Research And Implementation Of Direct Spread Spectrum System Based On FPGA

With the rapid development of modern communication technology,commucation systems have higher and higher requirements for confidentiality and anti-interference,and spread spectrum communication can improve the confidentiality and antiinterference of communication systems,in which the direct sequence spread spectrum system is structured.It is simple and easy to implement,so it is widely used.The modeling,simulation and implementation of the traditional FPGA-based direct sequence spread spectrum system are developed by the hardware description languages Verilog HDL and VHDL.Such development is inefficient and cannot be fully interactively designed using the powerful simulation functions of MATLAB.In this paper,the modeling,simulation and implementation of FPGA-based direct sequence spread spectrum system adopts Xilinx's digital signal algorithm special modeling tool System Generator combined with MATLAB's powerful simulation function for interactive design,which is more traditional than hardware description language modeling.The efficiency has been significantly improved,which is unmatched by traditional hardware-based description languages.This thesis mainly studies the direct sequence spread spectrum system based on FPGA.Starting from the advantages and basic principles of direct sequence spread spectrum system,the basic principles of each part in direct sequence spread spectrum system are introduced in detail,including pseudo random code principle and difference.Coding principle,bipolar non-return to zero code principle of baseband transmission signal,shaping filter principle,signal interpolation and extraction principle,carrier modulation principle,despreading principle,phase-locked loop demodulation principle,differential demodulation principle,frame header The principle of the matched filter is captured,especially the difficulty and performance loss based on phase-locked loop demodulation and differential demodulation are compared.Finally,differential demodulation is selected as the demodulation method according to the difficulty level and the acceptable performance loss.In this thesis,the theoretical derivation formulas are carried out in each part of direct spread spectrum.The theoretical derivation formulas of direct spread spectrum are used to model and simulate each part in MATLAB and System Generator,and the simulation results are analyzed.System modeling,simulation,and implementation are done on MATLAB2016 B,ZYNQ7020,VIVADO2017.4,and System Generator platforms.Model establishment and simulation include differential coding,coded spread spectrum,spread bipolar nonreturn to zero code coding,shaping filter,digital upconversion,despreading,differential demodulation,sampling decision,data frame header Capture,output of frame data.Finally,after each part of the modeling and simulation is correct,the two parts of the whole simulation are modulated and demodulated.After the simulation is correct,the generated DCP file is imported into VIVADO,and the timing constraint and ILA generated bitstream file are downloaded to the FPGA.Perform on-board verification,use the waveforms captured by ILA and then compare the data with the model simulation map to verify the model.Finally,the demodulated data is completely consistent with the transmitted data,that is,the model of each part of the direct sequence spread spectrum system meets the design requirements.