Research On DSSS Signal Acquisition Technology Under Strong Interference And Low Signal Noise Ratio

Spread spectrum communication technology with its good performance is widely used in satellite navigation,aerospace monitoring and deep space exploration and other complex environments.Direct sequence spread spectrum(DSSS)technology is the most commonly used technology in spread spectrum communication.In the complex and harsh environment,the weak DSSS signal is susceptible to various interference.Although the spread spectrum technology itself has certain anti-interference ability,the intensity of interference is too strong that the system need to take some measures to improve the system anti-interference ability to ensure the stability of the system work.With the function of global position reporting of Bei Dou being proposed,it is of great significance to study the fast acquisition technology of DSSS under conditions of strong interference,low signal-to-noise(SNR)ratio and limited hardware resource.This paper which is based on the background and indicator requirements of the project,the signal's characteristics which are short duration of burst signal,low SNR,and with narrowband interference suppression and limited hardware platform resources designe and implemente the joint algorithm for the time domain adaptive filtering narrowband interference which is based on the least mean square(LMS)algorithm and the coherent accumulation acquisition algorithm which is based on the fast Fourier transform(FFT).Firstly this paper introduces the basic principle of the DSSS system,and analyzes the accumulation technology of DSSS.The part of analysis is mainly analyze and compare timefrequency two-dimensional search process in the acquisition method and the performance of accumulation.Secondly,the interference suppression method is introduced.The frequency domain windowing technique and the time domain prediction technology are introduced in detail,and the performance of the windowing technology is analyzed.The overall coherent accumulation performance based on FFT is better than non-coherent accumulation of 2d B,which is better than differential coherence accumulation of 0.5d B.The acquisition frequency accuracy is 30 times better than the other two schemes.According to the parameters and indicators in the project,this paper analyze the coherent accumulation acquisition algorithm that is based on FFT and the time domain adaptive filtering narrowband interference suppression method that is based on LMS,and simulate them in Matlab.Meanwhile it simulate and test performance of the joint algorithm.According to the simulation results of Matlab,the overall scheme is designed,achieved and tested under the condition of limited FPGA hardware resources.The program of hardware for LMS algorithm is verified by Modelsim.Simulation and actual test results show that the performance of the program can meet the target requirements.