QAM Modulator DDS-based Design

With the coming of the information age, communication and data transmissionbetween people is growing. But due to the scarcity of band resources and the channelcapacity is limited, the traditional communication mode which relys on constantlyincreasing the number of channels can’t meet the need of modern communication. Inthis way, people are in urgent need to use a medium high frequency spectrumutilization, high rate and high flexibility of modulation method to adapt to thedevelopment of information era. So how to solve this problem has become a hot issueof the third generation mobile communication.Compared with the traditional modulation mode, digital modulation mode has astrong anti-jamming capability and good ability to resist channel attenuation, as wellas good flexibility, so it has been widely applied in the third generation mobilecommunication. Quadrature Amplitude Modulation is digital modulation technologyof high-efficiency. It takes advantage of two independent baseband signalssuppressed carrier double sideband modulation of two mutually orthogonal way ofsame frequency carrier, compared with the integration of ASK and PSK entering achannel. It can make full use of the modulation bandwidth and has the advantage ofstrong ability to resist noise. In the case of band resource scarcity, QAM can not onlyobtain higher efficiency of spectrum utilization, and also can transmit moreinformation in the limited band resources. Thus it has high theoretical and practicalsignificance in-depth research on QAM.This thesis mainly studies on the design and implementation of64QAMmodulator which baseon DDS. Firstly, this thesis analyzes various signal modulationalgorithm, focusing on the QAM modulation algorithm. In this thesis, a new systemstructure which is suitable for FPGA to implement MQAM modulator is putforward, On this basis, the thesis further studies the working principle of64QAMmodulator. At the same time, the serial-parallel conversion module, the frame form module, scrambling module, differential encoding module, error-correcting encodingmodule, constellation mapping processing module, DAC module, DDS module are allFPGA designed by VHDL programming.Based on CORDIC algorithm, this thesisadopts the DDS modulator, which can output cosine and orthogonality signals to actas the carrier signal and modulate I/Q signal. At the same time, the pair cosine andorthogonality signals has reduced the effect of frequency noise and phase noisecaused by cosine and orthogonality signals generated from NOC.The error correctionmodule adopted in this thesis is LEE ’s code-8hexadecimal SLEC codes (84,81), itcan correct a single LEE ’s mistake. And the module simulation waveforms and64QAM modulation module signal spectrum are also given in this thesis, which haveproved the validity of64QAM modulator software design based on DDS.