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Research on Spread Spectrum Code Acquisition of Double Threshold Based on Sliding Correlator

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Tutor: TianRiCai
School: Harbin Institute of Technology
Course: Information and Communication Engineering
Keywords: PN sequence acquisition,changed step,double adaptive threshold
CLC: TN914.42
Type: Master's thesis
Year:  2008
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Spread spectrum communication is a cutting-edge technique developing rapidly in the field of information technology. It was first used for military purpose and has already been applied broadly in many fields as navigation, measurement and remote controlling. Now, it is permeating fast into individual communication and computer communication. It will become a hotspot of information processing and transferring technique in the 21st century.Acquisition methods about spread spectrum acquisition in the direct-sequence spread spectrum system are studied, and based on analysis of the existing acquisition methods, an improved algorithm is proposed. Based on the sliding correlator acquisition, the improved method replaced the single fixed threshold with two adaptive thresholds and introduced the concepts of changed step and assisted acquisition. Tracking circuit of the improved acquisition system is proposed, and acquisition and tracking circuit can be integrated. The paper presented the model and flow chart of the improved acquisition system, analyzed the whole system and simulated it with Matlab. Under the assumption of white Gaussian noise channel, the expressions of detection probability, alarm probability and average acquisition time were present. The performance of the improved method and the sliding correlator acquisition method is compared in the paper. The result shows that detection probability and average acquisition time has been improved remarkably, and for alarm probability, adaptive threshold system has a better performance than fixed threshold system. The performance of the improved acquisition system in anti-jamming for impulse noise is analyzed. After theoretical analyzing, the paper presented the value of worst case jamming duty factor in the improved acquisition system and the simulation results with Matlab.With the advantages of better acquisition performance, high dependability, and less equipment, the system can be applied in the direct-aequence spread spectrum communication system to improve the communication performance.
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