With storage capacities increasing much faster than data rates, fast read-out of content is becoming a bottleneck for the convenient use of optical storage devices. Two-dimensional optical storage (TwoDOS) is a new concept that solves this data-rate problem by using a multi-spot parallel readout system. In addition, the storage capacity is increased with a factor of at least 2. Using the same read-out physics as in the Blu-ray disc standard, single layered 12 cm discs with capacities up to 50 GB have been read out successfully at bit-rates as high as 560 Mbit/s. Basic pillars of TwoDOS are advanced signal processing and disc mastering techniques, and a proper design of the optical path.

A new and challenging concept for optical storage is being developed, in which the information written on the disc has a two-dimensional characteristic, with the aim of realizing an increase of a factor of two in data density and a factor of ten in data rate over the current 3rd generation of optical storage (Blu-Ray Disc, BD). Experimental channel characterization provides insight into the magnitude of intersymbol interference, signal levels, modulation and noise distribution from the measured signal waveform. This information is used to evaluate the quality of the mastered discs, and provide feedback in the optimization process. It also yields essential input to the actual design of the signal processing solutions. The stages involved in characterizing the channel are downsampling and model fitting using a scalar diffraction model. The information gathered from channel characterization is demonstrated with experimental measurements from discs with an initial density of 1.4/spl times/BD using the same physical read-out system (blue laser and high-NA lens).

The paper introduces the concept of two-dimensional optical storage (TwoDOS). In this concept, bits are written in a broad spiral consisting of a number of bit-rows stacked together in a hexagonal packing. Bits with a value '1' are represented physically as circular pit-holes on the disc, while bits with a value '0' are characterized by the absence of such a pit-hole. A scalar diffraction model is used to calculate the signal levels for various diameters of the pits. A stripe-wise Viterbi detector is proposed to perform 2D bit-detection with a limited state complexity of the trellis. Simulation results are shown for various diameters of the pits. A 2D modulation code is applied to eliminate patterns that yield a high probability of erroneous detection.

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.

Random channel errors that may occur in the run-length limited (RLL) channel bit-stream after bit-detection, are commonly repaired by error correction (de)coding (ECC) after demodulation of the RLL bitstream. RLL parity-check coding makes it possible to correct random errors already at the level of the channel bit-stream, at a much lower overhead than needed for standard ECC. With parity-check coding, a certain parity-check constraint is realized on segments of the RLL channel bit-stream. Violation of the parity-check constraint in the as-detected RLL bit-stream enables error detection; for error correction, some side information from the channel waveform is needed. One scheme from the literature considers parsing of parity-check blocks into the original RLL bit-stream. Another scheme is concatenated parity-check coding. While the parsing scheme has the drawback of low coding efficiency, its advantage is its simplicity and the lack of error propagation. The concatenated scheme has a high efficiency but it suffers from error propagation, and local demodulation is needed to derive the parity checks. As an alternative solution, we propose to use a parity-check coding scheme based on a combination of codes. Such a scheme is called 'combi-code', a term that was proposed within the framework of DC-free RLL codes. Apart from a main RLL code, a second RLL code, the parity-check enabling code, is required. The latter code is used to set the parity-check constraint of a segment to a predetermined value. Parity-check coding via combi-codes combines the advantages of the two other schemes: simplicity, a high coding efficiency, and no error propagation.

This study is concerned with the development of a simple yet sufficiently accurate model for the replay signal in optical discs. A method is proposed which models data storage (the write channel) as a nonlinear process and data retrieval (the read channel) as a linear one. The result is a low-complexity nonlinear model, of which the linear binary-PAM model is a special case. The performance of the proposed model is demonstrated by application to experimentally measured DVD data, and is found to be both accurate as well as robust to different recording media and conditions.

The freedom which is offered by the adaptable MPEG video encoders is meaningfully exploited by means of a "rate-distortion optimal" framework using a Lagrange formalism, as is well known from the literature. One such feature of interest is "optimal quantization". We propose some practical short-cut solutions, which reduce the computational complexity typically associated with "rate-distortion optimal" coding. The Lagrange multiplier, which is the most important parameter controlling the encoding of a single picture, is successfully predicted on the basis of a set of histograms for the amplitude distribution of each DCT-coefficient. In combination with a block-based bit-rate control the selection of the optimal quantizer step-size is further simplified.