The Design And Realization Of High-speed Digital Modems

The rapid development of modern science and technology has brought the requirement on the transmission rate of images, high-capacity data and multimedia information to a record high. Therefore, the research on high speed data transmission technology has become an urgent demand. High speed modulation and demodulation refers to the transmission technology with a transmission rate higher than 10Mbps. This kind of technology can meet various signal processing requirements in communication field, and it is of great importance in the real-time processing and transmission of the radar signal, high-definition images, etc.In this paper, we make a research on the design and implementation of high speed modulator and demodulator. Focusing on the QDPSK modulation, an analysis of a variety of modulation technologies is made. After an in-depth study of the QDPSK modulator, we offer a complete FPGA programming of the data scrambling module, convolution coding module, differential coding module, symbol mapping module and the interpolation filter module. Then, this paper gives the simulation waveforms, hardware verification waveforms and QDPSK modulation IF signal spectrum. The results show that the QDPSK modulator software design is correct and reliable.The paper also gives the hardware system block diagram of high speed digital modulator and demodulator. The hardware system includes high-capacity FPGA, CPCI data interfaces, high speed A/D and D/A. On the basis of a detailed analysis of the high speed A/D module, digital down conversion module, high speed D/A module, IF driver module, FPGA circuit module and power module, a study on the high speed PCB design based on Cadence is also conducted.