Akiomi Kunisa

Video Disk Recorder System Using Magneto-Optical Disk

We have developed a video disk recorder system using a magnetically induced super resolution (MSR) magneto-optical (MO) disk 120 mm in diameter and achieved a user data capacity of 4.1 Gbytes per disk using land/groove recording technology, a laser wavelength of 685 nm, and (1, 7) run-length limited (RLL) code. In this case, track pitch is 0.7 µm and minimum mark length is 0.4 µm. The system can record 125 minutes of moving images encoded using the MPEG2 method. In this paper we describe our high-density magneto-optical recording technology and the video disk recorder system which incorporates magnetic field modulation.

Cross-layer optimization for A-MPDU with HT-immediate block acknowledgement in non-competitive channel environment

This paper presents a cross-layer optimization method for MAC protocol data unit aggregation, abbreviated to A-MPDU, with high throughput (HT) immediate block acknowledgement in non-competitive channel environment. We derive the goodput as a function of the transmission strategy, including the aggregated number of MPDUs and length of each MPDU of the MAC layer, and modulation and channel coding scheme (MCS) of the PHY layer. Among all the possible transmission strategies complying with packet error probability (PER) requirement, the one with the highest goodput can be selected. The simulation result shows that the systems goodput attained by the proposed method is twice as large as the one without A-MPDU.

Informed digital watermark embedding based on guided scrambling

Digital watermarking systems are required to embed as much information as possible in a digital media without the perceptual distortion as well as to extract it correctly with high probabilities even though the media is subjected to many kinds of operations. To this end, guided scrambling (GS) techniques, usually used for a recording channel, are applied to digital watermarking systems. A simple GS scheme can make the power of a watermark signal larger against the power of media noise under the condition of preserving the perceptual fidelity, resulting in smaller error probabilities of the retrieved watermark bits. In addition, watermarking systems based on the GS can have more robustness to some specified operations if the prior information on the operations is given to the embedder. JPEG compression is a good example of such an operation when still images are transmitted over the Internet. In order for watermark signals to be more tolerable to the known JPEG attack, the GS-based watermark embedder having advance knowledge of the JPEG compression is realized. Further, the GS concatenated with turbo coding is introduced to lower the bit error rate more.

An 8-15 Modulation Method Suitable for High Density Digital Recording.

Previously we proposed a DC component suppressing method which adds an extra one-byte data to a data block of fixed bytes and converts information data into channel codewords. In this paper, we propose 8-15 channel coding which has no DC component suppressing capability, and 8-15 modulation method which is based on 8-15 channel coding and DC component suppressing method. The window margin and the minimum interval between transitions of the 8-15 channel data are about 6.6% longer than those of (2, 7) RLL codes, and are theoretically the most suitable length when 8-bit data words are translated into 15-bit codewords. The 8-15 modulation method is superior to the (2, 7) RLL coding in respect to some of their characteristic parameters and suppresses low-frequency components efficiently.