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Theory and practice of multilevel method in high-definition discs

Multilevel storage is the easiest two-dimensional storage technology. On the basis of recording and read-out optical system of Digital Versatile Disc (DVD), by the method of multilevel run-length coding, the storage capacity can be increased by 60 percent of DVD9's, reaching 14 Giga Bytes. In order to meet the requirement of a 10-4 raw Bit Error Rate (BER) of data readout, this paper presents a method of multilevel run-length coding with changeable level numbers. This method can take advantage of run-length redundancy to the utmost and reduce Inter-Symbol Interference (ISI) caused by multilevel run-length. Multilevel run-length coding uses the method of two steps modulation. This paper introduces a coding method of DK (1, 9) and R=1 code rate. Realized by Pulse Width Modulation, multilevel run-length modulation coding with changeable level has good symmetry. Its readout characteristics are the same as that of DVD with normal run-length modulation, therefore the servo control system needn't be changed. Also the signal can be recognized in two aspects respectively, run-length and level. In the sample disc, average raw BER in the two aspects is less than 10-3. Multilevel run-length modulation coding could be applied in various systems of run-length modulation coding. On the basis of the structure and characteristics of the primitive system, the comprehensive efficiency of coding could be increased by 33 to 50 percent.