A Complexity Reduced Frequency Domain Receiver for Galileo and GPS L1 Signals

F. Xu

Abstract:	The L1/E1 band will soon be populated with four different signals, namely the GPS L1 CA code, L1C code, Galileo E1B code and E1C code. The frequency domain receiver, which can provide parallel correlation and process all the signals in a common structure, becomes a promising solution for multi-code and multi-modulation processing. However, the conventional frequency domain receivers require quite high computational capacity to perform the FFT and IFFT operations, especially when the receivers operate at a high sampling rate. The high computational complexity would exert a negative effect on the size, power consumption, and cost of the receiver. To reduce the computational complexities of the frequency domain receiver, a new correlation method with signal down sampling in the frequency domain is proposed in this paper. The down sampling is achieved by pruning the high frequency parts of the signal spectrum and then performing IFFT in a smaller size. The correlation gain loss will be small because the pruned spectrums contain little energy. The results show that the correlation gain losses of BPSK (1) and BOC (1,1) are less than 0.4dB with a sampling rate of 16.384MHz, while the operations in the IFFTs can be reduced to 40% of the conventional method with original sampling rate of 40MHz. And because the IFFTs are the most computationally consuming parts in the frequency domain receiver, the new method can significantly reduce the computational load by reducing the IFFT size. In addition, because the closed code delay tracking loop cannot be applied in the frequency domain receivers directly, a correlation interpolation method, which can produce the EPL correlation as in the time domain receiver, is then usually applied in the existing frequency domain receivers. But the interpolation method will lead to extra operations. In this paper, a novel open loop code delay estimation method without correlation interpolation is also proposed. The method first obtains the integer parts of the code delay by the correlation peak detection, then gets the residual errors by code delay discrimination and finally obtains the precise estimation by post filtering. The results indicate that this new method not only reduces the complexity, but also improves the tracking sensitivity comparing to the conventional closed tracking loops.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	3198 - 3208
Cite this article:	Xu, F., "A Complexity Reduced Frequency Domain Receiver for Galileo and GPS L1 Signals," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 3198-3208.
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