| In modern digital communication systems, because of various imperfect reasons, signals will have distortions when transmitted through channels. In order to recover the transmitted signal totally on the receiving end, the channel should be compensated efficiently by adaptive equalization technology. Adaptive equalization is a primary means to handle ISI ( Intersymbol interference ) caused by multipath effect and unevenness of channel bandwidth.This paper concisely introduces basic concepts of digital modulation and demodulation, then thoroughly deals with QAM modulation and demodulation technology in accord with DVB-C standard. QAM demodulation chip architecture in accord with DVB-C standard is introduced in detail, the position and the relation with other modules of adaptive equalizer module are also defined. This paper describes the basic principle and architercures of adaptive equalization and interrelated equalization algorithms detailedly. Through in-depth understanding of architecture of QAM modulation chip,various equalization algorithms and structures and performance analysis, the DFE structure adaptive equalizer, which uses the Constant Module Algorithm-CMA and DD-LMS algorithm (Decision Directed-Least Mean Square), is finally chosen. It completes equalization of 16/32/64/128/256 QAM signals and satisfies the requirement of cable channel.Design of general architecture and function modules of DFE equalizer is the key of this paper. In the VLSI implementation of algorithms, through simplifying and optimizing methods, such as logic simplifying, hardware resource is decreased, circuit's area and power are reduced. Finally, simulation and verification of the design are descibed, the final design results are given, they meet the demands of QAM demodulation system , such as BER ( Bit Error Rate ), echoes etc. |
