A New Adaptive Code Processing Scheme for High-Sensitivity Acquisition in Dual-Frequency GPS L1-L2C Receivers

Sana Ullah Qaisar and Mohamed Khalaf-Allah

Abstract:	The synchronized ranging codes on the L1-C/A and L2C signals allow for their combined processing to enhance the acquisition sensitivity, in a dual-frequency GPS L1-L2C receiver. The presence of unknown and independent navigation message bits on the C/A and L2C codes, however, prevents their coherent combination. Consequently, researchers so far have adapted only non-coherent and differentially-coherent combining schemes for joint acquisition of the two codes. In this paper, we propose an adaptive processing scheme for coherent combining of L1 C/A and L2C codes in the joint L1-L2C signal acquisition. In this approach, L2 CL and C/A codes are compared with reference signals available at the conventional CM correlator output. The comparison identifies chips of CL and C/A codes which disagree with polarity of corresponding reference chips. The polarity of identified CL and C/A chips is then inverted. This results in all three (C/A, CM and CL) codes lining up during correct CM code phase trial and maximising the signal to noise ratio. The proposed scheme is validated through theoretical analysis and testing with real GPS signals and it is shown that the proposed approach outperforms all existing schemes of combined GPS L1-L2C signal processing in the context of acquisition sensitivity.
Published in:	Proceedings of the 2013 International Technical Meeting of The Institute of Navigation January 29 - 27, 2013 Catamaran Resort Hotel San Diego, California
Pages:	536 - 656
Cite this article:	Qaisar, Sana Ullah, Khalaf-Allah, Mohamed, "A New Adaptive Code Processing Scheme for High-Sensitivity Acquisition in Dual-Frequency GPS L1-L2C Receivers," Proceedings of the 2013 International Technical Meeting of The Institute of Navigation, San Diego, California, January 2013, pp. 536-656.
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