Research On Fast Algorithm Of Spread Spectrum Code Acquisition Based On Matched Filter And FFT

In recent years, due to the explosive growth of communication service and theincreasing demand of telecommunications, satellite communication has been paidmore and more attention. And among them low earth orbit (LEO) satellites receivemost concern. Compared with the GEO satellites, LEO satellites have theadvantages of smaller path loss and less long distance transmission delay for theorbit is low. In LEO satellite communication system commonly use DSSS to resistmulti-path fading, EMI and other unfavorable factors. To communicate effectively itmust ensure the PN code synchronization. Since LEO satellites move very fast, largeDoppler shift is brought into the system. So the PN code acquisition will no longerbe simply the acquisition of PN code phase. This paper based on the matched filterand FFT algorithm for fast acquisition of PN code is actually focus on the solutionof PN code acquisition under large Doppler frequency shift.First of all, this paper gives a brief analysis of the spread spectrumcommunication technology, analyzing DSSS system’s working process and thetheory. Meanwhile, it is a research on the theory of PN code generation, whichanalyzes the generation principle of two kinds PN code sequence commonly used,given the performance simulation results. Analyzing RASE algorithm shows that thetraditional method is not applicable in LEO communication system.Secondly, this paper analyzes matched filter and digital matched filter algorithm.It also proves that they cannot handle large Doppler frequency in a mathematicalway. To reduce the Doppler frequency shift sensitivity of DMF the input data iswindowed. To reduce the complexity of the sysytem proposed an improvedalgorithm of differential.Finally, it introduces the FFT algorithm to improve DMF algorithm. Giving ananalysis of the combination of FFT and DMF algorithm:PMF-FFT. The windowedmode successfully solves the problem of shell loss. Which expanded the main lobewidth windowed the PMF part. Finally, it carries out a series of performancesimulation in AWGN channel which proved the improved algorithm’s superiority.