Acquisition of Weak Signals in Multi-Constellation Frequency Domain Receivers
- 1 Department of Electrical Engineering, école de Technologie Supérieure, Montreal, Canada
- 2 Department of Geomatics Sciences, Université Laval, Quebec, Canada
- 3 Department of Electrical Engineering, école de Technologie Supérieure, Montreal, Canada
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 fre quency 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 re move the need for double buffering. The proposed methods are implemented in a configurable Simulink model, devel oped for acquiring recorded GNSS signals. For weak signal scenarios, a Spirent GPS simulator is used as a source. Ac quisition results for GPS L 1 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 accommodat ing 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.
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