Asymmetry, also known as domain bloom, is a systematic imperfection caused by the writing process in optical or magneto-optical recording. At the reading end of the system, asymmetry causes shifts of adjacent signal transitions in opposite directions. We present a simple nonlinear model for the replay signal in the presence of asymmetry. The model is specified by a single parameter, which is proportional to asymmetry, and its accuracy is demonstrated by application to replay signals from digital video disk drives. Based on the proposed model, a maximum-likelihood sequence detector is designed for replay signals with asymmetry. Simple modifications of the proposed detector lead to significant reductions in complexity, while the attainable performance, evaluated both analytically and through error-rate simulations, is superior to that of conventional techniques.

Modeling and compensation of asymmetry in optical recording

In 2002, the "limit equalizer" which we developed was utilized in the Blu-ray disc format. The limit equalizer improves signal-to-noise ratio without increasing inter-symbol interference and improves jitter and error rates during operation. The limit equalizer is a nonlinear equalizer and deterioration of individual data patterns had to be verified. We used two methods of computer simulation to study behavior of every data patterns of modulation code. We calculated jitter and error rates on individual data patterns in the case of adding low frequency noise as the degradation factor, and in the case of adding random noise or defocus as the degradation factors. We derived the characteristics of both jitter and error rates on combinations of neighboring run-lengths (preceding and succeeding run-lengths). The results confirmed that both jitter and error rates were improved by the use of a limit equalizer throughout the series of data pattern combinations.

Effects of limit equalizer in Blu-ray disc format

Two adaptive PRML/Viterbi bit detectors have been evaluated based on DVD. They are able to handle non-linearities. It is shown that adaptive PRML/Viterbi detection can help to improve the tangential tilt margin or to increase the possible density.

Evaluation of adaptive PRML/Viterbi bit detection for DVD and beyond

This bit detector for d=2 modulation codes is remarkably simple, supports very high data rates, can be adaptive, and is capable of handling nonlinearities. The performance approaches that of a full-fledged maximum-likelihood sequence detector.

Transition detector for CD and DVD

In this paper, a novel post-processing scheme that significantly enhances the performance of a threshold based bit-by-bit detector on d=2 optical channel is proposed. The equalizer for this system is designed by jointly optimizing the target response and equalizer coefficients to minimize the noise and intersymbol interference (ISI) at the detector input. The bit-error-rate (BER) performance of the proposed scheme is close to the maximum-likelihood lower bound over the range of channel densities used on EFM/EFMPIus (2,10) coded channels for CD/DVD application, and it is better than that of the other schemes at all densities. The detector is simple in structure compared to the conventional partial response Viterbi schemes.

A novel post-processing scheme for threshold detection on d=2 optical channels

We have developed a Viterbi decoding circuit which is suitable for DVD players. We designed it to be compact and efficient by utilizing the rule of the DVD recording code. By experiment, we confirmed that the Viterbi decoder reproduced digital data more precisely than a conventional bit-by-bit decoder did. Thereby it improves the reliability of the DVD players. It was integrated into a data processing LSI which restores digital data streams recorded on the DVD. By employing this LSI, we have developed DVD video players, DVD-ROM drives, DVD-recordable drives, and DVD car navigation systems. We applied the Viterbi decoding to home-use optical disc players for the first time.

M. Umezawa

Papers

DVD players using a Viterbi decoding circuit