Disc Defect Handling in Optical Disc Drives

This report is on the handling of disc defects in optical disc drives. The goal of the research is to investigate how the influence of disc defects can be characterized and utilized on the servo level, in order to achieve playability improvement. After a general introduction on optical disc drives, three aspects of the problem are treated in detail. From extensive measurements and theirasubsequent analysis we show how disc defects influence various servo signals. Especially the MIRN signal proves to be indicative for the occurring changes in laser light reflection caused by disc defects. Based on these observations we present a classification method that groups the numerous disc defects in a limited set of distinctive clusters. The classification is obtained from a hierarchical clustering structure that is based on a geometric dissimilarity measure. Mapping the affected MIRN signals to a specific property space provides the input for this algorithm. Finally the defect classes are represented by fitted polynomial functions in order to achieve the desired data reduction. The last aspect we discuss is that of disc defect detection. We present a detection algorithm, based on the principle of maximum likelihood. A simple 'block form' defect reference model proves to give the best results with respect to detection speed and reliability. Next to the detection of disc defects we discuss the closely related subject of disc defect identification. An identification algorithm that is based on the derived classification method is developed. The presented results form the basis for an integrated detection algorithm. This algorithm can be used to initiate countermeasures that will improve playability with respect to disc defect.