Research On Acquisition Algorithms For Weak CPM Signals In High Dynamic Environment

Continuous phase modulation (CPM) signal has several advantages of constantenvelope, high power efficiency, high frequency spectrum utilization and goodanti-jamming performance characteristics which make it a new transmission schemefor GPS modernization system, Galileo Satellite Navigation system, BeiDouNavigation Satellite system and UHF-SATCOM system of the United States. A keytechnology for CPM modulation applied to these systems is how to implement CPMsignal acquisition under high-dynamic condition at extremely low signal-to-noise ratio（SNR）.In this thesis, high dynamic weak CPM signal acquisition is studied in detailbased on the CPM and direct sequence spread spectrum (DSSS) technology. Firstlyaccording to the characteristic of CPM signal, a new DSSS-CPM model adding CPMsoft information extraction before dispreading which ensure the reliability ofDSSS-CPM system is presented. Secondly, based on analysis and comparison of twokinds of basic acquisition algorithm, we set forth a novel preprocessing method-halfsymbol averaging on the basis of correlation function acquisition algorithm using FFT,which effectively solves the problem that acquisition performance degrades sharplywhen DSSS-CPM signals use the basic capture algorithm without preprocessing.Computer simulation results validate its feasibility; then several accumulationacquisition algorithms for the high-dynamic weak CPM-DSSS signal are discussed.We consider their applicable occasions and factors of affecting properties, and throughcontrast analysis we choose simple differential coherent accumulation acquisitionalgorithm as high dynamic weak CPM signal acquisition scheme, which efficientlycaptures the CPM-DSSS signal under the environment of the large doppler frequencyoffset range, large doppler frequency shift rate range, extremely low-SNR; Finally weadopt methods of frequency domain shift and reducing the number of IFFT points tooptimize the acquisition scheme, which effectively reduce the operation complexity ofthe acquisition scheme.