Novel acquisition of global positioning system signals based on parameter prediction and the chirp z-transform

Abstract

The acquisition stage in global positioning system receivers provides a coarse estimation of the Doppler shift and the code phase of the incoming signals. The accuracy of the estimation, especially the Doppler shift, greatly influences the subsequent tracking loops. Based on the parameter prediction and the chirp z-transform algorithm, a novel acquisition approach to acquire the Doppler shift accurately is proposed. The code phase and the Doppler shift are predicted first according to the desired trajectory of the vehicle and satellite ephemeris. Then, frequency refinement of the code-stripped signal is conducted within a small interval around the predicted Doppler shift by using the chirp z-transform algorithm. To reduce the computational load, the data sequence is down-sampled with an integrate and dump accumulator without degrading the performance of the proposed algorithm. Results indicate that, with only 1 ms sampled data, the proposed algorithm can achieve a high-frequency accuracy. Besides, the proposed algorithm can acquire signals with the carrier-to-noise ratio down to 31 dB-Hz.