Weak signal acquisition enhancement in software GPS receivers - Pre-filtering combined post-correlation detection approach

The Civilian Global Positioning System (GPS) receivers often encounter problems of interference and noise which degrade the receiver performance. The conventional methods of parallel code phase search acquisition with coherent, non-coherent and differential coherent detection for weak signal acquisition fail to enhance the signal for all conditions especially, when the Carrier to Noise ratio (C/N0) falls below 15 dB-Hz. Hence, the GPS receiver has to employ sophisticated techniques to excise the noise and to improve the Signal-to-Noise Ratio (SNR) of the signal for further processing. In this paper, a pre-filtering technique of reduced rank Singular Spectral Analysis (SSA) is proposed for noise excision and is processed through coherent, non-coherent and differential detection postcorrelation methods to retrieve the signal embedded in noise. Monte Carlo simulations carried out to examine the acquisition sensitivity at various power levels with the different postcorrelation approaches indicate that the SSA combined with differential detection approach provides a significant performance improvement with lesser mean acquisition time. It has 96% probability of detection at a worst signal power level of −159 dBm (i.e. C/N0 15 dB-Hz), compared to other conventional methods.