New code delay compensation algorithm for weak GPS signal acquisition

Abstract

Global positioning system (GPS) is a system combining code division multiple access (CDMA) and trilateration techniques to obtain precision position and timing information. The main goal of this paper is to present a high-sensitivity receiver for acquisition of weak GPS signals. A new peak-finding algorithm is developed to search the C/A code phase in the FFT-based correlation domain. This method can estimate the peak location accurately and provides a faster performance in software-based signal acquisition. Because the received frequency increases as the satellite advances the receiver and decreases as it recedes from the user in the Doppler circumstance, the code delay compensation (CDC) algorithm is proposed to enhance the capability of waveform search under indoor conditions. Using the carrier-aiding information, the CDC method can find the autocorrelation peak value effectively under both Doppler shift and weak signal environments. A step-by-step acquisition procedure is designed for indoor GPS receivers to detect the C/A code delayed phase effectively and reliable operation in a diversity of weak signal and Doppler environments. Simulation results demonstrate that our proposed scheme can achieve a significant improvement in processing gain over the traditional methods and acquire the GPS signal efficiently under the power levels of - 155 dBm in frequency domain processing.