Qam Modulation And Its Multi-channel Modulation Method

Quadrature Amplitude Modulation is a modulation mode which Mobile Communication Technology expert attaches much importance to in recent years. The information is transmitted on the basis of amplitude and phase in QAM. Different amplitude and phase represent different symbol of information. QAM have some advantages, such as high frequency band utilization rate, good anti-interference ability and so on. It is widely used in mobile communication and satellite communication, especially in the cable digital television transmission. More and more signals need to be transmitted along with the development of the communication technology, however, traditional QAM can only process single channel signal. Multiple channels QAM uses the Multirate Signal Processing Technology, and modulates multiple channel signals and mixes them to single channel signal with synthetical digital filter banks. It can satisfy the request of modulating multiple channel signals at the same time. So, multiple channels QAM is more suited to the new communication technology.First of all, the thesis introduces the principle of Quadrature Amplitude Modulation, and analyses the Multirate Signal Processing Technology, such as interpolation, decimation, polyphase representation of filter, digital filter banks and its high performance structure, then simulating them with MATLAB. In addition, the method of multiple channels QAM is studied on the basis of digital filter banks. Then, this thesis also detailedly describes the design and implemention of single channel QAM, FPGA is used to carry out baseband processing and modulation. There are sync 1 inversion and randomization, reed-solomon (RS) coding, convolutional interleaving and baseband shaping in baseband processing. Modulation consists of differential encoding, QAM mapping, NCO generating orthogonal carrier, multiplier and adder realizing modulation. Because of the need of design, the interpolation, filter and the polyphase representation, serdes are also joined to the design. Then each part of it is simulated by Modelsim and is debugged by SignalTapⅡLogic Analyzer after downloading it to FPGA. In addition to the design in FPGA, a high performance digital-to-analog converter is needed to convert the output signal of FPGA to analog signal. And there is a clock generator providing clocks for DAC chip and FPGA. Ultimately, oscilloscope is used for measuring the output signal of DAC chip and clock generator for analyzing their performances, and QAM-Analyzer is used for measuring the constellation diagram and frequency spectrum of QAM.Several signals can be modulated in multiple channels QAM system at the same time, so the space and cost of the equipment are reduced, the algorithmic reaserch of multiple channels QAM system provides basis for its realization. The single channel QAM system basing on FPGA not only is the basis of multiple channels QAM system's realization, but also is an advanced QAM system, and digital QAM system has a good performance in anti-jamming and is designed easily.