Joint Acquisition of CM and CL Codes for GPS L2 Civil (L2C) Signals

Chun Yang

Abstract:	"The GPS L2 civil (L2C) signal is developed to satisfy the needs of precise navigation with a second frequency so as to eliminate the ionospheric errors. As a time division multiplexed (TDM) signal, L2C has unique features that make it very different from C/A-code on L1 and I5/Q5 code on L5. Indeed, the two TDM codes of L2C, namely, the civil moderate (CM) code and civil long (CL) code, are significantly longer, thus having better correlation and spectral properties. It thus presents technical challenges and at the same time opportunities to devise new acquisition algorithms that can explore the signal structure to better fit different applications. This paper presents FFT-based techniques for acquisition of L2C signals in three areas. The first is the acquisition of the CM code alone per 20 ms. Based on the overlap and discard algorithm (ODA), a segmented FFT approach is set forth. Since it can process small segments of incoming signal samples as they arrive, it can reduce the latency, memory, and computation requirements per segment. Second, three acquisition schemes are described for the CL code, namely, the CM code-assisted CL code acquisition, the CL code alone per 20 ms, and the entire CL code over 1.5 s. In the latter case, the cascaded FFT of the second kind is developed to deal with code and carrier Doppler effects over the long integration interval. As a focus of this paper, the third area is the joint acquisition of the CM and CL codes per 20 ms. A composite complex replica is constructed to account for the TDM nature of the two codes as well as the unknown data modulation on the CM code. After describing the L2C signal structure, the three FFTbased acquisition techniques are presented. The paper also provides simulation results for the algorithms to illustrate their functionality and performance under various signal conditions."
Published in:	Proceedings of the 61st Annual Meeting of The Institute of Navigation (2005) June 27 - 29, 2005 Royal Sonesta Hotel Cambridge, MA
Pages:	553 - 562
Cite this article:	Yang, Chun, "Joint Acquisition of CM and CL Codes for GPS L2 Civil (L2C) Signals," Proceedings of the 61st Annual Meeting of The Institute of Navigation (2005), Cambridge, MA, June 2005, pp. 553-562.
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