Adaptive Nonlinear Equalizer Research Articles

Adaptive nonlinear decision feedback equalization with channel estimation and timing recovery in digital magnetic recording systems

In high density digital magnetic recording systems, the nonlinear effects in the write process appear in the readback waveform as shifts in the peak positions and changes in the amplitude. The pulse shift causes a nonlinear intersymbol interference (ISI) on the readback signal. In this paper, a Volterra-DFE, in which a Volterra filter is used in the feedback section of decision feedback structure, is proposed to equalize the nonlinear ISI. By theoretical analysis, the minimum mean squared error (MSE) of the Volterra-DFE is found to be a function of sampling phase. This will affect the output signal-to-noise ratio (SNR) of the playback system. A baud-rate timing recovery system in conjunction with a channel estimator is used to operate the sampling clock on the optimum phase. By computer simulation, Volterra-DFE is found to outperform conventional DFE in both output SNR and BER in a high density magnetic recording system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Elimination of adjacent channel interference Via nonlinear filters

In recent years, eliminating adjacent channel interference (ACI) for effective utilization of frequency resources has been considered important in digital radio communications. As an effective method for eliminating interference, adaptive equalizers have been utilized and limitations associated with their linear form processing have also been clarified. In this study, as equalizers showing better interfering wave-eliminating characteristics of adaptive linear equalizers (ALEs), an adaptive nonlinear equalizer (ANLE) containing the conventional nonlinear ALE and a nonlinear canceller, which eliminates ACI by nonlinear processing, in its body are proposed and their efficiencies are verified by computer simulations. First, the optimal number of taps of the proposed ANLE was determined by computer simulations and the characteristics obtained with an optimal number of taps have been compared with those of the conventional method. The results showed that the proposed ANLE can effectively eliminate the interfering wave component whose spectrum has become overlapped with a desired wave and thus gives better interfering wave-eliminating characteristics than the ALE and the nonlinear canceller.