Multi-rate Modem Design

Modem is one of the basic elements of digital communication system. Applying multirate signal processing to the hardware and software design of modem can make the hardware design simpler and the algorithm design more convenient. This thesis mainly focuses on the design of multirate modem and its hardware implementation. The modem has been applied to a satellite communications system.At first, based on the model of satellite communications system, the basic principles and hardware implementation of π/4-DQPSK modulation / demodulation, as well as the design of band-limited signals for no intersymbol interference are introduced. Then, the principles of interpolation and decimation, as well as half-band filter design of multirate signal processing are introduced. After that, based on the project of a satellite communications system, this thesis applies the principles of multirate signal processing to the system design and hardware implementation. Then, the automatic generation of FIR filter VHDL codes is simply introduced. Then, based on FFT, this thesis dose research on the algorithm of frequency deviation estimation, and implements the alogrithem in the carrier synchronization. And then, the algorithm based on the interpolation of MPSK symbol synchronization, as well as the hardware implementation of the modules is introduced. At last, the performance of the modem in the actual system is listed.