Design And Implementation Of Physical Layer Of High Speed Mobile And Multi-mode Spread Spectrum Communication System

With the vigorous development of high-speed aircraft communication such as aviation and aerospace,spread spectrum technology is widely used because of its good anti-interference characteristics.Combined with burst communication system,the antiinterception performance is further improved.This thesis designs the physical layer link of DSSS system combined with TDMA burst slot frame,which can resist the frequency offset in the range of ± 400 k Hz,and has a variety of communication rates to adapt to different SNR conditions.The core of burst spread spectrum communication is synchronization.This thesis compares the traditional acquisition algorithms and explores the PMF-FFT algorithm.Through simulation,the number of segments suitable for the system is determined,the zero padding FFT is used to improve the scallop loss.Besides,the decision strategy is determined and the denoising optimization is carried out to improve the synchronization ability.The fast synchronization of spread spectrum signals under [-100 k Hz,100 k Hz]frequency offset is realized under low SNR.According to the basic PMF-FFT,combined with the requirements and complexity,the frame structure of the system is designed to reduce the complexity by offset point sampling.Then,the design of synchronization scheme and MATLAB simulation verification are given to complete the search of frequency offset in [-400 k Hz,400 k Hz]range and code synchronization.In the process of FPGA implementation,a 32-parallelPMF-FFT structure based on pseudo code offset is proposed,which can take into account resources and processing delay.Finally,this thesis gives the MATLAB simulation and implementation scheme of other modules in the physical layer,and tests the system.The actual measurement shows that the system can complete the fast synchronization and decoding of spread spectrum signals in the burst communication state with large frequency offset.