A Design Of Adaptive/Blind Equalizer In QAM Demodulation Chip

At present, Quadrature Amplitude Modulated(QAM) is a primary transmission mode for digital CATV signal. Because of the HFC channel's imperfections, such as reflection and noise etc, QAM modulated CATV signal has distortions. In order to recover the transmitted signal totally on the receiving end, the channel should be compensated efficiently by adaptive equalization technology.Firstly, this paper concisely introduces QAM modulation&demodulation system in accord with DVB-C standard, and then thoroughly deals with QAM modulation&demodulation technology in accord with DVB-C standard. In this paper, the QAM signal characteristics are analyzed, the effect of channel and noise are also expounded. QAM demodulation system architecture in accord with DVB-C standard is introduced detailedly, the relation between adaptive equalizer module and other modules is also defined.The adaptive equalization technology overcoming ISI (Intersymbol interference) is exhibited in detail. After the basic principle of adaptive equalization, different adaptive algorithm (the major algorithm: Least Mean Square-LMS, Constant Module Algorithm-CMA) and different types of the adaptive equalization structures are discussed fully, the DFE structure adaptive equalizer, which uses the mutual transformed CMA and LMS algorithm, is finally chosen.This paper concretely introduces the general construction of DFE equalizer. Its function module mainly includes three parts: data cell, tap-coefficient cell and multiply-adder cell. The other primary modules are accumulator, error decision and tap-coefficient update. The multiply-adder cell, accumulator and error decision modules are simulated with Synplify pro 7.2, VCS simulation software.Finally, the above chosen adaptive equalizer is optimized partially and evaluated totally, the evaluation results meet the FEC module demands(SER≤4%) of QAM modulation &demodulation system .