Research On Key Techniques In Blind Equalization For High-Order QAM Signals

Blind equalization technology is gaining extensive attention and widely studied due to its advantages of high bandwidth efficiency, etc. In some application environments with no possible to get training sequence, such as non-cooperative communication systems, blind equalization technology is an essential key technology. With the pursuit of faster transmission rate and the adoption of higher order QAM signals in modern communications, to design new blind equalizers that satisfy the development requirements is a subject to be solved urgently.A new blind equalization algorithm which can adaptively change its contours is proposed, based on the fact that the reliability of the decided symbols made on the output of the equalizer increase gradually in the convergence process. Relative to algorithms using a single contour or several fixed contours, the proposed algorithm has better convergence properties, and is of universal validity for square-and cross-shaped high-order QAM signals. Whereas the fixed-length equalizers, which are widely used at present, is defective inherently, a blind equalizer provided with adaptive tap length is designed. Under different communication circumstances, the blind equalizer can automatically search for the optimal tap length, and gives better consideration to various property index including the steady-state error, convergence speed and computational complexity. Simulation results demonstrate the validity of the proposed algorithms.