Design and implement of QPSK modem based on FPGA

This paper presents a method to designs QPSK modulator and demodulator of a spread spectrum system, which use field programmable device. The method uses the tool of Quartus II of American Altera Co. The whole system is divided into several small models based on top-down design method, and using VHDL hardware description language to design each model. The direct digital synthesis (DDS) principle is briefly presented and used to design orthogonal cosine signal module. In demodulator, we use the low pass FIR filtering to filter high frequency component. The QPSK module is ultimately implemented on the FPGA device. The whole system has been simulated in the Quartus II7.2 simulation environment and successfully downloaded to the chip of the Cyclone II EP2C5F256C6. The operating results and the theoretical results are consistent, so it's verified the correctness of this design. The results showed that the proposed method can greatly improve the developing efficiency, shorten developing period and reduce costs.