Digital Modem Design

Digital modulator and demodulator are the most important parts of a digital communication system. The digital modulator and demodulator, which choose high-efficient modulation mode, transmit data at a higher rate and can meet different systems, are the key parts of a wideband digital communication system.This paper designed a full digital modulator and a full digital demodulator for the millimeter wave communication machine based on the soft radio theory. After investigating several key techniques of modulation and demodulation, this paper designed a digital modulator, and a wideband programmable modulator HSP50415 was used to support IF quadrature modulation and the TMS320VC5402 DSP signal processing board was used to support baseband signal processing. This paper also designed a digital demodulator, and a digital quadrature tuner HSP50110 and a digital Costas loop HSP50210 were used to support IF demodulation and the TMS320VC5402 DSP signal processing board was used to support baseband signal processing. In the ideal condition, the rate of the modulator and the demodulator can reach up to 12MSPS. By modifying DSP software, different modulation and demodulation systems can be implemented. The π/4QPSK. digital modulation and demodulation algorithm and the digital modulation and demodulation system were simulated and validated using the software MATLAB and System View.