Research And Implementation Of Wideband Variable Rate Modem Based On16QAM

In the rapid development of wireless communication，the available bandwidth ofevery communication device decreases sharply, the spectrum resource becomeextremely valuable, so that the research on high spectrum efficiency modulationtechnology is very significant.The cognitive radio technology is a new method toimprove the spectrum utilization. Modem can achieve broadband timely throughchanging the modulation rate according to the condition of the channel and the neededbandwidth.Compared with other modulation mode, QAM has higher spectrumefficiency. Therefore, combining QAM and cognitive radio technology becomes moreimportant in further improving of the spectrum efficiency.Firstly, this thesis discusses the basic principles of the QAM modulation anddemodulation,the constellation mapping performance, the carrier synchronization theoryand the sampling theorem, interpolation basic theory basic theory in software-definedradio decimation.Secondly, the key technologies of broadband QAM modulation and demodulationare researched.The broadbandQAM modulation includes broadband modulatedwideband signal shaping filter and digital conversion variable interpolation factorinterpolation filter.The broadband adaptive QAM demodulation includes the baud rateestimation, digital down conversion variable decimation factor decimation filtering andsampling decisions. TheFarrow structure filter is illustrated in broadband shaping filterstudy and the fixed-length variable bandwidth Farrow structure filter for any bandwidthshaping based on least squares fittingis put forward.Then, the signal rate varies from8Kbps to16.384Mbps is designed by using MATLAB, which corresponding to themodulation bandwidth from2kHz to4.096MHz variable adaptive QAM modulation anddemodulation system parameters that including the square root raised cosine shapingfilter coefficients and variable interpolation factor stage interpolation filtercoefficients.The costas loop, baud rate estimation algorithm and samples judgment ofthe performance of the algorithm are also simulated.In the last, the key broadband modem modulesare implemented on FPGA, which including clock management module, the module of the distributed architecture of theshaping filter, broadband digital up conversion module, wideband digital downconversion module, the baud rate estimation module and samples judgment modules.The critical signals are tested and analyzed.The bandwidth variable QAM modem that has signal rate varies from8Kbps to16.384Mbps, modulation bandwidth varies from2KHz to4.096MHz, the variable orderof the rate and bandwidth is12, and the central frequency is16.384MHz are realized onthe FPGA after algorithm research and simulation.