frequency-based tracking architecture.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	790 - 798
Cite this article:	Anyaegbu, E., "A Frequency Domain Quasi-Open Loop Tracking Loop for GNSS Receivers," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 790-798.
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