In order to improve the acquisition sensitivity of the weak and dynamic GNSS signal, the Fractional Fourier transform (FRFT) is introduced to deal with the acquisition process. The acceleration can be estimated using the FRFT approach, and the gain of coherent integration as well as the detection probability could be significantly improved. Partially matched filter (PMF) technique is used to be compared with FRFT. The digital computation complexity and the mean acquisition time are provided. Moreover, theoretical analysis for the detection probability has been proposed, and simulations are also conducted to verify the high performance of the technique.

In this letter, we propose the phase-locked loop with discrete wavelet transform filtering and redesigned Kalman filters (KFs) to enhance the global navigation satellite system signal carrier tracking robustness under ionospheric scintillation, being of the paramount importance in safety critical applications and advanced receivers. By normalizing the discriminator in the loop using the signal amplitude estimated with the discrete wavelet transform filtering, the phase variation due to scintillation is well estimated. The adaptive KF is modified with an additional amplitude state to copy with the scintillation-induced disturbance so as to stably track the fluctuated phases. Simulations are offered to verify the performance improvement of the proposed method versus the previous ones in the case of ionospheric scintillation.

For vehicle positioning with Global Navigation Satellite System (GNSS) in urban areas, open-loop tracking shows better performance because of its high sensitivity and superior robustness against multipath. However, no previous study has focused on the effects of the code search grid size on the code phase measurement accuracy of open-loop tracking. Traditional open-loop tracking methods are performed by the batch correlators with fixed correlation space. The code search grid size, which is the correlation space, is a constant empirical value and the code phase measuring accuracy will be largely degraded due to the improper grid size, especially when the signal carrier-to-noise density ratio (C/N₀) varies. In this study, the Adaptive Correlation Space Adjusted Open-Loop Tracking Approach (ACSA-OLTA) is proposed to improve the code phase measurement dependent pseudo range accuracy. In ACSA-OLTA, the correlation space is adjusted according to the signal C/N₀. The novel Equivalent Weighted Pseudo Range Error (EWPRE) is raised to obtain the optimal code search grid sizes for different C/N₀. The code phase measuring errors of different measurement calculation methods are analyzed for the first time. The measurement calculation strategy of ACSA-OLTA is derived from the analysis to further improve the accuracy but reduce the correlator consumption. Performance simulation and real tests confirm that the pseudo range and positioning accuracy of ASCA-OLTA are better than the traditional open-loop tracking methods in the usual scenarios of urban area.