Design And Realization Of DS Spread Spectrum Communication System Based On Two-Stage Acquisition

In wireless communication,because the wireless channel is open,the transmission of information can be affected by noise,multi-site and multi-path,which makes the environment of wireless communication very bad.As a result,how to take anti-interference measures to ensure a safe and efficient communication is an issue which must be solved out in modern communication system.Spread spectrum technology is one of the most widely used anti-jamming technology in the field of modern communication technology.Capturing and tracking performance are the core technologies of it.On the basis of the research of various spread spectrum systems' methods of capturing and synchronization,this paper presents an overall scheme of the DSSS communication system,which based on the two-stage acquisition and lock-tracking.The scheme includes sending subsystem,the wireless channel subsystem,receiving subsystem and sequence synchronization subsystem,which based on FPGA design flow,used verilog hardware description language for programming the function of module.In the sending subsystem,the spread spectrum modulation and carrier modulation have been mainly accomplished;in the wireless channel subsystem,the noise simulation module and transmission delay module have been accomplished;In the receiving subsystem,which uses pre-filter filtering noise,and adopts the homodyne reception mode to complete the design of carrier demodulation and despreading;in synchronization subsystem,which uses two-stage acquisition method to capture pseudo random sequence,the first stage acquisition adopts the matched filter and the sliding correlation method in two ways,and the second stage acquisition adopts the sliding correlation method;the synchronous tracking is completed by adopting delay locked loop;and the synchronization control module is designed.After the design of each module,Modelsim 6.5a professional simulation tool has been used to make each subsystem and the entire system simulation.If the simulation turns out to be correct,the DS communication system will be downloaded to the FPGA hardware board for test.As a result,the function of system and synchronization's performances are analyzed.Simulation and test results show that direct sequence spread spectrum communication system can accurately realize signal sending and receiving.Sliding correlation,matched filter and two-stage acquisition can correctly capture spread spectrum signal,and delay locked loop can correctly track.As a result,analysis of capture and synchronization's performances give the relevant conclusions of the two-stage acquisition system.