Two-Stage Generalized Multilevel Modulus and Soft Decision-Directed Based Fast Blind Equalization for High-Order QAM Cable Systems

In this paper, a fast blind equalization with a two-stage generalized multilevel modulus algorithm (GMMA) and soft decision-directed (SDD) scheme is proposed for high-order QAM (64/256/1024QAM) systems on the downstream wired cable channel. The proposed fast blind equalization algorithm applies the two-stage convergence scheme and the SDD part uses the scheme with an adaptively selected decision region. In the first convergence stage, the joint GMMA and modified SDD equalization is applied for the purpose of the fast convergence. When the convergence process reaches the enough steady state, the convergence detector changes the first stage equalization to the second stage. In the second stage, the modified SDD scheme is applied to reduce the mean square error (MSE) further. On the wired cable channel at the 64/256/1024QAM modes, the proposed blind algorithm performs faster convergence speed than the previous blind methods do; meanwhile, the proposed algorithm also achieves smaller MSE than the other methods at the same signal-to-noise ratio (SNR).