Joint Code Acquisition and Frequency Offset Estimation for GPS L5 Receivers

Miin Wang and Shang-Wei Chen

Abstract:	Because the GPS acquisition and tracking process is a two-dimensional (code and carrier) signal replication process, to detect a certain GPS signal, both the code and carrier shifts should be known. Serial or parallel searching method is widely used in the traditional GPS receiver to detect the signal. However, due to the much higher chip rate (10.23 MHz) of the C/A code transmitted on L5[1], the serial search method or the simple parallel search methods are not suitable. The larger chip rate indicates that there are more code phase uncertainties to be searched. Therefore, the time consuming serial search method cannot be used anymore. Besides, parallel search method that simply use lots of correlators is not a good solution. Recently, many parallel search methods are proposed to reduce the mean acquisition time. One example is the discrete Fourier transform (DFT) method which is usually implemented in the GPS software receiver. Computation complexity is the major problem if the DFT method is selected. Another common method is the matched filter. Although this algorithm is simpler than the DFT method, the hardware complexity increases. In this paper, we propose a new method that simultaneously acquire code phase and estimate the frequency offset. The new algorithm first uses the partial matched filter[2] method to acquire code phase. Taking advantage of the special matched filter structure, we then apply the Luise and Reggiannini (L&R) [3] estimator to estimate the frequency offset. We also provide theoretical analysis for the acquisition performance. Based on the results, we are able to derive the optimal threshold minimizing the probability of acquisition error. Simulations show that the acquisition performance is similar to that of the DFT approach and the frequency offset estimate is accurate. The computational complexity of the proposed algorithm is low and suitable for real-world implementation.
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:	2246 - 2253
Cite this article:	Wang, Miin, Chen, Shang-Wei, "Joint Code Acquisition and Frequency Offset Estimation for GPS L5 Receivers," 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. 2246-2253.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In