IF Signal Processing Algorithm for GPS Software Receiver

Based on simple comparison between a conventional navigation receiver and a GNSS software receiver, a generic GNSS receiver architecture is given, which focuses on the GPS IF signal processing algorithm in the channel. According to the channel states the algorithm falls into four parts: signal acquisition, confirmation, fine frequency estimation and tracking. A frequency domain acquisition based on FFT operation is proposed, but the acquisition results need to be confirmed because of the false alarm probability. Signal confirmation is formed on the basis of the conventional threshold detection method using the changes in the Doppler shifts and code phases during several consecutive sampling periods. The fine frequency estimation adopts signalspsila phase relation obtained from FFT. Signal tracking is a combination of a Costas Phase Look Loop (PLL) and a non-coherent Early-Late gate delay lock loop (DLL). At the end of the paper, the results of the experiments with real GPS IF signal confirm valid operation of the proposed GPS signal processing.