FUNDAMENTAL RESEARCH ON MULTI-LEVELIZATION OF MAGNETO-OPTICAL RECORDING

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This research project has investigated the effectiveness of multi-levelization of magneto-optical recording for higher density storage.The subject of the investigation is limited to both "light modulation" and "magnetic field modulation" methods.In order to avoid any additional introduction of higher costs, our project has fundamentally been based on a restriction that the multi-level recording system is to be realized by applying the conventional head and media for the binary recording systems. We could overcome this problem through the selection of writepulse widths in proportion to the code symbols 0,1 or 2.Next, the required CN ratios at the read back points used to attain a bit error rate (BER) of 10^<-4> have been computer-simulated at transmission bit rates ranging from 12Mbps to 24Mbps, the former rate being the upper limit one for the present state.The results showed that, for the(1)light modulation method : edge recording achieved by the use of a (1,7) code+PR (1,2,1) ML is the best combination at bit rates ranging from 12 to 20 Mbps. At 24Mbps, the 3B2T code+PR(1,2,1) ML combination is the most effective.(2)magnetic field modulation method : the 3B2T code+PR (1,1) ML (or PR (1,2,1) ML) is the best combination at bit rate ranges 12 - 20 Mbps while the 2B1Q code+ PR(1,2,1) ML one is the best at 24 Mbps.Additionally, we also investigated the effectiveness with trellis codes and two-dimension codes for next generation codes.