RLL modulations that have d equals 1 constraint, such as RLL(1,7) 1) ,2), are widely used in the optical disk systems to enlarge a window margin. While 2 to 3 variable length modulations, which is representative coding rate for those modulations, were difficult to control digital sum variation (DSV), a common solution is inserting marginal bits2). However a drawback of this method is a loss on the recording capacity. This paper introduces new RLL(1,k,4,6) modulations which can generate various k constraint, k equals 7 or above, codes with a cording table. All of those have 4 to 6 fixed coding rates and can control the DSV without marginal bits. It can be emphasized that all the modulations use the same coding table and the same decoder. The table is constructed by 4 states sliding block encoder. Since code words by the (1,k,4,6) modulation is decoded only by a symbol look-ahead decoder, error propagation is within 8 data bits. The high coding rate and sufficient DSV control ability can bring an extra capacity or system margin.
D8-15 modulation, which is a RLL(2,10) modulation, is extended to enable to store an extra information. The extra information is multiplexed to main data with no capacity loss by the modulation of k constraint value. Since a coding table is applied no change by this operation, the same decoder can be used to decode the main data. It means the extra information is invisible from the main channel decoder. The extended code indicates similar DC control performance as the original one.
The noise reduced disc and the advanced signal reproduction system with the asymmetry compensatory function enhance the disc capacity up to 19.8 GBytes per DVD size. The noise was reduced by applying Aluminum based multi-component alloy for the reflective layer, moreover all the loops in the system accurately function even under the signal asymmetric condition by using the newly developed Error Feedback type PRML. The error rate characteristics versus disc tilts suggest that the ROM disc system has sufficient performance for the practical use.
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