Implementation Of The Direct Sequence Spectrum Signal Acquisition And Tracking

The traditional monopulse auto-tracking technology has been extremely mature.However due to the limitations of the system itself,it is difficult to further break through the technical bottleneck of low anti-interference and anti-interception ulteriorly.Therefore,it is of great significance to research the application of spread spectrum system in this technology to improve the ability of signal acquisition and tracking.Among all kinds of spectrum spreading methods,the Direct Sequence Spread Spectrum(DS-SS)method has the lowest complexity and the most extensive application.Studying and inplementing the single-channel monopulse acquisition and tracking scheme for Direct Sequence Spread Spectrum signal can not only further reduce the complexity of the system,but also avoid the problems of phase and gain deviation among different channels in multi-channel structure.Based on the acquisition and tracking technology of Direct Sequence Spread Spectrum signal,studied the implementation of four steps in the FPGA chip,including pseudo-random code acquisition,pseudo-random code tracking,carrier wave acquisition and carrier wave tracking.In addition,investigated the calculation of azimuth angle deviation and elevation angle deviation and the piecewise control of automatic gain control(AGC)in the DSP chip.The algorithm implemented in the FPGA is more complex and difficult to realize,therefore Matlab/Simulink simulation software was used to carry out sufficient simulation implementation work for this part of the algorithm.An external test system was designed for the signal processing hardware platform of the algorithm implementation to test AGC,DA output,serial port output and other functions.After comparing and analyzing a variety of pseudo-random code acquisition methods,choosed the Part of the Matched Filter-Fast Fourier Transform method,which is more suitable for the application scenario of satellite signals in this topic,to achieve pseudorandom code acquisition.In the carrier wave tracking section,an improved method based on the traditional Costas loop was used to further improve the anti-interference performance of the module.In the process of calculating the angle deviation signal,the normalization method was adopted to avoid the influence of signal amplitude on the calculation result.Finally,the performance of the system was tested jointly by the self-checking Direct Sequence Spread Spectrum signal generated in FPGA and the external test system of the signal processing hardware platform,and the results of the angle deviation signal and the automatic gain control signal were displayed in real time.According to the results of the simulation and hardware implementation verification,it was found that the algorithm researched in this topic can correctly calculate various target signals under the condition of low SNR.and send these signals through DA and serial interface to the servo drivers at the front of the signal processing hardware platform for reporting at the same time,realizing the acquisition and tracking of Direct Sequence Spread Spectrum signal.