PAPER EFFECTIVE NONLINEAR RECEIVERS FOR HIGH DENSITY OPTICAL RECORDING

SUMMARY The starting point of this paper is the defini-tion of a nonlinear model of the read out process in high density optical discs. Under high density condition, the signal read out is not a linear process, and suffers also from cross talk. To cope with these problems, the identification of a suitable nonlinear model is required. A physical model based on the optical scalar theory is used to identify the kernels of a nonlinear model based on the Volterra series. Both analysis and simulations show that a second order bidimensional model accurately describes the read out process. Once equipped with the Volterra channel model, we evaluate the performance of various nonlinear receivers. First we consider Nonlinear Adaptive Volterra Equalization (NAVE). Simulations show that the performance of classical structures for linear channels is significantly affected by the nonlinear re-sponse. The nonlinear NAVE receiver can achieve better perfor-mance than Maximum Likelihood Sequence Estimator (MLSE), with lower complexity. An innovative Nonlinear Maximum Like-lihood Sequence Estimator (NMLSE), based on the combination of MLSE and nonlinear Inter-Symbol Interference (ISI) cancella-tion, is presented. NMLSE offers significant advantages with re-spect to traditional MLSE, and performs better than traditional equalization for nonlinear channels (like NAVE). Finally, the pa-per deals with cancellation of cross talk from adjacent tracks. We propose and analyze an adaptive nonlinear cross talk can-celler based on a three spot detection system. For the sake of simplicity, all the performance comparisons presented in this pa-per are based on the assumption that noise is Additive, White, and Gaussian (AWGN model)