We have proposed Inter-Track Orthogonal Coding (ITOC), for digital magnetic recording, that excludes crosstalk by orthogonalization between neighboring tracks. It could improve the track density, but it had problems of decrease in linear density. Then we studied some improved methods with higher coding rates basing on a Dispersing Write and Collective Reading (DWCR) system. It was found that the ITOC with a parallel combined spread spectrum communication method was a hopeful system. Furthermore, a simplified coding/decoding method for the system was proposed.

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One of the major merits that binary two-dimensional codes have over the binary one dimensional codes is the achievement of the property k<d. In this paper, we constructed a practical two-dimensional code based on the Marcellin-Weber's method and derived its state transition diagram. The constraints used in the construction are such that, the track numbers L=2,k (=k_y)=1,and d=2. Additionally, under the same constraints d and k_y, we clearly showed that when L is increased, the property n<m could be realized. Here, m and n are the dataword length and codeword length, respectively.

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In order to accelerate the achievement of high density recording on magneto-optical disk systems, We have developed a new ternary-level recording code called the 8B6T code which is characterises by the constraints d=1,k=4 and c=2. We have also investigated the BER performance of different combinations between recording codes and PRML methods. The performance of the 8B6T code's required CN ratio has been compared with that of the 8B6T, 8B10B and 4B3T codes, respectively. The results show that, the combination between 8B6T code and PR (1,2,1) method has the best performance among several combinations.

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Conventionally, the main function of recording codes has been thought to be matching the property of a signal sequence to that of the recording channel. In this paper, we try to use effectively not only the correlation property of PR systems but also that of recording codes. This idea is truly consistent with the TCPR (Trellis Coded Partial Response) method. Firstly, trellis codes which have code efficiency η=1/2 and 3/4,respectively, have been constructed. Then, a bit error rate (BER) comparison between these coded PR (1,1) ML methods and the non-coded PR (1,1) ML method having η=1 is given. The results show that the trellis coded method does improve the BER.

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In digital magnetic recording, discriminating method using neural networks was proposed and its feasibility of higher linear density capability was presented [MR94-16 (1993-10), MR94-16 (1994-07)]. In self-clocking system, clock-phase margin characteristics for noise are very important, especially for this new discriminating system, because of no data. In this paper, phase margins by simulations ware studied and described. Since neural networks have the leaning capability, if phase shift waveforms are leanend, phase margin widening effects can be expected. This effect was tried and obtained results of ±7% margin for one bit peiriod. Furthermore, composit effects widening maximum achievable linear densities by exstra high density waveforms were found and discussed.

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A channel coding for high-density recording is being studied. It is intended for use in small-sized Hi-Vision digital VTRs. We propose a new 8-16 channel coding which improves linear recording density since its minimum codebit reversal length (Tmin) is 1.5 times as long as the bit length before coding (Tb). Moreover, it suppresses low-frequency components equivalently to a DC-free property. This paper describes the characteristics of the 8-16 channel coding and a method for designing the codewords. The encoding and decoding algorithms are also summarized. We report on some estimation results of suppression of the low-frequency components by simulation. Both the digital sum variation (DSV) and the power spectral density (PSD) of the channel coding were suitable for the Hi-Vision digital VTRs.

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This report proposes an algorithm of realtime variable bit rate video coding on MPEG2. In this algorithm, a parameter called complexity which is the degree of dificulty to compress video is used. Through computer simulation and realization on an MPEG2 realtime video encoder system, it is clalified that the quality of decoded video using the proposed method is greater than one using a constant bit rate video coding method. And it is confirmed that stable operation is obtained by the proposed method for long time video coding.

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