Research And Implementation Of Synchronization Technology In Direct Sequence Spread Spectrum System

In the complex electromagnetic environment,how to realize the high-reliability transmission of the digital communication system has always been a continuous hot issue.Spread spectrum communication is a high-performance communication technology developed from the military and electronic communication fields because of its advantages such as antiinterference and strong confidentiality.When communicating between some high-speed mobile communication carriers,such as in some special application scenarios such as air-toground,bomb-to-ground,etc.,because these communication carriers have relatively large relative motion speeds,there may even be relative accelerations.In such a high dynamic environment,due to the influence of the Doppler effect,the digital synchronous receiver will not work normally,which will seriously affect the communication quality of the two parties.Usually,this kind of high dynamic environment is generally used.All are short-time burst communication modes.This article first introduces the analysis of the synchronization capture method of the DSSS system in the conventional environment,and then introduces it into the high dynamic short-term burst environment and under the condition of low signalto-noise ratio,the performance of the synchronization capture algorithm for the DSSS system is carried out.After analysis and comparison,the Gardner-based timing symbol synchronization algorithm is discussed and simulated.Finally,the FPGA implementation of the DSSS system in the high dynamic short-time burst environment is carried out.The main tasks completed in this paper are as follows:1.Aiming at the impact on the direct expansion system under the high dynamic environment to be studied in this article.First,by introducing the technical theory of the DSSS system,the structural principles of the transmitter and receiver of the DSSS system and the commonly used phase modulation methods of the DSSS system are given,and then the Doppler effect in a high dynamic environment is analyzed.The appearance of deviation,and the influence of frequency deviation on receiver and DSSS signal.2.Aiming at the problem of synchronization capture in the direct expansion system.First,it briefly describes the principle of the synchronization acquisition of the DSSS system,and then analyzes the synchronization acquisition algorithm of the DSSS system in the conventional environment,and then researches and analyzes the synchronization acquisition technology of the DSSS system in the high dynamic burst environment.In contrast,the system finally selects the PMF-FFT synchronization acquisition algorithm based on the system in this paper to complete the MATLAB simulation of the system.3.Aiming at the problem of timing symbol synchronization in digital communication systems,the timing symbol synchronization algorithm based on Gardner is studied.First,it briefly describes the impact of timing symbol synchronization on system performance,and then introduces the working principle of timing symbol loop in modules,and focuses on performance analysis of four different timing error detection algorithms commonly used at present,and finally completes based on Gardner algorithm Synchronize the timing symbols of the QPSK modulated signal,and provide detailed loop parameters and MATLAB simulation analysis.4.This article is a system based on DSSS-RS-QPSK digital modulation.First,the specific communication system structure block diagram in the high dynamic short-time burst environment is given,and the burst frame structure is designed,and then the specific FPGA implementation of the technology used in the system is carried out,and PMF-FFT The FPGA measured data of the synchronous capture algorithm was simulated and verified,and finally the performance of the entire FPGA hardware system was tested.