Study And Implementation Of Digital Direct Sequence Spread Spectrum Communication System

Spread Spectrum Technology has feature of good privacy, strong anti-interference, anti-multipath, anti-fading and anti-noise performance, can be reused multiple access and low power. And it has unique advantages when being used in many areas such as communication, position, ranging and control. So it has drawn wide attention in the international community and has rapid development. Direct sequence spread spectrum (DSSS) communication has become a kind of spread spectrum technology that is used most widely currently because it has advantages of strong anti-interference performance, long communication distance and high reliability and so on.With the rise and development of software radio, spread spectrum system is gradully developing toward digitalization and software. All digital spread spectrum system has advantages such as low power consumption, small size, high stability and reliability, good universality and flexibility and so on. Therefore, all digital of spread spectrum communication system has been the trend of development of today.The theory and acquisition performance of the digital direct sequence spread spectrum (DSSS) communication system are researched deeply in this thesis, and an all-digital DSSS system with FPGA is realized. The main content and work of the paper are:①The simulation module maps of transmitter and receiver of DSSS system are given. And the simulation waveforms are also given in the thesis.②Principle and performance of digital matched filter (DMF),adaptive threshold technology based on automatic decision threshold level control (ADTLC) circuit and improved COSTAS loop are analyzed in the thesis, and simulation platforms are built in MATLAB/Simulink for simulation and analysis.③An improved structure of DMF is presented. The acquisition performance such as detection probability ( Pd ) and the false alarm probability ( Pf ) of this structure are analyzed and simulated.④Various modules of the DSSS system are designed, simulated and implemented in Quartus environment, including the key modules such as digital upward frequency conversion (DUC), digital down conversion (DDC), digital COSTAS loop, digital matched filter (DMF), de-spread spectrum module and so on. And simulation waveforms of them are given in the thesis. ⑤The design, procuction and debugging of hardware circuit are completed.