Design And Implementation Of Digital QPSK Modem System Based On FPGA

QPSK modulation and coherent demodulation technology has many applications in communi- cation system, this topic will research digital QPSK demodulation system design and realization based on FPGA.This paper, the major work and contributions are as follows:Firstly, we have analyzed the method of costas carrier synchronization based on QPSK, calculated the important parameter by matlab simulation. Then, got the FPGA solution of QPSK costas carrier synchronization loop, which include NCO,match filter, phase discrimination tran- smitters and loop filter.Secondly, we have analyzed the methond of QPSK bit synchronization, established the model of sampling rate error on both sides of transceiver, and then we have simulated the synchronization algorithms in MATLAB. Then, Then, got the FPGA solution of QPSK Gardner bit synchronization loop, which include interpolated device, phase discrimination transmitters and loop filter. Design Verilog HDL of costas carrier synchronization loop and Gardner bit synchronization loop based on XC3S1400AN, and do functional simulation and timing simulation for each moduleFinally, we have introduced a hardware design method of digital QPSK demodulation system, which can support midrange and baseband signal input/output, include the core of FPGA, digital-to-analog converters of AD9779, analog-to-digital converters of AD9236 based on software radio design thoiry. We have also tested the whole verilog HDL program code of QPSK on this hardware platform. We have tested many results of different SNR and frequency offset and observed the experimental phenomena through Chipscope and ordinary oscilloscope, the QPSK signal is generated by agilent E4438C. the testing results show that The digital QPSK system can work steadily, the technical indexes also reach the expected requirements.The research results of this paper has the very important value on the application of QPSK technology.Due to the FPGA chip built-in the FLASH memory, so this system can use as the FPGA digital QPSK modems chip, which has very important practical value.