Improved Double Block Zero Padding Algorithm for P Code Direct Acquisition

A segmented rotation double block zero padding (DBZP) algorithm was proposed based on the improved traditional DBZP algorithm for direct acquisition of P code in the environment of heavy noise and large frequency dynamics. The input complex-valued baseband signal was first segmented into finite-length records, and then transformed into frequency coefficients by fast fourier transform (FFT). By estimating the initial value of the frequency offset and its slew, the center frequency offset was determined for each temporal record, which was then compensated by cyclically shifting the corresponding Fourier coefficient record. Once the compensation was done, the correlation between the input signal and the local PN code was performed in frequency domain, and the correlation output was non-coherently accumulated over a number of records. For the last step, the constant false alarm rate (CFAR) detection and parabola interpolation were utilized with the maximum value of the accumulated correlation output. It is found for typical acquisition scenario that the presented algorithm may cut down computational overhead, memory consumption and the mean acquisition time by 64%, 99% and 80%, respectively, in comparison with traditional DBZP algorithm, without noticeable SNR penalty. The principles for choosing key parameters of the algorithm are discussed to meet various practical requirements.