Acquisition of the GPS L5 Signal Using Coherent Combining of I5 and Q5

Chun Yang, Chris Hegarty and Michael Tran

Abstract:	This paper proposes a method for acquiring the new GPS L5 signal using a coherent combination of I5 and Q5. The performance of the method is demonstrated via analysis and computer simulation. The proposed technique takes advantage of the synchronicity and orthogonality between signal-to-noise improvement compared to the usual method of non-coherently combining I5 and Q5 correlator outputs. The paper examines various mechanizations for coherently combining I5 and Q5. Both non-FFT and FFT-based techniques are considered. In the FFT-based implementation, circular correlations for the 10 ms and 20 ms boundary alignments are used corresponding to the I5 and Q5 Neuman-Hofman (NH) codes, respectively. This technique can be directly applied to the Q5 NH code, which repeats every 20 ms. However, it is not as straightforward to apply to the I5 NH code because of the unknown data modulation. In addition, there may be residual Doppler frequency errors up to ±250 Hz in the 1 ms complex correlations, which are known to be detrimental to NH code acquisition. Both problems are solved in our approach with zero-padding and judicious design of replica code patterns. Simulation results of the proposed techniques are provided in the paper to demonstrate performance in a variety of signal-to-noise conditions with varying initial Doppler frequency uncertainty.
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:	2184 - 2195
Cite this article:	Yang, Chun, Hegarty, Chris, Tran, Michael, "Acquisition of the GPS L5 Signal Using Coherent Combining of I5 and Q5," 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. 2184-2195.
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