Study And Implementation On Compressed Acquisition Algorithms For Direct Sequence Spread-Spectrum Signals

High dynamic pseudo-noise(PN) code acquisition plays an important role in the field of satellite navigation and spacecraft measurement and control. In recent years, with the proposition of Frequency Compression Search(FCS) technique and Two-Dimendion Compressed Correlator(TDCC) technique, compressed acquisition for high dynamic PN code has become a new research direction. The thesis focuses on the compressed acquisition algorithms for DSSS signals, and the main research contents are as follows:(1) The development status of PN code acquisition techniques based on FFT is introduced. One is parallel PN code acquisition based on FFT/IFFT whose performance is seriously influenced by Doppler frequency offset for long PN code acquisition. The other is parallel frequency offset acquisition based on FFT whose resource consumption is serious for long PN code in high dynamic environment. The structure of the high dynamic spread spectrum receiver and three traditional acquisition algorithms are introduced.(2) Aiming at the disadvantages of parallel PN code acquisition based on FFT, an improved algorithm FCS-DBZP is proposed which combines the FCS algorithm and FFT to improve the ability to overcome Doppler frequency offset. In the algorithm, the received signal is mapped to the sub carriers with different frequencies, and the sum is obtained. Then, the parallel acquisition is performed by using FFT. The theoretical expressions of false alarm probability, detection probability and mean acquisition time performance are derived, and the correctness of the theoretical analysis is verified by Monte Carlo simulation. The simulation results show that the improved algorithm is suitable for long PN code acquisition in high dynamic environment.(3) A double dwell PN code acquisition algorithm CCPC-FFT is proposed, which is based on Compressed Code Phase Correlator(CCPC) and FFT. In the first dwell, a rapid and rough compressed search is performed for some neighboring code phases using CCPC, at the same time the parallel search for Doppler frequency offset using FFT is completed. In the second dwell, all the neighboring code phases acquired in the first dwell are searched accurately using conventional correlator. The theoretical performance analysis model for double dwell acquisition system is presented, whose correctness is verified by Monte Carlo simulation. The simulation results show that the proposed method has obvious advantages compared to TDCC on mean acquisition time and other performance in high dynamic environment, and can realizes the fast PN code acquisition under large Doppler frequency offset.(4) The implementation scheme of CCPC-FFT based on FPGA is studied which uses the pipeline technique for double dwell acquisition system, focusing on the design of CCPC and FFT frequency offset acquisition circuit. The system is divided into data channel and control channel, and the correlation length of CCPC can be set reasonably to acquire Doppler frequency in different ranges. The system is implemented by using Verilog HDL in FPGA and the functional simulation is completed in certain system parameters. The test results meet the expected requirements, and it is proved that the algorithm can be realized.