Grouping FFT Based Two-Stage High Sensitivity Signal Acquisition With Sign Transitions

The acquisition performance of weak global navigation satellite system signals, especially those with secondary codes, is susceptible to sign transitions. To better understand and overcome the negative impact of sign transitions, this paper derived a new receiver auto-correlation function. The straightforward formula shows that sign transitions can reduce the accuracy of the Doppler estimate. To meet the initialization requirements of the tracking block, a two-stage high-sensitivity acquisition frame is proposed based on sign combinations search using matrix notation. The first stage adopts the conventional non-coherent combination (NC) algorithm to obtain the coarse code phase. And the second stage achieves high-resolution frequency estimation through fast Fourier transform (FFT). Besides, a novel grouping FFT algorithm is proposed to reduce the complexity of the second stage. The Beidou navigation satellite system (BDS) B1I signal is used as an example to verify the performances. Compared with conventional NC algorithm, the statistical performance of the new algorithm, in terms of the detection probabilities and frequency errors, can be greatly improved. To be specific, the proposed algorithm can actualize the 90% detection possibility of BDS B1I signal at a carrier-to-noise ratio (C/N₀) of 23.9 dB-Hz within 200 ms with a Doppler accuracy of about 31 Hz. And the computing load of the second stage is reduced by about 11.6% compared with the conventional FFT approach. Actual data test further verifies the superiority of the new method. Inevitably, the total processing time increases by about 30%.