A Novel Threshold Setting Method for FFT-based GPS Acquisition

Abstract

A FFT-based partial matched filter (PMF) acquisition threshold setting method for fast GPS acquisition is presented. Normal distribution and numerical fitting technique instead of real decision variable (DV) distribution are used in derivation to approximate the threshold expression, and the modification method for the threshold expression is also presented. The threshold expression is based on the individual FFT Doppler bin false alarm probability rather than the convention whole detector false alarm probability. The proposed threshold expression can be adjusted according to the false alarm probability, the noncoherent accumulation (NCA) length and the estimated noise variance. Additionally, how to select the optimal FFT point number is discussed. Furthermore we discuss the implementation of zero-padding FFT with its advantage and limitation. The performance is superior compared to the reference method in terms of signal-to-noise ratio (SNR) when detection and false alarm probabilities are used as measurement criteria.