Sharpen the Correlation Peak: A Novel GNSS Receiver Architecture with Variable IF Correlation

Chun Yang

Peer Reviewed

Abstract: Correlation plays a critical role in the operation of a GNSS receiver. However, correlator design faces a dilemma. Fast acquisition favors a wider correlation peak for fewer search grid points while accurate tracking needs a narrower one. With a narrower peak, a receiver can better reduce the detrimental effect of multipath and spoofing signals. A code with a wider bandwidth produces a sharper peak, e.g., GPS P(Y)-code (10.23 MHz) vs. C/A-code (1.023 MHz). A code with more energy toward the band edges also has a sharper peak, e.g., GPS M-code (BOC) vs. P(Y)-code (BPSK). However, a BOC code develops secondary peaks with significant strength, which are ambiguous and may lead to false lock. In this paper, we propose a new receiver architecture that performs correlation at a variable intermediate frequency (IF). By up-converting the code replica to a suitable IF, we effectively perform a joint code and carrier correlation, which has the ability to afford a correlation peak as sharp as the upper IF allows. By progressively varying the IF, we not only sharpen the correlation peak but also provide an easy and reliable means to lock onto the main peak among secondary peaks without ambiguity and false lock. The principle of correlation at variable IF is described in this paper together with implementation options. Simulation results are presented to demonstrate the viability of the new receiver architecture.
Published in: NAVIGATION: Journal of the Institute of Navigation, Volume 63, Number 3
Pages: 249 - 265
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