Post-Correlation Peak Sharpening

Correlation between an incoming signal and a locally generated replica of it is a fundamental operation in a GNSS receiver. The height of the correlation peak above the noise floor indicates the presence or absence of a desired signal while the location of the peak provides an estimate of the time and frequency of the acquired signal. However, due to limited bandwidth and inherent code structure, the correlation function is not an ideal delta function but rather has a certain width and shape. The spreading of energy into neighboring code and frequency bins not only makes the peak location imprecise in the presence of noise (thus also called the ambiguity function) but also renders it vulnerable to such interference as multipath. Methods have been introduced in the past to sharpen the correlation peak either prior to or during the correlation process. In this paper, two post-correlation peak sharpening methods are investigated, namely, the nonlinear Teager-Kaiser (TK) operator and the two-dimensional (2D) deconvolution. The TK operator was shown to outperform the classical narrow-correlator method against multipath. The 2D deconvolution, implemented either as a modified inverse filter or a Wiener filter, is analogy to image-deblurring but in the delay-Doppler domain. Simulation results are presented to illustrate the functionality and performance of post-correlation peak sharpening methods.