Research And Implementation Of Fast Synchronization Of Spread Spectrum Receiver With Large Pole Frequency Shift

Short-data transferring via LEO(Low Earth Orbit) micro-satellite communication systems seems to have a brilliant future in the field of special communications and national defense, because of its inherent characteristics. The thesis is based on the research and development of a LEO Micro Satellite Earth Receiver, and specialized in-depth research of the system architecture and crucial algorithms. The key point of the research work is to find a novel method for fast acquisition and tracking of CDMA ( Code-Division Multiple Access ) signal under low S/N and large Doppler-Frequency-Shift, which are regular in LEO satellite communications.The thesis mainly aims at the CDMA receiver synchronization problem caused by large Doppler-Frequency-Shift. The basic procedure and method for code-frequency two-dimension acquisition are explained first. Then the thesis brings forward an optimized method for fast code acquisition, which accelerates the acquisition remarkably with only slight increment of hardware scale.After the code acquisition and coarse estimation of carrier frequency, the thesis then studies carrier recovery for highly-dynamic input frequency and puts forward a FLL(Frequency-Locked Loop)-assisted-PLL(Phase-Locked Loop) scheme for residual frequency error estimation and tracking.The synchronization algorithms for LEO Micro Satellite communication receiver have been fully realized in large-scale FPGA(Field Programmable Gates Array), and experiment results show that the system requirements are fully fulfilled.