Run Length Restriction on the Output of PR4 Channels
Original Publication Date: 1985-Aug-01
Included in the Prior Art Database: 2005-Feb-19
In a data transmission and/or recording system, sequences of 8-bit long words are encoded, transmitted, received and decoded using a PR4 channel. The encoding maps 8 data bits into 9 code bits, so that, on sampling a received coded message at the output of the PR4 channel: a) no more than 4 consecutive zero samples are ever seen. This ensures a continuity of timing and gain control data; b) considering only the odd or only the even samples, no more than 6 consecutive zero samples are ever seen. This limits the complexity of a Viterbi detector; and c)non-zero samples are ensured at odd and at even time at a code word boundary. This ensures that an undetected error can not corrupt more than a single 8-bit word of data. Naming the data bits of a word a b c d e f g h and the mapped code bits i . j k 1 m n o p .