C/A-code Synchronization Using Analog Feedback Shift Registers (AFSR)

Daniel Megnet-Kagi, Heinz Mathis, Pascal Flammant and Andreas Thiel

Abstract:	Analog feedback shift registers (AFSR), which are related to the more commonly known linear feedback shift register (LFSR) can be of great use to the acquisition task in a GPS receiver to acquire the C/A-code. In many applications such as A-GPS (assisted GPS), the number of SVs to look for as well as the frequency search dimension (for example through GSM-derived references) are reduced and the only dimension remaining large is the code phase. With the algorithm proposed, the search over the code phase space is accelerated to a very high degree. The AFSR receiver concept, which is fundamentally different from the traditional correlation method, is explained and adapted for use with Gold sequences. Difficulties and solutions associated with practical implementations are discussed. An analysis of the required precision at different stages and the number of operations used is provided. The proposed algorithm has been verified by computer simulations and by a realtime implementation (using fix-point arithmetic) on a DSP. The hardware demonstrator built is based on a conventional dual-converter L1 receiver architecture followed by an A to- D converter connected to a Texas Instruments DSP, on which the AFSRs are implemented.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	32 - 42
Cite this article:	Megnet-Kagi, Daniel, Mathis, Heinz, Flammant, Pascal, Thiel, Andreas, "C/A-code Synchronization Using Analog Feedback Shift Registers (AFSR)," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 32-42.
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