Bit Transition Cancellation Signal Acquisition Method for Modernized GPS and Galileo Signal

Sanghoon Jeon, Hyoungmin So, Ghangho Kim, Changdon Kee, Kiho Kwon

Abstract:	This paper proposes a new method for bit transition problem in GNSS signal acquisition process. If the incoming data samples contain a bit transition caused by navigation data or secondary code, the acquisition result is no longer the same as the information of the incoming signal data. GPS L1 C/A code does not have the secondary code and its data bit duration is the multiples of code period length. For a single code period acquisition of C/A code, a simple method could be applied. New GNSS signals like GPS L2-CM and L5, on the other hand, have data bit duration of the same as the code period length, and need another method to solve the bit transition problem. There are two main problems due to the bit transition problem. The one is the reduction of the maximum correlation power. It decreases the signal detection probability. The other is that the correlation peak is not maximized around true Doppler shift. If the bit transition does not exist in the incoming signal, the shape of the correlation function envelope represents a sync function in frequency domain when the code delay of the replica is synchronized with that of the incoming signal. However, if the incoming signal includes the bit transition, the Doppler shift in the cell of the correlation peak may not represent the approximate Doppler shift of the incoming signal. The difference between the Doppler value of the incoming signal and the ambiguous Doppler shift result of acquisition process is so large that tracking process could lose tracking lock. To solve the bit transition problem, bit transition cancellation (BTC) method proposed in this paper. This method has simple structure and its own characteristic. It uses two code replicas. The one is the code replica to acquire signal. The other is the modified one. The correlations are performed independently using each replica, and the results of correlation are summed after integration. Then, new correlation function without the Doppler ambiguity is made. The envelope of new correlation power function appears the combination of two sinc functions in frequency axis. The envelope represents correlation peak that corresponds to the Doppler shift of the incoming signal. To test the performance of the proposed method, the computation time and the signal detection probability are analyzed by Monte-Carlo simulation. The simulations of other literature methods are also performed for comparison. The simulation result shows that the proposed method successfully solves the Doppler ambiguity problem and has advantages compared with others.
Published in:	Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011) September 20 - 23, 2011 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	1028 - 1039
Cite this article:	Jeon, Sanghoon, So, Hyoungmin, Kim, Ghangho, Kee, Changdon, Kwon, Kiho, "Bit Transition Cancellation Signal Acquisition Method for Modernized GPS and Galileo Signal," Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011), Portland, OR, September 2011, pp. 1028-1039.
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