TITLE:
Acquisition of Weak Signals in Multi-Constellation Frequency Domain Receivers
AUTHORS:
Kaveh Mollaiyan, Rock Santerre, René Jr. Landry
KEYWORDS:
FFT Acquisition; Frequency Domain Receiver; Weak Signal; Multi-Constellation
JOURNAL NAME:
Positioning,
Vol.4 No.2,
May
22,
2013
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.