| 摘要 |
<p>Method and apparatus for encoding digital information to be recorded on a magnetic medium is disclosed. The invention provides for receiving a sequence of (2<m>n + d) user bits, mapping the sequence of user bits to 2<m> dc-free codewords, and recording the 2<m> dc-free codewords on a magnetic medium. A modulation coder, which includes a memory containing multiple non-intersecting subconstellations of dc-free codewords, performs the mapping in a non-equiprobable manner such that a particular codeword from a larger subconstellation is more likely to be used than a particular codeword from a smaller constellation. Less desirable codewords, such as those containing relatively long strings of bits having the same value, are assigned to the smaller subconstellations, thereby lessening the likelihood of loss of timing and gain parameters in the system, as well as maximizing the transmission rate and efficient use of the set of possible dc-free sequences of a given length. <IMAGE></p> |
