Significance of Cell Correlations in Matched Filter GPS Acquisition Engines

Due to their attractive acquisition time performance, matched filter correlators are widely used in GPS signal acquisition engines. Existing methods to evaluate the GPS signal acquisition engine performance parameters viz. probability of detection and mean acquisition time are based on the assumption that the detection among the neighbouring test cells is independent. However in a matched filter correlator, depending on the spacing between the test cells, there could exist strong correlations among the consecutive outputs which affect these performance parameters. Taking into account these correlations in the analysis does not make the acquisition faster, but make the performance parameters more accurate. These improvements then contribute to the quality of the threshold setting process, which is very important in receiver design. This paper provides a detailed analysis of the significance of the cell correlations in the matched filter correlators used in GPS L1 C/A signal acquisition. Justifying the theoretical analysis with Monte Carlo simulations, it is shown that the error caused by omitting the cell correlations in estimating the probability of detection and the acquisition threshold will be around 6-7% at the signal strengths of 32-33 dB-Hz, even for the search step size of 0.5 chip. The trend also shows that the error worsens for lower signal strengths.