Research And Design Of Variable Rate Modulation Based On FPGA

All-digital modulation is a hot field in modern communication systems. Aiming at realizing an all-digital programmable QPSK modulator with data rates covering 2k~2.048Mbps, this thesis puts research on modulator architecture, base-band signal shaping, programmable interpolation algorithm, and digital signal processing algorithms with FPGA. We have completed the program design and the timing simulation, the PCB board has been fabricated. the similation result is given to verify the design.The emphasis of the thesis is base-band signal shaping and programmable interpolation algorithm. we introduce the basic theory of base-band signal shaping, and the effect of the digitizing of the ideal raised cosine rollof signal g(t) is attentioned. the shaping filter parameters are determined based on the system specifications, and the simulation results are given. based on the features of shaping filter, we put forward the look-up table and the polyphase algorithms. the contents in the ROMs are given.Later on we discuss the basic theory of multi-rate signal processing, and the polyphase algorithm for interplation filter, then produce the efficient algorithms for interplation: Half-band filter and CIC filter. We analyze their computing quantity and performance, especially the mirror elimination feature and the at-tenuation in the passband. Then produce the frequency complement algorithms and detemine the funcion x/sinx as the complement frequency response.With the combination of their different merit, we put forward the multistage interpolation algorithm.Based on the efforts above, we determined the overall architecture of the variable-rate modelation and each unit design, and the emphasis is the 3-stages algorithm for the variable-rate interplation. The simulation results of the modulator are also given and verified by Matlab signal procesing toolboxes.