Abstract
New positioning applications’ availability requirements demand receivers with higher sensitivities and ability to process multiple GNSS signals. Possible applications include acquiring one signal per GNSS constellation in the same frequency band and combining them for increased sensitivity or predicting acquisition of other signals. Frequency domain processing can be used for this purpose, since it benefits from parallel processing capabilities of Fast Fourier Transform (FFT), which can be efficiently implemented in software receivers. On the other hand, long coherent integration times are mainly limited due to large FFT size in receivers using frequency domain techniques. A new method is proposed to address the problems in frequency domain receivers without compromising the resources and execution time. A pre-correlation accumulation (PCA) is proposed to partition the received samples into one-code-period blocks, and to sum them together. As a result, the noise is averaged out and the correlation results will gain more power, provided that the relative phase between the data segments is compensated for. In addition to simplicity, the proposed PCA method enables the use of one-size FFT for all integration times. A post-correlation peak combination is also proposed to remove the need for double buffering. The proposed methods are implemented in a configurable Simulink model, developed for acquiring recorded GNSS signals. For weak signal scenarios, a Spirent GPS simulator is used as a source. Acquisition results for GPS L1 C/A and GLONASS L1OF are shown and the performance of the proposed technique is discussed. The proposed techniques target GNSS receivers using frequency domain processing aiming at accommodating all the GNSS signals, while minimizing resource usage. They also apply to weak signal acquisition in frequency domain to answer the availability demand of today’s GNSS positioning applications.
Highlights
Using Fast Fourier Transform (FFT) as a new way to carry out the correlation was first introduced by Van Nee and Coenen [1]
Frequency domain processing can be used for this purpose, since it benefits from parallel processing capabilities of Fast Fourier Transform (FFT), which can be efficiently implemented in software receivers
They apply to weak signal acquisition in frequency domain to answer the availability demand of today’s GNSS positioning applications
Summary
Using FFT as a new way to carry out the correlation was first introduced by Van Nee and Coenen [1]. The main contributor to the computational load of FFT-based approach is the complex multiplications, the number of which increases with the number of samples. This is especially problematic where the number of samples becomes larger. To capture all the modernized GNSS signals in a single frequency band, a multi-constellation GNSS receiver should sample the signal at a high sampling rate. This raises lots of issues in multi-constellation receivers as well as weak signal situations. Solutions to the bottlenecks in FFT acquisition using long coherent integration times are discussed and an acquisition scheme based on parallel code phase search is proposed for BPSK signals
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