Analysis of GPS Signal Acquisition Performance

Acquisition is to detect the presence of the GPS signal. Once the signal is detected, the estimated frequency and code phase are passed to a tracking loop to demodulate the navigation data. In order to detect the weak signal, multiple length of data integration is always needed. In this paper, we present five different acquisition approaches based on circular correlation and Fast Fourier Transform (FFT), using coherent as well as non-coherent integration techniques for the multiple length of collected GPS satellite signal. Moreover a general approach of determining the acquisition threshold is introduced based on noise distribution which has been proved effective, and independent of the hardware. In the end of this paper, the processing speed and acquisition gain of each method are illustrated, compared, and analyzed. The results show that coherent approach is much more time consuming compared to noncoherent approaches, and in the case of multiple length of data integration from 2ms to 8ms, the processing times consumed by the fastest non-coherent acquisition method are only 25.87% to 1.52% in a single search, and 34.76% to 1.06% in a global search of those in the coherent acquisition. However, coherent acquisition also demonstrates its better performance in the acquisition gain, and in the case of 8ms of data integration it is 4.23 to 4.41 dB higher than that in the non-coherent approaches. Finally, an applicable scheme of combining coherent and non-coherent acquisition approaches in the development of a real-time Software GPS receiver in the University of Tokyo is provided.