A Robust GPS Signal Acquisition Technique Using Discrete Wavelet Transform

Abstract

A novel Global Positioning System (GPS) signal acquisition scheme based on Discrete Wavelet Transform (DWT) is proposed to improve acquisition performance. Acquisition in GPS system is primary and important step to calculate the code phase in Pseudo Random Noise (PRN) code and Doppler shift in carrier frequency of received GPS signal, which is used for continuous tracking of the satellite. The performance of a GPS receiver system depends on the ability to precisely measure the code range and Doppler shift continuously in the presence of noise. Conventional GPS receivers use Fast Fourier Transform (FFT) to carry out convolution in the acquisition process. This method is unable to precisely acquire the GPS signal in the presence of noise. In this paper, a substitute algorithm using DWT is proposed to perform convolution in order to carry out robust, less complex GPS signal acquisition. The proposed algorithm is implemented on Intermediate Frequency (IF) GPS signal with different levels of noise and also compared with the conventional FFT search algorithm. The proposed algorithm allows implementation of the FFT with a reduced number of samples (2500 instead of 5000 samples), is implemented by collecting the one millisecond period data sampled at 5MHz. Performance of the algorithms are compared based on correlation ratio. Results show that the proposed algorithm using DWT outperforms the FFT search method of acquisition.