Dqpsk Modem Fpga-based Research And Design,

This project studies the modulation and demodulation of differentially encoded Quadrate Phase Shift Keying technology base on FPGA, by using DQPSK digital modulation method to realize digital signal transmission. The bit rate arrives 200Kbps and the carrier wave frequency is 3.2 MHz, bandwidth 180 KHz, out band suppression excess 45dB. Modulator design requirements achieved. Demodulator has not fully realized. But the project has accomplished the CIC filter, carrier tracking loops, bit synchronization and several important blocks. Some experiments show the relevant design is correct. The carrier synchronization functional of demodulator has been able to achieve.The paper mainly introduces the realization method of the DQPSK modulation and demodulation techniques base on FPGA. Specially discuss the differentially coded and encode, the pulse shaping filter, the Cascade Integrator Comb filter and Costas carrier tracking loop, etc. Then briefly shows the main circuit schematic design and object pictures.On every important design points, the paper does carefully Matlab or System View Simulation and given interpretations. Then using the VHDL hardware description language design and verifies the system. At last, the paper innovate the bit synchronization method and improves CIC filter for variable speed using.