Study On Blind Equalization Method For High Order QAM Signals

In communication systems,reducing Intersymbol Interference(ISI)is critical for high-capacity,high-rate communications.Blind equalization technology can effectively reduce ISI without periodically sending training sequences,and has become a key technology in demodulation systems.Quadture Amplitude Modulation(QAM)modulation mode simultaneously carries information in amplitude and phase,which has the advantage of high frequency band utilization.In order to obtain higher channel capacity,the modulation order of QAM is getting higher and higher,the constellation diagram is more and more dense,and the traditional algorithm is not effective anymore.Therefore,the research on blind equalization algorithm of high-order QAM signal has important practical application value.Bussgang type algorithm is the most classic and most commonly used blind equalization algorithm.For high-order QAM signals,the traditional Bussgang blind equalization algorithm has the characteristics of slow convergence and large steady-state error.Based on the analysis of the classical Bussgang type blind equalization algorithm,this paper systematically and deeply studies the serial and concurrent dual-mode solutions for high order QAM signals.For the characteristics of the cross signal constellation,the ?-Multimodulus Algorithm(?MMA)was improved to make it suitable for cross signals.The main work of this paper is as follows:(1)Firstly,the new Regional Multimodulus Algorithm(RMA)is studied in depth,and a new serial dual-mode blind equalization scheme is constructed by using its excellent ability to process high-order QAM signals.In this scheme,the first mode uses MMA,and in the second mode,the commonly used Decision Decision(DD)algorithm is replaced by RMA.The serial MMA-RMA dual mode solution not only has the ability to solve high-order QAM signals,but also provides a new idea for the selection of the second mode algorithm in the dual mode scheme.The simulation results show that the serial MMA-RMA solves the defects of poor adaptability and slow convergence of RMA.Compared with the traditional serial dual-mode scheme,it has the ability to equalize 1024-order and higher-order QAM signals.(2)Secondly,for the switching mechanism between the two serial dual mode is complex and the computation cost is high,considering the concurrent dual-mode blind equalization scheme does not require switching between algorithms,and the computational complexity is relatively small,based on the serial MMA-RMA,this paper further proposes a concurrent MMA-RMA dual mode blind equalization scheme.In addition,in order to further improve the processing ability of the algorithm for high-order QAM signals,a new concurrent ?MMA-DD dual-mode blind equalization scheme is proposed based on ?-Multimodulus Algorithm(?MMA).Experiments show that the two concurrent dual-mode schemes have faster convergence and lower steady-state error than the traditional concurrent dual-mode scheme.(3)Finally,based on the in-depth study of the cross QAM signals constellation,this paper improves the ?MMA for the cross QAM signals,and further constructs the concurrent ?MMA-DD dual-mode blind equalization scheme to solve the blind equalization problem of high-order cross QAM signals.