The Design And Implementation Of The Quadrature Amplitude Modulator

Nowadays, digital cable television is a prosperous industry. More and more clients are attracted by its advantages such as vivid vision, plenty of channels and quasi-Video-on-Demand services which make it outweigh the traditional cable television. However, the feature of digital cable television lies in the bi-directional communication which facilitates many enjoyable services. Some of them are on the horizon like distance and remote education. As a result of all the benefits come from the bi-direction communication, the cable net is under the reconstruction from traditional uni-direction communication net to the bi-direction communication net. But the high cost of cable modem, the kernel of this bi-direction communication net baffles this reconstruction. The design, QAM modulator discussed in this paper aimed at implementing some basic characteristics of the modulator working in the up link at relatively low cost.The design of this QAM modulator complies with the standards listed in DVB-C[1] together with physical layer protocols in DAVIC[2] by using 16QAM modulation. It also meets all the concerned requirements published by our nation. At the beginning of this project, the simulation was completed in Matlab. In order to compare different methods in implementation, in-depth simulation by using C is included. After the verification of the novel methods such as using FFT to filter in frequency domain and making advantage of DDS to synthesize the carriers.The design method is utilized in one FPGA which decreases the modulator's cost. The sub-systems like baseband shaping filter and DDS mentioned above are developed in QuartusII by coding in VHDL. the results are consistent with all the basic requirements.