Fast PN code acquisition for satellite spread spectrum transponder

Large Doppler offsets are inherent to direct spread spectrum signal due to high dynamic environment in low earth orbit satellite communication scenarios. Frequency offset can be dozens of kilohertz, which cause traditional acquisition approach failed to complete PN code acquisition. A part-coherent combined with FFT technique was proposed for this problem. It utilized fast Fourier transform(FFT) to compensate coherent loss resulted by frequency shifts. It simultaneously searched code phases and got Doppler offsets, thus acquisition time could be significantly reduced. Acquisition structure was given, and FFT compensate performance was analyzed. The selection of part-coherent parameters and FFT points were given. Auto adaptive threshold technical was used to realize code acquisition when input signal power varied widely. Theoretical analysis and simulation results verify that the approach can complete fast code acquisition in high Doppler shift and low signal to noise ratio environment, and take up fewer field programmable gate arrays resources.