Research And Implementation Of Key Algorithms For High Dynamic Direct Sequence Spread Spectrum Communication System

The direct sequence spread spectrum(DSSS)communication expands the frequency band of the signal to be transmitted,so that it has unique advantages in terms of anti-noise interference and anti-interception.Therefore,it is more commonly used in navigation and location,survey and measurement,military and civilian communications and other fields.However,continuous improvement of spread spectrum communication technology,on the one hand,communication conditions have become more stringent,making traditional spread spectrum communication methods no longer applicable.On the other hand,public's requirements for communication quality are continuously increasing,the capability of DSSS receiver faces new challenges.In a highly dynamic communication environment,the carrier frequency of the signal received by the receiver is superimposed with the Doppler frequency offset,and the offset changes with time,forcing the traditional capture algorithm to increase the capture time and reduce the capture accuracy,or even fail.Therefore,it is very important to propose a high-efficiency capture algorithm under high dynamic scenarios.Firstly,this article starts with the principle of DSSS communication technology,and explains the acquisition algorithm and implementation form of the spread spectrum receiver,as well as the influence of the Doppler effect on the acquisition efficiency of the receiver.Expand from the two directions of pseudo-random code phase and carrier center frequency,the serial two-dimensional search method and the parallel one-dimensional search algorithm after dimensionality reduction using Fast Fourier Transform(pseudo code phase parallel search,carrier frequency parallel search)are studied respectively.The Pros and cons of the above three methods are compared in terms of capture efficiency and resource occupancy rate.A more efficient method with partial matching correlator and fast Fourier transform(PMF-FFT)as the core is proposed.It analyzes its advantages over traditional methods in principle,and uses MATLAB to simulate and illustrate.Secondly,this article uses FPGA platform to complete the generation of high dynamic direct sequence spread spectrum signal,as well as the design and implementation of the baseband part based on PMF-FFT capture method.The main tasks include: estimating the design resource requirements,completing the selection of FPGA chips;synthesizing the technical background of direct sequence spread spectrum communication and the complexity of the design,setting the specific design parameters of the communication system;Use Quatus II software to complete different parts of the hardware description,synthesize and compile the design,and generate simulation files;Use Model Sim software to verify the design results,modify and repair the parts that do not meet the design intent.Choose a bottom-up design method and combine the various modules into the entire communication system.Finally,after testing the entire design and deriving the principle,the performance parameters of the design based on the PMF-FFT capture method are obtained.This design can capture correctly in a high dynamic environment with a carrier offset range of ±50k Hz and a Doppler change rate of 20 k Hz/s,and the capture time does not exceed 20.70 ms,and the false alarm probability does not exceed 0.003,which meets the expected indicators.