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

The L1/E1 band will soon be populated with four different signals, namely the GPS C/A, L1C, Galileo E1B, E1C codes. 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 have high computational loads to perform the FFT/IFFT operations, especially when the receivers operate at a high sampling rate. To reduce the computational loads of the frequency domain receiver, a new correlation method with signal down sampling in the frequency domain is proposed. The down sampling is achieved by pruning the high frequency parts of the signal spectrum and then performing IFFT in smaller sizes. In addition, a novel open loop code delay estimation method without correlation interpolation is 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.